ALERT: This post is going to be about geek stuff. In particular, insulation.
When it comes to the exterior envelope of a building, there are many factors to consider. First and foremost we need to protect the occupants from the rain and weather. But after that, the building technology advancements over the last 100 years have required two things:
- A tighter and tighter (as close to air tight as possible) envelope.
Both serve to mitigate thermal transfer. As local consultant XRG Concepts will testify, good work in insulating and air-sealing will lead to a more comfortable indoor environment as well as lower energy bills. Who doesn't want that?
I will ignore the discussion of how this tighter envelope has basically necessitated a mechanical air system and focus instead on insulation and air-sealing.
There is a lot of complexity to this topic, but in the simplest terms, the insulated envelope is trying to keep the temperature different on either side of the enclosure. If it is very hot outside, it wants to keep that out so the inside stays very cool. If it is extremely cold outside, it wants to keep that warmth in, instead of letting it escape. This thermal transfer is further complicated by the fact that warm air contains moisture vapor. We need to control moisture transmission as well, otherwise we can get water inside our walls which is detrimental.
For decades, the exterior wall has been constructed with stick/stud framing and then stuffed with insulation between the studs in the cavity. This utilized the thickness of the stud as a space to slow down that thermal transfer. But starting last year, in the State of Minnesota, the new energy code goes a step further and now requires a "Continuous Insulation" on the exterior of the cavity.
This science behind it is legit. This adds more insulation, without any gaps or "bridges" created by the framing itself. It also moves the dreaded dew point (the point where water vapor turns into liquid water) further outside the enclosure to prevent water inside the wall. But it has sent some architects scrambling for new details. In particular, regular old wood siding cannot be nailed to foam. So there needs to be additional parts added to the enclosure.
For Pure Rock Studios, we utilized a new system to combine the continuous insulation with a nailable substrate suitable for traditional siding. It is called ZIP System R Sheathing.
In its bright green finish, it provides solid structural sheathing necessary for lateral loads and cladding attachment. Plus it creates a continuous layer of insulation outside the cavity that is required by the Minnesota Energy Code. This is then coupled with additional insulation inside the cavity to create a wall system that is rated up above R-26. That means better resistance to thermal transfer and thus lower energy bills.
The ZIP System R Sheathing boards come in 4'x8' sheets and were installed with a prescribed nailing pattern and then seams covered with a proprietary butyl tape. The sheathing is now installed at Pure Rock Studios and the exterior cedar cladding will be going on this week. But before the green monster is covered up, we thought we would explain a rather insignificant but crucial detail about it.