glennster, Metal roof over shingles

Rollie NE PA

Well-known Member
As for your question yesterday about putting a metal roof over shingles, old-9 mentioned fire.
I don't know if fire is a concern or not but I thought I would post some pictures. The fire started as a chimney fire at the eves and then traveled between the metal roof and the shingles. The space between the nailers gives the fire oxygen.
 
The pics didn't follow the text. I will try again.
a224558.jpg

a224559.jpg
 
I think putting steel over shingles is a bad idea, but would the outcome have been any different if the roof was stripped and purlins had been nailed over the sheathing? For that matter, would it have been that much different if the steel was attached directly to the sheating? Anyway you look at it, there's flamable material under the steel.
 
On our cabin we put 7/16 OSB on the trusses and then 15 lb. felt, and screwed the steel to that. If I was doing it over I would use 1/2, we had a few screws strip, and had to put blocks inside. We built it with a 5/12 pitch thinking the snow would slide off, but it stays put until spring and then comes off all at once, making a big pile in front of the door, so we put snow bars on it.
 
Thanks for the pictures ,very educational! Shows another reason why a chimney should never be down by the eaves. Leaving shingles on under steel is just being cheap or lazy, the weight is bad and you don't need insulation there either.
 
All the instructions from Fabrel and ABC steel call for 1.5" long screws screwed into wood at least that thick. with screws placed at each side if the ribs on the tails, and one on the overlap side of each rib in the field.
Loren
 
From a firefighter prospective it does make a difference. Roof ventilation becomes a little bit more difficult when purlins are used over sheeting or shingles.
 

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