Freeze frame? Optimising framing for warmer homes

 

 

In framing, every little piece of timber has its purpose, whether it’s meeting structural requirements in the Building Code, ensuring the home is weathertight, or to give cladding, linings and additional fittings something to attach to.

Even when each piece plays its part, something doesn’t add up. Studies by BRANZ have shown that the typical amount of framing in a Kiwi home is leading to massive heat loss. Timber framing takes up an average of 34% of the wall area in a residential new build, but it acts as a “thermal bridge”, where warmth escapes outside through the framing.

This means most homes that are properly built to code still fail to meet the minimum R-values for insulation once the thermal bridging effect is taken into account. Even with R2.8 insulation installed, the final R-value ends up being only R1.2–R1.4. What’s the best way to mitigate this heat loss?

BRANZ has researched a number of solutions. They found that insulating the floor slab edge on single-level houses makes the biggest difference, improving R-value by around 40%. BRANZ also found five main weak points in a home’s framing where heat can escape. When all these were addressed along with the floor slab edge, they saw the R-value improve by up to 68%.

Another option is to substitute 120mm studs for the standard 90mm studs, which allows for thicker R2.6 or R2.8 insulation. Services in the wall usually compress the insulation and degrade its performance in standard 90mm stud walls, so wider spacing allows the insulation to do its job properly. BRANZ also recommends making dwangs narrower than the studs, to reduce overall timber use and heat transfer.

A more radical step, but one that had the greatest impact, was building a second layer of insulation over a standard 90mm stud wall. That could be either on the inside or the outside of the wall, creating an effect similar to double-glazing. While this undoubtedly adds more upfront costs, homeowners who are keen to reduce lifetime heating costs, condensation and mould stand to save significantly with a “second skin” on their walls.

We stock a full range of insulation products to help you meet the insulation requirements for your next build, including New Zealand’s top brands like Bradford Gold and Pink Batts.  

For more information on the studies and how some firms are boosting thermal performance in homes with different techniques, click here.