I would love to discuss my design with Bruce Greenlaw if at all possible–does anyone know how to contact him?
So far, I have not found any good resources with a great deal of experience in this area of California (Sacramento) for green roofs and earth-bermed walls. And there are a mulititude of products to choose from nowadays with regards to water/damp proofing.
I am looking into Safecoat(R) DynoSeal products, GenFlex roof membrane systems, and Akzo(R) Enkadrain systems at this time.
The structural roof deck will be a composite of hollow-core conc. planks topped with 3″ of rein. concrete sloped at 3%. All retaining walls are CMU with parge coating. A complete foundation drain will be installed and a free draining fabric envelope will be against the walls. The main retaining walls will be non-insulated so that thermal coupling is enhanced between the earth mass and the house. A watershed umbrella will be extended approx. 20 feet from the the retaining wall over the earth mass. The watershed umbrella (water proofing, insulation, and earth) follows the Passive Annual Heat Storage (PAHS) concept as developed by John Hait.
So that is a lot and most likely not enough to understand with clarity.
Anyone out there with experience in this area?
Replies
Sounds Interesting. I guess the objective would be lots of thermal mass and a cool place in the hot summer. What part of Sacramento are you building in? I have a house in River Park.
I live outside of Lincoln, near Camp Far West Lake.
Anyone out there with experience in this area?
Yup. Been living in one for 10 yrs. Built one for a client a couple of years ago. Have another out of the ground, for us. Welcome to BT. A search will probably show up quite a few posts and pictures of PAHS here.
I used bentonite rolls for waterproofing, insurance was the way I viewed it. My client decided to forgo the expense. Several layers of 6 mil plastic have kept him dry very nicely. We used scrap carpet to protect the plastic both from the concrete and rocks in the backfill. Worked fine. I won't be buying waterproofing again. With reasonable siting, your insulation umbrella will be all you need to keep your mass dry.
I would strongly question your decision of cmu. Don't see any cost savings and the drawbacks are obvious.
When you say "retaining walls", do you mean outside the structure? If so, you really do want to insulate the back of the wall, where your umbrella meets the wall. Having an uninsulated wall, exposed to air and connected to your mass is a large mistake. You also won't need a foundation drain. I've installed 2, neither has seen a drop of water come out. Didn't want to do the second one, client insisted.
If cost is a large concern, buy the insulation but re-evaluate your roof system. Steel bar joists with a thin concrete slab over, will likely be very attractive. Both of these houses have 15' of earth behind the rear wall. Serious engineering involved. The building inspector was flabergasted with our footings. Still came out extremely low cost housing. Client house mortgage appraisal came in 50% higher than construction cost.
Good choice on your heating/cooling system. <G>
PAHS Designer/Builder- Bury it!
Thanks for the information. I am also torn between what I think will happen and what is recommended based on conventional wisdom. The hillside behind the house is composed of a shallow upper soil underlain with fractured rock of varying degree of fractures. Winter rains saturate the hill and shallow groundwater travels along the fractured rock-soil interface until it finds larger fractures on its migration down. This poses a potential problem with water during late winter and early spring. I have the insulated mass behind the house terminating in a curtain drain located at or below the soil-rock interface. This is the first line defense. The bottom of the curtain drain will be more than 5 feet above the foundation. The actual path of water through the fractured rock is hard to predict. Even protecting the area behind the house with the umbrella and curtain drain, I feel there is a good chance that water may travel in a fracture under hydrostatic pressure during peak runoff periods--it can even go up hill in these fractures--piping. In such a case, the dry foundation and surrounding dry soil would soak up the moisture. Because of the nice climate here, I am not overly concerned about the soil mass getting wet due to this condition--there is little I can do to prevent it; however, I am concerned if the foundation gets wet--so I am using a perimeter drain for that worse case condition.
The retaining wall behind the house will be under the umbrella. I am not planning to insulate the back retaining wall because it is my thermal coupling to the mass behind the house. All other walls are insulated against the environment to prevent thermal breaks in the mass.
Thanks again for any help.
Edited 3/24/2005 1:43 pm ET by hmr
You're welcome. Not an ideal site. Remember what Hait says about ground water moving through your mass. PAHS will be extremely compromised. Water will do a great job of moving the heat considerably faster than that 6 mos/20ft, to the point you may have no storage.
