Underfloor Vapour / Moisture Barrier

Forums › Home Workshop DIY › Underfloor Vapour / Moisture Barrier

Willuknight

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#191203 27-Jan-2016 16:14

I'm buying a 1960's house, it has roof insulation but no floor insulation and no heatpump (wood burner only). I'm guessing I'm going to need floor insulation and since I'm doing that it seems like I need this vapour barrier thing also I like the idea that it will make doing wiring under the house easier.

1) Have you had a barrier installed? How did you find it?

2) If you have, how much did it cost you / how long did it take you to DIY it?

General thoughts on the effectiveness of underfloor insulation / moisture barriers? I don't even know if the house is going to be cold, but given it's christchurch, it seems safer to just go ahead and do it.

Thanks heaps!

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#1479967 27-Jan-2016 16:22

This thread might cover some of this area: http://www.geekzone.co.nz/forums.asp?forumid=141&topicid=175203

Willuknight

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#1479982 27-Jan-2016 16:29

Yeah I've been reading all the past threads, but people didn't specify any info in terms of install cost or how complicated a DIY job it is which is why I made a new topic. Thanks though!

andrewNZ

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#1480072 27-Jan-2016 17:28

Just an important note.

If you do DIY underfloor insulation
- Polystyrene must not touch electrical cables. The two react and the electrical cable insulation melts.
- Please don't staple through electrical cables. About 3 people a year die installing underfloor insulation.

Sorry, that's all I have to contribute.

Willuknight

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#1480128 27-Jan-2016 18:12

Thanks for the advice!

I'm actually going to go the batts route, http://www.earthwoolglasswool.co.nz/earthwool-range looks pretty good, but will be making sure I have good lighting and avoid stapling any wires.

tchart

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#1480133 27-Jan-2016 18:24

We had a vapour barrier installed when we had underfloor insulation installed. I can't recall the exact figure but I think it was roughly $1000 extra for the barrier (about 90m2).

mattwnz

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#1480143 27-Jan-2016 18:40

I would investigate installing polyester or even wool underfloor. Then you are not breathing in any glass fibres. Although they are supposedly a lot safer these days, you really don't know until 30-50 years down the track. A polythene vapour barrier on the subfloor ground is also good.

Willuknight

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#1480185 27-Jan-2016 19:05

The earth wool is actually safe to handle and doesn't contain any glass fibres, so no need to worry about what you're breathing in :) It's made from recycled plastic.

The other option that I'm going to investigate also made of the same stuff - greenstuf - http://www.autexindustries.com/greenstuf/

I like that it's made in NZ, though Earthwool has better documentation and packing principals - plus you can order directly from the manufacture.

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

bfginger

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#1480227 27-Jan-2016 20:19

Knauf Glasswool isn't polyester like Greenstuf. Knauf contains some recycled glass while Greenstuf contains some recycled plastic.There are other companies that produce polyester insulation, see this earlier thread:

http://www.geekzone.co.nz/forums.asp?forumid=141&topicid=190824

I wouldn't install fibreglass like Glasswool or Pink Batts under floor. It can't be directly attached and needs strapping plus you're getting glass dust in your face.

The polythene sheets aren't expensive at not too much more than $1 per m2. Go for a thicker grade sheet.

Here are some instructions

https://www.energywise.govt.nz/assets/Resources-Energywise/NZS_4246-2006_installing_insulation.pdf

http://www.communityenergy.org.nz/i%E2%80%99ve-been-told-that-the-ground-under-my-house-is-damp-and-that-i-should-get-a-polythene-moisture-barrier-installed-so-that-the-house-is-drier-and-easier-to-heat-can-i-do-this-myself/

http://www.ecodesignadvisor.org.nz/assets/Installing-a-Ground-Vapour-Barrier-Factsheet-no-12.pdf

Holding down the sheet with rocks wouldn't require holing it like pegs would.

Beyond polythene Terra Lana R2.6 wool-polyester underfloor batts should have greater effectiveness for dealing with dampness over those that don't absorb and deabsorb humidity. It'll be relatively expensive but you should be able to buy direct from the Christchurch factory.

Old wiring can overheat if it's enclosed under insulation. Old types of ceiling insulation can have lost effectiveness as the old fibreglass batts slump and tear up and weren't thick to begin with.

Adamanski

54 posts

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#1480241 27-Jan-2016 20:54

Can the vapour / moisture barrier be an aluminium foil? Reflective so should be great for thermal - just querying it around electric cables?

I'm sure we have some surplus aluminium/kraft/aluminium at work that could be a deal if suitable, just need to check it's the non-perforated. Let me know if you're interested and I'll take a look tomorrow.

Willuknight

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#1480243 27-Jan-2016 20:55

Thanks bro,

I did see your post in that other forum, are you also saying that with Terra Lana, you're less likely to need the moisture barrier, or just that it works in tandem well with it?

With the pegs in the groundsheet, can you tape over the pegs to contain the seal?

I've never even heard about a moisture barrier before reading about it on this forum, but it makes sense, I guess my main thought is is it just something that's a good idea generally to install or is it site specific? Ie should every house have it or only if there's a moisture problem?

Thanks for the info about earthwool, nothing on their site says anything about glass, so I assumed it was safe to use.

Jeeves

301 posts

Ultimate Geek

#1481111 29-Jan-2016 11:08

I would only install a vapour barrier if

A) The water table is very high where you live

B) Water drains under your house

C) The dirt under your house gets wet

If the dirt is dry year around and you have good ventilation in your sub-floor, I'm not sure it will make any difference putting in a vapour barrier. Our old house had a very high water table as we were near the beach and only ~3m above high tide level - so in winter the dirt would be wet etc. We threw in a vapour barrier which helped quite a bit. Installation wasn't terribly difficult - just dirty and uncomfortable. Hardest bit was getting a good seal around the piles.

flyingdutchdude

31 posts

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#1481129 29-Jan-2016 11:36

Effect: Installing a 250 micron polythene moisture barrier was the best thing we did for our 1950's home in Christchurch. It made a massive difference to the house - more than the Earthwool / Expol underfloor insulation which I did prior. The best way to describe it is that the floorboards were not cold after it was laid down (something to do with the rising damp?).

Cost: 100m2 roll from Mitre10 Mega was $99 or $4.90 per linear metre (4m wide) from TradeMe. Plus decent quality builders tape to tape up and around the piles.

Time: Depends on the space, took me around 2 days to do a 100m2 house with 60cm space to work in.

Comfort level: Its amazing how cussin words sound in a confined space...

Willuknight

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#1481186 29-Jan-2016 12:49

Now you're selling me!

What area is your house?

flyingdutchdude

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#1481201 29-Jan-2016 13:18

Yeah, MUCH cheaper to DIY. House is in Kaiapoi.

See page 47 for succinct requirements: https://www.energywise.govt.nz/assets/Resources-Energywise/NZS_4246-2006_installing_insulation.pdf

Trademe seller is http://www.trademe.co.nz/Members/Listings.aspx?member=2963708 Web: www.home-insulation-christchurch.co.nz

Willuknight

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#1481204 29-Jan-2016 13:27

Yeah, i saw an ad for install for $599, which then vanished but it seems like the going rate is $1000. I can buy the material for $200 and save $800? done!

Thanks for the help!

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