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Airtight house

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Airtight house

Posted 25 May '11 09:42 PM

There are many discussions here about the importance of insulation but what are peoples thoughts on the important principles of building an airtight home? How can this be achieved?

Re: Airtight house

Posted 25 May '11 11:27 PM

I am afraid it can only be done by letting go some of the things and building methods we are used to and to take an open approach to some proven methods, detailing and materials from overseas. e.g.

Re: Airtight house

Posted 25 May '11 11:49 PM

Leaving the MDF aside which I wouldn't touch anywhere in the World.

Re: Airtight house

Posted 26 May '11 01:32 AM

My impression is that normal NZ building techniques provide adequate airtightness. A BRANZ study measured a range of NZ houses - leaky old villas were about 1 ACH (air changes per hour), many were around 0.5 ACH, and some 1980s+ houses were down to 0.2ACH. 0.4-0.5ACH is considered adequate.

So if you build a very airtight home (maybe even the typical spec house built by the big volume housebuilders), you will not be getting enough ventilation unless you add a ventilation system. Then you need to run a heat exchanger to avoid wasting energy and we are back to the whole forced ventilation thing again.

If you build to code then ventilation will contribute less than 1/4 of your heating losses so you would have to insulate to 3x code before it would be worth running forced ventilation (at least based on this factor alone).

MDF... most NZ MDF is illegal in many countries because of its high levels of formaldehyde. However, we do make low and zero formaldehyde MDF (E0 and Super E0) for export, and you can buy it if you insist.

Re: Airtight house

Posted 26 May '11 02:57 AM

Standard NZ building practices aren't quite good enough unless it is modified. Sheet lining of the framing instead of wrap Windows which shut properly rather than those standard aluminium windows Insulated airtight joints between window and studs/framing rather than the E2 method. Proper training of trades people would also help. Trusses are cheap but a real pain to install insulation properly and a wind barrier above. The way leaky homes were built was considered as "adequate" by BRANZ at the time too.

Re: Airtight house

Posted 03 Jun '11 08:33 AM

@nikoftime Airtightness & wind barriers should go hand in hand and yes they are important. At this stage in NZ ProClima Intello will be the most appropriate product for airtightness. @ Robert where do you get that information from in regards of the airtightness of existing buildings? do you have a link to follow that up. To be honest I find it hard to believe that some of the older homes meet the ACH for Passiv Houses. Whether E0 or Super E0, they still can evaporate Formaldehyde. Good news are: apparently its evaporates only on the cuts. seal the cuts and you are sorted.

Re: Airtight house

Posted 06 Jun '11 10:40 PM

The BRANZ airtightness research is here

and they seem to have adopted that research in their ALF software:

Re: Airtight house

Posted 07 Jun '11 12:28 AM

Hi Robert, I'm sorry can you explain your statement: "If you build to code then ventilation will contribute less than 1/4 of your heating losses so you would have to insulate to 3x code before it would be worth running forced ventilation (at least based on this factor alone)." thanks

Re: Airtight house

Posted 07 Jun '11 01:11 AM

It's a bit rough, but it comes from the calculations of my own house. The thermal losses through the ceiling, windows etc came to 400W/K, and through ventilation came to 120W/K at 0.5 ACH. And this is insulated over code already. I would have to double my insulation levels on all sides (which would take it to R9.6 in the ceiling, close to passive house standards) before the heat losses from ventilation would become a significant fraction of the total heat loss.

However it would be a good idea to repeat this calculation for a standard new house.

Re: Airtight house

Posted 07 Jun '11 03:44 AM

Wow, Just found this document and about half way through reading. it answers a lot of my questions and provides some really interesting and usefull info.,18749,en.pdf

Re: Airtight house

Posted 07 Jun '11 09:02 AM

here is an eco home claiming to be airtight and developed in NZ. the 2 bedrm version villa reportedly circa 70k.

