A roofing system's critical job is to stop liquid water. Stopping air greatly reduces energy use but can trap moisture—UNLESS the peel-and-stick roofing membrane is vapor-permeable, like VaporDry from Benjamin Obdyke. Atop the VaporDry, we added a layer of cedar Breather, an entangled mesh material that creates a ventilation space, allowing multi-directional airflow. This ventilation space will remove any vapor escaping from the roof, remove some of the summer heat generated by the dark metal roof that will go above, and help prevent any ice dams in winter.
Building Resilience episode transcript:
Last time on Building Resilience, we were Installing a minisplit heat pump from Mitsubishi poking tubes through walls, connecting them, and setting the outdoor unit, the compressor, in place. It’s a great option even for cold climates
Michael Anschel, of OA Design + Build + Architecture
Heat pump adoption up here in the north has not been the smoothest of roads. In fact, 20 years ago, we weren't allowed to use them as a primary heat source.And frankly, the technology just wasn't there yet, but a lot has changed since then. And now they are an option worth considering, especially with things like hyperheat for Mitsubishi, which can comfortably perform down to minus 20 degrees. And when it's not freezing cold out, boasts a pretty impressive efficiency of 4.68 COP, which is like saying 468 percent efficient. And when it does get down to zero or minus five or minus 20, that might drop down to say. 1. 6, 1, which is like saying 100 percent or even maybe as low as 70%.
But you compare that against a traditional furnace or boiler that's running 96, 97 percent efficiency at its peak performance. And that's still a pretty good deal.
With the cover screwed on and the minisplit fired up, we’re up on the roof to put down some peel-and-stick underlayment from Benjamin Obdyke.
VaporDry is a roofing membrane that stops air and allows vapor to escape
They call it VaporDry SA because it is vapor permeable, meaning that it stops liquid water from getting through, but moisture molecules, Vapor, can escape, allowing the structure below to dry.
We're all familiar with Ice and Water Shield. That's that peel-and-stick stuff you put around the eaves. Typically from there, we switch over to a synthetic or some other kind of underlayment for the rest of the roof that's stapled down. Benjamin Obdyke has a product called VaporDry, which is a self-adhered membrane.
It's got a solid acrylic backing, and when you lay that down over the roof deck, you have continuous air sealing across the entire surface. However, one of the big advantages is unlike on ice and water shield. which is vapor impermeable. This product is fully vapor permeable. This means that any moisture that manages to get from the inside of the house up into the rafters or the truss area has the ability to get through this membrane and out into the world and away from all your wood products.
Another advantage of Obdyke's VaporDry roofing underlayment is the ability to walk on the surface with confidence. Unlike a mechanically fastened system that's using a cap fastener or staple to hold it down to the roof deck, because it's continually adhered, it's insanely grippy and there's no sag, there's no movement in it, as you walk across that surface.
So we've got a product that is vapor permeable, it's easy to walk on, it's giving us a good air seal across the entire roof deck. This is all pretty awesome, but one of the things that our crews really love about Benjamin Obdyke's approach to the whole enclosure system is that they have both a wall self adhered product like their HydroGap SA and now the VaporDry SA product for the roof deck.
So I can get air sealing up the wall, across the eaves, around the fascias, whatever I want, the entire structure. I can get my air sealing, my air control layer on the outside, and I'm not relying on the OSB or plywood to be that air control layer.
Installing VaporDry: Put it on the line and stick it
The first step in the installation process is snapping a line to position the top of the first row. Sections of VaporDry are then cut to length. David is using a handy little jig, which is basically a 2x4 screwed into the underside of the rafters that ensures the piece will be long enough to fold over onto the subfascia on both ends. Sealing those edges is extra protection from water and air leaks.
The strip is positioned onto the line, and the top release sheet is peeled off. After the top of the membrane is stuck on the line, they pull off the bottom release sheet and fold the VaporDry over the fascia.
The next row goes on remarkably similar to the previous one, with the added detail of overlapping the seams. Horizontal seams overlap at least four inches but don’t worry about memorizing that. It’s printed on the membrane. The top course is overlapped at the bottom and folded over the fascia at the top.
Repositioning the roofing membrane is simple
The acrylic backing adhesive allows the sheet to be repositioned easily. Eliminating wrinkles is important because a continuous and flat connection between the membrane and the roof sheathing creates a superior air barrier to one with wrinkles. As with the peel-and-stick wall product HydroGap SA, VaporDry SA is very forgiving when positioning.
At roof-to-wall intersections, the VaporDry can be run up the wall to protect that vulnerable spot from water leakage and create a continuous air barrier. At the bottom edges, where the membrane folds over the fascia, Joseph folds the side flap into the corner and then folds the top flap over that. Because it is just a smart overlapping technique.
When the membrane is positioned where you want it, use some sort of tool to apply pressure and activate the adhesive into the substrate. This is often done by rolling it. Not usually like that, though, but like this.
Cedar Breather creates a ventilation space
Now that the peel-and-stick membrane is peeled and stuck, we roll out another Benjamin Obdyke product, Cedar Breather, which creates a ventilation space between the roof deck and the roofing. Developed for use under cedar shakes, we’re going to use it under a standing seam metal roof. It will provide an air channel so that any vapor that passes through will have an escape path.
Even though VaporDry is rated for temperatures up to 250 degrees Fahrenheit, metal roofs—especially dark ones — can get hot in the summer. The air channel will also allow heat to escape, reducing the amount of work that the roof insulation and AC equipment must do to keep people cool inside.
Next time: Standing seam roofing and dry-stack manufactured stone
And not only going to install that standing seam roofing from ABC; we’re going to finish covering the walls with some dry stack-style manufactured stone from StoneWorks. It goes on with mortar, like three-coat stucco, but the mortar remains invisible, like a dry stack.
Like a dry stack that looks freakin’ awesome with the other cladding systems and roofing package.
And that’s gonna wrap up season three of Building Resilience, the show about design and construction for extreme climate, healthy homes, and sustainability.
More Building Resilience episodes: The Building Resilience Show