SIP Sliding Away

This week, I threw up my hands in frustration and did a small redesign.  I have been planning all along to use SIPs for the first floor flooring (above the basement).  Unfortunately, I have been so busy with other projects like fencing our back yard against deer and dealing with my duties as volunteer Treasurer for my community, that I didn’t actually get an order placed.  Add to this that the time frame for getting SIPs delivered turned out to be 3-4 weeks ARO (“after receipt of order”), this would have put me receiving the materials somewhere around when the average daily high temperature crosses below 50°F/10°C and the snow starts to fly.  Plus, the quotation came in about $2,000 over my budgetary estimate.  I could save some of this by using a lower insulation SIP – which would probably be OK – as the basement will generally stay closer to ground temperature than outdoor temperature, I won’t lose as much heat through the floor as through the walls.

The local code enforcement officer indicated that I needed to either get a floor in place or put up a (rather permanent-sounding) fence around the site before the winter, and I didn’t want to spend a whole lot of money on fencing if I could just get the floor on.

To top it off, I was having trouble getting a useful structural load analysis that reflected my intended usage.  Somewhere in here, while I was busy trying to compute the transverse load for a 4′ span from the modulus of elasticity of extruded polystyrene, I turned a corner.  Was this really worth going out on a limb and then jumping from treetop to treetop over?  Load tables and beam strength calculations for wooden joists were incredibly easy to come by.  And they showed that all it would take was a 2×6 member spaced every 24″1 to span over 8 feet.  Heck, even a measly 2×4 would span 5 feet.  If these were then reinforced with a bottom layer of plywood (which would effectively prevent the bottom of the beams from stretching and make them even stronger) and topped with subflooring, I would have a structurally sound flooring solution.

It would need to be insulated though.  Polyisocyanurate foam board (often abbreviated PIR) is about the best insulation density you can get in an off-the-shelf product (R-6.5 per inch) and so 4 inches of this would put me at R-26 – exactly where the cheaper SIPs would have put me.  However, that would involve a lot of cutting foam to fit around the structural members.  I was also worried about the thermal bridging from all of the wood, particularly if I needed to space the joists 16″ OC to ensure a rigid floor and not need multiple layers of subflooring to achieve it.

I finally came up with what seemed like the key innovation to me.  If a 2×4 can span over 5′ at 24″ OC or nearly 6′ at 16″ OC, then as long as it’s structurally supported every 4′ or 5′, the 2×4 can actually serve the role as a floor joist.  Adding a 2×6 for every 3rd member would increase the strength further.  The PIR foam board I was looking to use2 is 2″ thick, meaning that it would in principle fit in the difference between a 3.5″ 2×4 and a 5.5″ 2×6, and from there it would actually provide some additional support to the 2×4.  At this point I could get away with only cutting each PIR board a little bit to fit between 2×6 members, and around the supports.

But now I’m only at R-13!  That isn’t very good insulation for a potential 25°F/14°C temperature differential.  Adding batts of 3.5″ rock wool, which is exactly designed for 2×4 spaces, adds another R-15 (total R-28).  The final assembly looks something like what is shown here.

And, I should be able to start getting the parts more-or-less immediately.  And, the whole thing will probably save me some money relative to even the cheapest of the SIPS.  Some extra labor, to be sure, but the sooner I can get started on it, the more likely I am to get this done before real winter hits.

  1. The construction terminology is 24″ OC standing for “on center” – that is, the centers of the boards are 24″ apart.
  2. I don’t really care for Dow but the appears to be the only suitable PIR I can get locally.

When It Rains, Do Like The Romans

I may have my idioms mixed up, but rainwater catchment goes back a very very long time in history.  Although it certainly goes back to the Indus Valley, in some sense it probably is prehistoric.  The Romans, however, applied their engineering skills to the task (along with the famous aqueducts), and made some significant innovations.

In this post I’m going to talk in some depth about my plans for rainwater harvesting, which has the two-fold purpose of demonstrating some interesting sustainability techniques, plus also reducing the ecological footprint of the construction and residence.  This post is also an experiment in a different writing style – I’m going to explain not only the design outcome, but many of my steps (and missteps) along the way.  A lot of people have written up their finished rainwater systems; it seems less common for people to talk about the ideas they have considered or the attempts they have made, which they later ruled out.  I hope this provides some interesting fodder for people designing their own systems.

Going back to the ecological footprint, there are three factors I wanted to consider: stormwater runoff, consumption of limited groundwater, and exposure to the potentially toxic chemical byproducts.

  1.  One of the major considerations for new development (at least in NY) is the “stormwater pollution prevention plan” or SWPPP.  The addition of impermeable surfaces (like roofs and roads) interferes with the normal absorption of water into the ground, and potentially causes significant additional runoff to arrive in streams.  Along with this runoff are various types of pollution that would be found on the surface, ranging from silt to fertilizer to motor oil from cars.  To the extent that we can minimize the amount of runoff, we can reduce the magnitude of the required catchment areas and reduce the amount of material deposited there.
  2. The sole source for drinking water in our community is groundwater (wells).  We have a pair of high-performing artesian wells that dip into a local aquifer that was recently studied extensively by the USGS.  (One of the wells was even part of their testing.)  However, as more homes are built both in our community and elsewhere in the town, the demand on this aquifer will increase, and it’s possible that at some point it will have trouble being replenished quickly enough to supply all of the needs.  Thus, having an independent source of water (rainwater) will both reduce dependence on, but also demand on this aquifer.
  3. Because our community exceeds the minimum size set out by the EPA for a “community public water system”, we are required to use “approved” chlorine treatment in our community water.  Many people respond badly to the chlorinated water and are filtering it back out at their own homes.  Even the CDC is now questioning some of the potential health effects of the by-products of chlorination.  By using rainwater and then not sending it underground, it should be legal to use filtration combined with UV sterilization (which is actually more effective than chlorine against cryptosporidium and giardia) to supply potable water to the home.  (The effort to get this approved in Tompkins County NY was led by a couple of intrepid “Earthship” homebuilders, for which I’m very grateful.)

