i disagree with rosskestle.
i think moisture transfer between cavity brick and timber frame is an issue. nobody wants to admit it though , i have noticed that.
one of the primary purposes of cavities is to allow moisture an escape path . i'd be interested in what others think.
cavity wall insulation versus external cladding
(33 posts) (20 voices)-
Posted Wednesday 19 Sep 2012 @ 6:39:01 am from IP #
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hamish05
MemberRosskestle said:
Wall insulation has been installed to homes in ACT for the past 20 years or more and there has not really been any problems. We have been installing wall insulation for about 5 years without a problem.
Regards
Ross
http://www.insulbloc.com.auNo response yet to phone or email messages left 4 days ago!
Maybe business is just so good!
Posted Saturday 22 Sep 2012 @ 10:47:00 am from IP # -
Buzzman
MemberWhen I did my training as a builder we were taught that the cavity in the cavity wall system was to prevent moisture ingress into the timber stud frame and interior, and this was also the reason why, in double brick construction, brickies left a brick out on the bottom row every few metres, so that mortar that dropped down inside the cavity could be raked out, preventing build-up which made a moisture bridge above the DPC. The bricks were then replaced, but 'weep holes' - vertical mortar joints (perpends if you want to know the term) were left free of mortar every 1.8m to enable any condensation build to weep out and drain away at slab/footing level.
So despite the claims of the vested interests*, I would ensure that insulation added to timber stud walls of a cavity brick veneer system did not bridge the gap to the brick outer skin. Which should not be hard to do if the batts used are the same thickness as the depth of the studs (usually 100mm).
What I would further advise to anyone in this position and willing to remove and replace the internal gyprock cladding is to add a 50mm block the full height of each stud, thus increasing the depth of the stud wall to 150mm, and using proportionally thicker insulation batts.
This would provide for insulation of R4.5, with approx R6 across the whole wall thickness. [Someone correct my math on this as I have done it off the top of my head..I'm uselss at maths ;)]
But in any case, much much greater thermal mass, and therefore less need for HVAC and its attendant power consumption and GHG production.
[* Not meaning to be direspectful of those who add comments and provide assistance, but, for example, polyurethane has been found to be not too hygrophobic over time, with Expanded Polystyrene next best and Extruded Polystyrene the most hygrophobic of the alternatives. This comes from their use as buoyancy foams in boatbuilding and their use as cores for laminated products used in boat hulls. If it absorbs water *at all* it is useless as buoyancy foam, and so would be equally useless as an insulator where water or moisture was present, as it would, eventually, absorb that moisture and 'bridge' the gap to the frame and gyprock. It just hasn't been happening long enough for this to have become a real problem...yet... But the foamed polyurethanes that were previously used to full cavities in boats for buoyancy are similar in proerties to those PU foaming insulation products. As a builder and boatbuilder I would not use PU in either.]
Posted Saturday 29 Sep 2012 @ 7:59:42 am from IP #