But you're right, wet walls would be considerably worse than just lost heat. Given your situation I'd probably do the same thing. The PAHS umbrella doesn't cost much and even though you won't know up front how well it'll work, it's a small gamble. Might be that your ground water doesn't compromise the PAHS all that much.
The houses I've been involved with all had uphill slopes behind the house, but not a problem with water moving through. By extending the umbrella that 20', we've had dry dirt without any difficulty. A bigger issue for us has been surface water channeling to direct it where it wouldn't pose a problem. Swales have worked fine.
For your site you have another alternative, Annualized Geo Solar (AGS). Is this a concept you're familiar with? Originated by Don Stephens of Spokane. He and I've butted heads several times over his disparaging PAHS (which works far better than he'll admit), but he uses other systems, usually active, for annual heat storage. He finds great fault with using the house at the heat collector (another disagreement I have). Your climate is close enough to his to be applicable. Humid summers, like Va, are outside his realm. You might take a look at his web site.PAHS Designer/Builder- Bury it!
Thanks Tom,
So in your opinion, the multi-layered PAHS umbrella with 6 mil visquine is the way to go. I am thinking about a little higher grade plastic sheeting for the first layer. SOCOSHIELD (polyolefin) 10 MIL @ 0.20 per sq.ft. out here in Calif.
I have personnaly uncovered "visquine" (polyethylene) sheeting and found it brittle and deterorated. But I did not know the history behind the installation. I understand the view from John Hait. Have you investigated the differences, if any, in the garden variety polyethylene "visquine" sheeting products. I have faith in ployethylene as a substance but I don't have faith in all manufactures--any preferences?
Edited 4/8/2005 6:51 pm ET by hmr
Not attempting to discourage you from using waterproofing, just make sure it really is waterproofing, not dampproofing. We've been successful using solely our umbrellas to keep the mass dry, making waterproofing unnecessary. If your mass is going to be wet, I'd want waterproofing, and it'd be bentonite. If water is moving through your mass, annual heat storage won't happen.
The poly I've dug up was 12yrs old, no sign of deterioration. Now, if I'd left it exposed to sunlight for a few months before burial, it certainly would. We're pretty quick to cover. And as you point out, it's several layers, not one or two. A larger problem with our fill is to avoid puncture from rocks. That's where the carpet scrap comes in. Takes a lot. We keep the carpet stores real happy for awhile.
Regarding manufacturers, I haven't paid any attention. Clearly, thicker will be safer, primarily from abrasion. I once operated machines that make poly sheets. Extrusions blown into huge balloons before collapsing and cut into ribbons. Any appreciable dirt in the extrusion process compromises the product, independent of thickness. At the time I was told that environmental factors precluded this happening in the US. Don't know the current situation as I've been away from the industry for a long time, but what we made 30 yrs ago certainly had an incredibly long lifespan if unexposed to sunlight. How long? Don't have any idea.
Another possibility would be greenhouse sheeting. What I'd use if I couldn't get it buried promptly. Not something I have experience with. Is SOCOSHIELD a version of that?
We're at the end of winter here. Got the first morel yesterday. Our mass has reached it's minimum temp, ready to perform its other function, keeping us cool through a hot summer. In 6 mos that'll reverse. Pretty easy way to live. A friend here has a similar house (20,000 cu ft but better insulated than we are), bermed but no PAHS, and burns 4 1/2 cords every winter and runs AC summers. If they can find the right place, guess what they want?
Good luck.
PAHS Designer/Builder- Bury it!
Edited 4/9/2005 8:48 am ET by VaTom
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I think its best to describe the probability our PAHS Mass becoming wet from water movement through the fractured rock zones as about 5% chance. I am not overly concerned because there will be a curtain drain some 20 feet away from the back wall. This curtain drain will be founded in parent rock. This will provide a path of least resistance for the any water traveling in the fractured zone above and/or near-zone below. The curtain drain will coincide with the surface drainage alignment and be the termination point for the PHAS umbrella.<!---->
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My foundation will be in parent rock, 7,500 psf allowable bearing pressure per GEO-RPT. We only get about 18-inches of rain annually. The shallow soil profile (2’), underlying fractured rock zone (6” to 6’), and parent rock beneath with larger fractured zones create an unknown with regards to water movement. Looking at options with regard to water proofing in addition to the umbrella is a mere added precaution in the design. I think bentonite is an overkill at this site--there is no chance of hydrostatic pressure against the walls.