For me the first logical step in thinking about rainwater is understanding rainfall conditions in our area.  So I created a rainwater calculator that utilizes raw data from the local weather station month-by-month over ten years.  Later, I realized that the effects of averaging over month-by-month data really prevented me from understanding important parts of the system, so after some digging for a reasonably trustworthy data source, I shifted to a model based on day-by-day data.  Even that has some limitations I don’t really like, but I was not able to find an hour-by-hour rainfall source that I could trust and match up with the seemingly reasonable daily and monthly data.  I’ve used these data to come up with an estimate of the average rainfall, to look at the amount stored over time, to understand how the amount of storage would impact both full and empty conditions, etc.

Basic Operational Features

First, let me explain some of the principles at play here.  I’m going to shamelessly lift some images from the Texas Manual on Rainwater Harvesting, one of the widely-cited references on the topic.  These steps are:

  • Rainfall – what are the regional properties of rainfall relevant to the design
  • Catchment – how is the water collected; how much area; relation to rainfall
  • Leaf filters – removing large objects such as leaves from rainwater
  • First Flush – cleaning sediment deposited on roof during dry intervals
  • Prefilter – removing smaller objects which might clog storage tanks
  • Storage – bulk water storage volume
  • Pressurization – bringing stored water up to usable pressure
  • Postfilter – remove remaining small particles that interfere with treatment
  • Treatment – making water safe to drink

The process for designing has been somewhat iterative.  For example, I first looked at the gross rainfall numbers, catchment area, and storage to get a ballpark idea of how much storage was likely to be required.  Then I later had to fine-tune these numbers based on expectations for filtering losses, greywater reuse, etc.  As I describe the work below, I’m working from the high level considerations down to the details.

Just as a note, I’m going to use some abbreviations below so I don’t have to keep writing out complicated units: gal = gallons, sf = square feet, gpd = gallons per day, gpm = gallons per minute.

Catchment and Storage

First, consider the roof footprint or “catchment area.”  Except in the case of a flat horizontal roof, this area is always less than the area of actual roof material.  Using this number doesn’t really account for unique aspects of the weather (such as prevailing wind direction) or the site (trees blocking rainfall or wind) but it’s still the best general approximation for how to convert “inches of rainfall” into “gallons collected” – specifically, 0.623gal of water for every square foot of area.  In my case, I began work using the slightly conservative estimate of the house footprint (648sf) rather than the roof, which will have some additional overhang (giving perhaps an extra 16%, or 754sf).  The smaller number gets me 404gal per inch of rain.

By using my modelling spreadsheet, I can see that he roof is collecting on average 43gpd given our local rainfall conditions, and that is cut down to 37gpd by some of the filtering considerations below.  (Some more is lost when the storage capacity is full, but we’ll talk about that in a bit.)

That covers the input (production) side.  However, in order to effectively simulate performance around the storage tanks, we also need to measure the output: water consumption.  Guesstimating water consumption is pretty difficult, particularly since I don’t even know who is going to be living in the home.  One could use anything from single occupancy up to a reasonable (by residential code) limit of 4 residents.

Because of my involvement with our Infrastructure Committee, I happen to have data that says that the average use in our community, measured as a function of the number of bedrooms, is about 38gpd/bedroom.1  Given that this is a 2-bedroom house, that would nominally mean 76gpd, corresponding to 4-person occupancy.

However, I’m going to adjust my estimates assuming that we’re able to implement greywater recycling for toilet flushing.  (It is easy to buy a simple version like SinkPositive that just allows you to wash your hands and uses that to refill the toilet tank, but I want something that works with an accessible sink and isn’t limited to just handwashing water.)  Toilets flushing is one of the largest single contributors to home water use, about 27% on average in the US.  Even using estimates for low-flush toilets rather than the less efficient ones many people still use, it is easy to account for 25gpd (32% of our 76gpd).  So let’s take this 25gpd, arriving at 51gpd for all other uses, for 4-person occupancy.  For 2-person occupancy we’ll just halve the number.

Hopefully it’s fairly obvious that the relationship between production and consumption is the most important aspect of system performance.  If you’re collecting only 37gpd on average, and using 51gpd on average, you’re not collecting enough water.  If you’re collecting 37gpd and using only 25gpd, you’ve got a surplus.  Storage helps at times, but it won’t change the overall picture, as shown in the graph below.2  With two people, we’re overflowing any reasonable amount of storage ~30% of the time.  With four people, we have a shortfall with similar regularity.  This is a direct reflection of the collection capacity of the roof. 

 

 

In the long run, one obvious way to address this is simply to increase the catchment area.  If we were, for example, 35% short, we could add another ~225sf of rainwater collection area.3 For this reason, I’m imagining that I may use a ground-mounted solar array, in part to increase the potential area for rainwater catchment.

So in essence, with the current roof area, the system right now is sized for what you might consider an average 3-person occupancy.  We will just work with this starting point and assume that either (a) the residents limit their water usage to what can be harvested from rainwater; or (b) the residents don’t mind using community water when they run out.  Of course, if you make those assumptions, then by definition you can’t compute anything interesting about storage.  We do want the system to have some storage, so for that purpose we’ll consider the 3-occupant, 37gpd model, i.e. where production and consumption are roughly similar.

