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Building Homes or Extensions/Insulation between old wall and addition


We built an addition out the back, so they are two inside walls. I know the contractors did not insulate the whole wall because they said it didn't have to do it because it is an inside wall, but there is a gap between the two walls, which obviously goes up to the food. We have a problem with ice damms and snow melt. Should we open up the wall and insulate the whole wall. it is a cathedral ceiling/, at least 15 feet. I need help!

wall insulation
wall insulation  

If there is an un-insulated gap between the walls and it is in contact with an outside wall and/or roof surface, then it should be insulated at its exterior perimeter (see attached sketch). The goal is to prevent heat loss and air infiltration at exterior surfaces.

I hope this answers your question.  Please let me know if you need more information.  

Thank you,

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Stephen Major (Owner--Major Design Group)


I can answer any questions regarding the design and construction of homes and additions. This includes trade-specific questions (how-to) in all major building trades: framing, foundations, site prep, electrical, HVAC, plumbing, water treatment, interior finishing, trim & cabinetwork, exterior finishing, roofing, siding. PLEASE indicate your state or region, so I can provide the best possible answer. PLEASE provide photos whenever possible.


30 years experience in building design and construction, all hands-on, including the construction of dozens of single-family homes and hundreds of remodeling projects in the northeastern US.

Author: "Architectural Woodwork - Details for Construction" published by Van Nostrand Reinhold (now Wiley).

BS Cornell University.

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