Insulating the foundation

the pit

the pit

There is now a big pit against my foundation where the gas pipe heads under ground. This has been hand dug in advance of the mini-excavator, which will show up in 2.5 weeks and will finish digging the pit around my foundation. This part had to be dug by hand, because believe-you-me – hitting a gas pipe with an excavator is a big deal! It wasn’t too hard to dig – I’m pretty good with a shovel and Gil and Osh both put in a couple of hours too. For a pit about 4 feet deep by 8 feet long by 4 feet wide, I figure it was about 8 (wo)man-hours of work. The big thing is motivation – so much easier to kick back with a lemonade than start, though pretty hard to quit once you are going, too. I am loathe to do any more by hand, though, since I know the excavator is coming. Actually the big pain is all the big concrete blocks thrown in when they backfilled originally.

But that is the pit, what’s the whole story here? I’ve been planning external insulation of the foundation since I bought the place. It was built in the days when you didn’t insulate the slab or basement, except on the inside when you finished it for living, and that lets lots of heat out through the floor and walls of the basement. Not too bad, since the earth helps keep temperature swings smaller – the deep ground temperature in Anchorage is about 36 F year round, instead of -20F to 80F outside air temp, but bad enough. I like external insulation on a foundation wall for a number of reasons, the main being that it keeps the masonry inside the insulation layer, letting it serve as thermal mass in the heated building. My favorite technique is passive annual heat storage, but I can’t really do that full blown here.

So in May I finally got my home energy audit for the state’s rebate program, and not surprisingly, foundation insulation is by far the most cost effective measure I can take to save heating energy at home – more than insulating the upper walls and attic more, WAY more than replacing doors or windows. My computer-printed recommendations include adding R-14 to the basement walls, then going out 2 feet around the perimeter of the slab. I am doing a slightly buffer version of this – I am going down 4 feet below grade and also doing the 3 feet of concrete block wall above grade, then going out with the insulation 4 feet once I am down 4 feet. I am using 4 inches of blueboard for approximately R-20 added. This should trap quite a bit of the heat of the basement in. The state program’s computer printout indicated that the installed materials cost should be about $2300, partly because they have me covering less square footage with less R-value insulation, but also I think they have underestimated. The break-even point is calculated at $7000, and that is about what it is going to cost me – ~$4700 for 102 sheets of 2″x4’x8′ Dow blueboard (extruded polystyrene) delivered from Lowes, a bit over $1000 for excavator rental, ~$700 for hired friends’ labor, and misc. for adhesive, stucco, flashing, waterproofing membrane/tar if needed, etc (probably a bit more than $7000 in the end), but I will have achieved a higher insulation value than that assumed in the end too. I will get money back from the state program for this. That amount is dependent on how many energy points I go up for all the work I do in the next year or so (18 months from my first energy audit), how much I spend, and is capped – no more than $10,000 total, but quite likely less. My auditor said I am at a cusp and it will be fairly easy to recover $4000 for anything I do.
I did a quick calculation given the heating degree days in Anchorage, an assumed current insulation value of about R-10 on the basement walls, an upgrade to R-30, the local cost of gas (grossly about a buck a therm), a boiler efficiency of 82% – and got a payback of about 35 years, or a savings of about 2.5% of the installed cost every year in gas bills. I may have made some errors, as it really should be more than this I believe. One obvious error is assuming that the cost of gas is not going to go up. I’ll try to ferret that out a bit better, but the real test will be real utility bills. The interplay of thermal mass and thermal resistance of the ground messes with the straight-forwardness of an R-value thermal conductance static problem.

Cost of efficiency measures

Cost of efficiency measures

This graphic (unreadable – I know) came from today and was from a report on efficiency being likely underestimated as a negative cost (i.e. it pays you) way to achieve meaningful carbon cuts. Basement insulation is on there – about smack dab in the middle.



Drunken Tiramisu

Drunken Tiramisu

Other recent endeavors have included painting the entry door and area and making drunken tiramisu (‘drunken’ describing both the human state while making it, and the alcohol content of the final dish – probably interrelated) at a wonderful impromptu dinner party at Dallas’.


6 responses to “Insulating the foundation

  1. 35 years to recoop what you spend? Sully wants me to remind you that the world will end by 2012, so not likely to get that all back.

    And he says if you can dig all that, what’s little North Arlington wind farm? Get on it! We expect to review the blueprints by next fall… have such high hopes for you.

    No, in all seriousness, you dig an impressive hole. Is that like a fringe benefit of your job? Learning how to dig holes?

    I admit you lost me a big on all the math (my eyes glaze over), but now I’m intrigued about the thought of basement insulation. Though I’m going to give a guess that Arlington is less likely to need the added insulation.

    Well, i’d better catch up with the rest of the blog, I’m very far behind. but now I have this strange craving for tiramisu… what’s that about?

  2. Hey – you do dig a mean hole! And don’t contractors have a wonderful disposal methods – reminds me of all the dead (what did you expect them to be?) trees around the foundation of my old house when I added on. Trees don’t rot in the Anchorage soil. Save something for me next summer – and hope the weather holds. Digging in the rain ain’t no fun – I know!

  3. Dallas Wildeve

    Happy to see all the new pics!

  4. Wow. That’s not half a hole!

    I don’t see how this can be at the top of the cost-efficiency scale if you’re really only going to save $150-$200 per year as a result of all this work. And if the calculation is right, well jeez, no wonder we use energy the way we do at those prices. In our house the energy bills are pretty much down in the noise of the other expenses. $13/month for gas and $30/month for electricity, split between two people. Crappy though the house’s insulation is, there’s nothing we could conceivably do (even if we owned it) that would be financially worthwhile.

    On the other hand, some decent insulation, non-plate glass windows and a white roof would probably keep the interior temperatures above 50 in the winter, and below 90 in the summer… which would be a nice non-financial gain 🙂

  5. And that Passive Annual Heat Storage site is also advertising some “resonant field theory” anti-gravity machine BS. And I don’t mean Bachelors of Science.

  6. Wow – didn’t see the anti-gravity hullaballoo, that takes it down a notch in my books. I do think the passive annual heat storage concept seems intriguing with limited applications, but yikes.

    I redid the calc quickly, trying to account a bit better for the horizontal bit of the insulation, and I think it may be closer to a $330 per year saving and a 21 year payback. Of course with the incentive of at least $4k, thats a 9 year payback and closer to a 10% per year return on investment. Like I said though, I haven’t accounted for many real world thermal behaviors. We’ll see. I have a legal requirement to supply heat to at least 68 F, and most of my tenants take me up on that. Heat in the summer is not really a problem though. My basement tenants have been known to use an electric space heater in the bathroom when it gets too cold in there (no baseboard), and my pipes froze when the heat was on the fritz and the basement got to about 50 F (-20 F outside). So the insulation outside should help keep pipes from freezing, whatever the outside temp, help eliminate the cold bathroom and the need for mega-expensive electric heating, and have other beneficial results.

    New windows and doors are very expensive without a big effect. The wall cavities and roof are pretty topped off, so other insulation will also be exterior foam, which means ripping off and replacing siding – not cheap. The boiler is already pretty good, and the water heater is new and efficient, so not much else I can do along these lines. My monthly gas bill ranges from about $100 to about $400, electric is about the same range. Lows for both in July/August, highs for both in Jan/Feb. Utilities are my biggest expense, in that rents pay the mortgage, so the lower I make them, the better off I am!

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