Building certification issues for rendered straw bale walls

4 years 1 month ago - 4 years 1 month ago #31 by Bill Ennals

My name is Bill and I'm in the final stages of getting building approval for a new straw bale residence in Brisbane. We've struck a bit of a hurdle with our private building certifier in relation to the weatherproofing and condensation/water vapour management aspects of a lime-stabilised, earthen rendered strawbale wall, and I'm hoping someone out there has some ideas on how to satisfy him.

This will actually be my second third straw bale building project (back shed and my own home being the first two) so I'm totally confident in the capacity of a well constructed strawbale wall to keep the weather out whilst allowing moisture and vapour to exit the wall. It's just the certifier, who has no experience with strawbale (couldn't find one that did), that needs to be convinced.

The certifier has requested that a 'Performance Solution' be undertaken by an expert to ensure compliance with the following two parts of the Building Code of Australia (BCA):

3.5.4 (P2.2.2 Weatherproofing) - so we need to demonstrate that a rendered strawbale wall (properly flashed around all doors and windows of course) will prevent water ingress;

and (P2.4.7 Condensation and water vapour management) - in this bit he writes "Except for single skin masonry or single skin concrete, where a pliable building membrane is not installed in an external wall, the primary water control layer must be separated from water sensitive materials by a drained cavity." I explained that strawbale walls don't have pliable building membranes and we don't want to clad the walls with a rain screen (which I guess would provide the drainage cavity), so now we have to prove that condensation will be managed with our lime-stabilised, earthen rendered wall.

I've discussed the relevant parts of the Australian Strawbale Construction Manual with him (and joined Ausbale to access it) but he's insisting that we obtain the "Performance Solutions" for both matters, and from what I can tell from reading the ABCB website on developing performance solutions (link below), they essentially require an elaborate experiment to be designed and carried out to prove that the solution works!

So, I'm wondering if anyone has any kind of documentation or data that might act as the "performance solution" in this instance, or if anyone has encountered similar obstacles that they've been able to navigate their way past? I don't really fancy paying an expert to build a test wall and subject it to a bunch of tests.


Last edit: 4 years 1 month ago by Bill Ennals.

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