planning to do this at home - as i understand it you now need a consent for this , and a 20mm cavity is required between underlay and back of the cladding just wondering if anyone out there in the trade can tell me this *how did you hold building paper taught to create 20mm cavity *if wall is 100mm rimu minimised to 80mm with cavity, and wall batts are 90mm , then what did you use .?
tweake,
Oct 26, 8:18am
i have no heard that you need 20mm space. they may be getting mixed up with a rain screen setup. but maybe the local council has other ideas.
if they really want a god drainage plane there is a drainage mat type product thats very open to allow air through. can't think of the name at the mo.
bergkamp,
Oct 26, 8:20am
i was shocked that one needs a consent
pauldw,
Oct 26, 8:29am
Looking at "NZS 4246:2016 Energy efficiency – Installing bulk thermal insulation in residential buildings" it looks like you need either building paper or you have to maintain a 20mm gap between insulation and back of cladding. It doesn't require both.
tygertung,
Oct 26, 6:24pm
We did it after the earthquake when we had the jib off. Just staple the building paper onto the framing from the inside in a sort of a half box shape. Just cut it on four corners so you can staple it in the squares of the framing. A bit hard to explain in words.
The polyester batts are nicer to work with and you can just tear them.
rak1,
Oct 26, 6:54pm
I have done this and did it with a consent. I used heavy roofing paper. I cut it to the height of each individual cavity. Fortunately they are mostly the same height so I unrolled a good number of meters, rerolledit an cut it to the height I needed. Then I measured between the stud and added 40mm per side. Come in 40mm from each side and fold the paper. Then fold the 40mm fold to give you a 20mm fold of double thickness. This is to give it some strength. Then I used 30mm flat head nails to attach the paper 20 mm out from the external wall. I used flat heads because the framing was rock hard old native timber and the heavy staple gun wouldn't go near it. No need to be too fussy about the 20 mm. The inspector will randomly check a few to verify. NB, i only attached on two sides.
clangie,
Oct 26, 7:18pm
just fit 50mm polystyrene-nice and rigid-cut to close size and fill any gaps with expanding foam
pauldw,
Oct 26, 7:58pm
Where is the inspector getting any requirement for building paper to have a 20mm gap?
pauldw,
Oct 26, 8:32pm
Answering myself. In the Standard I referenced there's a comment on a clause "C5.4.1 A wall underlay installed in accordance with Method 2 will help protect the insulation from absorbing or transferring water from the backside of the wall cladding. However, wall underlay installed in this manner could reduce the water management ability of the existing wall. Leaving a 20 mm minimum gap between the back of the cladding and the wall underlay inserts or insulation is unlikely to compromise the water management ability of the wall." Not sure that this is mandatory. A direct fixed wall with existing building paper won't have this gap.
tweake,
Oct 26, 10:43pm
thats actually quite a bad thing to do in nz climate. the problem with polystyrene, while technically classed as permeable, it has low permeability. ie it will stop a lot of moisture from moving trough the wall. ie it can stop the house and wall from drying out.
this is also why you should be using a high permeability building wrap instead of building paper and avoiding any roofing wrap/paper.
you have to be very careful in using any product that will stop moisture from moving.
tweake,
Oct 26, 10:44pm
one of the main causes of leaky homes is people screwing up the drainage and drying of walls. councils do not want another round of leaky homes that they might be held responsible for.
pauldw,
Oct 26, 11:45pm
Yet Thermacraft describe their bituminous wall/roof paper as highly permeable.
tweake,
Oct 26, 11:56pm
it pays to check the actual numbers, manufactures say all sorts of BS.
bergkamp,
Oct 27, 12:32am
The main cause of LBS is bad design ,untreated timber,complex penetrations, little or no eaves ,monolithic claddings . not homeowners insulating their 100 yr old "air leaky" WB houses - making air leaky claddings consent able for retro insulation is counterproductive
tweake,
Oct 27, 1:23am
i think you completely misunderstand the causes of LBS. main cause is thinking cladding can be made water proof, therefore failing to allow it to drain and dry.
this ties directly into 100 year old houses because they use the wall cavity as a drainage and drying area. if you fill it with insulation you remove that drying potential and typically fill it with a product that must not get wet. so you need a means of keeping the insulation dry and allowing for some drying to take place, as all claddings leak. if the retro fit is not done right a 100 year old home becomes yet another leaky home. which is why council oversight is required.
monolithic cladding, untreated timber etc are just redhearings, a scapegoat. something to take the blame instead of blaming the real culprit, lack of understanding building science.
bergkamp,
Oct 27, 1:34am
. nope I fully understand the "d"s , always have. . to think direct fix monolithic claddings and untreated timber are red herrings is delusion
kenw1,
Oct 27, 1:35am
The main cause of leaky homes was the totally inadequate inspection regime.
Like BI's telling homeowners that the laser line was bent and that is why it dipped in the middle.
tweake,
Oct 27, 1:42am
monolithic claddings are still used today and are perfectly fine. plenty of untreated timber houses that are perfectly fine. there is no issue with them. blaming them is a red hearing.
bergkamp,
Oct 27, 1:46am
. Direct fix monolithic is not a red herring . pure delusuon
tweake,
Oct 27, 1:49am
lack of decent inspection is still an issue, but was never a major cause to leaky homes. even well built, properly inspected homes still leaked and rotted.
councils got their information from the building industry which was full of bad information and practises, so it became more of a fox guarding the chicken coop situation. councils failed to get outside information to check that nz building industry was doing it right.
tweake,
Oct 27, 1:54am
correct, the big difference here is "direct fix". Direct fix monolithic is still a failure to drain and dry, part of the idea that cladding can be water tight. monolithic is not the only cladding that has issues if not installed properly.
bergkamp,
Oct 27, 8:24pm
and what insulation did you use ? not standard 90mm batts?
bergkamp,
Oct 27, 8:40pm
agreed , and any house can be leaky - but LBS is predominantly about non cavitied claddings , not "air leaky" weatherboards .Retro fitting a 100yr old WB wide eaved house with batts and paper is no different from a direct fix weatherboard situation (still allowable depending on risk matrix)
IMO i think its wrong to make something so low risk consentable,
tweake,
Oct 27, 9:37pm
i think your still missing the bus. LBS is about people not understanding how walls work and how product substitutions effect it. ie assembling parts without understanding how it all works together.
retrofit insulation is not a hard job and low risk IF its done ok. the problem is people don't understand how it works together and don't always do a good job, which can create yet another leaky home. thats where oversight is required.
imho 90mm batts is ok if paper/wrap is done ok. tho i would much prefer some better detail on the bottom plate and nogs where pooling may take place. imho using some of the drainage matt or crinkly building paper products would be an excellent idea as that maintains a drainage gap even with insulation pushing up against it.
marte,
Oct 28, 1:01am
Is the OP's house weatherboard or brick?
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