OSBlock Is an Interesting Inside-Out Building System

Man standing in front of an OS Block display

Philippe and OSBlock / Lloyd Alter

It's like a cookie with the filling on the outside.

While wandering among the hot tubs and Vita-Mixers at the National Home Show in Toronto, I came upon Philippe Paul and OSBlock, a really interesting structural system invented and manufactured in Quebec.

OSBlock up close

OSBlock up close/ Lloyd Alter/CC BY 2.0Basically, it is a sandwich of two layers of expanded polystyrene foam with a filling of four layers of Oriented Strand board (OSB) 12" high by 8' long. Just stack them up and you have an instant R-32 wall. Want more insulation? Just stick it on the outside. Most importantly, there are no thermal bridges, one of the major sources of heat loss in buildings. It is sort of an inside-out Structural Insulated Panel, with the wood on the inside and the foam on the outside.

How the Panel Works

I usually don't have the patience for a three minute video but I was captivated by this. Two people can easily lift each piece and stack it on top of the one below. Then you use a long tool to turn the plastic lock mechanism that holds it tightly together. There are corner fittings to tie it all together, clever window details, and a lot of spray foam caulk to seal it all up. Unlike Structural Insulated Panels, there is no waste in cutting out windows, there is hardly any waste at all.

OSBlock wiring

Lloyd Alter/CC BY 2.0

I would be very curious to see how it does on a blower test with all those joints, but suspect that with a bit of tape and caulk it would do just fine. The elimination of thermal bridging might make it useful for Passivhaus construction. There are even furring strips to attach siding on the outside and drywall on the inside, there are channels for electric wiring. They have really figured this out.

Materials Used in OSBlock

This TreeHugger has never been fond of insulated concrete forms, not being a fan of plastic foam or concrete, and have had some concerns about traditional SIP panels where the wood is on the outside and sometimes is damaged by moisture. But this OSBlock is really interesting, with the wood deep in its core, the smaller pieces, and the ease of construction.

Chart of insulation materials

EPS foam is mostly air, but is still a solid fossil fuel full of flame retardants. On the bright side, it is now made with not-so-terrible blowing agents and has a very low Global Warming Potential compared to XPS and polyurethane. As they say at BuildingGreen of another SIP with EPS:

BuildingGreen does not generally recommend EPS as an insulation material because it is made with several problematic materials, including benzene and the brominated flame retardant HBCD, but we list EPS-core SIPs because they provide a relatively easy way to create walls with superb energy performance.

One can say the same thing about the OSBlock; it is doing such interesting things here. What a clever way to build.