Perimeter drain insulation
escyr
| Posted in General Questions on
What is the best type of rigid foam to use underground, above my perimeter drain pipe?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
I would use XPS here, for best tolerance to being kept in a wet enviornment. Some will also recommend EPS, but I don't think it holds up as well when constantly wet. I reference the DOT study from Alaska regarding the performance of these two materials when kept wet underground.
Bill
Just to clarify, this is my perimeter drain extension to daylight. It's a solid SDR35 pipe and won't see daylight until about 200' from the house.
Why do you want to insulate the pipe? Is it close enough to grade to freeze in the winter?
It is to protect the water from possible freezing in the pipe as it is only 2' below the surface and frost depth is closer to 4' in Southern Maine.
If this is for freeze protection, I'm not sure reasonable amounts of insulation alone is going to be enough, especially if you're in one of the more Northern climate zones and the pipe won't be buried very deeply. I'd consider running a GOOD QUALITY self regulating heat tape in there (Raychem makes good ones). You don't need to run it all the time, just when it gets really cold. You can get controllers to automate this for you. I wouldn't rely on the self regulating nature of the cable itself here, because it's likely to run more than you really need it to when operating underground like this, which just wastes energy.
Bill
This is old but a good resource for calculating how to protect pipes with foam insulation.
I hadn't seen charts like the ones on p. 8 before. Clever way to incorporate a bunch of information.
This is excellent information, thank you.
Also, does it matter if it is faced or unfaced?
In general, foam insulation with facings should not be used underground, because they limit how readily the foam can dry if it gets saturated.