frost line interior rigid foam depth?
So previous owner lined the basement walls with 2″ rigid foam from the joists to 24″ off the slab.
I’m just starting the process of finishing the basement – any reason I should carry the rigid to the floor?
The house is in southern interior British Columbia. Average winter temps in these parts are +5 C to -15 C. Not crazy cold but big time snow belt. House is heated with electric throughout and a wood stove on the main floor.
Happy long weekend to all the Senator Fans!
Ripper
Replies
I'm living on Vancouver Island and the new house right beside me failed the final inspection because the crawl space insulation did not go down to the floor. Coming from the east I never ever saw insulation stop before the floor.
Spend the extra bucks and do it right.
roger
Is there any evidence that the insulation was there but removed? Might be a clue as to a previous problem.
Nope no foam on the lower side. I've seen homes in BC with this style of insulation before - just wondering if I'll get a warmer basement if I run it to the slab - but if the cold doesn't get that far down why bother?
Where you have no foam the ground outside is around 50° or so year-round. Much higher temperature than at the frost line or above grade, where it will essentially match the average air temp.
By leaving the foam off the installers were thinking short-term, protecting the house from the worst of the cold, but saving money by not installing expensive foam where it was less needed.
There would be no harm in finishing off the foam to the floor. The concrete will conduct cold from above down the wall, so you'll protect against that. Also the basement air won't condense on the cold concrete wall so you'll have less dampness down there.
While you're at it make sure the rim joist is well insulated. Rigid foam sealed with spray foam does a great job at this.
Thanks Mike - I'll insulate to the floor and frame it up. You're bang on about the cost of foam. Thanks for the tip about the rim joist. Right now it is def a bit ugly; old ratty insulation hobbie-joed in place. I was planning on replacing it with Rockwool but a airtight cavity would be best.
Edited 5/19/2007 12:11 am ET by ripperathome
It's easy if you cut the foam on the tablesaw, about 1/4 to 1/2" smaller than the space it's to go in.
If you really want to get fancy, throw some rigid foam down on top of the mudsill too.
Last winter I had to repair two houses that had freeze-ups directly resulting from poorly sealed/insulated mudsills.
There should be nowhere on the wall that you can see concrete or framing lumber directly connected to the concrete.
Average for Maine four feet down is 55-56°
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Isn't that "around" 50°?
Have you ever tested the 55° number? Once I put a thermometer on a basement slab and it read 50°. I'm not sure why. So now I figure the soil is between 50 and 55.
I heard that from the professor up in Bangor on the WVOM sat morning show, HOT and COLD. Dick Hill. He was discussing geothermal that day.
I am less certain about water, But I think he mentioned most well water running around 58°. 'Course it comes from a bit deeper.I can understand a thermometer on surface of crete reading that. Moisture evaporating whould keep it cooler than the soil down beneath it.I guess his discussion was examining whether to do geothermal with a ground trench running parralell to the surface or to drill a deep well and use water to extract the heat. He went into the fact that if the equipment has a problem, you could end up pumping bad polluted water into the water table and facee a liability there and that the cost of drilling the two wells would be high so his conclusion I think was to run a ground trench for extracting heat is the better cost analysis choice for this area.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I haven't heard Professor Hill's name in a while. An old friend of mine had him as a Mech. Engineering advisor at UMaine and I used to hear all kinds of good stories. Prof. Hill sounds like a pretty smart guy.
Your theory on my thermometer reading sounds plausible.
Interesting about the geothermal options. I've thought it would have more to do with how much land you have. If you're only on a small lot you obviously want to go deep. If you have the space, horizontal seems like it would be more economical. Good to hear he came up with the same conclusion, albeit for different reasons.
I am going to assume that at that depth your soil temp is similar to here - about 55°F year 'round.
So when you are tryuing to maintain a temp of 70°F interior, you are losing heat to the soil. At what rate, I cannot say, because i don't have the software or knowledge to calculate it, but foam is not terribly expensive so sooner or later, you wil recoup.
In the nmeantime, you will be more comfortable and eliminate or reduce the amt of condenstation there that can cause other problems.
I would insulate it.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!