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Here is the data on SOCO-SHIELD. I am not sure of the difference between a “Polyolefin” and “Polyethylene” sheeting but they are likely to be similar polymers of the same basic materials.
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A 15 mil sheeting for the top layer of the umbrella is what I was thinking. Your use of carpet scraps is another option—I will look into the carpet places for scrapes—I already have some carpet to use that was headed for the landfillJ. So, I am still eaning towards just using the 6 mil poly--we will see.
TECHNICAL DATA--SOCO-SHIELD 15-MIL <!---->
Puncture Resistance 206.0 pounds <!---->
Tensile Strength 36.7 pounds @ 997% MD <!---->
Tear Resistance 8.74 pounds <!---->
Low Temperature Impact Resistant to -105° Celsius <!---->
Water Vapor Transmission Rate (WVTR) 0.00585 grams/hour/square foot <!---->
Perm Rating 0.014 grams/square foot/hour/inch Hg <!---->
Chemical or Environmental Attack Unaffected <!---->
Life Span Indefinite <!---->
Color Brick Red <!---->
Thickness 15-mils <!---->
Roll Dimensions 12 feet x 120 feet <!---->
Roll Core 3 inches x 6 feet <!---->
Roll Weight Approximately 86 pounds
Thanks again for you comments.
You're certainly welcome. Very happy to see the interest.
Sounds like you're getting pretty well informed. 18" of rain isn't a lot and you mentioned it happening in winter. Clearly I'm not knowledgeable about Sacramento climate, but it seems a small risk. At your assessed 5%, it's smaller risk than yearly variations. I ran into considerably more consternation on another site over earth tubes. They were worried about exact installation, which would clearly be climate/site specific. The differences might make a 2º difference at most, hardly significant. I'm getting good performance without any at all.
Somewhere in here it's going to come down to your budget. Cost effective is going to be very difficult to determine. If you have a large budget there's no reason to avoid lots of insurance. Otherwise, consider the possible consequences of a compromised PAHS. Not difficult to live with. Still going to be better than anything else going, IMNSOHO.
Joe Anderson, the guy responsible for that excerpt I linked to, is a Colorado engineer who offered to model PAHS for me. I never asked how much. Haven't corresponded with him for awhile, nor do I know his credentials. That same site where they were concerned with placement of earth tubes had a Washington State engineer of some sort who claimed to know all about modelling. I didn't see a reason to employ either, but if you do, give me a yell.
Good luck with your house. Did I convice you to dump cmu? There is an undergound house near here, not PAHS, that's post&beam with cmu infill, dry stacked and parged, maybe 6" earth cover. Owners are happy. Their performance is not ours, but not a problem for them. It's a continuum.
PAHS Designer/Builder- Bury it!
I am still using CMU bearing/wall system. Not sure on the exact reasons you are against cmu. Please let me know why you think I should change and to what bearing/shear wall system I should investigate.
Cast-in-place needn't cost any more and is considerably stronger and more water resistant.
It's also DIY friendly if that's your inclination. When we built this place there were very few poured walls done here, all block. I got astronomic quotes, bought a how-to book about forming, and had at it with two guys who knew less (nothing) than I did. Since then I've poured several hundred yards of concrete. CDX plywood makes good forms. Also allows curves, which is my preference, along with arched windows and doors.PAHS Designer/Builder- Bury it!
I also looked at having either pre-cast or cast-in-place bearing/shear wall system. Contractor prices were too much. So that left forming and pouring or using cmu. It was my understanding and still is that special inspection would be required here for either concrete or cmu wall system design under full stress allowances; however, under working stress design if I used half-stresses I could eliminate special inspection requirements. This is what started me down the path of cmu. I have designed all the walls with half-stresses--however, a few of the spans require full stresses and I have had to use a full concrete beam design under the strength method. I am a one-man island with the design. I feel its a little late to backtrack at this stage--I have prepared all the design documentation for cmu; however, I am always open to comments and alternatives--thanks.
