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Continuous rigid foam at the Jersey shore

Hello everybody.

I am currently designing a new single family vacation home in southern New Jersey on the beach. The project is going for LEED for Homes and Energy Star certifications. My main wall section from inside-out calls for 1/2" gypsum, 2x6 stud wall w/ batt insulation, 1/2 plywood, 1-1/2" rigid foam, WRB, 1x4 furring/air space, fiber cement siding. Air sealing details are similar to those offered in the GBA detail library. As a summer vacation home the main usage would be during the cooling season.

My contractor has expressed concern for this wall section because he claims to have built a similar assembly in the 90's which resulted in major mold and moisture damage due to the coastal climate in the summer. Further details about that installation are lacking but it still has me concerned.

Does this wall section have any flaws I am missing that might lead to moisture damage or long term durability concerns?

Any suggestions or reassurances about my strategy?

Also, what would be the appropriate type of rigid foam?

Any help would be much appreciated.



Asked by kevin field
Posted Jul 30, 2014 8:47 PM ET
Edited Jul 31, 2014 5:00 AM ET


1 Answer

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First of all, it's important to state that it's possible to screw up any type of wall.

The main source of moisture entering wall assemblies (especially near the shore) is rain. If you want to avoid moisture problems in walls, the first step is impeccable flashing. (Flashing techniques for windows and doors have come a long ways in the last 20 years, so it's important that you and the builder both be up to date on methods for flashing rough openings.)

The second step is to include a ventilated rainscreen gap between the siding and the sheathing. For more information on this topic, see All About Rainscreens.

Finally, if you are worried about wall rot, you probably want to read this article: All About Wall Rot.

Q. "What would be the appropriate type of rigid foam?"

A. Either EPS or polyisocyanurate would be a more environmentally friendly choice than XPS. To learn why, and to read more information on this topic, see How to Install Rigid Foam Sheathing.

Answered by Martin Holladay, GBA Advisor
Posted Jul 31, 2014 5:10 AM ET

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