Underfloor insulation mandatory?

[Phil Squire]

Hi folks

Can anyone let me know if underfloor insulation is mandatory (where it can be installed) for new build? Or does a new build just have to comply with H1? I got a question from a lawyer last night at a talk and told him I would get back to him.

Cheers, Phil

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[Ian McChesney]

Hi Phil
My understanding is that the building will need to comply with H1. But H1 contains flexible options. The normally prescribed R1.3 for floors that you are probably thinking about is the minimum value contained in various ‘schedule methods’ for meeting the code. Schedule methods are like off-the-shelf prescribed solutions. The alternative is the ‘calculation method’. The latest H1 compliance document states:

“… “calculation method” of NZS 4218
compares the proposed building with the “reference
building” which is insulated in accordance with
Tables 1, 2 and 4 (as modified by Paragraphs 2.1.3
and 2.1.4). This method permits roof, wall, floor and
glazing insulation combinations which differ from
these Tables, but the building must still perform at
least as well as the “reference building”.

Note that the tables referred to above are the schedule methods. Therefore my understanding is that the Calculation Method of H1 would allow for low floor R values, so long as other elements of the house compensate with higher R values.

I suggest you confirm this understanding with someone regularly dealing with new houses.

cheers
Ian

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[Eion Scott]

Ian is correct, and the calculation method is one of the “cheats” that designers can access to implement poor insulation, usually done though to bypass the schedule method requirement for double glazing. That’s a complete disservice to clients, and I’m now getting single-glazed homes that were built in the mid-2000s that the client is wanting to retrofit double glazing at huge additional cost. Re floors, the schedule method requires R1.3, which can be achieved by an uninsulated slab, but will depend on the complexity of the footprint (calculated via perimeter to area ratio). Without being blinded by the science, the best advice is to have new builds insulated under the slab and with perimeter (edge) insulation to achieve passive solar design/thermal mass. Wooden floor houses will need to be insulated to achieve R1.3.

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[Richard Popenhagen]

I agree with the comments above. The other point to remember is that if you are using the schedule method and the floor is a heated floor then the minimum required floor R value is R1.9.

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[Gleb Speranski]

Hi Phil,

I agree with all the earlier comments but would like to add something for clarity.
Unfortunately NZS 4218 is still sited in H1 in its old, 2004 version. The standard treats draped foil as a ‘deem to comply’ insulation option for suspended timber floor. That means that even though BRANZ already established that the installed performance of a floor with draped pliable membrane is a fat zero, new builds still comply with the schedule method with foil. That is how deficient the whole ‘performance based’ approach of the Code is.
It should be noted that the more recent version of 4218 published in 2009 (?) is a lot stricter and introduced some good changes like a 6% limit, by surface area, on doors (including garage doors).
However, the political climate has already changed at the time the 2009 version was published and therefore it still remains a voluntary standard.
Back to your question- no, insulation is not mandatory: a house can be constructed in such a way that compliance with H1 is achieved by other means- solid walls, smaller double glazed windows, etc.

Regards,
Gleb

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[Ian McChesney]

Hi Gleb
Thanks for these points. In response to your comment “That is how deficient the whole ‘performance based’ approach of the Code is”, I don’t think that a ‘performance based’ approach per se is the issue (and maybe you didn’t mean that).
I think it is the way performance (or lack of it) is specified e.g. the still relatively low thermal performance of the Code’s “Reference Building” and the relatively low R values specified in the schedule methods (I’ve just had a quick look at Code requirement in Australia, and in their Zone 7 (mainly Tasmania – roughly equivalent to Zone 3 here, R values for ceiling, walls and floors are way higher (and there is a Zone 8 where R values are higher still)); the lack of any minimum values for building elements if a calculation method is used, the convoluted and often highly delayed process for recommended changes to the Code to be actually made mandatory (as you refer to), the lack of any performance issues around overheating….
It is also a code that has been highly influenced by the performance of certain parts of the building industry.
regards
Ian

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[Gleb Speranski]

Hi Ian,

Thanks for your reply. The issue with the Code is not so much in insufficient levels of thermal efficiency required (even though that is important as well) but in the fact that the Code offers absolutely NO means to validate whether those levels are actually achieved.
Insulation gets ticked off by council’ inspectors visually- mainly based on the fact that it is present (installed). How well it was fitted and, subsequently, how well it is going to work is NOT being checked. There are some more vigilant inspectors who are trying their best but even they don’t have a guidance document to work against. NZS 4246 for installation of insulation is not recognised in the Code as the compliance document and NZS 3604 does not even mention insulation even though that one is a builder’s Bible.
In our research we evidenced very poor thermal performance in new builds- in a brand new home with R2.6 insulation in walls, the in situ performance of the entire wall was R1.3.
It is never one problem only: in my experience it is a combination of things- poor thermal design, products not being fit for purpose and, of course, installation.
So, here we are having ‘performance’ requirements that are insufficient on one hand and often not achievable on the other.
After walking streets of Christchurch in August I was horrified to see that energy efficiency does not even feature in new houses being built around Wigram. It looks like the opportunity to improve the housing stock in the city is being wasted which is a real shame.
I recently presented a paper on the issue of insulation in new builds at the Building Better New Zealand conference in Auckland.

Regards,
Gleb

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[Paul Hansen]

All great technical rationals added above.

Insulation for the under floor, most definitely, with out question, do it

In a simple view, my personal opinion is we focus in NZ on the “minimum requirement” way too much. This will clearly be the cheapest budget way to get council approval for your build but why focus on the minimum. A constant issue I faced when insulating new builds was “what will get me council sign off”. Clients would happily spend thousands on nice tap fittings etc, but want to scrimp on what can’t be seen behind the gib/under the floor. 1-2% of total build cost is all the insulation will cost and the improvement to total house performance is massive, virtually vital in my view.

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