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Community and Q&A

Standing Seam roof system advice in PNW (Seattle area)

OriginalRusty | Posted in General Questions on
I’m looking at having a metal roof installed, and would like to get feedback on my material choices to make sure the system will be problem-free in the long term, and also so that I can verify that whomever I have do the job has experience with the best materials for the job.
My roof is currently asphalt shingle with a 4/12 pitch, with no valleys and 2 vents as well as a chimney on the side of the house. Closed-cell foam sprayed between the rafters in the main house and we plan to do the same for the roof above the garage (open trusses). I have some evergreen trees nearby that shed needles and small branches on the back of the roof, and sometimes the front. We probably see snow that lasts a couple of weeks maybe once per year.
I’m looking at using the following materials and hoping for feedback on good/bad experiences with theses:
– TRI-BUILT Synthetic Roofing Underlayment (
– 26ga standing seam from Nu-Ray Metals (charcoal grey)
A couple of outstanding questions that I have:
– I see some people use the SA underlayment on the entire roof; should I consider this a best practice and be wary of installers who don’t recommend this approach?
– I’ve read that adding striations in the panels prevents oil canning. How much of a concern is that really?
– Do I need to worry about (or do anything to prevent) condensation with this roof system?
Should I be thinking about using foam panel on top of the garage roof deck instead of spraying insulation on the underside of the deck?

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  1. Expert Member


    I think your plan sounds like it will work well in the PNW climate. It should have no condensation problems. The main reason to favour the spray foam over roof top insulation is simplicity.

    You could use a self-adhered underlay over the entire roof as a secondary air-barrier, but you are safe relying on the spray foam instead.

    You will definitely notice any oil canning more with their entirely flat panels than say their NRM 6000 ones. Oil canning is an entirely aesthetic problem. It bothers some people more than others. I've never understood what the fuss was about.

  2. jimkas | | #2

    I would make sure your choice of a snap lock type of panel vs a true hemmed seam is appropriate for you conditions. The snap together seams are not quite and water resistant/ proof and the double rolled seams, and are also less resistant to high wind

    I am addressing this or a client in a fairly extreme location (8300 ft elevation, CZ7, high snow and wind loads).

    The snap is less costly, but may not be best for long term durability and wind resistance.

    This should be discussed with the architect/ roofer

  3. pnw_guy | | #3

    Rusty, have you already located the roofing company that will install the roof? If so, mind sharing who you will use? I may also be replacing a shingle roof with a metal one in the Seattle area in the next year or two, and might as well start collecting a list of potential contractors. Thanks!

  4. matthew25 | | #4

    The most recent Fine Homebuilding Podcast episode mentioned that self-adhered membrane are "required" at least along the eaves of roof based on the newest codes. I didn't know that was a requirement. The limiting factor seems to be compliance with ASTM D1970 for which you would need some sort of self-adhered product at least along the eaves (see IBC 1507.1.1). I don't know how important it is that the entire roof sheathing be covered in self-adhered WRB though.

  5. freyr_design | | #5

    You should find a company that specializes in metal roofing if you are not installing yourself. Often they will bend their own panels and know how to properly install standing seam (which I have found not everyone understands, even when you include manufacturer details in your plans….). They will also most likely have an underlayment scheme that they will warranty.
    One nice thing about the SA is an additional air barrier for when/if your foam separates.

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