skirt insulation for foundation.
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We’re still debating what to do with our basement. We have an old house (1927) that’s fairly dry, but has no waterproofing of any sort.
We’re about to tear up an old concrete patio and likely replace with pavers. A guide published by our university recommends using a skirt insulation system for renovations.
It’s consists of 1′ of insulation below grade along foundation, with another 1′ of insulation extending out perpendicular to the wall forming an L shaped skirt around the entire house.
digging down 1′ is’t a huge effort, so it seems like a viable method. Has anyone done this? What are your thoughts on the effectiveness of it?
In our case, I believe we’d still want to insulate the interior, as we have a high foundation around the house (top 3′ is exposed) so this skirt would be more of a water barrier than anyyhing.
Does thi insulation add much to the basement in terms of heat retention, or is it mainly a method to redirect ground water?
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Does thi insulation add much to the basement in terms of heat retention, or is it mainly a method to redirect ground water?
That's a junior edition of what I do with underground houses. Difference mainly in that I go out farther from the perimeter. And likely use thicker insulation.
The effect, far more than just providing dry walls, is to insulate the dirt which is both our sole heating and cooling system.
In short, it works extremely well. I'd suggest you go out more than 1' though. Don't forget to slope it slightly so surface water drains away from the house. In addition to the insulation, we also use multiple layers of 6 mil poly. Redundancy is good (and cheap).
You don't need to be 1' under your grade, just whatever depth will allow your finish of choice. We have our insulation directly under the concrete patio slabs on 2 sides of our house. No reason for any dirt over the insulation there.
The insulation should be on the outside of your basement walls above grade. Been much discussion here over why that is the case. Has to do with utilizing the mass inside your insulation.
If you're thinking of simply butting 1' of insulation against your uninsulated basement wall, 1' underground, don't bother. Won't keep the dirt below any dryer or appreciably warmer.
You've got 5-6' of wall below grade? When I've convinced a HO with that much buried wall to do the insulation/poly umbrella, it's turned out very well in comparison to neighbors who didn't. Dry, of course, and noticeably warmer in winter.
PAHS Designer/Builder- Bury it!
yea, it's an 8' basement. 5' under, 3' above.We can't insulated the exposed portion on the outside, as it's all brick, so I'm not sure how much we'd gain with the skirt alone. If/when we do the basement, we were planning on doing full insulation on the inside (EPS from floor to ceiling).If we were to do that, are we still gaining something via the insulation on the outside? Or, at that point, is it mainly just a water shield and would we better off just using poly alone?If we do do the insulation on the outside, what's the benefit of the 1' along the foundation and 1' out? could one not just do 2' diagonally sloping out?
First decision is where the mass lives, inside or outside the insulation. For us, there's a clear delineation. What's inside the insulation umbrella and what's outside. But I started with a complete plan, not trying to figure it out as I went.
If you're going to insulate inside your basement walls, any insulation on the outside is mostly pointless. ICF manufacturers are bound to disagree. But that's like saying that more insulation is better.
Best plan would have you start at the brick ledge and head out as soon as below grade. Then you'd have the better part of 5' of dirt, dry and insulated. That's enough to realize some heat storage, which will far outweigh your thermal bridge of the wall thickness (10"?). But you'd need to stop your inside insulation at that point to realize the benefit. Seems unlikely unless you wanted a shelf line at that point..
You'd do fine with simple poly water-shedding IF you're going to finish the basement soon. Otherwise, consider the small cost of adding the insulation which will make your basement more temperate until you do finish it.
If we do do the insulation on the outside, what's the benefit of the 1' along the foundation and 1' out? could one not just do 2' diagonally sloping out?
2' out is the better plan. I'd suggest 4'. Unless you have landscaping need for much dirt over the insulation, there's no point. Whereas more dirt (up to 20' from the house perimeter) under your insulation actually does make the basement better. There's a demonstrable reason for that 20', but I'll spare you as it doesn't apply very well to your house.
All this is assuming that you don't have a high water table. Moving groundwater changes things greatly.
PAHS Designer/Builder- Bury it!
This is a bit off topic, Tom, but if you don't mind I'd like your input on a couple of questions:I have 4" of foam buried to the top of the footing (about 5' below grade) along the north side of my house (the other sides are already landscaped). I could still fairly easily add a layer of foam perpendicular to the foundation that could go out 8' or so. Think it would be worth it since the existing foam would still go 3-4' down the concrete wall below the apron of foam, thus insulating between the concrete and the fill?I have a hard time seeing ICFs as a way to hold heat since the heat can't get back to the living space any better than it can get out of the house, yet they are promoted as such and many seem to believe it. What do you think?Is there any particular PAHS book that you think is the best?Thanks, (contemplating another project)+++++++++++++++++++++++++++++++++++++"Doubt is not a pleasant condition, but certainty is absurd." Voltaire
Your comparison to ICFs is apt. Probably not worth the expense of the horizontal insulation unless you want to remove that 4" of wall insulation. Heat calcs can be done, but I only know how to do them manually. It's tedious.
