Exterior Walls for the Future

All along, our design impetus has been to plan for the future and our wall system reflects that. The current Alberta Building Code essentially stipulates 2x6 walls with R20 fibreglass insulation as a minimum for our area, typically with a 6 mil poly air/vapour barrier just behind the drywall. We had a different idea. 

Instead of fibreglass, we used mineral wool batts for R22 between the studs. Mineral wool has the added advantage of draining and not sagging when wet, and does not support mould or pests.

Typically, the poly air/vapour barrier is punctured with every drywall screw, pipe and electrical box. Our system uses vapour barrier paint as primer on the drywall and puts the air barrier in the middle of the wall. Bice Stucco and Drywall applied a liquid air barrier to the OSB exterior sheathing. The pink colour caused lots of questions so we joked that it was the latest designer paint colour.

With stud walls, there is thermal bridging at each stud. So, we added 100mm/4” of insulation to the outside of our wall, just like a blanket. Initially, we had planned on a double stud wall (two stud walls with a separation), to achieve our insulation goal but we decided to simplify the system. A good thing too since wood prices skyrocketed during construction. 

The Mews features two exterior insulation systems. Our masonry contractor, Mayzes Masonry, installed rigid mineral wool batts, held in place by the Fero slotted Rap-Tie (made in Edmonton), with an airspace and the brick exterior. Simple and effective.

Our other exterior cladding is the Exterior Insulated Finish System (EIFS) installed by Bice Stucco and Drywall. It includes 100mm/4” of expanded polystyrene insulation and 4 finishing coats of reinforced stucco.

Both wall systems are expected to provide long-term durable high thermal efficiency to our project.