We also need to consider pragmatic limitations: the basement entrance won’t allow us to install or replace tanks larger than about 47″ in diameter; the ceiling limits us to tanks no higher than 92″ (and, if we want to be able to get any access to the top, probably more like 80″).  However, we can install multiple tanks, and interconnect them for more storage.  Each tank is adding system cost, but if they’re all ordered at once some of those costs (like delivery charges) will be constant.  My current working selection is a Rotoplas RP-590283 tank, which holds 300gal and is at present selling for about $250.  These are 36″ in diameter and 76″ high, so they are easy enough to get into the basement.  This means our storage capacity will be sized in 300gal increments.

Based on the graph above, you can see that more storage always helps, unless you’ve only got 2 occupants.  4 tanks (1200 gallons) will mean our 2-occupant family is only using community water about 1% of the time, and when starting from full tanks they can weather a 48-day total dry spell.4  For higher consumption, there’s always a return on storage, but even with just 3 occupants, reaching this 1% level would require more than 7000 gallons of storage, which is just silly.

For the present, I am satisfied with a 1500 gallon system capacity which will be more than enough for 2 occupants, leave 3 occupants on community water about 13% of the time, 4 occupants about 30% of the time.  Let us now turn to some of the more subtle design aspects.

Prefiltering and First Flush

The enameled steel roof that I will be using is pretty much ideal for potable water collection.  It doesn’t leach out much in the way of undesirable chemicals, like you might see from an asphalt shingle, plastic, or galvanized roofing material.  It doesn’t give off particles of its own, and it doesn’t particularly trap particles.  Also, since there are no trees of any size within hundreds of feet of the house, I don’t have to worry much about leaves.

Nevertheless, it’s helpful to put screen filters into the system to catch anything large that might be coming through.  Although these can go over the gutters themselves, or be put directly at the downspout entrance, that means needing a ladder to clean them, so I expect that I will opt for an inline filter basket in the downspout.  I haven’t definitively decided on a model, but some that I am considering are the AquaBarrel Slim Line at $50 or the Leaf Eater Ultra at $40.  Some of the cheaper products (Amerimax FlexGrate, $6) are not enclosed and seem like they would be too susceptible to letting as many things (dust, bugs, etc.) in than they keep out.  There are also more expensive products (WISY FS305, for $400 or more) that are pretty and made out of stainless steel, but which are likely overkill if there is additional filtration in the system, and needlessly push up the system cost.

For additional filtration, I plan on using a “first-flush diverter” to eliminate some of the fine particulates (e.g. summertime pollen and wintertime wood ash) so that the incoming water is cleaner.  The way this works is to assume that any time it hasn’t rained recently, the roof is dirty; based on this assumption, the first small amount of rain is shunted off to a holding chamber which captures the sediment along with that water.  When the holding chamber is full, the (now cleaner) water is directed into storage.  Typical recommendations are “13 to 49 gallons per 1,000 square feet.”5  I’m starting with a mid-range number of 23gal/1000sf, which roughly corresponds to another number I have seen, which is the first millimeter of rain.  Or, simply put, 15gal.

Now it turns out that if we have a rain of 1mm or less, then it all goes into the first-flush system – which based on daily rainfall data happens for about 27.5% of the rainy days.  On the other hand, because many rainfalls are heavy, I only lose a total of about 14% of the rainwater to the first-flush system.  (In fact, if we use the 2-occupant model, I actually lose more water – over 28% – due to the system being full and not having capacity for more water to be stored!)

You can buy a first-flush diverter, but you can also build one, which turns out to be pretty simple.  There are a number of ways, but one of the simplest (shown here, again from TMRH) is simply a standpipe with a “weep hole.”  The sediment falls to the bottom of the standpipe; when the pipe is full, the incoming water can’t go into the standpipe any longer, and gets directed to storage.  In this partial cut-away drawing, the “weep hole” is actually replaced by an adjustable valve (“hose bibb drip”) but that isn’t strictly necessary.  So one can calculate the capacity based on the number of gallons that fit into a given diameter and length of pipe.

I tried to find a nice table for this, and the best I could come up with was this chart from Wake County, North Carolina.  The most readily available pipe is usually “Schedule 40” rigid PVC pipe.6  I made up a quick table for practical sizes that one might consider.  It is interesting that there’s a sweet spot in price per gallon for 6″ pipe.  The problem, of course, is that if you are trying to fit 15 gallons of storage into a vertical pipe in an 8′ high room, you can’t fit it into a 6″ pipe.  The 8″ pipe, on the other hand, will come in a little under 6′.

Nominal SizeGallons/Ft$/Ft$/Gallon
3" Sch 400.384$1.83$4.76
4" Sch 400.661$2.18$3.30
6" Sch 401.5$4.02$2.68
8" Sch 402.6$11.70$4.50

So imagine that we have that piece taken care of, what comes next?  Well, ideally we want to filter out any particles that still make it through.  Unfortunately, we don’t have a huge amount of pressure so most of the conventional filters that are used for city water probably won’t work.  Another filter that is sometimes used for rainwater is a “slow sand filter“, which is a biologically active filter that takes out both particulates and microorganisms that may be coming in.  However, true to their name those operate extremely slowly (gallons/hr rather than gallons/min) so they would need to have a lot of capacity to avoid losing useful rainwater.   There are, however, some filters that are specifically made for rainwater catchment.

The filter I’m most likely to go with is the Maelstrom which is made in Australia – a country where rainwater collection has become a bit of an art form.  The advantages of this filter are that it filters down to 180 microns (0.18mm) even though it can handle flow rates of 80 gallons per minute with minimal losses.  (Some people even use the Maelstrom as a direct filter for the downspout water, but it seems like it would be more difficult to clean so keeping the larger particles out should make it require less service.)  Also, it works with standard 4″ pipes, and can be mounted in any of several convenient ways including directly at the top of a tank.  While it would be great to get to 30 microns or less, we’ll save that for after the storage tanks where the water is pressurized.