Re: Airtight house

Posted 07 Jun '11 08:39 PM

I have looked at the possibility to upgrade our 25 year old typical kiwi box which we unfortunatly had to buy as part of our property. Would have rather paid less and have grass there :-( I have identified the following areas which are potentially trouble (air leaks, moisture) if I try to insulate to a modern standard. Wall,soffit,truss junction The trusses itself prohibit the installation of a protective air tight floor over the insulation in the roof space. The timber floor and not enough room height to build insulation on top of the particle board rather than exposing it to rodents underneath the house. Vermin intrusion is not controlable due too poor workmanship and building technique. Conclusion: Retrofit is risky, time consuming and expensive. Removal and new built from scatch with proper detailing, much stronger walls and a rafter roof with insulation on top too create a full blanket cover is more cost efficient with less risk and better result.

Re: Airtight house

Posted 07 Jun '11 08:51 PM

Forget that it is also completly wrong in the direction to the sun and shape

Re: Airtight house

Posted 09 Oct '11 10:57 PM

Hopefully Robert is still keeping an eye on this forum back in June, Robert, you provided the following link The BRANZ airtightness research is here If you refer to page 2 table 1 and figure 1 you will see the report states air changes of 5per hr for a modern house it later talks about infiltration rates of 0.2 etc which for me in confusing! Anyone know if the NZ building code requires a minimum level of airtightness?? (Not the ventilation rate, which , I think is different)

Re: Airtight house

Posted 10 Oct '11 01:20 AM

Hi Nikoftime, yes I am still here! That table refers to the blower door test of airtightness in which the whole house is subjected to a pressure difference of 50Pa (see the blower door test page in wikipedia). This results in much greater ACH than you would get in normal use. However in a typical NZ gale I imagine the infiltration rate can increase markedly over "normal". eg 5 air changes/hour in the blower door test is about 0.2 air changes/hour in normal use.

Re: Airtight house

Posted 10 Oct '11 01:57 AM

Hi Robert, thank you for your reply. 50Pa is an extremely small pressure. Isn't the blower door test the standard method of testing airtightness? given that pressure differences are otherwise going to be very varied? Any idea whether the NZ building code stipulates any requirement for air tightness?

Re: Airtight house

Posted 10 Oct '11 02:45 AM

Yes, it seems small to me, only 1/2 a millibar, but one site I read compared it to a 30kph wind in its effect on the house. It will have been arrived at through tests in labs I expect. This paper has more detail: It says that the NZ code does not have an airtightness requirement. A few (but not all) European countries do, eg Belgium has a limit of 3 ACH (at 50Pa) for buildings without ventilation equipment, 1.5ACH with ventilation. Divide by 20 to get the ACH in normal conditions.

Re: Airtight house

Posted 11 Feb '12 11:10 PM

Wow, stumbled along this forum recently, interesting topic.

To my understanding, there is the mention of airtightness in H1: Energy Efficiency, in paragraph H1.3.3 Account must be taken of physical conditions likely to affect energy performance of building, including (c) the airtightness of the building envelope.

However, there are no given airtightness targets...

The 'divide by 20' rule is a rule of thumb used to determine the 'natural' pressure air exchange rates that informed the air leakage rates found in ALF. This was after blower door tests performed in the 80s by Mark Bassett and Synergy. However, in Europe there is a calculation, which we should be using, that gives a more precise value of natural pressure air exchange in relation to n50 rates. This is found in EN 13790 (Q = CLxP^n).

if using this equation 5ac/h (at 50 Pa) is 0.35ac/h at natural pressure

Re: Airtight house

Posted 01 Apr '12 07:10 AM

I found this short youtube video with a brief summary of the importance of airtightness and reference to possible mould is part of a Proclima marketing but I nevertheless still worth posting (in my opinion anyway)

Re: Airtight house

Posted 23 Apr '12 10:45 AM

I found this link on the Proclima website

Although the link is labelled as 'Guarantee / Code Mark Certification' it is actually only a codemark enrolment certificate. That's a bit misleading

There's another link 'View the pro clima Guarantee Determination - INTELLO' but it doesn't let you see the actual Guarantee/Determination. That seems a bit dodgy.

I had a look at the NZ price list and compared the price of the Intello Plus product in NZ with the prices on UK, European and US websites. The NZ price is 3 to 4 times the price overseas. No wonder they have hidden the price list away so that you have to request a copy.

Overpriced and therefore not justifiable (in my opinion anyway)

Re: Airtight house

Posted 23 Apr '12 06:41 PM

There are not many products which are not overpriced. ;-)

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