Owner Builder Forum
Jul 29, 2018 4:21 pm
Currently trying to investigate whether to use a slab or stumps for our house foundation. Have not got soil test complete yet - should this be done first to make this decision? We are not flood prone but in wet years in a big rain the area might get damp so open to stumps. However apparently Basix has new rules since July 2017, and I'm told our house plan Basix may fail without double glazed windows. I'm looking forward to business hours tomorrow when I can call places but would love to hear from anyone who has used stumps since July 2017 etc.
Nat & Fonz
Re: Any info on new Basix since July 2017 and using raised f3
Aug 28, 2018 9:51 pm
Stumps vs slab has nothing to do with the windows when it gets to BASIX.
But what you would need to do is to consider some sort of floor insulation.
It does have something to do with basix. The thermal component of the certificate has two parts, heating and cooling. And this is to do with thermal storage amongst many variables. Eg eave width, sill height, lintel height, orientation etc. You can’t specify your insulation anymore, only go with the offered spec which depends on your cladding type. I feel they are pushing the home designer to now pay for an energy assessment done by a number of companies with required certification. It’s funny but the one part of basix that is hard to pass is the thermal section and the standard cost for an assessment just on this section is 500 bucks. The assessment is done using a software in which greater detail can be added, like insulation and other wall construction types. Double glazing with argon and thermal broken windows does hardly anything using the self assessment online tool.
Yes, get your soil test done, it will need to be done for a DA assessment. Slabs are better then a well insulated raised subfloor for their thermal storage, but suck when you want to change the comfort level of the house in a short period.
Re: Any info on new Basix since July 2017 and using raised f4
Aug 29, 2018 1:05 am
Well, windows are attributed only for only 1/5 of your whole house thermal losses.
Flooring is roughly 15%. Properly insulated slab (edges + bottom) will be behaving well from the perspective of thermal comfort (to the extent that you can comfortably walk barefooted over tiled floor in the winter morning). Same thing applies to the properly insulated suspended slab too, but if it is not a concrete slab, you won't be having a thermal mass effect there, yes.
Secondly, properly designed house with thermal mass and well insulated from all the points, would not even require instant changes in comfort - the heating and cooling will be only needed to be applied for short periods of time during extremely hot or cold weather streaks only. Otherwise, 8-12 hour thermal lag due to insulated thermal mass will be able to keep inside temperatures in comfortable range by itself.
Thirdly, previously I found that BASIX assessments have no idea of insulated thermal mass effect and in their models brick veneer walls insulated to R2.8 are behaving exactly the same as double brick or ICF walls insulated to the same R value. Which is obviously far from reality, first because brick veneer with calculated R2.8 will be performing to R2.0 at best due to thermal bridging caused by the studs and inconsistency of insulation installation, secondly insulated thermal mass walls will still be thermally performing much better even with the lower R value insulation.
Re: Any info on new Basix since July 2017 and using raised f5
Sep 09, 2018 9:19 am
I agree with you. The problem is that you can no longer specify your insulation requirements using the online tool to compensate for the loss or gain in the thermal sections. This can only by someone who uses a nathers approved program in which you need to pay 500 dollars to get a certificate for the thermal section of the basix. I would a stacker door going to the covered deck, but thermal comfort dictates I either have a normal door, or no cover over the deck to get winter sun. Even thermally broken, double insulated doors don’t cut the mustard on the online assessment. It dictates the minimum requirement of r2 for walls and r3.5 for ceiling even though I am well above that using a better design/insulation combination and can’t add this to the tool.
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