Pressurization

In the storage tanks, the only pressure the water is under is its own weight – an 8′ high column of water gives about 3.5psi, and our tanks won’t even be that tall.  We need to increase the pressure to the level where appliances expecting city water (30-40psi) will operate normally.  If we were trying to handle large volumes of water, we would potentially need a big pump for this, and that means a lot of power.  However, if we have enough intermediate storage, we can potentially use a lower flow rate “slow pump” and thus avoid a big power draw.

It turns out this set of requirements exactly matches something that is widely available: fresh water pumps for recreational vehicles.  Pumps like the Shurflo 4048 from Pentair deliver exactly what we’re looking for: flow rates up to 4gpm, pressures up to 55psi, and operation from 12V at less than 10A.  We then need to couple this with a relatively large pressure tank to give the pump enough time to get the pressure back up for normal usage.  A Pentair WM25B, Goulds V260, or Amtrol WX-255D each provide 25-30 gallons while keeping the pressure between 30 and 50psi.

Postfilter and Treatment

We’re ready to make this water drinkable.  Because the water is not going underground again after treatment (for which the only approved solution in NY state would be chlorination), we have a number of options.  The most appealing, because of the lack of chemical residue, is UV treatment.  It wasn’t clear to me how much power this was going to take, but it turns out that it’s the equivalent of a light bulb.  One of the critical things for UV treatment, however, is ensuring that there is no sediment in the water that could block the UV light from treating it effectively.  A convenient solution to this is a combined sediment filter and UV unit.

While I was originally looking at Viqua (first some of their high-volume units such as VH410M and then later at S2Q-P/12VDC), none of these included a sediment filter.  I found the UV006 unit by PuraUV which includes the sediment filter, supports a higher flow rate (8-10gpm), and like the S2Q-P/12VDC can be operated from 12V for off-grid applications.  This draws only 22W – it requires less power than the pump!

To save myself from having to replace the filters in the PuraUV too often, I also plan to include one additional filter, a Rusco 15 micron spin-down filter.  The nice thing about these filters is that they can be cleaned simply by opening a “flush valve”, and the pressure of the water itself washes the accumulated grit off the filter.  Although they may need to be replaced eventually, they can be reused thousands of times rather than needing a replacement filter every 6 months.

Community Water Backup

There’s one step I’ve left off above, because it seems like it would confuse things, which the the backup for using community water when we run out of rainwater. I considered two slightly different ways to approach this: adding the backup water into the storage tanks, or switching the backup water on after the treatment system.  (Since this water is already chlorinated, it doesn’t need to be treated again.)

The advantages of going into the storage tanks are:

  1. The solution can be purely mechanical – like the valve on your toilet tank, a float valve can be used to turn this water supply on only when the level in the tanks is so low that they’re considered “empty.”
  2. The chlorinated water can effectively disinfect all the subsequent portions of the system, if there is every any sort of issue.
  3. A minimum level of water can be maintained which is always available with solar power, even if grid power is out.
  4. An “air gap” can be installed to prevent any chance of rainwater backflowing into the community system.

The advantages of switching the water on after the treatment system are:

  1. The pressure pump and UV system can be shut down when we’re out of rainwater, drawing no power and saving wear and tear.
  2. The backup water can be used to supply additional pressure if the rainwater system is not keeping up.
  3. Easier to integrate rainwater system after-the-fact.

Probably based entirely on the last reason in the list, I expect to start out with the house plumbing directly connected to the community water supply, and then as time and money allow, add in the rainwater system.  Then, if it appears at that point like the direct-to-storage-tank solution would be better, I can adjust the inlet plumbing to accommodate that.

Conclusion

Collecting a little rainwater for watering your garden is something anyone can do.  It is easy and certainly worthwhile.  In contrast, attempting to supply water to an entire household based entirely on rainwater, while making this more-or-rainwater_calculatorless invisible to a “western, developed-world” homeowner who expects never to think about where their water comes from, is an undertaking of an entirely different scale.  I hope that the data, tools, components, and overall thought process that I’ve shared here will make it easier for others to pursue similar projects in the future.

P.S. The complementary conjugate idiom, “When in Rome, it pours,” is probably somewhat less valid.  Rome gets less rainfall than Ithaca, averaging about 31 inches/year.

  1. This arcane way of measuring is what is utilized by the NY Department of Environmental Conservation in determining how to size a septic system.  But it gives us a hand-waving first approximation.
  2.  The orange/green/blue lines represent a 4-, 3-, and 2-person occupancies (51, 37, 25gpd) respectively.  The solid lines represent the system shortfalls at a range of storage capacities; the dashed lines represent water collection that exceeds storage capacity (i.e. overflows).
  3. As noted above, if I add to the house footprint 1′ roof overhangs on all sides, this increases the system capacity by 16%, and we’re now just 120sf short.
  4. The NY drought of 2016 is part of the main daily dataset I am using.  Our intrepid rain-drinking family of 2 might still have gotten 899gal (more than half of their water) from rainwater in June and July, taken a net 553gal from storage, and required only 108gal from the community supply.  Their longest dry spell would have been March 2015 when they would have gone for 19 days on primarily community water.
  5.  Texas Manual on Rainwater Harvesting
  6. I won’t digress right now into explaining what “Schedule 40” means… just take it as “the white pipe that doesn’t say ‘not for pressure use’.”

Time to Build, Less to Write

We’re having a big thunderstorm this afternoon.  Before this, the weather had been good enough for the past few weeks that much of the free time I might have spent blogging about the Little Rental House was instead spent building it.  This is one of the reasons things have been so quiet here lately.  The other is that I sank a whole lot of time into a long, detailed post about rainwater collection, which still isn’t finished, and so what writing I have done hasn’t gotten published.  I promise, I’ll get that one out soon.

