15 lb or 30 lb underlayment? - DIY Chatroom

Hossman · 08-20-2005, 05:57 PM

I was told the roof pitch on my house was a 12 to 4 (?) and it is just fine to use a 15# underlayment vs the heavier 30#. Is this ok or BS? I'm wanting the new shingle roof I'm gonna have installed to last as long as possible and wouldn't mind spending a little more for the better stuff. What do ya think? TIA

GMW · 08-20-2005, 07:06 PM

15# is fine. 30# is usually used on steeper roofs as it is thicker and can stand up to being walked on. Also you should use an ice and water barrier along the front.

Grumpy · 08-22-2005, 09:13 PM

I don't use anything other than 30# because I do not trust 15. I only use 15 when it's new construction and the builder refuses to pay for 30, and I don't have much work.

Use Ice and water shield in the critical areas regardless of the felt weight you choose. Those areas are gutter lines, valleys, and penetrations like chimneys skylights pipes etc...

Hossman · 08-22-2005, 11:15 PM

Thanks, guys. I think I'm gonna stay with the 30# stuff for piece of mind. Thanks for the tip on the ice/water shield.

mjswindows · 09-06-2005, 08:59 PM

Go with #30 i'ts heaver and is the same price, ck home depot.

jproffer · 09-07-2005, 12:37 AM

Quote:

Go with #30 i'ts heaver and is the same price, ck home depot.

That's true....sorta. The 30# and the 15# are the same price usually, but the 15# covers 4 sq. per roll, and the 30# covers 2, so per sq, the 30# is double the price of the 15#, as you would expect.

AaronB · 09-14-2005, 12:47 AM

I do not think it makes a difference unless youre leaving the roof dried in for a long period of time. The felt does absolutely nothing as far as waterproofing after you nail the shingle roof assembly on top of it....it is full of a gajillion holes and if water gets into the shingle assembly, youre in bigger trouble than your dry in material/separator sheet.