2/12 pitch on screen porch roof

[westbrooklawn]

I am helping my son cover a portion of his existing deck to build a screen porch. We will be tieing into the back side of a two story house with a 18x13 shed roof (covering 16x12 screen porch). Due to the location of second story windows the best roof pitch we will be able to get is a 2/12. A builder friend says that will be fine, and we can cover it with asphalt architectural shingles to match his existing roof.

In researching the topic I find differing opinions on being able to use shingles on a 2/12 pitch roof. Those who say it can be done suggest more overlap on roof felt and a 4" offset shingle pattern.

What do you think?

[Rich]

Personally I wouldn't do it.. but if that's what you want I would take extra special care to flash it correctly and then flash it again, give good overlaps on felt (as suggested) it should be alright.. do you have snow loads?
Grumpy might give a more technical answer.

[westbrooklawn]

Rich -

Thanks for the quick post! Snow is not much of a problem here (Piedmont North Carolina). The span is 12 feet and I am using 2x8 southern pine rafters, so it appears to be overbuilt based on the span/load tables I have seen. I will look for more replies....thanks again.

[westbrooklawn]

Oh....I forgot to ask, are you suggesting double flashing material? Nail the first one then install second....or nail one time through both???

[Rich]

I would probably put some type of ice and water shield on first, then flashing with a 6" vertical leg, then ice and water shield over the top of that. Then re-install the siding over everything.
But I'm kind of anal when it comes to water infiltration :)

[grumpydasmurf]

Shingles on a 2/12? Which manufacturer will warrant that?

Use a Self Adhering (SA), also called Peel N Stick modified bitumen. It's easy to install and intended for use on 3/12 and lower. Certianteed makes a product called Flintastic. We've used it many times.

If your worried about cosmetics, don't be. It's not likley a 2/12 can be seen and if it can be seen the modified bitumen is available in multiple colors.

As far as flashing goes, you want to remove a few panels of siding where the roof meets the wall and wrap the modified up the wall. Adhere the modified to the wall and mechanically fasten with a termination bar, then reinstall the siding. Make sure to put the modified UNDER the tyvek, or similiar house wrap. This is a great method of counter flashing.

[westbrooklawn]

Thanks to everyone for the suggestions. After discussing this with a local builder we are leaning towards covering the roof sheathing with a self adhearing membrane which will be run up the house wall under the siding at the point the shed roof meets the house. This area will also be flashed. Shingle roof will then be installed over the membrane......my builder friend insures that the adhesive on the membrane will seal all shingle nails as they pass through. Does this approach make sense?

Also, should felt be laid over the self adhering membrane before shingling, or is the membrane sufficient in place of felt?

Thanks again!

[westbrooklawn]

to the top......................................

[Rich]

The membrane should be sufficient.. but watch out if the product you use is smooth topped.. water on it can send you flying off the roof - even at low slopes.