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wall insulation options

wall insulation options

Posted 14 Oct '19 10:39 PM

Hi, we are looking to build shortly, (titles came through this week) approx 210 sqm, and im wanting to put as much of the spare "upgrade" money into insulation as possible.

Looking at the walls, im trying to get a gauge on what options are best to get an insulation value above R3, on a budget of course, With an old fashion builder, 150mm framing for 140mm batts is the default option.

Ive scoped out a few options, Hebel cladding, Mitten vinyl cladding with 30mm polystyrene backing, or perhaps a standard wall with 90mm spacing and a PIR board, (1 I've explored goes as far as R4)

What has been your choices in wall options, and pros and cons?

RE: wall insulation options

Posted 15 Oct '19 07:19 PM

We're doing 140mm walls with 90mm nogs. Cladding is vertical on cavity, so attaches to the nogs. Insulation is then 90mm batts with a 50mm blanket over the nogs. i.e. only studs are thermally bridging. Also less timber at corners (i.e. 2 stud corners). This gives around R3.6 or so. Main reason we're going 140mm though is it allows better window install (thermal break aligned with cavity, no WANZ bar defeating it) and also allows slab edge insulation more easily (floor is heated).

I'd take care of windows first. i.e. reduce size on south, west to minimum, make optimal use of solar gain on east/north (check overhangs vs head height to limit sun in summer, maximise in winter).

RE: wall insulation options

Posted 18 Oct '19 04:15 PM

Double layers of wall insulation doesnt cost so much more but will perfome much better.
Sprayed insulation might be 1st choice with regard to performance.

RE: wall insulation options

Posted 30 Oct '19 12:04 PM

Thanks, ive talked to the father in law who will be our builder, and as he is "vanilla" I think this solution you have used would work best, just ordered some samples of Mitten Vinyl, which he isnt so hot for though, based on past experience with vinyls.

RE: wall insulation options

Posted 18 Nov '19 05:01 PM

Kinda like the story with engine size, 'there's no substitute for cu" size displacement'. JMarshall's reply is right on and sensible if you're going with wider timber framing. If budget permits and willing to sacrifice livable space. Without going off topic, site orientation is a greater factor than wondering what kind of insulation or windows to choose. Anyways.

My 2 cents about the vinyl siding / cladding marketed in NZ by Mitten. As growing up in Canada with many friends in the building industry there, virtually NO ONE uses the Insul-plank vinyl siding in Canada. It offers absolutely no benefit to the R-value of the wall because the way the vinyl siding is installed, the loose air cavity like underneath, allows for moisture to evaporate. My suspicion why the EPS insulated siding is marketed in NZ has more to do with differences in construction. In Canada, whole house and roof are OSB or plywood sheathed (air barrier) vs in NZ, typically only the corners get the plywood treatment to serve as bracing and NOT as an air barrier. Because of the lack of the rigid air barrier, this means the non-insulated vinyl siding can not have a proper fixing to the timber framing. ie say single story 450mm to 600mm stud width apart. Since the non-insulated planks are very 'flimsy', it is not ideal to install at wide fixings and quite often, the siding could sag in extreme weather. Whereas if the whole house was OSB or plywood covered, then the vinyl siding can have fixing at any interval say 100mm apart. Therefore, the insulated EPS version provide 1 key benefit. That is they are more rigid and thus can get away with wider interval fixings on the wall with minimal sagging.

Personally with the extreme weather in Canada, they've worked out the efficient method of construction. Go with wider walls with the air barrier. Bespoke methods like the Passive Haus criteria we've seen in NZ is not wise use of money. Look at TV sensationalist Mike Holmes about insulation. He's a big fan of spray foam insulation but only in certain areas of the house. Typically in the basements or where the house is against the soil or in cold zone areas - but he would not advise spray foam use in the walls where permeability is an issue. He's quoted time and time again that the walls must have some permeability in case of trapped moisture to get out. Keep in mind, Cdn homes don't focus much on sun orientation and instead, focus on keeping the heat in so key factors are 'draftproofing' and insulation. Compare the way have windows are installed in NZ vs in Canada and you can see why quite often NZ builders are missing the point.

RE: wall insulation options

Posted 26 Nov '19 10:09 PM

Thanks, I got the Mitten cladding, and well, for the cost fitted being similar to brick, it seems underwhelming, The only advantage is the weatherboard look with 0 paint/maintenance. So it will end up being a bit more of a cosmetic decision on cladding,
Speaking to the father in law/builder, hes quite keen on JMarshalls approach, its vanilla, and "why hadnt he ever thought of it"

RE: wall insulation options

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