I mentioned in my last post that we were getting toward more esoteric wall systems like the PERSIST walls. Well, the REMOTE wall system is a variation on PERSIST, making it like an esoteric second cousin, once removed.
And up front, I’m admitting that I’m flat out copying a lot of material from the other post.
The benefits of exterior foam insulation have been beat like a drum by building scientists for years. When done properly, it can work in any climate, avoids condensation issues and prevents thermal bridging across wall studs. It’s like the Batman of wall assemblies. However, Batman was funded by Bruce Wayne’s fortune and exterior foam board approaches have been held back by the expense.
The REMOTE System pares back some of the most expensive parts of the PERSIST system while retaining the concept’s strengths.
What is REMOTE?
The PERSIST wall system is what you get when building scientists drink all night and make notes on the cocktail napkins. The end result is to blow up the standard wall concept and start from scratch.
The REMOTE System (Residential Exterior Membrane Outside insulation TechniquE … I know, it’s a reach) is what happens when the building scientists sober up and realize they have a budget.
Where would you locate the vapor barrier and how would you vent it (or would it be vented)? How would you frame the walls and what about eave overhangs that exist mostly to give homeowners a place to store their ice dams?
The PERSIST system tackles all this stuff. The system locals most, if not all the insulation on the exterior, ensuring the wall cavity stays warm.
The REMOTE approach modifies REMOTE by installing a standard vented, unconditioned attic. This removes all the expense of sheathing, foaming and installing the exterior vented roof assembly.
A PERSIST system includes:
- The vapor barrier is typically a rubberized asphalt peel and stick membrane. This is installed directly on the exterior plywood or OSB sheath, beneath the exterior foam.
- No eaves or gable overhangs. This gets toward the ‘simple is easier’ concept. By removing the kinds of complicated framing elements like one finds in McMansions or Colonials, you create a perfect continuous impermeable barrier. When the peel and stick membrane is applied, it can be wrapped down over the roof edges.
REMOTE Variation – A REMOTE built house has a standard vented attic, meaning soffits and eaves.
- Exterior foam board insulation, typically 6+ inches of foil-faced polyisocyanurate. This wraps over the entire house, roof and walls.
REMOTE Variation – A REMOTE built house has a standard vented attic instead of wrapping foam board over the roof exterior.
- The framing walls are left uninsulated. The exterior foam board is doing that job. The walls can be built with 2 x 4 studs as there’s no need for deep wall cavities to accommodate insulation. The empty wall cavities are used exclusively for electrical and plumbing services.
- Siding is attached to the exterior with vertical strapping. The strapping allows for a back vented drainage of the exterior.
- A vented roof is created by essentially building a standard vent roof outside. 2 x 4 are installed on edge, fastened to the rafters through the roofing foam. OSB or plywood sheathing is installed on the 2 x 4s, creating an exterior vented roof.
REMOTE Variation – A REMOTE built house has a standard vented attic. This replaces the exterior installed venting.
The advantages and disadvantages understandably mirror those of their parent system but there are enough variations that it’s worth revisiting.
R-Value – Like PERSIST, it is built with 2 x 4 framing with no cavity insulation and 6 inches of exterior polyiso foam board. The walls will have a very high R-value and no thermal bridging.
The REMOTE approach also has an advantage in achieving high levels of attic insulation. It is far easier to reach the desired R-49 to R-60 with cellulose on an attic flat than foam board on a roof exterior.
The cellulose entails blowing 18 inches of cellulose with the appropriate air sealing attention. Exterior foam board would require 10 inches (assuming R-6 per inch for polyisocyanurate) with special screws to go all the way through to the rafter beams.
Thermal Bridging – The exterior foam board addresses thermal bridging in exactly the same manner as a PERSIST wall. Even without wall cavity insulation, 6 inches of exterior polyiso can help achieve close to an R-40 whole wall value.
Air Leakage – REMOTE framed houses are much more air tight than standard framed houses but require some extra attention to detail. PERSIST constructed framing adheres an air impermeable pull and stick membrane over the entire structure. This makes it quite tight.
REMOTE built houses only do this on the walls, insulating the attic as a standard vented unconditioned attic space. That means they require all the air sealing details a standard vented roof would to prevent air driven heat loss.
Moisture – Largely the same as PERSIST but with a roof assembly that is simpler and more familiar to builders. The wall’s peel and stick membrane is typically wrapped over the top plate of the wall.
For the first time with the wall assembly write-ups, I’m including a ‘plus/minus’ category. This would be areas the REMOTE systems differs from both the standard framing and PERSIST with an advantage over one but not the other.
Ease of Installation – Harder to install than a standard wall, much easier than PERSIST. The full PERSIST approach means the peel and stick membrane goes over the roof, followed by 6 or 8 inches of foam board, then an exterior vented roof assembly, plywood and shingles. With REMOTE, you insulate the attic and install a roof.
Cost – Even using less materials, the project will cost a good deal more than a standard wall and roof framing. The good news is that it’s considerably less expensive than a full PERSIST built house. The two most expensive elements of the PERSIST approach are all that peel and stick membrane and the added roof structure and overhangs. The REMOTE technique uses half as much membrane and eliminates the extra structure entirely.
Green – The REMOTE approach is a big green improvement on PERSIST. It substitutes all the extra attic foam, wood sheathing and wood studs with standard attic cellulose. Less foam board means less chemical blowing agents, less petrochemicals and less embodied energy.
There are a number of different approaches for high performance building enclosures. PERSIST delivers the kind of building for extreme cold weather but REMOTE achieves much of the same results for less money.