Is the ZIP sheathing system good or bad for water control?
Do you have any experience with this system and know how it would compare to regular OSB sheathing with a fully adhered sheathing membrane?
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ZIP Sheathing is a pretty hot topic with some differing opinions. The ZIP System is a structural sheathing intended for walls and roofs, with an OSB base and WRB (weather resistive membrane), which is basically a mesh that is attached to an OSB sheathing panel with a paint applied. So it is an all in one product acting as the sheathing, the weather barrier and air barrier. It’s a great concept, but you are not alone in your skepticism. Before you give it a yay or nay, here are a couple of pages that will help you understand how all these systems work, and you will probably see for yourself how it may be a problem:
Choosing Between OSB and Plywood Sheathing – How they Work
Choosing a Home Wrap (or Weather Resistant Barrier / WRB)
And our reluctance to give it a thumbs up or down in terms of water management is that we have questions about its permeability as part of a complete system depending on how and where you use it. so, can you tell us - what is your climate zone or city, and were you planning to use it for your walls or roof? And what other products would accompany it?
I’m currently trying to decide what would be the most effective/economical option for the walls on a project in Donald BC (Zone 6). Below is the wall assembly that I am planning to use:
My main concern is at the horizontal joints on the ZIP system. Typical practice with membranes is to always have a positive lap when joining two pieces of membrane together; However, this is not possible when just slapping on a piece of special tape. I struggle to believe that this tape will be able to keep the water that runs down the wall out for the entire life span of the building.
Another issue is cost. Would you happen to know what the cost difference would be between a fully installed Zip system and typical OSB sheathing with a fully adhered sheathing membrane?
About the Zip System tape as a drainage plane – I wouldn’t be concerned myself. I don’t trust the cheap building tapes that regrettably dominate the mainstream house building market, because too often I’ve seen them turn brittle and peel right off the wall, particularly when they are subjected to the freeze / thaw cycle or are left exposed to UV rays for extended periods before covering them. But this stuff is better.
So tape it properly, cover it soon afterwards, and, that’s another good reason to maybe go for the 4 inches of exterior insulation rather than just 2 inches, it will stay warmer. A 4 inch layer of rigid board insulation in Douglas BC would not be overkill.
Further to that, if you build your wall well then you shouldn’t be experiencing a regular water fall in there. That’s just my two cents, you seem to know your way around a wall assembly so it will have to be something you are comfortable with or you’re going to sit there staring at the wall wishing you had x-ray vision wondering if its leaking.
So if you want options, here is our peel and stick exterior weather barrier DIY installation video.
And where did you find the vapor barrier paint here on our site or somewhere else? We tried it (we could because we did the exterior peel and stick membrane I mentioned above), it was part of an overall strategy that included 5.5 inch Rockwool batts in the wall and 8 inches of Rockwool rigid insulation boards on the exterior.
As for cost comparison of ZIP sheathing vs normal sheathing and home wrap , there are way too many variables to pin that down accurately. You’d have to price out home wrap (Tyvek, Typar or whatever brand talks to you), plus sheathing (we prefer Plywood over OSB for Sheathing), then the labour to install it all. ZIP System is only one trip around the house. And if it’s a bungalow or you’re up and down scaffolding will even make a difference in labour. Sorry, not trying to dodge it but I’ll be blowing smoke up your wazoo if I told you I had an accurate price :)
Thanks for all this info! Seems like the system is effective and it may just come down to a cost exercise.
The first time I discovered the vapour barrier paint was in one of your videos about the wall assembly used on the Edelweiss demo house. I am an architectural technologist at a commercial firm in Calgary and we only do exterior insulation with a combined air/vapour barrier on the exterior sheathing and therefor have never needed to worry about poly vs. vapour barrier paint. In my opinion, the paint seems like a great solution that removes good amount of material from your wall. My only concern is at the top and bottom of the walls where you need to connect to the vapour control layers of the other assemblies. Maybe an article about membrane continuity between floors/walls/roofs could be a good idea for you guys (if you don’t have only already that I’ve missed).
This project is for my family’s new cabin so I’m trying to keep costs down as much as possible while still getting a great building.
I have looked at remodels where some of the original felt paper was replaced with a sythetic house wrap. In one case, a decade later, exactly at that point, the rot started. A clear line of defining the edge of the replacement synthetic "breathable" wrap, where the sheathing became spongy and mottled, wheras behind the original paper it was totally acceptable and sound. This is coastal north Pacific. So please consider me a skeptic about any new product or system in conjuction with wood in a marine climate. The Zip tape is very good tape though.