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Best way to flash a porch roof

Basic rectangle farm type timber frame. SIPS, house wrap, ventilated cladding, right now thinking furring strips with fiber cement board. This house will have a porch on all 4 sides. Two ledgers for porch, one for roof the other maybe 2' below for ceiling. Would the ledgers be attached right to the SIPS, interrupting the furring strips, slice the house wrap and slip the flashing between wrap and SIPS? That would certainly drain everything out to roof. Cladding above porch roof would still be ventilated. Maintaining ventilation in the section below the ceiling is what I'm wondering about. It could be configured to vent into area between roof and ceiling with the ceiling or soffet ventilated. Would that be an acceptable solution? Any thoughts on vents in ceiling or soffet? Any drawings out there that would show the details would be helpful. That would save me the trouble of doing my own as I am not to well versed on a CAD program.

Asked by John H. Stehman
Posted Thu, 01/02/2014 - 11:26


3 Answers

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There are several issues here. One issue is ensuring that your ledgers (the rafter ledger and the ceiling ledger) are adequately secured to the SIPs. I think that you should contact the SIP manufacturer to make sure that your plan meets the company's approval.

The air intake for your rainscreen above the porch roof should be detailed just like the air intake at the base of a wall.

The lower rainscreen will be protected by your porch roof, so that part of your wall won't get any rain. I don't think there will be any problems if you vent the top of the lower rainscreen in the attic area between your porch ceiling and your porch roof.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 01/02/2014 - 12:30

Helpful? 0

Martin- there will be an additional 8" beam running around the house for the purpose of attaching the roof ledger. The ceiling ledger will attach to the beam at the 2nd floor level. The appropriate sip screws or heaver lags will be used. The detail from the sip manufacturer shows running the screws from the inside thru the sips into the ledger but then again, that wasn't a timberframe. I think the way I am doing it is a bit more substantial. Thank you for your answer. It was what I expected but I wanted to hear it from the pros.

Answered by John H. Stehman
Posted Thu, 01/02/2014 - 17:44

Helpful? 0

A couple of caveats to Martin's advice:

You have a greater chance of wind-driven rain or water splashing up behind your rain screen above the roof than you do at ground level. Make sure the end wall flashing extends up sufficiently to deal with this possibility.

Depending on their width, many jurisdictions do not allow continuous wall cavities to extend up into concealed roof spaces without fire blocking. Check your code before extending the rain screen strapping into the porch roof.

Answered by Malcolm Taylor
Posted Thu, 01/02/2014 - 20:42

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