Installing cedar shake siding over Zip-R sheathing – GreenBuildingAdvisor

Hi all, 

We are looking to install cedar shake siding on an upcoming project and are looking for some input from others with experience here.

The project is in zone 6 in Canada, so it will get cold winters and hot summers. 

We are looking to use Zip-R9 as our sheathing and WRB layer for the continuous insulation benefit. We looked at doing rockwool over plywood but were advised against it given that it could create waves with the shakes. So we are about 80% set on moving ahead with Zip here. 

We do a lot of siding details, but not a lot of shake. With siding, we strap the wall with furring to get our rain screen/P.E.C.  

Now with cedar shake, we can either do cross strapping of 1×4’s, but this is a more labour intensive route and can be a pain for detailing at openings etc. Or we can install the cedar over Ventgrid 12 to get our rain screen. 

We were initially sold on using Ventgrid since it is less labour. However, with ventgrid every nail used to fasten the shakes would penetrate the Zip sheathing. With strapping, the shakes would fasten to the horizontal straps and not penetrate the zip sheathing. 

We are concerned that having so many nail penetrations going into the zip sheathing could be an issue long term for air sealing and water damage. We were looking to use densepack cellulose and the insulation, so if water did get in that would be a huge issue. We could swap to rockwool batts though as a counter measure. 

The builder does a fantastic job of installing zip properly and with their tape/flashing details. So I am not concerned about the basic installation of the zip. It is more so the cedar shake penetrations, which cannot be taped or flashed that worry me. 

I know this happens with roofing all the time, but roof sheathing is acting more as a water shedding layer than an air barrier, so its a bit of a different beast. 

Are we overthinking this? Does anyone have any experience with this that could help in this situation?