I mentioned your helpfulness to my wife ans mentioned that it would be nice to visit the houses you have been involved with. It that a possibility? Can we get a tour of a few?
Edited 4/19/2005 1:29 pm ET by hmr
I used bentonite rolls for waterproofing, insurance was the way I viewed it. My client decided to forgo the expense. Several layers of 6 mil plastic have kept him dry very nicely.
Wow.
What was the savings, plastic vs. bentonite rolls ?
If the plastic starts to leak, what do you do to fix it and how much would that cost ?
carpenter in transition
Hi Tim, for PAHS, there's an insulation umbrella that covers the house mass and extends ideally 20' out from the perimeter, with ground water chanelled away from the house. The umbrella consists of layers of plastic and rigid insulation. My use of bentonite was next to my concrete, an insurance against leaks if my umbrella failed. Here's a book excerpt about PAHS:
http://www.axwoodfarm.com/PAHS/UmbrellaHouse.html
If the umbrella fails, there's no (or less) heating/cooling system. Care must be taken with installation. Found my notes from my original construction indicating bentonite rolls were .52/ft. IIRC, the last time around was closer to $1, which would have added $3k material, plus installation. I consider bentonite the best waterproofing there is, assuming adequate earth pressure. It's been the waterproofing of choice by the gov't around here. With the umbrella we feel comfortable with a layer of plastic, over carpet, on the concrete. It's to keep the house dry until the umbrella is in place.
I know of no reason why the umbrella would "start to leak", if properly installed. Far as I know it doesn't degrade underground. It's also not one layer, but several, with rigid insulation between. I think we spent $250 on the plastic for the last house. Comes in large enough rolls that there aren't even any seams. I've been asked about burrowing animals, but that hasn't been an issue. Bear in mind there's some nice topsoil on top of the umbrella that's more attractive as a home.
To answer your question, it would take me a day to remove the dirt from the house and 2 more days, with 2 helpers to replace it. Plus the roof landscaping. This is very inexpensive housing, requiring minimal skill and time. PAHS Designer/Builder- Bury it!
Thanks for the link, very interesting.
I like the use of green building materials and the lack of a heating system ( or a minimal one ). As I read the article, I thought this really isn't for me, but I did appreciate the second generation home in Montana. It seems to address my concerns about the feeling of living in a cave.
carpenter in transition
It seems to address my concerns about the feeling of living in a cave.
Here's my "cave", with 400 ft of windows:PAHS Designer/Builder- Bury it!
If you haven't done so already, you should check out http://www.greenroofs.com which has a lot of links to other organizations as well as quite a bitof information on the site. There is a long list of resources, but I didn't see anything specifically for the Sacto area - the Bay Area Council was about as close as they seemed to get. http://www.greenroofs.com/resources.htm
There is also a book out called Planting Green Roofs and Living Walls, by Nigel Dunnett and Noël Kingsbury 2004 from Timber Press, Portland, OR. I looked at over at the Green Roofs conference in Portland, OR, last year. It seemed to have a lot of information on the plants that will survive and the soil preparation, but I don't remember anything specifically on the brand names of materials to use as a roof membrane.
I suppose you could post something on your local "Craig's List", although from my experience you are likely to get responses from guys trying to get started and without much financial backing.
Thanks, I will vist the that website.
The Solar Living Institute/Real Goods in Hopland is a good source for all kinds of green and alternative building solutions. Don't know if they have anything about green roofs, but I'm sure it would be worth a visit. Of course, afterwards be sure to stroll up the street to the Mendocino Brewing Company!
Thanks, yes. I have a catalog or two from them and my wife has been to the store. I have not had a chance to visit them.
Edited 4/8/2005 6:41 pm ET by hmr
Don't know how green you want, but check out Ducks Unlimited. They have a building at Oak Hammock Marsh ( Northern Manitoba ) that grass grows on the roof and is designed so as not to impact the ducks migration. You should be able to find the web site and get some more info.
IF IT WAS EASY, EVERYONE COULD DO IT!
Thanks, I will go after this reply and check out the website.