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Installing exterior rigid insulation to existing walls

Andrew Bush| Posted inGreen Building Techniqueson

I am looking to add exterior rigid insulation to an existing house that is located right at the border of Climate Zones 4 & 5. I have read many conflicting ideas about the proper way to construct the revised wall. The current wall construction is (from inside to out):
1/2 GWB
3 1/2″ studs w/ R-13 Batt Insulation
1/2″ OSB sheathing
house wrap
Wood siding

My plan is to remove the existing siding and house wrap (both are deteriorated) and resurface the wall as such (inside to out): PDF attached

1/2″ GWB
3 1/2″ studs w/ R-13 Batt Insulation
1/2″ OSB sheathing
1′ strips of 1 1/2″ Polyiso Rigid insulation between 2×4 studs running vertically
Tyvek Drain wrap
Aluminum siding

My other option is to put the furring outside the rigid insulation (which seems more common) but I still would like to use the drain wrap between the rigid insulation and furring.
Any thought, comments or suggestions?

Thanks
Andy

File format

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Replies

  1. Stephen Sheehy||#1

    It would be much easier, faster and more efficient if you apply the foam to the sheathing in full sheets and apply furring to the outside.

  2. GBA Editor
    Martin Holladay||#2

    Andy,
    It's always best to install rigid foam as a continuous layer (rather than cutting it up into rectangles and inserting the rectangles between furring strips). A continuous layer will perform better from a thermal perspective -- the resulting wall will have a higher R-value -- and will do a better job of reducing air leakage.

    Moreover, installing the furring strips on the exterior side of a layer of continuous rigid foam gives you the benefit of a rainscreen gap.

    For more information on these issues, see these two articles:

    How to Install Rigid Foam Sheathing

    All About Rainscreens

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