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Community and Q&A

Siding, vapor barrier and insulation

GBA Editor | Posted in Energy Efficiency and Durability on

In San Rafael CA (climate zone 16, Sunset Western Garden Book), I will be replacing siding on an ikeler home built around 1960. One story. Currently has the 2-inch vertical siding that I’ve heard will be hard to find or very expensive. I’m a recently certified green builder and still have a lot to learn — so my question is, what is the best material for the this job? Cost will be critical.

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  1. GBA Editor
    Martin Holladay | | #1

    1. Best siding? There is no answer to that question. Choose whatever siding you want.

    2, Best vapor barrier? None. Instead, use a vapor retarder (for example, vapor-retarding paint).

    3. Best insulation? On a siding replacement job, I'd say rigid foam (either EPS, XPS, or polyiso) installed on the exterior side of the existing sheathing.

  2. jon | | #2

    Let me catch up to you, Martin. I've been reading some older post here but I'd like to confirm a couple points. Not sure what I will find underneath the old siding as far as sheathing but I suspect whatever it is it will be there. When you say no VB is that because the rigid foam is enough? (No felt paper either) Is it wise to use the reflective on one side type?
    Do I simply use long screws to attach the new siding through the foam? Do I need a gap for circulation like I would in ceiling application?

  3. GBA Editor
    Martin Holladay | | #3

    It sounds like you need to do some basic studying about vapor barriers and vapor retarders. You might start with these two articles:

    Vapor Retarders and Vapor Barriers

    Forget Vapor Diffusion — Stop the Air Leaks!

    There is no need for exterior foam sheathing to have foil facing.

    The exterior foam should be tacked up with any old fasteners and then secured permanently by 1x3 or 1x4 vertical furring strips screwed through the foam to the underlying studs. These vertical furring strips create a rainscreen gap between your siding and your sheathing or foam.

  4. jon | | #4

    Thanks Martin, I appreciate this.

  5. Lee | | #5

    what is the best exterior foam including the best rating, use before placing the vinyl siding / want to avoid molds/ moisture behind the vinyl siding. I want durability and reliability/ thanks

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