In the mean time, a little status update:

  • The basement slab was poured on Aug 5th.
  • I now have all five of the I-beam floor supports in place and bolted down (the photo below only shows the first two).
  • The 1″ insulation around the basement walls is about 60% finished, but has slowed down because I’ve found I need to clamp the boards in place while gluing, and I only built one clamp apparatus.
  • I’ve measured, cut, and started mounting the stringers for the basement stairs.

Finishing up the slab

De Basement

On Friday Jul 12, forms went up.  Actually, first they went down, slid from truck to hole along one of the same 2x12s that were used to form up the footer.

The forms are a pretty clever thing – they have both holes in the top and bottom flanges to allow them to be stacked and linked (my walls took two 4′ courses) as well as holes through that allow for breakaway ties that connect them against the weight of the concrete pushing outward when they’re filled up.

Originally, they were planning to pour the same day, but between the availability of concrete trucks, the length of the process, and the heat, they wound up calling it off and rescheduling for Monday.  Thus, on Saturday Jul 13, I had a chance to check the work, which seemed great overall.  I also took a number of photos to provide to our local Code Enforcement Officer, since he was out during the week and wasn’t able to visit the site between the forming and the pour.

I verified a number of things like the distance from the lot lines, which all seemed OK.  I did find a pair of pipes (for utilities) that were on the wrong end of the wall, but I was able to easily put in another pair.  The two grey pipes are the ones I added.

However, by the time I was done my clothes were covered in the release oil that they had put onto the forms.  Even though this was an “eco-friendly” release agent, it smelled so strongly that Raederle had a migraine within 15 minutes and I promptly tossed the clothes in a pile outside.

On Monday Jul 15, they came back in the morning to do the pour.  As much of the work (which is a lot) is done by the concrete truck, the team still had to stir and push the concrete away from the chute and into the forms with long 2×4’s.  It was a hot (80°F/27°C) and sunny day, but not yet the peak of the week.

For the end of the pour, they used the very clever “conveyor truck” which allows them to direct the concrete just by moving around a long tube.  That let them focus their efforts on the finesse of getting it level so they could finish the top surface easily.

Then they installed the anchor bolts that will hold the house down to the foundation.

Here is what it looked like at 8pm, several hours after they finished, as the concrete was setting.

The next day, Tuesday Jul 16, they were back to take down the steel forms.  Here is what it looked like partway through at a little after 10am.

Those steel forms that were easily slid down into the hole then all had to be lifted back out and loaded onto the trucks.  A lot of hard, hot, and thirsty work, on a day that got up to 88°F (31°C) with bright sun all day.  I brought them a gallon of ice water mid day when their own reserves were running low.  And here at last, is the finished product.  I now own (well, once they cash the check) a basement!

Set In Motion, Set In Stone

Today was a big day for the Little Rental House.  Today was the day when it became rather more difficult to get cold feet and quit.  What was just a hole in the ground yesterday is concrete in the ground today.  The footers were poured.  On Friday, they expect to return to build and pour the basement walls.

Today was perhaps the hottest day of the summer so far – something like 92 degrees Fahrenheit with high humidity, so I do not envy the team who came out to do the work, despite their bronzed skin and 6-pack abs.

A few interesting steps occurred along the way.  First of all, as they were setting up the forms, they asked me to order a load of stone (“Crushed Number 2 Gravel” looks something like this, although I got it from H.L. Robinson which doesn’t have pretty pictures on their web site).  They spread this on both the inside and outside of the forms to support the weight of the concrete.  Second, I got the first formal building inspection from the Town of Danby, when they came to review the installation of the rebar inside the forms before the concrete was poured.  They included the new NEC mandated ground connection to the rebar, where an extra piece of rebar was bent so that it protrudes out of the footer to provide a place to make a ground connection.

When the truck arrived to do the pour, they had to move around the chute of the truck, and an auxiliary chute that they used kind of a little “marble run” game to redirect the concrete to various areas.  They would then push (with shovels) the concrete to get it spread out evenly from where it was being dumped. 

One fellow generally worked with the concrete “float”1 while the other was working with the truck and pushing the concrete level.  They would also sometimes stir it up by rapidly inserting and removing the shovel, which helped to get it to flow and self-level.  (It’s not clear to me whether they were taking their level more from the nails in the forms or from the concrete’s own natural flow.)

They were also going around inserting the vertical rebar which will tie the walls to the footers.  They told me that with 3 people they could generally keep up with the truck’s pour, but with just 2 they were having to switch off jobs and had to stop the truck for several minutes at a time while they caught up.  Nevertheless, the whole pour was only 1h40m of the whole footer project.

The last part of the pour they had to do with the wheelbarrow (I believe I counted 8 loads), because the reach of the truck’s chute wasn’t far enough, and their own extension chute had a broken chain so they couldn’t attach it to extend the fill the remaining distance.  But pretty quickly, the pour was finished and smooth.  Because of the heat, it was already starting to set up by the time they got around to making the two ends meet.

So, if I’d ever considered having second thoughts about embarking on this project, I think the time is now past.  We’re building a house!

 

  1. I searched google to try to figure out where that name comes from, but didn’t find any good answer.

Making Plans – The Road Ahead

I’ve decided to upload a full copy of the plans for the Little Rental House, for those who might be interested in seeing more details.  When I was first designing, I found that most house plans out there were behind a paywall.  Since I drew these plans myself, there isn’t any reason I can’t share them with the world, but if you find them useful I’d be happy if you wanted to make a donation that you feel reflects the value you’ve gotten from them.

I’m including some notes below, and as I have time to write up more aspects of the project, I will try to update this page with links to more detailed posts.

E – 1: Elevations

The original design work was done in an extremely old 3D Home Architect (version 10) from Punch Software.  While it has plenty of limitations and occasional crashes, the mere fact that it still loads and runs under Windows 10 is so gratifying that I’m willing to put up with a few glitches.  This allowed me to trivially create the 3D renderings shown on the first page.  They’re pretty, but they don’t necessarily communicate the technical details needed for construction.

