Damian McGill: Healthy Home Cooperation Director on spray foam insulation and the risk of moisture build up

There’s a chance your home-reno could keep you from selling your house. 

A couple in the UK was recently unable to sell their home after installing spray foam insulation. 

The way the foam is installed and how much ventilation it has could cause damage to roofing timber, particularly in colder climates, and New Zealand installers have to produce a statement saying the work complies with the building code. 

Healthy Homes Cooperation Director Damian McGill told Ryan Bridge that there’s nothing wrong with spray foam per se, and it can be a great product when used correctly. 

But he said that when you add retrofit insultation, you have to improve the ventilation as well, otherwise there’s a risk moisture could build up in the cavities.  

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Episode Transcript

Speaker 1 (00:00):
Spray foam insulation is commonly used to retrofit uninsulated homes,
but could it prevent you from selling your house? The
way the foone is installed and how much ventilation it
has could cause damage to roofing timber, especially in colder
climates like ours. A couple in the UK recently were
unable to sell after installing the insulation. They had problems

(00:21):
with the banks with the insurers who didn't like the foam.
In New Zealand, installers have to produce a statement saying
the work complies with the building Code, but the work
doesn't have to be inspected. Damien McGill is the Hothy
Healthy Home Cooperation direct journeys with me this morning. Hey Damien,
sure to Ryan?

Speaker 2 (00:40):
How are you? Yeah? Good?

Speaker 1 (00:41):
Thanks, thanks for coming on the show.

Speaker 2 (00:43):
There's nothing wrong with the spray fome per say. It
has one of the best insulation ratings of any product
on the market. It can be a great product when
used correctly. The issue is how it's used and how
it's being.

Speaker 1 (00:58):
Applied and how is it being used in New Zealand
is it Do you have any concerns about it about
the way it's regulated.

Speaker 2 (01:07):
Well, so you just mentioned that for the regulatory context
is now that should you want in the building now
exempts under floor and roof insulation retrofits for a building consent.
But you need to retrofit insulation into a wall cavity
and that needs a building consent. The problem is that

(01:31):
when you add retrofit war insulation, it may affect moisture
transfer inside walls and change drying rates, which in turn
may cause moisture to accumulate in the walls and affect
the durability of timber framing and cladding. This is directly
from NBI's website. In my opinion that a statement applies

(01:52):
equally to roofs too, which is my comment in the
article about Newton's third law emotion. You know the house,
it is a whole system. So if you improve the insulation,
you must also improve the ventilation. When you improve the
insulation and ventilation, you should improve your tightness and look
out for thermal bridging. And by the time you add

(02:15):
some windows that you have the five passive house.

Speaker 1 (02:17):
Principles right, So that standard currently covers walls, but not roofs. Roofs. Rather,
is that what you're saying.

Speaker 2 (02:25):
There must have been a relaxation recently to exempt underfloor
and roof insulation from a building to sent so it
doesn't necessarily it doesn't just apply to spray frame. It
applies to all insallation additions. Give you a couple of examples. Recently,

(02:47):
I have upgraded my rental properties by adding an extra
one hundred and eighty milimeters of wall insulation in the ceilings.
But because of this I've also upgraded the ventilation too.
Otherwise I would I was concerned I'd have significant and
issues in the ceiling cavity. For what happens.

Speaker 1 (03:09):
For your own For for our listeners, if you have
had this work done by a registered professional, should we
you know, we should have nothing to worry about. I
mean they should be looking at the ventilation. If they're
doing the insulation too right, they.

Speaker 2 (03:24):
Won't be looking at the ventilation. They won't be. They
won't be. They won't be. So that's that's that's where
the issues. So in the UK, a couple of things
have been happening. One have been spraying directly to the
underside of concrete tiles, which I guess we have. You

(03:45):
know the state that the brick and tile fifties houses
are a similar type of construction, but if the roof
is leaky, then there's nowhere for that. So basically you're
going to fill up a gap underneath the tiles or
in the roof space probably seventy five one hundred mills

(04:06):
of phone and and you're going to seal that up
so any moisture gets in there, it's not able to
dry out.

Speaker 1 (04:15):
Understand Yeah, yeah, yeah, I understand what you're saying, Damien,
and I'm I appreciate you you running us through exactly
how it works. Yeah, as you say, it's not it's
not foam, it's not. This is not a foam as
bad story, but it's a cautionary tail. I suppose if
you are insulating to think about ventilation as well. Damien,

(04:38):
really appreciate you coming on the program. Damien McGill, Healthy
Home Cooperation Director. For more from News Talks B listen
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