Need help with transition from TPO to shingles at peak

I am adding an addition to my house in Los Angeles. The slope of the roof on the addition is 1/2:12 and the existing roof is 4:12. I would like to use single-ply TPO membrane on the addition due to the low-slope and energy efficiency. It is at the back of the house, so not really visible from the street so appearance is not an issue. My question is how to properly transition from the membrane to the shingles. I am afraid of wind driving rain under the shingles at the peak. We are still at the planning stage so still time to change the design of the structure if needed.

Thank you for any advise you may have.

Use coated metal at the transition. The TPO can weld off and the metal can run over the top layer of shingles.


Thank you, Donl. Makes sense. So something like this, right?

Basically, yes. You really don’t have to strip off the metal with TPO, you can bring the field membrane directly onto the metal and weld it off at the outside edge (the ridge). The metal should be at least 4 inches wide under the TPO. Stagger nail (ringshank nails) at 4-6" apart leaving at least a 1.5" welding area at the outside edge (ridge). If your roof substrate is wood/plywood, the drawing should include a thermal barrier such as Two layers of FR base sheet or 1/4" Dens Deck/SecureRock to meet a Class A fire rating.

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While I’m not the guy with the most tpo experience on here, I personally would put metal over the field membrane then strip it in like in the pic. Do you know any documents saying which way is preferred by manufacturers?

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Personally, I would, picture for example, run the tpo over the transition and then weld to the clad metal. In doing so, water would have a tougher time running up hill on 4/12 rather a 1/12. Most manufactures are ok with 1 1/2 inch weld, considering that when you turn the heat gun at a 45 degree angle to weld, its about an inch and half.

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Generally, you only strip in the metal when you are not using coated metal. Standard edge details showing coated metal all call for a weld. The heat bond between the coated metal and membrane is a very solid termination. If you don’t want the white TPO metal showing on the shingles, use galvanized or colored metal and strip it in with pressure sensitive flashing. In that case, I would run the membrane over the ridge and cover it with the metal.