F – 0: Basement

I’ve written about the choice to include a basement in this blog.  The elevator speech I give people when they look at the big hole in the ground and say “oh, it’s going to have a basement?” is: Well, yes, but it’s really just for mechanicals.  It turns out it’s about the same cost to build a basement where I can do the other work myself, as it is to build a slab and hire people to do all the work that has to get done perfectly the first time before concrete is poured.  Plus, it allows me to add some features like waste water energy recovery that I wouldn’t have room for otherwise.

On the technical side, I’ve elected to go with cast-in-place walls for cost, making them 8″ thick so there is plenty of “bearing space” for the I-beams that constitute my floor supports.  These will run underneath the SIP flooring to provide a relatively low cost and low labor support structure that will prevent floor sagging.  I may at some point share some of the details of the engineering calculations for the beam strength here, but the short form is that spanning 24′ with wood would require huge timbers or manufactured wood beams that are much more expensive and not much more renewable than iron, and splitting the distance with a single 27′ beam and 12′ joists would have more susceptibility to the kind of “droop” that I’m experiencing in my own home, where doors need to periodically be adjusted so they latch properly.  It seems like steel beams are rarely used in residential construction, but I’m not entirely sure why not.

I explored the use of precast stairs, but found out that the maximum opening they would allow is 39″ wide, which would significantly limit the size of tanks and other items I might want to move into the basement.  It would also potentially need to be longer than the 6’4″ shown on the plans, which would make the stairs at risk of coming too close to the lot line.  Bilco’s standard “Size C” door will allow for a full 4′ wide staircase, which I’ll then have to build.

F – 1: First Floor

Because I’m building an accessible home, all the living areas are on the first floor.  Two bedrooms of 100 sq feet take up the east; an accessible bathroom is centered on the north wall; a large living/dining room area is at the southwest, and a small galley kitchen begins just after the front entrance at the northwest.

The layout optimizes the appliances that need water and drains (kitchen sink, bathtub, bath basin, toilet, and clothes washer) within a very small area, which will reduce the heat losses for hot water and the overall plumbing materials cost.  The stove is at the outside edge to allow it to be directly plumbed with an external propane tank.1

F – 2: Second Floor

This floor represents an L-shaped area of extra floor space.  It won’t be accessed by stairs, but rather by a ladder of some sort.  Some might choose to use it for storage, others as a play area for kids (it will have a railing around it), and others as an office.  Because it’s not accessible like the first floor, I didn’t want it to have any necessary functions, but getting a good roof slope for solar more or less automatically produces a space here and I thought many would find it useful.  There’s a small area at the southeast that is so low (below head height even for kids) that it’s not useful floor space, but some mechanicals (such as a heat-recovery ventilator) could conveniently be installed here.

M – 1: Electrical

This sheet shows the placement of various electrical fixtures on the first floor.  It includes the placement of various low voltage LED lights, low voltage (24VDC) electrical outlets, and the conventional 120V outlets and switches as required by code.  What it does not specifically cover is how the outlets and switches are wired to two different service panel – a primary 150A service panel and an auxiliary smaller (probably 60A) subpanel for “critical loads” which can be supplied from a solar battery bank inverter.  I’ll write about these details in a separate blog post.

S – 1: Sections

These fun little details show cross-sections of three portions of the design: the roof, the basement wall and first floor, and the slab/footer.  The roof details show how the different layers of insulation (which together add up to approximately R-53) are installed, which prevents condensation within the cellulose insulation.  The basement wall details show the relationship between the footer, footer drain, basement slab, wall, backfill, I-beams, SIP flooring, and SIP walls.  These details help identify how the structural components work together and also identify particular elements which need to be purchased and installed such as the “mud sill” and “rim joist” boards.  Finally the slab/footer NEC detail reflects the (relatively new) requirement that portions of the foundation which are in electrical contact with the ground must now have their own ground connections, in addition to the normal requirements for grounding rods.

W – 1: Schedules

This shows the window and door “schedules” that list the particulars of the windows and doors to be installed in each location.  Although I’ve listed preferred manufacturers here, this piece of the design isn’t 100% set in stone as the availability of different windows from different companies seems to vary a lot over time.  One of the key elements is the fact that the bedrooms must have “egressible” windows with a significant clear area (5.7 ft²) through which residents can evacuate and/or firefighters can enter.  In addition to the mandatory egressible window in each bedroom, I’ve also included one “E1” window in each bedroom, which meets the requirements only on the first floor (clear area 5.0 ft²).

N – 1: Notes

This page covers a lot of technical details which are better stated in text than in drawings, ranging from the general “do the work according to code” to details like the structural lumber stress values and the requirements for smoke and carbon monoxide detectors.

  1. I’m not thrilled with the use of propane, but it provides a backup in case electric energy winds up being in short supply.  At present, propane is produced in surplus as a side effect of oil drilling, and when there isn’t a market for it, it is often flared off.  So by using it I’m choosing to put that heat somewhere useful instead of making it a waste disposal process.

Ground Breaking News

I am now the proud owner of a big hole in the ground and several huge piles of dirt.

Additionally, at the far corner, you can see a couple of white drain pipes that will carry water away from the foundation (footer drains) and from overflow from rainwater collection, and dump them above the level of the nearby retention pond.  In contractor speak, these are referred to as “daylight drains” because they can see daylight at the downstream end; they don’t need a sump pump because they drain above ground just by gravity.

Excavation began at about 9am on Monday, when it looked like this:

Using the survey stakes set earlier, Enslow Landscaping1 dug about 7′ into the ground with about 3′ of extra space on the outside of each wall as working space for the foundation contractors.  The picture at the top was shot at just before 4pm.  Not bad for a day’s work, right?

