Recladding weatherboard house & insulation retrofit - two layers of wallwrap?

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Recladding weatherboard house & insulation retrofit - two layers of wallwrap?

(9 posts) (5 voices)

Started 4 years ago by 0438snappy
Latest reply from backward

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0438snappy
Member

Hi there,

Long time listener, first time caller

We are about to replace the external cladding on our 1940's weatherboard house located in the inner northern suburbs of Melbourne. The house runs south to north so has a long exposed western wall which gets a lot of sun in summer.

We will be removing the old baltic pine weatherboards and replacing with bgc nuline fibre cement weatherboards.

Whilst the walls are open, I plan to install R2.7 insulation batts (already purchased) and wall wrap before recladding.

Regarding the wall wrap, I already have a roll of Tyvek HomeWrap(~2.75 or 3.00m high x 30m length) as well as a couple of rolls of sisalation wallwrap EXHD breather single sided foil (1.35M high x 30 or 60m).

Just wondering if there would be additional insulation or draught stopping benefits by using two layers of the wall wrap?

I've done a lot of reading online and my current thoughts about the wall construction would be this:

Option A: Batts + foil wrap + cladding
-----------------------------------------------
layer 1) R2.7 batts - friction fit between the wall studs
layer 2) sisalation wallwrap with the reflective side foil facing inwards (would be directly touching the studs and insulation batts)
layer 3) fibre cement weatherboards nailed to studs

some other variations on this might be as follows

Option B: Batts + tyvek + cladding
-----------------------------------------------
layer 1) R2.7 batts - friction fit between the wall studs
layer 2) tyvek homewrap (would be directly touching the studs and insulation batts)
layer 3) fibre cement weatherboards nailed to studs

Option C: Batts + foil wrap + tyvek + cladding
-------------------------------------------------
layer 1) R2.7 batts - friction fit between the wall studs
layer 2) sisalation wallwrap with the reflective foil side facing inwards (would be directly touching the studs and insulation batts)
layer 3) tyvek homewrap over the top of the reflective foil
layer 4) fibre cement weatherboards nailed to studs

Option D: Batts + tyvek + thermal break + foil wrap + cladding
---------------------------------------------------------------
layer 1) R2.7 batts - friction fit between the wall studs
layer 2) tyvek homewrap over the top of the reflective foil
layer 3) some sort of thermal break on top of the foil over the studs(e.g. the james hardie "hardiebreak" thermal strip?)
layer 4) sisalation wallwrap with the reflective foil side facing inwards (there would be a ~12 mm gap between the foil and the tyvek homewrap)
layer 5) fibre cement weatherboards nailed to studs

I'd be interested if anyone out there can make any suggestions for potential improvements to the above, which option they'd go for, etc.

thanks,

Tyrone

Posted Monday 23 Oct 2017 @ 5:13:47 am from IP #
dave lawrence
Member

put battens between sarking and weatherboards creating a ventilated cavity .
also known as a "weatherscreen". standard (and mandatory )building practice in most other countries. the sarking works much better ,the cladding breathes better ,thus drying out better and paint systems last longer .
A little bit extra work packing out openings to suit but the results are worth it .
I have written about this a lot on this forum .check my other posts inf interested .

Posted Monday 23 Oct 2017 @ 8:08:58 pm from IP #
jdaley
Member

I have used that technique, the space between he sacking and the exterior. I did not know it had a name. But I think next time I will make the place in a traditional way, insulation, sacking, cladding and seal up with flashing etc and then add another layer on the outside. I hope to get more benefits of being fully weatherproof and the airspace etc working independently.
Also I am in a fire area and I think its a better job

Posted Wednesday 8 Nov 2017 @ 10:38:41 am from IP #
dave lawrence
Member

the cavity between the sarking and the cladding is both necessary and functional.
It improves weatherproofing , insulation performance , longevity of cladding and performs other functions .I don't understand why Australians are SO slow to adopt such a basic building technology method. It has become standard in other countries.

Posted Friday 10 Nov 2017 @ 10:33:47 pm from IP #
dave lawrence
Member

any other opinions on this thread ?

Posted Tuesday 21 Nov 2017 @ 7:46:16 pm from IP #
jdaley
Member

Possibly because people do not know there are alternatives.

Posted Wednesday 22 Nov 2017 @ 6:56:03 am from IP #
dave lawrence
Member

yes a little knowledge is a dangerous thing. beware of experts who claim to konw the whole story .

Posted Wednesday 22 Nov 2017 @ 7:46:10 pm from IP #
Ruffy
Member

Good suggestion Dave Lawrence.

I can't see any benefit to a double layer of wrapping. The functions of the wrap are as a vapour barrier and a radiant barrier, and 2 layers won't improve either of these functions.

Only other suggestion is to cut batts to fit or use expanding foam in any wall penetrations and small gaps (such as around window frames). Insulation performance is rapidly reduced by gaps and thermal bridges, so minimising them is essential.

Good luck!

Posted Tuesday 28 Nov 2017 @ 1:12:52 am from IP #
backward
Member

Hi,
I have considered doing this with:
weatherboards - ventilated cavity - sisalation - 90mm open cell spray foam - plaster.

The spray foam acts as an airtight barrier and is about R2.4. At $22m2 would it be worth while?

Posted Thursday 30 Nov 2017 @ 6:53:29 am from IP #

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