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Community and Q&A

Unfinished Basement Insulation Requirements – IECC 2009

dirtydan123 | Posted in Energy Efficiency and Durability on

Hello All,

I recently just purchased a new home. When I signed the contract, the local residential building code was to use the IECC 2009 requirements. I built in zone 5. 

As far as I can tell, it explicitly says that basement walls should be insulated.

The builder insulated one wall cavity (approximately 12′ x 4′) and thats it. The entire basement has concrete walls.  Additionally, they did not insulate the ceiling, or the walls against the staircase which I think they are required to do if they did not insulate the basement? 

I am using 2x more natural gas then average in my area for a brand new home. Something does not seem right.  I am very obviously a layman so I don’t want to try and fight the builder to do more insulation without some ammo. I would appreciate any advice. Thanks!

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  1. Expert Member
    ARMANDO COBO | | #1

    2009 IECC Table 402.1.1 Insulation requirements for basement walls in CZ5 are R10 continuous insulation or R13 cavity insulation. I would make sure your sill plate, rim joist and any opening thru the walls are well sealed and insulated as well. Insulating the ceiling will work if there is a door between floors.

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