Do I need to worry about frost heave
I am wanting to insulate my basement for the the government grants, but I have a relative keep saying that my foundation walls will heave from adfreezing. He is a concrete guy, built his own house.. he isthe go to guy when we have building issues. So, my wife is concerned
I am thinking that if this was a problem, there would be more about it. I am sure that Mike Holmes would have covered this by now, oh, but wait, he probably would not get much cooperation from the insulating contractors or manufacturers…
I found this article and copied it in, it is from Canadian Government, they approve new building technologies/products :
CBD-128. Adfreezing and Frost Heaving of Foundations
http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-128.html
….Heated Basements
Adfreezing of soil rarely occurs on uninsulated foundation walls of heated basements because of heat losses to the surrounding soil. Figure 4 shows the thermal regime around such a structure. Even under severe winter conditions the 32 °F isotherm does not intercept the foundation wall if the basement temperature is sufficiently high. Difficulties of frost heaving are avoided, even though the soil used for backfill may be potentially frost susceptible. If heat loss from the basement area is reduced to the point where the soil in contact with the wall freezes, difficulties may be encountered. Adfreezing may be induced if an excessive thickness of insulation is applied to the inside of exterior foundation walls, or if heat is excluded from certain areas of the basement, as for cold cellars
Here are my thoughts:
1. the above contradicts everything that the gov’t is promoting (super-insulating, R-22)
2. My house, a solid brick bungalow circ 1940’s, has an asphalt drive on 2 sides, an addition on the back, and somewhat sandy soil, (noticed from digging the piers for a deck and a catchbasin in the rear yard), so wouldn’t that reduce the chances of Adfreezing.
Any thoughts?
Replies
Location?
Unless you frost depth is really deep, you will have no problem with insulating the interior of the basement walls. Without knowing where you are located it would be unreasonable to guess at what you local frost depth is.
That said, unless you are in the frozen north or at extremely high elevation the actual achieve frost depth penetration very seldom reaches the code prescribed footing depth unless you ahve very wet soil.. In you case the sandy soil is a plus because it tends to be well drained.
In my area, Louisville, KY, the frost line is 30" and all footing must below that. Basements as a rule are much deeper the 30" and seldom less than 5 or 6 feet below grade. At roughly 4' of depth the soil temperature is close to "earth normal", or 55 degrees F. At that temperature for your concrete walls and floors you need to make up 17 dgrees to achieve a comfortable conditioned space. (That's very loose assumption when you factor in other conditions) Not many BTUs when you considered that the above grade winter conditions may present you with 32 degrees outside air temp and you need to add enough heat to achive the same 72 comfort level inside. Conversly that 55 degree soil temperature is also a heat sink that is sucking heat out of your basement wall/floor year round. Next to water and metal, concrete is an excellent termal conductor and the earth is huge heat sink. No point in fighting thermodynamics and trying to heat it. Insulate the snot out of those walls and keep your energy $$ where you get some use out of them
Uh, he's in Canada.
Soil matters most
I used to live in Alaska and drill sites for thaw stability of permafrost. What you need to know is the thaw stablity of your soil and the moisture content. Coarse grained soil, such as gravel, has a lot of space between the individual soil grains. This is important in two ways; 1) the space helps liquid water drain away, and 2) the space is a place for ice crystals to grow without pushing the soil grains apart. So if your soil is really dry, freezing won't be a problem. If your soil is coarse grained and not too wet, freezing won't be a problem. Where you will run into problems is when you have wet, fine grained soil. If you want a good answer for your site, take some soil samples to a geotechnical lab and have a grain size analysis done. This just means the soil is run through a set of screens, coarsest on top and the mass of soil retained on each screen measured. This information can be used to estimate the thaw stabiliy. Note: multiple samples are needed if the soil is not uniform around your house (and it ususally is not).