Can tape fill in missing poly vapor barrier?
Hey all,
I had an insulation company foam my ceiling and the company was cheaper than what I could buy the wall batt insulation for, so I had them do the batts too. I’m required to have a vapor barrier. The company’s poly install has some missing areas on double studs. I am in zone 5b, SLC, Utah.
I purchased Tuck Tape (blue) to tape up all the poly seams and will acoustical caulk the tops and bottoms to framing.
They have some rough work on the poly. Now, I get on this forum poly is not loved. That said, it has to be there for building code. It already passed inspection.
With that all, they left some areas with obvious mistakes where poly is missing. I have scraps that they left hanging. I know I can patch those in to gaps. but on one area, they left the corner studs without any. Should I seal up what’s there with the caulk or can I use the Tuck Tape in long lengths to “build” a continuation of the poly?
Where the poly doesn’t reach the floor, can I use the Tuck Tape to extend and then caulk that?
I’m not super interested in calling them back or buying more poly to fix unless you all call for it.
Thanks
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Replies
Ryan_SLC,
What is the function of the poly? Is it your primary air-barrier, or just a vapour-barrier?
I ask because if it is just there to limit vapour intrusion into the walls, it is a lot more forgiving, and good sealing or small missing pieces don't matter much.
I'm not that familiar with US codes, but isn't Salt Lake City under the IBC? It calls for vapour-retarders not vapour-barriers.
Good question.
Prior, I taped the seams of the OSB sheathing with 3M tape.
The insulation and with a vapor barrier passed inspection. I was given the go ahead to drywall.
It's required as a vapor barrier. I know I'm walking the line of a vapor sandwich, but I've also read here that those fears were a bit overstated? Just looking for perfectly done, given it's not all that intensive to do it right given my small addition.
Ryan_SLC,
I think you are wrong about the requirement for a vapour-barrier, but lets leave that aside.
"Just looking for perfectly done."
Perfectly done is continuous sheets of poly from ceiling to floor. Taped joints should be located over backing (studs or plates).
It's totally possible. I called my city inspector and asked. He said a vapor barrier was required. I had called a while ago because I had read so much on here about not doing one.
It might be a misspeak, but I know he said vapor barrier.
I'm not sure everyone is 100% on everything in my area. My inspector that came out had never seen the liquid flashing in windows and was going to look up if the city allowed it. I said I was using tape too and it passed. I guess while Zip is very popular around here, no one uses the liquid Zip flashing.
So i don't know.
Do you think Vapor Barrier Tuck Tape (blue) can serve as gap filler in the poly?
Ryan_SLC,
Sure - and as I said, if it's just there to stop vapour movement, a few gaps and incidental holes don't mean much.
Perfect. Thanks Malcolm!
Malcolm...what if I want to air barrier too?
You answer is suggestive, and I want to go there!
Ryan_SLC,
Bet & suspenders and all that...
The more continuous you make the poly, and the more you seal the perimeter and any gaps or penetrations, the better will function as a secondary air-barrier.
If you have a good primary one in the sheathing, the drywall functions fine as a secondary one.
Wonderful. So I taped the sheathing well, I attack the poly with as much tape as I can, and then drywall...I've only wasted time at worst?
Found this thread to be helpful too.
https://www.greenbuildingadvisor.com/question/repairing-polyethylene-vapor-barrier
Just curious, but what was the reason of not getting some poly to patch? The cost of a 100' roll of 12" wide poly is about the same as one roll of blue tuck tape.
Exactly right.
It wasn't being lazy or cheap, it was my non trade understanding. A patch requires extra poly plus tape...but how big should a patch be? So the questions get even more obtuse in my mind.
So my question was, if tape sufficiently covers poly seams, is it sufficient to act as poly in small void areas. It seems like it should according to others here. I will say, I've been slow to drywall and I can see the improved sticky blue Tuck Tape is not 100% sticking to perfectly flat areas of the poly but not taught areas. It's getting the job done I'm sure, but it's not like it's perfectly fused/welded.
The perm rating of 6 mil poly is so low that I don't think it matters if it overlaps an inch or a foot. I think it may have been easier to cut poly patches and tape where it was flat and easy to tape. At least that is what I plan on doing if I have any gaps and don't feel like calling the insulation guys back.
Yep. I didn't call them back for their voids and said they did a great job.
I have since read in other areas that there could be a level of over lap in vapor barriers where vapor/air/moisture exchange becomes more theoretical than actual in a wall. Not saying I believe it! :)