Shortly afterward, it rained, and then I had several inches of water in the bottom of the hole.  My cat Zephyr decided to check it out.  (Curiosity and all that… I don’t think he’d die if he’d fallen in, but he would have gotten very wet.)

Then somewhere around 11pm on Tuesday night, as I was trying to go to sleep, I noticed something on reflection that I should have seen while it was right in front of me.  There was no excavation done for the stairs that go down to the basement!  I sent them a text, and they came back today (Friday) to address this and also to adjust the drains to get rid of the standing water.  Within a few hours (between 9:30am and 1pm) they had both issues fixed.

  1. I’d give the Enslow team a link, but like so many small construction businesses, they barely even do email much less have a web presence!

Staking My Claim

The phrase “staking a claim” started out as a literal description of an activity: marking a piece of land with stakes.  Today, the figurative returned back to its literal roots.  This post is now at the northeast corner of my building lot.

The surveyors went further and put in marks for the corners of the house – actually, offset by 5 feet from each corner to allow room for excavation.  These days, surveying is mostly done with differential GPS (DGPS) which has such remarkable precision that the surveying team was able to determine which of several marks on a nearby manhole (within an inch of each other) was their previous measurement reference.  Taking advantage of this, they put in large (2″x2″) stakes for the house corner offsets, and then repositioned the point of the GPS on top of the stake so they could mark a specific point within that 2″ square and put in a nail at the point.

This then allowed me to run strings (which unfortunately are barely visible in the photo) to mark the actual location of the house.

Today I also received a new excavation quote which is $5,600 lower than the previous one and includes all the materials, which is a huge improvement.

Just as exciting, my friend an neighbor Steve took delivery today of his new tractor, with which he’ll be starting a farm on the east end of our community’s land.

There’s other exciting news on the horizon, but for today I want to get this posted.  Pun, as usual, intended.

Deep Thoughts

No, not a Jack Handey reference, although I did find those amusing at one time.

I’m here to talk about my basement.  Why on (or more accurately, under) earth would I put thousands of extra dollars into a basement which doesn’t even provide living space?  It turns out that there are a host of reasons, many of which are quantifiable in dollar terms.

  1. Rainwater storage: $5,000 saved without direct burial.
    There are conventional water storage tanks which are designed to rest on a floor, and there are direct-burial “cisterns”. Even though both can be found in the price range of $0.70 to $1.20 per gallon, the cisterns tend to be on the higher end of the price range.  For 1500 gallons of water storage, a difference of $0.50/gallon is $750.  However, this is the least of the concerns.  A direct-burial cistern needs tank heaters if the frost line is below the level of the tank (and of course, it is here1).  These would obviously consume precious energy.  Then, there’s the excavation cost (assume a tank height of 48″, buried at maximum depth of 36″, in a 15’x10′ hole, excavated 8′ deep and then partially backfilled with compacted sand) which could add another $3,000.  Plus the materials for backfilling, perhaps another $1,200.
  2. Doing plumbing labor myself: $4,000 saved with basement.
    When one is doing plumbing work in a slab, one is literally setting into concrete the pipes and drains.  Any mistake (due to inexperience, or a design change) becomes extremely difficult to rectify after the fact.  I think it is fair to assume that being able to do the plumbing entirely myself will save $4,000.  (Typical plumbing costs for the reference homes were $8,500 to $9,200.)2
  3. Reduced heating costs relative to slab-on-grade: $150 per year
    By using the super-insulated SIP flooring over a relatively constant basement temperature, we’re able to save significant energy costs for heating and also require a smaller heating system. 3
  4. Solar storage battery lifetime extension: $600 per 10 years.
    Lead-acid batteries have a significantly extended lifetime and better retention of stored energy (albeit at a somewhat reduced capacity) if they are kept at lower temperatures.  Assuming a $2,000 battery array with a basic lifetime of 10 years, the loss in capacity might require a 10% increase in size, but the lifetime might be extended to 16 years.  Obviously the larger the battery array, the greater the impact, and this is an ongoing reduction in maintenance costs rather than a significant difference in initial cost.  The lifetime of electronics such as inverters and chargers is generally better at lower temperatures as well.
  5. Space for drain water heat recovery: $100 per year
    With a ground floor bathroom, it would be difficult to install a drain water heat recovery system.  This system can provide significant savings in the energy required to supply the home with hot water.
  6. Space for solar batteries and inverters.
    Although this doesn’t have a calculable direct cost impact, the fact that these large items don’t take up space in the home means that the living space doesn’t need to be increased to compensate.
  7. Space for greywater recycling.
    Again, this has no easily measurable cost impact.  However, because the toilet by itself uses over a quarter of the water in a typical US household, reuse of greywater from other sources for toilet flushing can dramatically extend the capacity of rainwater storage, allowing for a smaller system or better performance of the same-sized system (fewer “dry spells” that must be sourced from groundwater supplies).
  8. Space for rainwater first-flush system.
    Probably the greatest source of contaminants in rainwater comes from dust that collects on the roof between rain storms.  A “first-flush” system which discards the first 0.1″ of rain during each storm allows these contaminants to be washed away, providing much better water purity at the input.  Meanwhile, the flushed water can be routed directly to the greywater storage.  Such a system could be installed outdoors, but then it would be susceptible to freezing and potentially need to be disconnected during the winter time.  By implementing it inside the basement, it can be easily interconnected, easily maintained, and protected from freezing all at once.

So on the assumption that I have the house for 10 years, the basement is saving me on the order of $12,000.  Although I don’t have a direct way of comparing, this is comparable to the cost of the basement, and it also provides a number of non-monetary benefits listed above.

So, we go deep.

