Heat Losses Through The Ground
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- Опубликовано: 24 фев 2024
- Did you know that heat losses through the ground to the outside air are the third cause of heat loss in American homes?
That accounts for more heat losses than air leakage, as our research found out.
In this video, we illustrate how heat escapes from the floor slab, through the dirt underneath the house, to the outside air.
We show this by looking at an actual project detail from a home retrofit in Montana.
#passivehouse #buildingscience #energymodeling 
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First time coming across this channel and after looking through their back catalogue and seeing the size and age of it I'm shocked they're not more popular. I'm a DIYer and have done tons of research on RUclips for my build and this was very insightful. Thumbs of this video to help them out
thank you!
Interesting comparison across the different ways to reduce thermal losses through soil. I'd be interested to see a similar study which also includes background thermal behaviour of the soil for the boundary condition below. For example, where I live, footing depth must be a minimum of 4' below grade when the building has a heated space below grade (basement), but when built over unheated space (ambient temperature crawlspace), the depth of frost is typically 7'. Clearly the thermal loss from the basement slab/wall prevents frost (and potential structural damage due to frost heave) from reaching the footing depth. What impact on frost penetration does insulating the slab have? With increased focus on improving the thermal envelope, is there an increased risk of structural damage?
How about moisture? Where I live (Sweden) it is seen as a risk to insulate from the inside. There were mutliple cases of problems in the 70-80s because of a lot of insulation beeing done after the oil crisis. Especially that piece of wood where wall meets floor is at risk of high relative humidity.
yes, moisture management needs to be addressed of course. in this case, we have a vapor barrier at the floor over the 1” polyiso board, and a smart vapor retarder at the wall on the interior of the insulation
The bottom plate of the interior wall will be substantially colder than the interior air temperature after that 1" polyiso insulation. Any humidity from air from interior that gets into that plate will condensate and the plate will rotten out fast. Does your program estimate temperature of that bottom plate? Imho the polyiso on the floor should go under the bottom plate.
@@samipoykko7789 I hear your concern, but based on the data we see I don't find the concern justified. If anything at the detail you mention we may have exterior air infiltrating into the building (due to the stack effect). One risk for the bottom plate is capillary action bringing moisture up from the existing slab, so we need to make sure we have some dampproofing done before installing the bottom plate. I hope this makes sense, please let me know if you have more questions
@@emupassive I would use treated lumber for it. And of course always capillary break.
@@samipoykko7789 yes we spec pressure treated wood for that bottom plate
One newer foundation thought is to sprayfoam the ground. That is, pour the footings, pour the layer of gravel under the slab, sprayfoam that gravel then pour the slab on top of that.
Yes that is a way to insulate under the slab. We’re not a big fan of that, as in our opinion spray foam is not a great product to begin with
Main benefit of the skirt insulation is that you do also maintain a lot of thermal mass in the home, where is insulating the actual slab means that the home will heat up and cool down faster, climate with bigger swings it might be more beneficial to therefore go for the skirt design.
correct, and please remember this project was a retrofit, meaning that adding insulation under the existing slab was not an option. once we look at the actual numbers of energy consumption, it is very clear that the thermal mass has a negligible effect compared to the effect of thermal insulation. One exception for that is very hot and dry climates, and even in those hot climates, other parameters have a bigger impact than thermal mass (eg interior setpoint temperature)
how was the amount of heat loss due to (1) air leakage and (2) conductive losses through slab/ground calculated or measured?
Unfortunately, we cannot isolate the air leakage of the slab alone. Air leakage is measured for the building as a whole
What about the poly-iso's loss of R-value as it ages, compared to other insulation materials. What is the R-Value in 10-years?
for polyiso, manufacturers declare an R/inch around 6 or 6.5. to account for aging, in our analyses we use a more conservative value of 5.5 R/in
@@emupassive Thank you, I just found your site, thank you for all the great information
our pleasure! please let me know if you have more questions