LEED Platinum V4 Wall Design: Building Science 

The wall we designed for the Edelweiss house, Canada's first LEED Platinum V4 Home is best categorized as a 'REMOTE' wall, a high performance building envelope developed by the Cold Climate Housing Research Centre in Alaska. REMOTE stands for 'Residential Exterior Membrane Outside-insulation TEchnique'.

Edelweiss house LEED Platinum V4 wall assembly detail © Cosella Dorken

Remote walls are framed the way you would be used to seeing it done with 2x6s and sheathing; the difference is that vapor and air control layers are moved to the exterior of the sheathing, then additional insulation is installed outside of that.

Stud cavities are still insulated with batts, but the majority of insulation is on the outside of the sheathing, this way the vapour control layer is sandwiched between layers of insulation where it can perform best in a wildly varying climate like we have in Canada.

There are many advantages to this system - it provides much greater thermal protection and energy efficiency, better drying capabilities and protects the air barrier from the assault it would normally receive from wiring and other penetrations when we rely on an interior polyethylene as an air and vapor barrier. See our pages on vapor and air movement & the difference between air & vapor barriers to get a better idea of how this works, and why it makes so much sense to build this way in cold climates.

1. After the concrete slab had sufficiently set, we began wall framing. We used detailed framing plans from a local lumber company. Each wall was planned down to the smallest framing member including a cut list  with the length of each piece. This made the framing process go fast and efficiently and reduced our waste, as the wood order matched the requirements of the walls.

We used FSC certified wood (Forest Stewardship Council) which is guaranteed to come from sustainably-managed forests and offers additional LEED points.

Delta Vent SA exterior air barrier © Ecohome

2. Sheathing was installed leaving a 1/8th inch gap at the seams to provide additional drying capability of the walls, along with providing room for sheathing to expand without buckling. This protects our exterior air barrier membrane and prevents any risk of walls warping.

3. Window openings were built out to allow for the additional exterior insulation. The air barrier was wrapped around the entire window box and into the interior.

Window build outs for exterior insulation © Ecohome

4. Trusses were dropped on top after walls were completed. The trusses we needed for this house were enormous by most standards, for a number of reasons: the long span from north to south (35 feet), the shallow roof pitch (2/12), and the added weight that would be coming in the form of soil for our live roof (green roof). This gave us a deep cavity for insulation, with mineral wool batts totalling R95.

5. The height of the south wall along with the large openings facilitate natural light and passive solar heat gain


The Ecohome R.E.M.O.T.E. wall

The difference here compared to what is commonly done with the REMOTE wall technique is that we used rigid mineral wool batts instead of polystyrene rigid insulation (EPS or XPS - see comparisons here) .

We chose this option for a variety of reasons. Mineral wool has high embodied energy but the final product is effectively inert, with characteristics that will remain unchanged with the passing of time. This is not the case with polystyrene, which over time will off-gas its blowing agents and cause material shrinkage, reduced thermal performance and the release of climate changing greenhouse gases. Read more here about how to choose the right rigid insulation board.

Furthermore, Roxul, or now Rockwool, contains no fire retardant chemicals such brome-based HBCD (Hexabromocyclododecane, spelling test to follow), a persistent bio-accumulative chemical found in EPS and XPS that is connected to a disturbing amount of human health issues.

Avoiding thermal bridges:

When one section of a wall conducts heat much quicker than another, we refer to it as a thermal bridge, and that can greatly reduce the overall R value of a wall. Virtually every thermal bridge in this wall assembly was identified and addressed in the design phase. 

Thermal breaks in exterior insulation:

It would have been quicker for us to attach the entire mass of exterior insulation with longer screws and only one course of strapping, but using THERM software, our engineer determined that the cold transmitted through the metal screws would have reduced the effective R-value of the exterior insulation by close to 1/3. Double strapping and screws that don't span the entire wall eliminates that potential thermal bridge without having to invest in expensive insulated attachments. 

Something we often hear when discussing this house is the extreme amount of insulation. It certainly can look like overkill when compared to the under-insulated homes that are typical of tract housing projects, as housing developers rely on building code minimum standards to determine efficiency. As performance isn't always high on the radar of home buyers, builders make more money that way, but leave homeowners with unnecessarily high heating bills for the rest of their lives.

In contrast, a hyper-insulated house will save occupants a lot of money over its lifetime, but even on the short term can actually be cheaper to own and operate from the  moment you move in, as the added construction costs are offset by greatly reduced operating costs.

In our next post we will outline the reasoning behind this wall design, associated monthly costs, and the concept of the 'sweet spot', which is the optimum level of insulation for a home, proper orientation, and designing for your local climate. There isn't one coat that would serve you well in every part of Canada, houses are the same.

The following diagram details the building envelope design of our LEED V4 Platinum certified Demo House. The drawing is not to scale, but performance values are accurate. Additional note:  stud cavities are filled with R24 mineral wool batts.




Now you know the building science basics, learn more about sustainable home comfort, energy efficiency and how to reduce the carbon footprint of homes on the following pages and in the Ecohome Green Building Guide.