Is using Zip System Sheathing on a ventilated roof a waste of money?
brentwilson
| Posted in General Questions on
On a ventilated cathedral roof where the ventilation channels are below the sheathing, would it be a waste of money to use Zip System sheathing? Why or why not?
Climate Zone: 6B
Snow Load: 80 to 100 pounds live load
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Replies
My thinking is that the air sealing properties of Zip sheathing would be pointless if air is being intentionally vented under the sheathing. Is that correct?
Brent,
I agree, and the advantage of not having to use a WRB that you get with Zip on walls is also not there with roofs.
Hi Brent.
Though I have heard nothing but good stuff about the quality of ZIP tape, if it were my build and if I wasn't looking for the air sealing qualities of this product, I would use a wood panel sheathing and a high-quality, mechanically-lapped roofing underlayment.
Waste money if you still have to/choose to apply an underlayment because the manufacturer of the asphalt shingles or whatever you choose to use won't warrant their product when used on ZIP.
Remember the whole purpose behind ZIP is that it's an All-In-One product designed to replace sheathing + wrb.
“All in one”.....because its so tough to wrap walls.
It’s a heavily marketed product in trade shows, free license CEU’s, salesmen push it, rebates, free rollers, reps throwing out gift cards (I know because I got all of it) and they were smart and made it green, a little homage to the Hardees orange. Green Building Advisor is crawling with it.
Use it if it works I guess, but number wise in dollars and sense it’s not worth it, can get the same or better for less.
The market will decide on whether or not there are sufficient cost savings by going ZIP vs OSB+housewrap. In my area over the last couple of years it seems to be the go'to product for custom builders. Tract builders are using their own branded housewrap w/OSB or another product which I call "cardboard sheathing".
Hooray for capitalism! YMMV.
You proved my point and the market has decided. Tract building is about numbers. If ZIP shaved dollars off cost, smart tract builders would require it. But they don’t use it, because it doesn’t help the bottom line.
Custom building on contract, the more I can convince someone to spend, ie explain all the wonderful benefits of this amazing product referred to, as an example Zip sheathing, the more money I make since my margin is on total cost not to mention kickback rebates to give me some extra lunch money.
Don't get me wrong, if someone wants it, I’ll use it and take the money. But as a builder being honest, my opinion of it is it isn’t remotely necessary.
YMMV
We don't have large-scale tract home builders where I live, but the production-minded builders are all using the Zip system as far as I can tell. It's rare to see a new home go up that's not "green." (For the record, their thicker panels are reddish brown.)
I never could see the appeal of Zip roof sheathing. The only one I see is the speed of getting water tight.
If you must have the cathedral ceiling I say put most of the insulation on the outside with a vented roof on top. Like peanut butter must have jelly cathedral must have pot lights. And there is just never enough room in the joist space for good insulation, air barrier, pot light and ventilation.
Walta
If you are not going to put finished material on your roof right away go with zip. The exposure time is far superior to OSB. If you are going to put your roof on in less than a month stick to OSB and underlayment.
The underlayments I use with a plywood roof-deck are all rated for six months exposure.
I think it's tricky. You should be sure your ventilation system is ok. For example, if you check handy man tips on https://www.familyhandyman.com/ you can compare with your roof to be more aware. Also, maybe it's even better to write him for extra advice.
What if I want the advice of a Handy Woman?
Ben
I smell Spam...
IDK, I wish I would have went with Zip on my traditional vented attic roof. This was because I Im building the house myself on three day weekends. I used 30# roofing felt as an underlayment. After working to get the felt down I was shocked in the shrinkage of the felt. Every day, after sun, afternoon showers, and freezing nights the felt would contract another 1/8-3/16". Hundreds of every increasing tears appeared at the plastic round cap nails. After 12 days, I realized i would have to tear it all off! The installation had failed before I could get the roof on... Because I was working by myself, there was no way I was going to get the metal on at any speed that 30# felt would actually work. I ended up using grace water and ice shield because it was readily available and I need to get something on the OSB. It was an expensive alternative!! Zip would have been cheaper, easier, faster and probably would have eliminated the need for H clips too. For solo builders, I see the value. Now I'm curious if roofing felt contracts and tears like that under the dark metal roofs? If so, what's the point?
Thats the advise from a self builder that knows just enough to be dangerous...
Great insight. Thanks.
rkytmnoffgrd,
I agree, roofing felt is awful to work with - and not a good choice with metal, as it get too hot, sticks to the panels, and deteriorates.
Luckily there are synthetic underlayments designed for metal roofs (one made by Grace), that can be left exposed for 6 months, and provide a great walk-able surface. So if you don't opt for Zip, they are a good alternative.
Snow load: 80-100lbs of live load sounds like a lot of snow, but then again you are in zone 6B. What is the pitch of your roof? What roof finish are you using - asphalt, metal, cedar shakes?
Do you have a concern about ice dams? Are you using a raised heel truss? Continuous eave and ridge venting?
You might find some information in this article from forensic building scientist Dr. Joe Lstiburek helpful (he has a lot of additional articles about roofing on the Building Science website as well).
https://buildingscience.com/documents/insights/bsi-046-dam-ice-dam