I looked hard at ICFs when they were still claiming R50. You're correct. Not in my future, but I recommend them for anybody who won't pour a standard wall and insulate on the outside. They're much better than most foundations around here which are like the foundation the OP got.
There's more than 1 PAHS book? Here's an excerpt and link for getting the only book I know of http://www.axwoodfarm.com/PAHS/UmbrellaHouse.html It's a continuation of the research done by The Underground Space Center, U. of Minnesota "earth sheltered housing design" ISBN 0-442-28821-2.
There's a Pacific NW center of interest claiming better performance than PAHS, which the originator dubbed Annualized Geo Storage(Solar?), something like that, (AGS). Mostly is dirt heat storage from hot air captured from under a metal roof or some other collector. Unfortunately the guy has never publically given any details on hot air movement, despite repeated promises on the alt arch lists. Nor does it readily provide the cooling we enjoy here. When he and I compared notes several years ago, my PAHS actually outperformed his AGS when climate-corrected, which he doesn't. I much prefer a totally passive system. Nothing to break or maintain.
My house greatly underperforms the original one. I know why and am building another with the same defects. Our 13º annual swing is huge, compared to 7º of Hait's. But it's still very easy to live with.
Recently caught up with the guy living in the PAHS I built (shell only) down the road. Takes a few yrs to stabilize. He needed a mortgage, installed a tiny air heat pump. Didn't bother to install the heat pump water heater we enjoy. All electric 26k cu ft house, well pump, and original (unheated) old house which is used for a charity, total under $100/mo electric during the worst months. He's happy. And maintenance free. With nothing to freeze, or even get cold, he hasn't bothered with a backup generator.
In your climate, you'd want better windows and more exposed-wall insulation than we need. Hait's PAHS was Missoula, 8125 heating degree-days. Pueblo is 5462, Alamosa 8529. Feel free to ignore his architecture. I did. Keep us posted.PAHS Designer/Builder- Bury it!
Thanks for the input. I've had that old U of M underground house book for a long time, didn't realize the rarity of info on the matter.For a three story house (including the half+- depth basement), I am really pleased with what I built here, but improvement is always interesting. My house is 24x32 for about 2300 sqr ft of heated space. We burn about 5/8th cord of wood per winter and our high electric bills are about $150 for hot water, cooking, etc. plus an electric heater set on low to keep my separate shop from getting below about 45 degrees. (we had to install elec baseboard to satisfy our bank, but only use it on rare occasions other than winter in the upstairs bathroom) Our lowest level, with our only serious mass, stays between 61 and 71 year round. Honestly, my house heats more easily than I thought it would.Thanks again.+++++++++++++++++++++++++++++++++++++"Doubt is not a pleasant condition, but certainty is absurd." Voltaire
You're welcome. You're doing great, as you know. The returns diminish when you try to go much below your current creature-comfort cost level. 61º I wouldn't want, but as you've learned, doesn't take much to raise it to a comfortable level.
My costs, however, compete very favorably with above grade construction. The client house appraised 50% above construction cost. Certainly not entirely due to the shell cost, but it was a large part. This was house, independent of the land. The appraiser, correctly, ignored the energy efficiency. His elec bills, btw, could be considerably lower if he tried. As could my annual temp swings.
My experience on the internet is that having built a PAHS, I'm a rarity. Surprising number of emails from that web page the PACCCS (passive annual climate control systems) guy put up about us. Best? No. But for me, the best I've found.
Low mass houses can work just fine. There's a guy I know who builds houses that weigh about as much as an SUV, and work very well. My temperament does better with high mass.
Exterior maintenance also comes into the picture. I don't want any, ever. Not that above-grade can't be that way, just gets very expensive. Like when I tried to talk you into a copper roof for your place. LOL Those prices are only a pipe dream today. Yeow!
Quite certain I'll never again build an above-grade heated/cooled structure. PAHS Designer/Builder- Bury it!
I'd like to build a PAHS just for the fun of it, but... time and money. I do like moving dirt around!Ever here of PAHS built for spec? The funny thing about my not being willing to spring for a copper roof is that within months of putting on my roof it was damaged by hail and we were paid for it. OOhhhhh, it we'd just been paid for a copper roof!And thanks again for the input.+++++++++++++++++++++++++++++++++++++"Doubt is not a pleasant condition, but certainty is absurd." Voltaire
Ever here of PAHS built for spec?
I only know of a very few that exist, none built on spec. The book was published in 1983. Hasn't exactly set the world on fire. There will be another one, sort of spec, built on this mountain if I ever get to it. A rental- with round second floor master bedroom, surrounded by rooftop garden. An expensive piece of land (needing a pricey house), the other peak, and while owning/building a rental makes little economic sense, I can then control what happens there while getting a modest return (I hope).
The shape of PAHS can be about anything. Thought I was going to be doing one for a GC here in the style of early F. Gehry (Santa Monica- with all that corrugated galvanized steel). Unfortunately the GC's wife had a major stroke.
Lots of "underground" houses around, just few PAHS. Surprising, in that the PAHS umbrella makes a world of difference in performance and doesn't add much to the cost. Hait didn't help much though. Wrote his book and then wandered off to other pursuits. Most assume you need to follow his architecture, a dome. Which clearly has marginal appeal.
