Frost Protected Shallow Foundation Retrofit For 100+ Year Old Limestone Foundation - Building & Construction - DIY Chatroom Home Improvement Forum


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Old 06-21-2010, 04:30 PM   #1
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


I recently discovered that my foundation gets gradually shallower towards one corner of my house. At the corner it is only one course (12-18 in.) of kasota stone (dolomitic limestone) thick! I don't want to change the dynamics of the 115 year old house by excavating and replacing part of the foundation. The foundation is solid with no sagging floors and barely even any squeaking floorboards. But I live in Minnesota, and global cooling is beginning, so I'd like to avoid future frost problems.

Can I basically use EPS foam to insulate the foundation from the exterior like in the drawing?

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Old 06-21-2010, 06:19 PM   #2
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


Maybe your post was sort of a joke, if so I missed the punchline. Your house has been there for 115 years, same foundation, no problem, and now you are worried about frost? Because of global cooling?

If you haven't had frost heave problems for 115 years, I truly doubt they are going to start any time soon. As for insulation, that would be to reduce heat loss through the foundation, and would have nothing to do with frost heave, unless you are on expansive soils, which I truly doubt, first because you are in MN, second because if you had expansive soils you would have found out long ago.

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Old 06-22-2010, 02:00 AM   #3
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


Yes. I am afraid the globe is cooling too much, so I excavated my foundation to make sure it would be warm enough.

Actually, I was just removing some surface soil around the foundation to do some repointing when I discovered the lack of depth of part of my foundation. I guess what I'm wondering is what to do now. Because I am also doing regrading, removing an old curb and gutter near the foundation, and digging porch footings nearby, I am concerned that I may have disturbed whatever luck I've had so far. So, I thought while it's exposed I could employ the fore-diagrammed fpsf method just to be safe. But, it sounds like I should just put the same dirt back where I found it and not worry about it? I hope that is the case, because it sure would be easier.

More info on fpsf
http://www.toolbase.org/Building-Sys...ow-foundations
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Old 06-22-2010, 09:37 PM   #4
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


You have a good plan there, to me. Heat loss through a slab/foundation wall is large in your area. I would never use EPS, though, as it is not waterproof. Use XPS instead (extruded); blue board, or pink board, it is called. I would not hesitate to use 3 or 4", either. If you Google isotherms, you'll see some interesting stuff, but it may encourage you to dig down four feet to install XPS deeper; lots of work. Your diagram is not typical of what I see, exactly, realizing that you were not necessarily intending what you posted to be complete and entire. Most isotherm diagrams show lots of arrows going down, under that foundation wall, then out. You almost can not insulate too much.... but if you have nothing under your slab, you are only getting a band aide effect. However, that is all you can do now, so do it. GL, and good thinking! j
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Old 06-22-2010, 10:19 PM   #5
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


Check out the compressive strength on the two colors.

http://www.oikos.com/esb/43/foundations.html

Be safe, Gary
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Old 06-22-2010, 10:41 PM   #6
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


The foam can only help, not hurt IMO. Go for it if you have it partially open now.
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Old 06-24-2010, 01:20 PM   #7
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


There is no slab, just a dirt floor that slopes up to that corner. Will XPS trap moisture against the foundation if some would happen to get behind it? If I remember 2 inches does constitute a vapor barrier, I think. Also, what should I use as fill? And, should I put a tile in? (There will be a "french drain" about 4 ft away from the foundation.)

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Old 06-24-2010, 07:33 PM   #8
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frost protected shallow foundation retrofit for 100+ year old limestone foundation


Quote:
Originally Posted by degnem View Post
Will XPS trap moisture against the foundation if some would happen to get behind it? Also, what should I use as fill? And, should I put a tile in? (There will be a "french drain" about 4 ft away from the foundation.)
Thanks!
Sure, XPS will trap water. Do everything in your power to keep water out, as with any foundation. Flashing at the wall, a large roof overhang, ground that seriously slopes away from the house, etc. If you have wet soil, I can not see how a well designed drain system could hurt a thing. See local building engineers for designs. I think they typically have a layer of dirt (to shed surface water) over porous material that goes down to a drain tile. Are you going to insulate that bare, dirt floor while you are at it? If there is conditioned space above the dirt, you are pumping dollars away by the truck load. Just looking for more work for you.... GL. j

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