Roof is 4/12 with a 20 inch overhang. On bids for re-roofing we are getting different recommendations. All agree we need about 24inches of ice and water protection at the edges but that is where the differences begin.
One roofer says we must have 2 layers of felt the other says 1 will do (local code seems to have 4/12 as the cutoff for using either one or two layers).
What are the advantages of either / extra cost for two?
Then there is the question of architectural shingles versus 3 tab. One says 3 tab sheds water better on low slope the other says that architectural shingles will be more resistant against ice dams.
If it makes any difference to your recommendations: we are planning to have all insulation taken out of attic, all bypasses sealed, airtight boxes put over recessed lighting and 14" of insulation put back in.
**All agree we need about 24inches of ice and water protection at the edges but that is where the differences begin. ** This is B.S. You need minimum of 24" INSIDE the warm wall.
**One says 3 tab sheds water better on low slope the other says that architectural shingles will be more resistant against ice dams. ** This is also B.S. GEt the shingles you like. Archs are no more ice dam resistant than any other water-shedding system.
Two layers of felt are no better than one in this scenario. It is all gonna have a gajillion holes through it anyways.
You might want to find a reputable roofer in the area and get some more info.
I have to agree with Aaron about the ice & water shield. Besides, if nothing else it comes in 3-foot wide rolls, so why would anyone want to cut it down to 24-inches anyway?
Again, I’ll agree with Aaron with regard to 3-tab versus architectural shingles on a 4:12 slope. It really shouldn’t make a difference.
I’ll slightly disagree with Aaron on the felt underlayment. Two is better than one, but Aaron is correct in the fact they will have numerous nail holes. What I would do is opt for either two layers of 15#, or I would prefer 1 layer of 30# felt.
I find it hard to disagree with cerberus on the felt, but nobody has ever been able to offer me any real reason why two is better than one on a non-mopped felt application with all the nail holes.
I have just never thought it any better protection. I will not install shingles under 4/12 , though.
[quote=“AaronB.”]**All agree we need about 24inches of ice and water protection at the edges but that is where the differences begin. ** This is B.S. You need minimum of 24" INSIDE the warm wall.
SORRY I meant to say he recommended 24" inside of where the wall comes down. This is all new to me and I missed the correct terminology. Thanks for clarifying[/quote]
Reason why he did that is because many contractors do not follow the building codes. With a 20 inch overhang it would be safe to say that a minimum of 6 feet is used but on those homes i use 9 feet. I never to the minimum.
[quote=“AaronB.”]but nobody has ever been able to offer me any real reason why two is better than one on a non-mopped felt application with all the nail holes.
I have just never thought it any better protection. [/quote]
I like to see someone reply this question to Aaron
Basically it is the premise of more is better, but with some logic behind it. If you install two layers of felt shingle fashion, so the felts overlap by 18-inches, then you have provided more protection against rain when prior to the roof being shingled. Also, it helps in areas where the top layer of felt gets torn, since you have a second layer. In other words, the two layers are generally recommended when the roof is left exposed, i.e., you temporarily dry-in the roof with felt.
As for the felt underlayment after the roof is installed, there isn’t much of a need for a second ply. This is why you will notice that I recommended one ply of 30# instead of the two plies of 15#. Still, that is not to say two layers of felt won’t help you on an installed roof. In some instances, if the roof leaks and water makes it past the first layer of felt, the second layer can offer you protection. I can’t tell you how often water makes it past the first ply and is caught by the second ply, or how often water makes it past both; I don’t think anyone knows that.
good point… i have seen cases where the second layer has water stains from a leak coming from the first one… we wont rely on the felt but on low slopes it does help .
