Is Unheated Basement Wall Insulation Necessary When Basement Ceiling Insulated?

[velvetfoot]

I was thinking about this recently.
If the walls are mostly below grade, the walls should mostly be above freezing, plus the floor will be above freezing.
I can't see any reason to isulate the walls if it is not a heated space.
I can see benefit in the summer for condensation purposes though.

I was thinking about maybe finishing the basement, but what would the effect be with foam on the walls and maybe floor in a space that was mostly unheated?

 

[homebrewz]

There was a good thread on a similar topic last year:

https://www.hearth.com/talk/threads/6060/

Maybe it will help?

The frost line can go as deep as 4 feet, so the walls may be mostly
above freezing, but not by much.

 

[velvetfoot]

Thanks for the link. I've been thinking about this for a while.
I guess it'd be one thing if my basement ceiling wasn't insulated already, then I'd likely insulate the basement walls.
I just wonder if the basement ceiling insulation in combo with the ceiling insulation would cause the basement winter temp to go down since the moderating influence of the earth has been reduced by the foam insulation. It would seem weird that adding insulation would cause freezing pipes, but I'm trying to puzzle this out logically.

 

[jklingel]

Velvet: I have a general philosophy on insulating. IF the insulation is not going to hurt anything (ie, water pipes are on the inside, etc), and IF you are in a cold place so that the insulating is cost-effective, then I'd look real hard at insulating. Here is why: The warmer the basement is, the less heat will travel to it from upstairs. One of the parameters of heat flow is "delta t", or the difference in the temps of the two bodies (rooms, in this case). If you live in a warm place, then the benefit of insulating may be marginal or negative, but as long as the basement is colder than the upstairs, it is going to suck out heat. It is a major PITA, but can you put waterproof (sort of...) foam on the outside of the building, if doing so inside is a problem? Just thoughts.

 

[velvetfoot]

Yeah, but I'll be darned if I'd take down the existing basement ceiling insulation to put in basement wall insulation instead. It would be weird if insulating the basement walls would cause problems.

 

[steam man]

I have 2" of blue styrofoam on the the outside of my 10' high basement walls that extends to the footer. It's always comfortable, especially when the wood stove is cranking. The concrete is nice and warm and acts like a giant thermal mass. Even the floor is warm. I do think that at least insulating on the outside from the sill down to below the ground, hopefully to the frost line (Dow-check out their site) would give a good bang for the buck. If anything the basement temp will go up since the floor and lower walls are warmer than the upper walls anyway. I imagine your exposed pipes and heating equipment has some loss to the surrounding air to keep the basement temperature up.

 

[jklingel]

Keeping the ceiling insulation....Roger that, and I assume there is a vapor barrier in there. I don't think the vap barrier will be a problem, but as mentioned above, warming the basement may present a moisture problem, depending on how warm it gets, etc. Another option would be to insulate the ceiling even more, and not the walls, making the basement even cooler. That may be easier and would avoid introducing a new problem (moisture). How cold can it get down there and not be a problem? As for using "blue foam" outside, excellent idea for sure, and very common, but a pain if there is already dirt there. Retro-fits are never too easy. Good luck w/ it.

 

[stoveguy2esw]

i think overall it depends on what you intend to use the space for. if its going to be used for habitation , then insulating the walls is a good idea, if for no other reason than that it makes the space more easily heatable. concrete takes a lot to heat up , given though once its there it tends to hold well also especially in a buried basement. insulating the walls makes it less necessary to heat all that mass which allows temps to come uup more rapidly with less output from the heating device. remmeber though the floor is likely concrete as well and that mass will have to be heated as well. usually when i talk to a potential customer who wants to heat an uninsluated concrete basement , i suggest looking for a unit with about 60% more heating capacity than the floor space would otherwise require , this allows enough extra output from the heating unit to give the btu's needed to warm the concrete.