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A Look at Net-Zero Ready Below-Grade Walls for Cold Climates

In Canada, it’s a distinct possibility that most new homes will have to be built to net-zero ready performance standards within about 10-15 years. Obviously, for this to happen, building envelope design and construction will have to change substantially from its current state.

This post will outline some of the expected changes to Canada’s energy efficiency standards and their effect on the building envelope. We’ll also walk you through the details of a possible solution for net-zero-ready (NZR) below-grade walls for colder climate zones.

Code Requirements Leading Up to Net-Zero Ready Homes

While Canada’s Net-Zero-Ready future is still at least a decade away, the 2020 National Building Code (NBC 2020) has already laid the groundwork for it. The latest iteration of the national building standards gives provinces a framework that will eventually make all new homes net-zero-ready by about 2030-2035.

The code implements a tiered approach, where tiers 1 and 2 represent the current energy standards, and each progressive level ups the ante until we hit Tier 5 — Net-Zero-Ready.

For builders like you, this imminent upgrade of the building envelope will present the most consequential and drastic change to how you build.

Net-Zero Ready — Implications for the Building Envelope

It’s difficult to predict 100% how Tier 5 (Net-Zero-Ready) walls will look in the various different climate zones. However, what we know for sure is this:

– Effective R-values requirements will increase. In colder climate zones such as Climate Zone 7A (Winnipeg, Edmonton), we’ll probably end up with approximately effective R-35 below- and above-grade walls. Farther north in Climate Zones 7B and 8 (Whitehorse, Yellowknife), we’re looking at approximately effective R-45 for the foundation and above-grade walls.

– The envelope will have to be more airtight and have fewer elements that act as a thermal bridge.

– The wall assemblies will have to be designed to be protected from moisture build-up resulting from condensation, which would occur if the interior face of the exterior sheathing falls below the DEW point.

With these criteria in mind, Logix Brands has developed a possible solution for below-grade Net-Zero Ready walls for colder climate zones.

Let’s have a look below.

Logix ICF Below-Grade Walls, NZR, R-40

Logix ICF Below-Grade Walls, NZR, R-40
R40 NZR Cold Climate Wall Assemblies By Logix Brands

Our team based this design on a effective thermal resistance of R-40 — a happy middle ground between the possible requirements for the colder climate zones 7A, 7B and 8.

This design combines 2 high-performance products — Logix PRO ICF blocks and Halo Subterra, or Subterra Plus rigid insulation. Let’s look closer at this assembly starting from the exterior and moving to the interior.

To provide a sufficient boost in R-Values, the Subterra board will have to be 3 inches thick, giving a nominal thermal resistance of R-15 with its advanced Graphite Polystyrene (GPS) core. Its exterior face goes right up against the crushed stone drainage layer, where its tough laminate helps keep water away from the wall assembly. All its joints are taped, and the board itself is fastened to the webs inside the Logix ICF concrete core.

The Logix ICF wall, with a 6.25-inch monolithic concrete core sandwiched between two 2.75” thick insulating expanded polystyrene foam panels, serves as the next layer of defense against heat transfer and moisture, adding a total of R-25 to the overall wall assembly. Note that even though a sheet of Subterra protects it, the exterior face of the Logix blocks must still be waterproofed (not just dampproofed).

Moving to the interior, we have an optional layer of smart vapor retarder with sealed joints. This additional and optional element functions as the air control layer and is a belt-and-suspenders approach that can help the wall assembly dry to the inside of the building, thus protecting the Logix wall from moisture build-up.

Finally, there’s a mandatory layer of gypsum wallboard finishing off the assembly on the interior, serving as a mandatory ignition barrier.

Looking down at the floor, the basement slab rests on top of a 3-inch Halo Subterra or Subterra Plus. The rigid insulation board gives the floor a thermal resistance of R-15 and serves as a highly efficient Radon barrier and, with taped joints, serves as an air barrier as well.

If you’re thinking of installing radiant heating in this slab, this design gives you the option to swap out Subterra for Heat-Sheet R-14, which is also 3 inches thick.

Wrapping It Up

It may seem complex on paper, but the NZR solution we’re proposing for foundation walls for cold climates primarily hinges on 2 readily available components — Logix ICF walls and a layer of Halo Subterra that is laminated to repel water.

With Halo’s Subterra and Logix ICF, this elegant and simple NZR foundation wall design is tailor-made to help homes preserve their indoor climate with minimal input from conditioning systems. 

By |2021-11-22T16:02:04-05:00October 22nd, 2021|

About the Author:

President, Logix Brands Ltd.
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