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Roofing/metal joining asphalt + valley ice


QUESTION: Good-day Mr Henderson
I have a wartime home in Northern Ontario with a very steep roof.Can I put a metal roof on the west side(with valleys from an addition) and asphalt on the east side due avoiding breakage on the heavily landscaped yard? As well, having gone through many contacters and many roof renos( last one 3 years ago, totally gutting upper floor and re-insulating) I am still getting ice dams in valleys and water back-up into ceiling on first floor. Last contracter said roof didn't appear to be a factor. I have soffits all around, ridge vent and gable vents. In one of the Q/A I read this seemed to be overkill and wonder if this is contributing to ice/water problems?

ANSWER: A steep roof usually does not hold snow, a slope of over 6:12 more like 7 or 8 in 12. That means a rise of 6 to 8 inches over a 12 inches horizontal measurement.

You can use metal roofs on all roofs regardless of slope but you would need to install snow guards so the snow would not come crashing down on an area where people walk.

You could have shingles tie into a metal roof but you should place metal in the valley that joins them. Also the metal roof if it is near the shingle roof, same slope, it should terminate under the shingles.

I would highly recommend an eave protection membrane under all metal roofs, valleys and tie-ins.

In regards to venting, the installation of a ridge vent and gable vent counteract each other. Use one or the other. The intent of venting under the building code it to remove moisture from the attic (Part 9.19 roof spaces).

The ice and snow build-up is usually cause by the exiting of warm moist air from inside the home into the attic space. Kitchens and bathrooms are the prime sources if this moist warm air. Spray foam (Icynene)in the attic at the wall/ roof junctions might assist in reducing this problem.

Hope this helps.

---------- FOLLOW-UP ----------

QUESTION: Just to clarify, I wish to join an asphalt side to a metal side at the peak of a very steep this possible.  Thanks

Yes it is possible. Recommend ice and water shield type product along at the peak, commonly called a ridge. I assume the ridge vent will come off and be re-installed, You have an option to reinstall the ridge vent and ridge cap shingles or install a metal ridge vent and extend the metal down the shingle roof at least 10 inches.

You may want to check with a roofer for other options.

Yes it is possible but you have to extend the metal over the ridge abs down the other side. Maybe it would best to install metal on both sides. There are some metal roofs that can be installed over asphalt shingles.

All the best


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D. John Henderson


My 33 years in the building science business has involved air barriers, waterproofing, and flat & steep slope roofing systems.


My roofing encompasses commercial systems (BUR, mod-bit, single-ply) and residential applications (asphalt shingles, cedar shingles, slate and metal. I am cognizant of code stipulations in regards to FM and UL for commercial roofs.

Attended numerous courses offerd by Roof Consultants Institute, Roofing Industry Educational Institute, Factory Mutual Research Corporation, University of Wisconsin, and BURSI. Lectured for RCI and mentored at a local university for a Building Science Certificate.

Past/Present Clients
Government, commercial businesses such as The GAP, hospitals, school boards as a roof designer.

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