underfloor insulation

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shaopu

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Master Geek

Topic # 95891 16-Jan-2012 12:05

Hi everyone, we just bought a 50s old house with timeber floor, i am planning to do the underfloor insulation by myself and really would like some advises: (BTW, i am in hillsborough Auckland)

1: what material woudl be the best suit? from both cost, effectiveness, insatllation difficulty perspective.

2: which suppliers would be recommended?

3: i have done my celling on my previous house before and this one does have the celling insulation done already.. i have never done the underfloor one and i hope it would not be too hard..i have heaps of rooms downstaires. any previous DIY experience/tips to share would be great!!

4: wonder if it would be the same cost if i get someone to installed it with the subsidies as i beliebe my house does qualify for the government subsidy..

thanks in advance and love Geekzone as i always receive highest quality help and answers...

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Reply # 569395 16-Jan-2012 12:10

The foil-backed building paper is about 80% as effective as the polystyrene stuff, and costs about $200 for 100m roll. We needed 2 rolls to do our house, as opposed to $4000-$5000 for the polystyrene. You will need a staple gun and a roll of the blue woven packing tape stuff to staple it on. But as long as you're OK lying on your back in the dirt under the house it's way cheaper, and it's really not that difficult to do.

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freitasm

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Reply # 569397 16-Jan-2012 12:17

We used foil-backed wool...

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Reply # 569405 16-Jan-2012 12:33

Foil doesn't get the official nod:www.energywise.govt.nz

Foil by itself doesn't meet Building Code requirements where it's formally deemed that underfloor insulation is required. www.waitakere.govt.nz/abtcit/ec/bldsus/pdf/energy/insulation.pdf

For $200 though it's better than nothing. It all hinges around creating an air type gap, just the same as double glazing. In practise this takes quite a bit of effort and thought to achieve. Watch you don't electrocute yourself either, that's not cool.

Mattnzl

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Reply # 569406 16-Jan-2012 12:35

Just don't stick a staple through a 240v wire (have read of a few people dieing this way while doing underfloor foil).

freitasm

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Reply # 569407 16-Jan-2012 12:37

Jaxson: Foil doesn't get the official nod:www.energywise.govt.nz

It's not foil only in my case. It's a thick wool blanket (about ten centimeters) with foil on the bottom to protect the wool, which is stapled under the floor.

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Reply # 569408 16-Jan-2012 12:38

The underfloor polystyrene stuff you see on TV (with the penguin..cant remember name of the stuff) seems to be hit and miss.
Friends got it put under their place and said its made a huge difference - their properly is on stilts (on hill side).
Yet anotehr friend put it in their internal garage ceiling (with bedroom above) and said its made absolutely no difference for their bedroom.

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Reply # 569409 16-Jan-2012 12:38

Jaxson: Foil doesn't get the official nod:www.energywise.govt.nz

Foil by itself doesn't meet Building Code requirements where it's formally deemed that underfloor insulation is required. www.waitakere.govt.nz/abtcit/ec/bldsus/pdf/energy/insulation.pdf

For $200 though it's better than nothing. It all hinges around creating an air type gap, just the same as double glazing. In practise this takes quite a bit of effort and thought to achieve. Watch you don't electrocute yourself either, that's not cool.

When we did it about 2.5 years ago it was acceptable in the Rodney district as underfloor insulation. Interesting to see where the Supercity sits on it.

As far as not stapling your wiring... I would have *thought* that went without saying. :-)

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Reply # 569419 16-Jan-2012 12:57

SaltyNZ:
As far as not stapling your wiring... I would have *thought* that went without saying. :-)

Yeah but hey, it's worth mentioning it if someone is new to the field.

2007 - 3 people did just that.
http://www.dbh.govt.nz/codewords-23-1

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Reply # 569421 16-Jan-2012 12:59

Jaxson:
SaltyNZ:
As far as not stapling your wiring... I would have *thought* that went without saying. :-)

Yeah but hey, it's worth mentioning it if someone is new to the field.

2007 - 3 people did just that.
http://www.dbh.govt.nz/codewords-23-1

Yikes!

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shaopu

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Reply # 569422 16-Jan-2012 13:00

Thanks all, after some reaserch looks like the penguin is good for timber floor. And it doesn't require stabling but just use the track to hold.

SaltyNZ

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Reply # 569424 16-Jan-2012 13:02

Actually now that I think about it they had not-dissimilar problems in Australia when they introduced subsidies for insulation. In Australian houses underfloor wiring is almost unknown; it's all in the ceiling. They had a bunch of fly-by-night installers start up and just dump bats on top of the wires.

Wiring is rated for a certain current according to temperature, with the assumption that it radiates into the roof space. Putting a nice layer of thermal insulation on top of it causes it to overheat.

Several houses were warmed for the rest of their (very short) lives.

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Toastiewarm

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Reply # 569430 16-Jan-2012 13:21

I have just helped my folks put the Expol (or whatever it is called, the polystyrene stuff) under their bach (on stilts)

Couple of things to note:

You need tape to go around the exposed cabling as the polystyrene eats away the insulation, the tape we got told to use looked similar to duct tape but not sure if it is the same.

You may well need to cut the sections to fit between the joist's under the floor so give them a bit of a measure up first.

also watch out for the polystyrene stuff as it gets everywhere! we used disposable overalls for the job.

Also you want some Poly matting stuff as well to absorb the moisture from the ground (if it sits on stilts above dirt).

Think that is all.. bit of a time consuming job, but 5 of us managed to do an 85sqm house in just over a day, once we got into it, we had 3 under the house and 2 cutting all the sheets up as for this.

Hope that helps.

Jaxson

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Reply # 569431 16-Jan-2012 13:21

Polystyrene has it's issues as well.

Often the floor joists aren't evenly spaced, so each piece has to be trimmed to fit, usually in place, ie under the house. Don't go cutting every piece based on your first measurement!

Also, Polystyrene should not be in direct contact with TPS cable, that's the white house power cables you'll find around the place. See Here . That can mean wrapping that section of cable in something suitable so it doesn't come in contact with the insulation piece.

EDIT: Ha, same content as post above. Must be too slow!

Very good point though about ensuring the ground is covered with plastic sheet. If that's not there, and ground seems a bit moist, that should be the first point of call. Also can make it a lot easier to move about too! If the ground is wet, try working out why whilst you're under there too.

Jaimita

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Geek

Reply # 569443 16-Jan-2012 13:41

Please be aware that in the past there have been accidents with DIY installers stapling through live wiring when installing the foil. Also make sure you leave no small gaps, as even when there is only a small gap, warmth will escape and you will not get the full benefit from your insulation.

It may be worthwhile to investigate the subsidies: Warm Up New Zealand: Heat Smart is the scheme's name and it is run by EECA. All house built before 2000 qualify with 33% subsidy for homeowners and around 60% for those with a Conmmunity Services Card but the scheme is only for insulation from registered installers.

Good luck!

shaopu

94 posts

Master Geek

Reply # 569445 16-Jan-2012 13:52

Thanks for all the tips and advices!! these info are really helpful!!!

so in terms of materials, i might choose from either the polystyrene or Fibre but not foil. my basement seems to be ok dry and quite a bag space as it has high celling. looks like both materials are good for timeber floor and fibre would relatively easier to be installed..

just wonder:

how different they are in terms of effectiveness and cost?

Thanks

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