  1. Frost depth for a normal winter in the northeast is usually no more than 4 feet, so traditionally pipes are buried at 4 or 4 1/2 feet (5 ft for the main).  With only one day in February above freezing so far, the frost line has gone well below normal.
  2. Electrical work might be similar, except that in general very little of it needs to be done in the slab.
  3. Detailed calculation: Slab-on-grade, 102′ perimeter, 0.5 BTU/(hr-ft-°F), 24 hours/day,  6803 degree-days, adjusted to 8628 70°F-degree-days, gives about 10.6e6 BTU/yr.  SIP floor, 648 sqft, (70-50)=20°F temperature difference for comparability, R-41 SIPs, gives 361 BTU/hr or 2.8e6 BTU/yr.  Assuming a heat pump at $0.14/kWh, this difference is about $156/year.

Budgeting for Construction

Below is the budget that I have developed for the construction of the Little Rental House.  The lot was already paid for a long time ago (to help the community get the funds it needed for legal and infrastructure work) so that aspect is already known with accuracy.

When formulating the budget for the Little Rental House (#3, 992sqft, 2br 1ba), I used a combination of numbers from three homes previously built here at White Hawk: my own home (#6, 1536sqft, 3br 1.5ba), the home next door (#5, 1408sqft, 3br 1.5ba), and my parents’ home (#2, 1800sqft, 4br 2ba).  Because #2 was built in 2014-2015, while #5 and #6 were built in 2007-2008, the former gives prices much closer to “current day” while the latter need to be significantly adjusted for inflation.  However, #2 is a 4-bedroom home built with double-stud walls, so many of the architectural elements are very different.  #6 is the only reference with a basement, but was built with a lot of extras such as oak trim and flooring, so those costs aren’t representative of what I’m building.  And #5 is a good reflection of the trim level, but is larger and built a decade ago.

In all cases, I have the budgets (actual cost for #5 and #6, builder-estimated for #2) broken down into great detail, rather than just a lump sum total cost.  Thus, I was able to pick and choose, taking for example basement costs from #6, flooring costs from #5, and roofing costs from #2, with appropriate adjustments for number of rooms, square footage, etc.  Contractors often estimate construction costs on the basis of cost per square foot, and on that basis we find a range of $105/sqft for #5 to $124/sqft for #2 to $142/sqft for #6.

My basic budget (without the “extras”) has the Little Rental House just below the high end of the range at $136/sqft, even with almost no labor costs.  With the extras, it pops up to $147/sqft, higher than all of the reference houses.  There are several reasons for this.  First, the actual living square footage of the house is the smallest, so even though it is the lowest total construction cost, this increases the cost per area.1 Second, the basement is adding a substantial cost (about 6%) to the total.  Third, the additional cost of more heavily insulated walls adds another 6%.  However, it’s also unclear whether it’s fair to compare 2008 prices to 2019 prices; perhaps the homes built back then would be substantially higher today. 2

The budget below 3 represents the baseline that I’m working toward, will provide the structure for reporting the actual costs as we go along, and also provides the initial basis for estimated return on capital.

Budget ItemEst CostBasis for Estimate
Lot lease fee$40,000Contractual
Site preparation and excavation$8,000Assume same as home constructed on adjacent lot
Utilities-Oversight - was not budgeted
Foundation$10,330Assume: $4,000 for slab, $4,000 for ICF, 24.3cu yd concrete at $100/yd
I-beams$2,084Estimated based on weight of steel at $1/lb
Structural Insulated Panels (SIPs)$14,118$7.25/sq ft budgetary estimate, 1830 sq ft, $850 delivery
Framing material$3,000Detailed estimate from spreadsheet, rounded up
Framing labor$0Building it myself
Roof material$2,178Rafter framed, plus sheathing and steel roofing
Roof labor$1,600Assume same as home constructed on adjacent lot
Siding$1,800$1.5/sq ft
Siding labor$0Install myself
Windows and exterior doors$5,077Detailed estimate from spreadsheet
Electrical$2,250$25x40 outlets, $50x25 light fixtures
Plumbing$2,000Assuming I hire someone for septic but not for DW/DHW
Plumbing fixtures$1,700Use numbers from adjacent home but refactor for single bathroom
Heating$1,400Daikin RXS12LVJU
Wall finishes$7,000Use 60% of number from adjacent house based on smaller area
Interior doors$1,3004 interior doors
2 closet doors
Floors$5,952$6/sq ft
Kitchen$1,850Detailed estimate from spreadsheet for cabinetry, plus kitchen sink cost
Appliances$5,300Unique UGP-24CT1
Unique UGP-470L1
Combo washer-dryer
Microwave
Insulation$2,5004" R-6.5 foam over 7.25" R-3.6 cellulose in cathedral ceiling
Deck/porch$0Not including in initial build budget
Contingency$15,88820% of sum of above (except lease fee)
Extras - solar$6,718Battery backup
LED lighting
Extras - water$4,000In-basement rainwater collection and treatment
Total$146,045(including extras)

 

  1.  Some items, including the lot, have a fixed cost, so the smaller the home, the higher their impact.  Others, including site prep, plumbing, electrical, and roofing, have a significant base cost even if they do scale with home size.  Another important consideration is the fact that the home is mostly on a single story.  While this helps with accessibility, it means that there is, for example, more roof per square foot of house than there would be for a two-story home.
  2. One source suggests that this could have increased by as much as 50%, so that even the cheapest $105/sqft would really be $157/sqft, but I think that exceeds the construction cost people are seeing for other homes here, ones for which I don’t have detailed budgets.
  3. I apologize for the somewhat awkward formatting – I was torn between using TablePress (which gives you content in a searchable text form but doesn’t let me control the layout at all); or alternately inserting an image (which would let me make the format more legible, but wouldn’t contain text that you could access).