Recently heard from an acquaintance, major concrete player in Oregon, who was excited to hook me up with a very interested Maryland archy to broaden my base. What he didn't understand was that I don't want a broad base. Like building my rental (which is always owner-subsidized in our market), quality of life is far more important to us than financial rewards.
I remember you enjoying that Bobcat. Gets even better when you go larger. My current rubber-tire tractor has an 8' wide bucket, weighs 23k lbs. Not that I would drive it on a roof, still have a compact for that. Get something big and IMERC'll come play...
Care to share what your next project might be? If spec house, how close are you to the tire bale/straw bale/earthship subdivisions? I haven't paid a lot of attention to just where they are. Have seen some very interesting resales. Apparently financing works. More difficult here. Which is one reason we used conventional commercial construction. The other reason, low cost.
Thanks for the interest. I proselytize shamelessly, get lots of lip service, few confirmed converts.
PAHS Designer/Builder- Bury it!
Edited 9/11/2006 9:33 am ET by VaTom
I move really slow, Tom.If I'm contemplating a project now it might get built in a few years.I have a reasonably nice 4 acre lot that I got for back taxes. The title will be perfected in about two years. Lot has a good view and gentle south slope.There are no "earthship" subd's around here.Despite the beautiful homes that Cloud builds, I agree that domes have a very limited appeal and don't sell well.Ever see a book called "the $50 and up underground house book"? It's a comvination of bizzare and useful.Everytime I see my wife sell a spec house I cringe at how it was built and I want to build again.I believe that those of us who leave behind homes that will economically comfort people in the future, people that we'll never know, it is a good thing.+++++++++++++++++++++++++++++++++++++"Doubt is not a pleasant condition, but certainty is absurd." Voltaire
Ever see a book called "the $50 and up underground house book"? It's a comvination of bizzare and useful.
Yup. I'll be politely quiet. Other than to mention that I don't find disposable housing interesting. Looks to me that Oehler's interest was selling books.
I believe that those of us who leave behind homes that will economically comfort people in the future, people that we'll never know, it is a good thing.
There you go. I don't imagine we'll be the last people living in this place. One strong influence I had was visiting the Pantheon (Rome), Hadrian built AD 120-124. Concrete. Not the same as I bought, but I'm pretty sure our place will provide somebody a comfortable life for quite some time.
Domes have been the kiss of death for resale here. Left over from leaky geodesics of course. There's a trailer where one once stood near here. Very unrelated to Cloud's Monolithic construction, but the stigma lingers. I empathize with his preference for "thin shell", or whatever, over "dome". Not that I find Monolithic construction attractive. Incompatible with PAHS.
I don't pretend to be any expert on spec homes, but I'm skeptical about the knowledge of the general buying public. You're appalled, but the average buyer apparently isn't. Does that translate into opportunity? I don't think so. Unless you want to undertake education of said average buyer.
What I'd look at is the unaverage buyer. Time on the market might presumably be longer, but so will profits. I don't want to try to start another Levittown. If that was even a remote possibility.
One thing I learned some time ago was to follow my dream. You want to build? Do it. You have enough wherewithall to figure out what will work (economically) for you. And there's plenty of time to plan. Have fun.
PAHS Designer/Builder- Bury it!
I actually met Mike Oehler. Weird guy, I thought. The thing I liked about his book was that it introduced me to the idea that even a buried structure could have various openings for light, views, and ventilation.If I build a spec it will be because I feel like it. If I build another spec I won't worry about selling it since I'm married to the most successful home salesperson in town. I'll be slowly mulling it over.Thanks again for your input.+++++++++++++++++++++++++++++++++++++"Doubt is not a pleasant condition, but certainty is absurd." Voltaire
You're right. Oehler did talk about some things most underground authors didn't. And they're important. Believe there was a second book, which I haven't seen.
We have only 1 windowless (N) wall, avoided roof penetrations, and yet we have one of the brightest houses I've been in. In no small part due to the roof slope, which also gives us a great thermosiphon. Extremely simple, surprisingly effective. Even the client house, with a 40' span wasn't dark in the rear. It also had only 1 windowless wall.
BTW, structural steel is sold by the pound. But the price/pound goes down with increasing size, making larger steel a bargain. Nobody explained that to me when I bought my 30' barjoists. The crane guy who set the 40'ers (600 lbs ea) had a hard time believing anybody would use such large steel residentially. When I told him the price, he about fell over. Pointed out that wood trusses would have been more expensive. And if we weren't supporting 300 tons of roof, we'd have needed far fewer barjoists.
Don't remember what you did for your house, but I'm a great believer in frequent airchanges. Takes a very small air system and exchanger. Does not increase the cost of the house if you substitute some fixed windows for operable. Here, opening a window would be unusual most of the year and yet code ventilation requirements are considered met if there's an operable window. Not unusual for a guest to mention our air quality. Partly 'cause it's fresh, partly 'cause we filter out pollens, particulates, etc.
Happy planning!PAHS Designer/Builder- Bury it!