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Discussion Starter · #1 ·
Hello. I'm A tile contractor possibly over my head with a siding project.

I started with an 800 ft addition. On the new portion of the house i used lp tech shield sheathing (.5" osb with a foil face that perforated with holes to allow vapor to escape.) LPs directions required a 3/4" airspace inbetween the foil and any other material. So, on the side where the old house met the new house, in one flat plane, I removed the old windows, furred them out, and the windows on the new addition were furred out as well. Then I placed furring strips over the old sheathing and new sheathing (after taping all the seams whith a foil tape, to block airflow). Figuring that since I was creating a vented airspace in between the sheathing and moisture barrier, I'd use 6 mil polly, since Ive heard bad things about the longevity of tyvek, felt would be a pain over furring strips, Poly seemed to be the ticket.

So I put up my poly and away I went. It was cool all day, so the poly stayed nice and tight. I did the old portion first to about the middle of the 35 ft wall, stopping at the trim around the door and to the top of the door where the next row would cross the top of the door. so 7' x17' (Most of the day was spent on removing reinstalling old windows, furring, flashing and trim.) I also put the poly on the other side of the door as well, completing the poly instalation to about 8 ft high for that entire side. I quit for the day. Then next day I came home from things I do know how to do (Tile) and the Poly was very loose. It was hot, and so it was touching the sheating in between the furring strips. :sad: Then it cooled down at night and the following morning it was nice and tight again. This time of year its around 70-80 deg f in the daytime, and 25 ish at night.

How badly have I screwed this up? I have no worries about moisture intrusion. I placed a j weep screed at the bottom, furring strips vertically over that, 1/4" redwood lattice strip to kick out the bottom row of the hardiplank 6" ship lap siding, and then the poly drapes over all that. My concern is that with the temperature swings, durring the hot times of day the poly will sag, and then stretch, untill eventually it just sags and stays there interfering with the airspace. Obviously there is still airspace next to the furring strips, but I'm worried about two things mainly. Durring humid weather, possible mosture being traped where the poly touches the sheathing, and the second being reduced airflow rendering the cool foil sheathing useless.

Any thoughts? Would you rip off the already installed siding If it were you? If so, do you have any pointers on removing with the goal of reusing?
 

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Discussion Starter · #3 ·
All the siding on is new. Installed by me. I'm trying to figure out if the poly over furring strips will cause me any issues.
 

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I have never ever seen poly used on the outside of a house. Seems like a great way to trap mold and mildew. What made you think of using poly?

I also looked up the sheathing you used and it is speced for roofs and gable ends only. I have never used it, so hopefully someone who has will know more than me by just looking it up on the LP site.
 

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My first thought is, tear it off and get that poly out of there, for more reasons than I can possibly type.
If you don't like building wrap, and a lot of experts don't, you can use two layers of 30 minute building paper, if your local code permits.
Did you have it inspected?
There are lots of guy's on here that know way more about it than I do, but I've never seen it done or even heard of it being done.
Hope this helps.
 

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Never, ever, ever, is poly installed inside & out a good thing. Please don't go any further with that & definately pull the siding & get that poly out of there. I too have no experience with the osb your using but it sounds like the foil backing id a substitute for tyvek or paper. The air space is called rainscreen hear. Using normal sheathing, the install would go: sheathing, tyvek or doubled paper, fur strip, then siding. This is why I'm suspecting the foil is a substitute, provided it is a recomended product for heated exterior walls. The fur strips always go on after your exterior wrap. Sorry for the bad news but you're guaranteeing a mould problem leaving the poly in there.
 

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the poly is over the vented rain screen?if so it's really not acting as a vapor retarder

but it could trap moisture on the back of the siding

over time it will probably become brittle
 
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