Hello
I am planning on building a sun porch onto the back of my house. The roof style I have planned is a simple shed type covered with standard 3 tab shingles . Because of existing windows on the second story wall (where I plan on tying in the top of the shed roof) I am limited to an (approximate) 3/12 pitch. I have read that you want at least 3/12 pitch for 3 tab shingles. Why is this? Does it have to do with the speed at which the roof can shed water? Snow load? Structural wind requirements?
If I am committed to 3 tab shingles and a 3/12 pitch are there any things that can be done to get around this limitation? Types of underlayment? More structure? …
Thanks
buzbe
Replies
If I wuz puttin shigles on my dog house, I'd wonder how seriously folks would take me here...edit whut? I'm pretty sure there's a way to bypass all of this...
best of luck...BB
Buzbe,
Check with the manufacturer of the shingles. I know that Certainteed approves of at least some of their three tab shingles on a 3 in 12 slope, but requires the entire surface to be covered in "Winterguard Waterproofing Shingle Underlayment or its equivalent, or two layers or 36" wide felt shingle underlayment lapped 19"."
Rich Beckman
Most manu's will let ya go to 3/12...but cut the exposure down to 4 inches. I did a shallow pitch....2.5/12...with approval from all...manufacturer and local build inspector...but called the manu........they wanted ice shield over the entire roof deck.....then the build inspector....they wanted full venting.......because of the full ice shield......both got what they wanted...and the customer got a shallow roof that matched the existing.
This was dimentional.....which may work better than 3-tab....for this application....but the 3-tab should still have the exposure shortened. Hand sealing each tab isn't unheard of either. Little dab'l do ya. Jeff "That's like hypnotizing chickens........."
You have absolutely no problem with three tabs on 3/12 with just 15#felt. Maybe lower in some instances and geographic zones.
Mostly it has to do with sheeding water before it backs up. If you are in Phoenix, I wouldn't worry about it at 2/12. In Chicago, I would worry at 4/12.
Depends also if this will be a heated living space. That affects the insulation, venting, ice damn formulae.
Ice and water shield underlayment is your safest bet for extra insurance if you are pushing the envelope.