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PAHS

 
Kelly Mitchell
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Any info on adding PAHS to an existing house?
This has 2 components:
Hilling up against my current house - what problems, benefits would it have?
Also, I'm planning an addition and wondering if it's feasible to integrate a WOFATI style for it.

How cheaply can these techniques be practically done?

I saw one website where the fellow was spending at least $300k for building his whole WOFATI house setup with everything (my guess).
I have very little in the budget. What's a realistic minimum for a 400 ft2 addition?
 
Philip Nafziger
Posts: 65
Location: Columbia, Ky
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Hi, Kelly
Practically speaking, it is not very difficult or expensive to create a PAHS hybrid with an existing home. The idea is to dry out and keep dry as much dirt surrounding your home as possible. I drew up a mock home on paint quick, showing a PAHS modification on a typical home. The yellow line illustrates the amount of heat storage capability before and the green line illustrates an added "umbrella" created with plastic and the new associated storage capabilities.

Does your house have a basement? Do you have access to any machinery? What is the geology of your land? Flat, clay, etc?
PAHS.png
[Thumbnail for PAHS.png]
 
Kelly Mitchell
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Yes, we have an old cellar - mortared stack stone, 4 ft thick.
Slight slope, rocky clay, very wet climate (Canadian maritimes).
I would hire an earthmover.
 
Philip Nafziger
Posts: 65
Location: Columbia, Ky
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Kelly Mitchell wrote:Yes, we have an old cellar - mortared stack stone, 4 ft thick.
Slight slope, rocky clay, very wet climate (Canadian maritimes).
I would hire an earthmover.


Very good.

As far as the addition goes. Do you have any building experience? Underground/WOFATI type structures can be done on the extreme cheap but you do need to know what you're doing. If you can find salvaged lumber or get a good deal on some, PSP (post, shoring, polyethylene) would be a great option. More conventionally is the permanent wood foundation or you could use whole trees from some woods nearby? If I was building a 400 sf WOFATI style addition and bought all of my materials from the lumber yard, it would cost about $1,300 plus the cost of your floor (earthen floor?), plus the cost of the excavator, plus the cost of finishing the interior. If you use salvaged materials the price comes down, if you use trees you cut yourself it comes down more. Hope that helps. If you have any questions about the different design methods I described please let me know. I would be glad to assist you more if you would like. Phil
 
Kelly Mitchell
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Thanks. - I do have some building experience, but not a lot. I have a friend who built his own conventional house and is quite good who will help/advise.

One question - I can't seem to figure a way to get the machine there fewer than 3 times - 1) initial dig, 2) covering the addition after construction, 3) covering the insulation after placement. Any thoughts on getting that to 2 runs?

I would use earthen floor with a bit of cement mixed in for hardness. Will that work? Can I put posts on the floor, or should I post them on gravel/cement pads, then build the floor around that?
 
Philip Nafziger
Posts: 65
Location: Columbia, Ky
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Kelly Mitchell wrote:Thanks. - I do have some building experience, but not a lot. I have a friend who built his own conventional house and is quite good who will help/advise.


Great! These types of structures aren't super complex anyway. Plenty of wiggle room.

Kelly Mitchell wrote:One question - I can't seem to figure a way to get the machine there fewer than 3 times - 1) initial dig, 2) covering the addition after construction, 3) covering the insulation after placement. Any thoughts on getting that to 2 runs?


I got nothing....

Kelly Mitchell wrote:I would use earthen floor with a bit of cement mixed in for hardness. Will that work?


It will, but it's not really necessary. Layer of gravel, 3" layer of clay, sand, straw mixture, and a 1" layer of clay, sand skim coat. Essentially. I could go into more detail but that's the basic.


Kelly Mitchell wrote: Can I put posts on the floor, or should I post them on gravel/cement pads, then build the floor around that?


Shouldn't put them on the floor. It's not designed to hold any type of load baring weight. Just sink it in the ground and float your floor around the post. No need for a pad.
 
Andrew Parker
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Location: Salt Lake Valley, Utah, hardiness zone 6b/7a
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Hmmm, if you have a lot of stone, you could extend your stone cellar, but picking, dressing and laying stone takes some skill and a strong back.

You could berm up the sides of the existing structure (with umbrella), at least on the North side. If you are unsure whether your walls can take the lateral load, you could separate the berm from the house with a small courtyard or side yard, and top the gap with the greenhouse covering of your choice.

Putting dirt on the roof is often more of an aesthetic or ideological choice than a practical one. A well insulated roof with walls and floors exposed to the "umbrella" covered earth will be far less complicated and costly to build and maintain. Still, a green roof is really cool.

It takes a tremendous amount of discipline to keep construction costs from creeping ever upwards. What your SO (if applicable), and you, ultimately wants (not what is discussed and agreed to in the design phase) can be a huge complicating factor. Designing with a mind for resale is a practical approach. Don't overbuild for your neighborhood (floorspace, bathrooms and finish), unless you are willing to take the loss. You may also need to consider code and insurance requirements.

Whatever you decide, have fun and good luck!
 
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