Insulation – ‘Pull it out and do it again, without the gaps this time.”

22 March 2019 by Jason Quinn

Whether our clients say it aloud or not, we know they want warm healthy homes. In order to give them that, we specify and install insulation. That insulation allows us to have a warm and healthy building without paying a fortune in running costs. Insulation in New Zealand is nearly always batt insulation, typically fiberglass, but the same applies to polyester, wool, cotton and mineral wool batts.

The issue is that we don’t always get what we’re paying for. Installation of batt insulation is not forgiving. Take the case of an R3 roof; if there’s 10% of the roof exposed between gaps in the insulation because the bats weren’t tightly laid in the roof space, you’ve lost 50% of the R value of that roof! If the design allows wind-washing through the insulation from gaps in the building wrap or lining, you can lose even more on windy days.

Installation quality matters. I’ve been in office buildings where there was clearly more than 10% gaps between the batts. The insulation was so poorly installed that there really was no other choice but to pull it all out and then start over again – painfully expense in a big office building. However, it is not just gaps between the batts. Consulting on a new home built in Wellington, the owner thought that the wall in her bedroom was uninsulated and had thermal camera images to prove it. The wall had insulation but wind was able to enter through the laps in the wall wrap, allowing wind to drive through on cold windy days. The only solution was to pull out the wall cladding, fix it and re-install. Ouch.

Insulation can be done right the first time. The photo below is a screen capture from a video put together by Kim Feldborg, from Valhalla Living Limited, with insulation being carefully cut to fit neatly between the studs. When the building was designed, the design team specified a wind-washing barrier on all sides of the insulation. Done right, done once.

Figure 1: Photo of Kim Feldborg of Valhalla Living Ltd installing insulation

Now, we need to fix this, and we should do it in three steps:

The first step is to inform. Designers need to specify a quality insulation installation standard and include wind-washing protection. Builders can do really good work and we’ve got good builders in New Zealand. They need to know the installation of insulation is an important job and that we are willing to pay for better quality installation.

The second step is to educate clients, designers and builders what ‘good’ looks like. I’d suggest we adopt the USA grading system which has photo guides and videos.

Figure 2: How to PDF – Achieving Grade 1 with Fiberglass Batts by Owens Corning

Grade one is has very, very few defects and it’s considered to meet the design performance rating of the wall. Grade two has some small amount of defects (less than 2% gaps) but it’s still considered acceptable, although the resulting lower insulation value of the wall still needs to meet code. Grade three is pretty much what I see in typical NZ homes, where the defects are so unacceptable that you have to fix it. Again to understand the scale, a Grade two ceiling would be R2.5 rather than the designed Grade one R3 ceiling.  A quality install does matter.

The third step is to change the way we inspect insulation in buildings. Changing the industry is not going to be straightforward and I think the only way to do that is going to be through requiring a quality graded code compliance for insulation installation. Otherwise, we’ll continue to face the current problem where many (or even most) builders and insulation installers are chasing the bottom line. It means that if providers do a slightly worse job at a lower cost than the person next to them, they’ll get the work, even though the building has lost 50% of its insulation value.

In the mean time I’d suggest clients take up the offer of on-site stage inspections by your design team.  I’ve had a couple of building projects where the architect had put in a fee to go onsite to do inspections but this was not seen as value add by the client. Let me be clear, there is a lot of value in having somebody onsite whose only focus is making sure that your building is built the way it should be – and not focused on saving labour costs and potentially cutting corners on the day it is built.


How to video – Achieving RESNET Grade I rating with EcoTouch® Fiberglas™ Batts
How to PDF – Achieving Grade 1 with Fiberglass Batts by Owens Corning
Kim Feldborg of Valhalla Living Ltd building highlights videos
Installing Fiberglass Right – It’s hard to do a perfect job by Martin Holladay 2009
A Visual Guide to Why Fiberglass Batt Insulation Underperforms by Allison Bailes 2011
How to Grade the Installation Quality of Insulation by Allison Bailes 2012