[Jim McC]

I read that dimensional shingles are not the best choice for low pitched roofs, such as a 3/12 or 4/12, and that flat 3 tab shingles are a better choice. Is that correct?

If so, what particular shingle do you recommend for a 3/12 or 4/12 roof?

Thanks.

 

[Windows on Wash]

Whichever is covered by warranty.

Either way. I would run a minimum of synthetic underlayment and cap nail and possibly full ice and water.

 

[joecaption]

And no way would I go with 3 tabs!
Why install a shingle with a weak spot every 12"?
Any company that makes shingles should have install directions on there website for low slope, steep and high wind installs.
Most will tell you to change the amount of exposure and a minimum of a double layer of 30 Lb. paper.
Windows suggestions would cost more but are a better way to do it.

 

[craig11152]

If one ice and water shields an entire deck it better be text book vented because that is a vapor barrier in a less than ideal spot.

The theory with 3-tabs verses laminates on gentle pitches is about capillary action. Where 2 shingles butt together vertically a certain amount of capillary action can occur wicking water under the exposed portion of shingles. In a fully sealed laminate its harder for that water to find a way out. In a 3 tab shingle that water can find a way out every 12". That is the theory.
If you live in Phoenix I would discard the theory. If you live in Seattle I wouldn't discard it so readily.

 

[Colbyt]

My roofer says the dimensional shingles are the better choice. I don't think either are warranted for a 3/12.

 

[1985gt]

I'm not sure about others but I have seen a lot of laminates on 3 and 4/12 pitches. IMO when the slope gets much lower then that, then the problems can and do start.

A lot of times we see this on porch roofs or sunrooms, venting is never good on those so as Craig said, id be careful with using full Ice and Water shield in those areas, as Joe and Windows mentioned synthetic or half lap #30 felt would be better in that situation.

 

[ddawg16]

My roof is 4/12 with dimensional shingles. I believe they are rated to 3/12

Of course I don't get the rain the OP does.

Considering the cost differeence between dim /3-tab, I can't imagine why anyone would go 3-tab. Cost difference is not much, but dim shngles are easier to install and don't show if the installer was off a little on the line. If 3-tab is off...it's really obvious.

 

[Jim McC]

Thanks guys. Cost is not a factor. I'm asking because I read that 3 tab shingles are the better choice for a low slope roof. I think it was at Roofing.com