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Community and Q&A

Can you do exterior foam without removing the windows?

Cortland15B | Posted in General Questions on

Hello, trying to plan an exterior rigid foam retrofit and need to know if I’m going to have to remove all the windows and reinstall them not or if there is a good way to flash them without taking them out? They would be “innie” windows then. House is 2×4 construction is zone 7 so I’m going for the R-10 minimum based on insulation charts. To get there I want to use EPS in two layers for offset seams. That will put it in the 2-3 range. Xps is possibly if I don’t want to go thicker, possibly high density EPS. 

Also, does it make sense to do this job but keep most of the windows I have and reinstall them? They are fairly new casement and some double hung double pane Pello windows. I would replace the older double pane windows. 

Looking at total r-value calculators of a wall assembly, it seems that exterior rigid foam doesn’t change it as much because of the horrible value of the windows dragging it down. So with this, is it better to upgrade the windows and not do exterior foam? 

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  1. Expert Member
    RICHARD EVANS | | #1

    Cortland, I would build "Dudley" Boxes around your existing windows and fill in the rigid foam around them. No need to replace windows.

    Here is a GBA article on the subject:

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