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Community and Q&A

Rigid foam over brick exterior in Maryland

JamesEric | Posted in Energy Efficiency and Durability on

I my house has all masonry wall with no insulation. From the inside I have plaster, 3/4″-1″ cavity, 4″ concrete block, and finally 4″ of brick on the exterior. I wall to add insulation and change the exterior to cement siding. I already own 50 sheets of XPS so I would to use it on the project.

Originally, I planned to attached the XPS, followed by 1-1/2 of spray foam to seal the envelope, then use 3/4″ thick furring strips to attach the siding. Based on a quick and dirty heat loss calculator that would add R19 to the walls and reduce the heat loss by 76%+-. If I use just the 2″ foam it would reduce the heat loss by 67%+-.

These are not exact numbers but they help to show the benefits of just a little insulation and house I sealing.

My questions are:

1. Do I need any type of house wrap over or under the foam board?
2. Where can I see details showing how to put foam over exterior brick followed by siding?

I am interested in any additional details and tips.



PS: I already searched but could not fine the answer. Foam board and siding over brick must be rare.

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Do I need any type of housewrap over or under the foam board?"

    A. Building codes require the installation of a water-resistive barrier (WRB) on all walls. If you don't want to install housewrap, you can use rigid foam as a WRB -- although it can be tricky to do it right. Here's more information: Using Rigid Foam As a Water-Resistive Barrier.

    Q. "Where can I see details showing how to put foam over exterior brick followed by siding?"

    A. I don't know of any document that answers that exact question, but I advise you to start here: How to Install Rigid Foam Sheathing. The trickiest steps will be attaching the rigid foam to the wall -- you'll probably end up needing something like Hilti IDP fasteners, which will require you to drill holes in the bricks or mortar -- and Tapcons to hold the furring strips.

  2. JamesEric | | #2

    Thanks...this has been very helpful. I will use house wrap as my WRB.

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