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Old 06-25-2010, 03:31 PM   #1
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hardiplank, roofing and sheathing flash gaps


the instructions are pretty clear that there should be a 1-2" gap between the hardiplank and the shingles. what i can't find is what size flashing people normally use or what the gap between the sheathing and shingles should be. on one area over my garage with 7/16 osb on 2x4s i was thinking at least a 1/4" gap or larger should be there even with the flashing on top and the hardi on that. what is the general rule with sheathing and shingles? also, the bottom of the sheathing, should it be Z flashed?

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Old 06-25-2010, 05:53 PM   #2
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hardiplank, roofing and sheathing flash gaps


I hold my siding about a inch off the roof. The flashing used is “Step Flashing” or "Roof to Wall”. Those details are part of the roofing and not the siding job.

I don’t flash the bottom of the sheathing but I suppose you could cap it. You should hold the siding about a inch below the sheathing.

I’m confused on the rest of your question.

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Old 06-25-2010, 06:21 PM   #3
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hardiplank, roofing and sheathing flash gaps







i put this up while i was doing the roofing job. the previous owner had painted cdx left exposed for siding. the bottom was rotting and i had a few left over sheets of osb from roofing which seemed like a good use for hardiplank to go over. after doing this it dawned on me a few hours later that i really didn't want the osb this close to the deck. step flashing is behind it as you can see. that being the case would ripping a 1.5" gap from the deck to the bottom of the osb be the way to go? i could then run the hardiplank at 1" off and have half an inch of overlap. also pictured is drip edge. would this work behind the hardiplank? it would look nice since only the 1" portion is on the deck and the hardi covers most of it. that would basically be a double flash install so even if water gets past the drip edge the step flash is behind it

by the way, does it really matter which way osb faces on siding? i know on the deck i installed it the reverse of this with the rough side up.
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Old 06-25-2010, 06:56 PM   #4
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hardiplank, roofing and sheathing flash gaps


I don’t see any step flashing but if you say it’s there behind the OSB, I believe you.

My question is why are you adding OSB over the T1-11?

If you had some questionable plywood siding you should have replaced the plywood siding with OSB not coverd over it.

There is nothing to be gained by what your doing.

If your covering rotted T1-11 with the OSB you should stop, rewind and fix it right.
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Old 06-25-2010, 07:34 PM   #5
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hardiplank, roofing and sheathing flash gaps


oh no, that would be cheesy and a total moisture trap disaster, it's torn off down to the studs. someone before pulled the t1-11 to put up plywood, all that's down. what you see is osb on studs with step flash behind it. i was just concerned about the gap with that osb since it's in contact with the roof. my idea is to rip the section touching the roof off, recut and install with a 1.5" gap which would expose that step flash i have behind, then i can install hardi following their instructions and not have anything near the deck. this sound good so far? what do you think of the drip edge idea? it seemed like an easy way to double flash since i have 20ft of it laying around

just incase that seemed a lil random

1. install osb on studs with 1.5" from deck, 6x6 step flash going 3 up and 3 under installed
2. install tar paper or tyvek
3. install drip edge {undecided on this per input}
4. install hardi starter strips 1" from deck which would have them hanging half an inch down over the osb

thinking like water {which i learned to do installing the roof} it seems like a valid plan. water will run down with the majority running off the drip edge. any that makes it under will run down the step flash. the drip edge basically serves as a sideways rain protector since it would prevent blow in this potentially getting the bottom of that osb wet.

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Old 06-25-2010, 07:48 PM   #6
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hardiplank, roofing and sheathing flash gaps


You should have replaced the plywood as you did and then roofed to that with the step flashing coming up over the OSB, felt over that, and then siding.
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Old 06-25-2010, 07:55 PM   #7
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hardiplank, roofing and sheathing flash gaps


so the step flash goes over the osb and under the shingle? hmm they had it under both on the old plywood. if that's the case i could easily protect the osb with another layer of flashing. actually makes sense though. with the flash over the osb the osb will sit snug on the 2x4s and there won't be any poke out which of course is the case now since osb is sitting on step. not exactly level with the 2x4 but easy to correct. i can pull the osb and snake it in behind the flashing

does it matter much which way i do this?

Last edited by racebum; 06-25-2010 at 07:59 PM.
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Old 06-26-2010, 06:56 AM   #8
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hardiplank, roofing and sheathing flash gaps


you should remember when holding your siding up off the roof,the step flashing should be made larger so you have adequate coverage

plus i think your better off cutting the shingles back and put the step flashing on top of the osb where it belongs

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