Retrofit wall insulation is unusual because most of the finished job is hidden from view. Once the holes are filled, you can’t look inside the wall and check that every cavity has been insulated properly.
That makes the company’s process, evidence and accountability particularly important. Two people are involved in a good install: the property assessor who inspects and measures your house, and the installer who does the work. These are the nine questions we’d want answered by any wall insulation company, including us.
How should the installer prove your walls are full? With thermal imaging.
Uninsulated areas of a wall show on an infrared camera as cold, darker patches. A thermal image of the finished walls, taken on the day and shown to you on the camera, is the only direct evidence of what’s behind the plaster. Insulmax® installers also fill a sample cavity before starting and use it to calibrate the machinery, then repeat the check throughout the install. Ask whether your company does anything similar.
How should the installer find every wall cavity? By locating the framing before filling.
Every wall is divided into cavities by studs, dwangs and bracing, and each cavity has to be found and filled separately. Insulmax® uses a variety of techniques to find the cavities, including high-resolution thermal imaging. Ask how your company does it; the answer should be a method, not a guess from the outside.
Who should arrange the building consent or exemption? The company.
All retrofit external wall insulation in New Zealand needs either a building consent or a council exemption, even in a house that’s been standing for eighty years. Ask whether the company prepares and lodges the application, and how the council fee is handled in your quote. A company that doesn’t raise consent either doesn’t know or is leaving you to find out later.
What certification should retrofit wall insulation have in New Zealand? CodeMark.
Ask for the name of the certification and the certificate number. CodeMark is the product certification scheme councils are required to accept as evidence of Building Code compliance when a product is used within its certified scope. “It’s approved” isn’t an answer; a certificate number you can look up on MBIE’s Building CodeHub register is. Insulmax® is CodeMark certified, certificate CMNZ70028.
What material is going into your wall, and can it settle, shrink or absorb moisture?
“Blown-in” covers cellulose, injected foam and dry mineral fibre, and they behave differently once they’re in the wall. Ask what the product is made of, whether it contains water or binders, what its settling rating is, and whether it absorbs water. Ask for a sample to keep.
Who repairs and finishes the installation holes afterwards?
Get the size of the holes in writing before the job, and ask whether the holes drilled on the day will be the same size as the ones you were quoted. Then: exterior or interior, who fills them, who sands them, who paints them. On exterior installs, ask whether you supply the top coat or the company colour-matches it. On interior installs, ask whether the plaster is finished or left for you to sand and paint. None of these answers is wrong on its own; what matters is knowing them beforehand.
What determines the R-value of your finished wall? The depth of the cavity.
The R-value of the finished wall depends on how much insulation the cavity holds, and cavities vary: around 90 to 100mm in most timber-framed homes, around 150mm in brick veneer. Ask what your finished wall will achieve. Insulmax® states its R-value as R2.9 per 100mm.
Who is responsible if there’s a problem after installation?
Who do you call, and who stands behind the work? For a franchise or licensed system, ask what the relationship is between the local branch and the national company, and what happens if you can’t resolve something locally. Insulmax®’s answer is on the what if I have a problem FAQ.
Why ask to speak to a customer from two or more winters ago?
A recent customer can tell you how installation day went. A customer from two or more winters ago can tell you how the house and the workmanship have held up. Insulmax® recently photographed one installation when the weatherboards were removed nine years later: the insulation was still firmly packed to the top of the exposed cavities. The photographs are in the settling article.
What to do with the answers
A good company should be able to answer these questions specifically and show you the evidence behind the answers. If several answers are vague, that’s useful information before you sign.
Insulmax®’s answers to all nine are on our FAQ page, or your local property assessor can take you through them at a free home assessment.
Read more
How do you know the wall is full?
How do you find all the cavities / timbers?
What is the Insulmax® installation procedure?
Do I need a building consent for wall insulation, and who arranges it?