Wow, I’m Floored!

For the last couple of weeks it has been “damn the winter weather, full speed ahead!”  And somewhat to my surprise, I managed to get the floor panels I designed (and wrote about here) completed.  Apparently after repeated exposures, my hands finally got used to working in 37°F (2.8°C) weather, and I didn’t feel cold any longer.  My ears were protected by 3M™ WorkTunes™ headphones, which may have been the single best tool investment I have yet made on this project.  Certainly the most consistently utilized, particularly with Spotify keeping my ears happy and not merely warm.

A big ($3000) order of materials was delivered in late October, and I immediately started trying to get the flooring in place.  Zephyr was intrigued.

Curious cat is curious

At first things went pretty quickly.

However, my birthday party happened just a day or two into getting the materials, so it was almost November before I really got going.  Below you can see the bracing ready for the 2x4s to come in above the PIR foam board, and the 2×6’s used for every third span (west side) and for all of the 7′ spans (east side).

Here is some of the PIR foam board in place, 2×4’s across the top and on the braces, spray foamed along edges of PIR, as well as the first batt of rockwool.

And finally here is what it looks like with all the rockwool in place.

Then I started to get the actual subfloor laid on top.  Unfortunately, not very long into this we had our first 4″ snowfall, and thereafter I was spending a lot of time with the shop-vac removing the snow and water that was stuck inside various cavities (either on top of the PIR board, or on the PT plywood bottom layer where the PIR board was not yet laid).  Furthermore, laying the tongue-and-groove subflooring with the appropriate staggered (and thus, diagonal) pattern turned out to be extremely time consuming.

It’s probably worth sharing that the necessary tools for this are one (or more) sacrificial 2×4’s and a sledgehammer.  You lay the 2×4 against the edge of the subfloor plywood (best if it’s the groove side) and whack the crap out of it to get the plywood to move across the glue and into place.  I shattered one 2×4 along the way and beat another one beyond the point of further usefulness.  Also, on occasion, you may want wood shims (used to force the tongue up into the groove) or a wonderbar weighted down with a heavy piece of PT lumber (used to force the groove plywood down onto the tongue).  Or, you could do this with more than one person, in which case, you get someone to stand on the edge to keep it aligned while you whack the 2×4.  This is definitely one of those “better done with a team” jobs.

But, in the end, I managed to get it all in place.  I still want to come back and add the house-wrap to the remaining 2/3 of the floor, to keep water out over the winter, but at least the main job is now complete!

 

Was it worth it to do all that extra complex framing for the 10% improvement in insulation?  I’m not sure – maybe not.  I’m estimating that adds up to maybe 85 BTU/hr or 25W of heating saved, whereas the remaining total loss through the floor is perhaps 875 BTU/hr or 256W.  The R-41 SIPs would have been closer to 553 BTU/hr for a savings of 94W.  (All these numbers may be lower if the equilibrium temperature in the basement is higher.)  But I learned a lot of interesting things along the way.

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.

A little afterword about the R-value.  Using data on individual components I’m estimating the average R-value for the entire floor at 25.9.  It’s interesting to see that 77% of the heat loss is through the two layers of insulation; 14% of it is through the 2×6 joists; and 8% of it is through the 2×4 joists.  Thus even though the 2×6 joists account for less than 5% of the total area, they’re responsible for a significant fraction of the heat loss.  If I had used 2×6 everywhere, the R-value would have been lowered to 23.6 (almost 10% worse) and the joists would have been 30% of the loss.

 

  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.

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).