Insulating Knee Walls Between Conditioned and Unconditioned Spaces
dsteketee
| Posted in Energy Efficiency and Durability on
In our attic we have closed cell insulation at the roof all the way from the ridge down to the soffits which are now sealed. We also have knee walls which are uninsulated creating an unconditioned but insulated space on either side of the living area. The HVAC system is located in one of these spaces.
Should these knee walls be insulated? Or, should we condition the areas behind the knee walls?
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Replies
If you don’t condition the attic space you are playing a game of Russian roulette with mold and rot.
Many people win at this game but not all!
Do you feel luck?
Walta
The main living space in the attic space is conditioned. Only the space between the uninsulated knee wall and the insulated roof is unconditioned.
I understand that you want to leave part of your attic unvented and unconditioned we all like the idea of a free lunch.
It seems likely that the dew point of the air in the unconditioned space will be above the surface temp of the foam from time to time. How often and how much water will condense on that surface is unknowable. Will this water evaporate before mold and rot set in is anybody’s guess.
The question remains, do you feel lucky?
Walta
It sounds like you have insulated the underside of the roof all the way to the eaves, where the roof insulation presumably "connects" to the wall insulation (likely by covering and sealing the top plate on the exterior walls). If that's the case, then the "attic" space is already inside the building envelope, so you would NOT need to insulate those kneewalls. A little air movement in those closed off areas would be a good idea, similar to what is needed with encapsulated crawlspaces.
Bill
By doing so, you've effectively enclosed the "attic" space within the building envelope. In this case, insulating the kneewalls may not be necessary since they are already within the insulated area. However, it's a good idea to ensure some air movement in those closed-off areas to prevent any potential issues, similar to what is needed in encapsulated crawlspaces. Overall, it sounds like you've taken the right steps to create a well-insulated space. Good job!
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