Thoughts on DIY Internal Insulation on new Build

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Paul1977

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#268046 25-Feb-2020 13:11

We're building a new house and would ideally like the internal walls insulated as well. To save money we are thinking about doing this ourselves with EarthWool. We'll likely only have a smallish time frame to do this in between the builder doing the external and ceiling insulation and gib fixing.

Is this something that someone who's never done it before should attempt? Is it relatively quick and easy?

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#2426864 25-Feb-2020 13:18

It's reasonably quick and easy, especially with some tips from the builder. Although the builder may insist that he does it as it will be checked during the preline inspection. If it is there they will have to make sure it's done right. The builder might not want to risk the fail.

I'm not a complete idiot, I still have some parts missing.

sittingduckz

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#2426865 25-Feb-2020 13:19

But may be ok between the inspection and the plasterboard... sometimes the owner jumping in can also be a PITA :)

I'm not a complete idiot, I still have some parts missing.

Paul1977

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#2426867 25-Feb-2020 13:20

sittingduckz:

It's reasonably quick and easy, especially with some tips from the builder. Although the builder may insist that he does it as it will be checked during the preline inspection. If it is there they will have to make sure it's done right. The builder might not want to risk the fail.

Builder didn't seem to have an issue with it, but if we go ahead I'll clarify that with him.

billgates

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#2426869 25-Feb-2020 13:22

The more hands you have available to help you over the weekend the better. Saying that most of your internal framing will be 800mm long and 600mm wide so if you buy 760mm long and 560mm wide earthwool batts then it's a 15 second job per frame as it will fit in very easily since its cut to that standard. Tricky one will be offcuts you will need to make for small size frames and cutting around electrical cabling, gas pipes, plumbing etc which you likely will not have a lot of as most will be run via external walls that your builder would have done for you. Take some sharp knives, extra blades and lots of hands. It's easily doable if you want to save some $$.

Do whatever you want to do man.

mdf

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#2426870 25-Feb-2020 13:27

You can definitely do it yourself (subject to builder approval). That said, in my experience it is hot, unpleasant, dusty work. Earthwool is much nicer than Pink Batts (IMHO), but you will still want a quality pair of gloves and dust mask at minimum, ideally full overalls, decent eye protection and a proper respirator mask, not just woven paper.

Set yourself up a decent work area - sheet of plywood/MDF on sawhorses is fine. If it is a new build, your stud and dwang/nog spacing should be reasonably consistent so make yourself a basic jig out of some straight timber or a big t-square, and a square reference edge. Pre mark your spacings on the bench. You can then line up your batts and cut square consistent pieces for installation with a craft knife. Check the installation instructions, but usually you want things flush without being tight or compressed. Save all your offcuts for packing in to odd spaces.

mdooher

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#2426916 25-Feb-2020 13:37

simple job, anyone with 2 brain cells to rub together can do it. One thing, do not split the insulation and sandwich it around electrical cables...that is a big no no, unless you want all your circuits de-rated for being "fully surrounded in thermal insulation (you don't)

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snnet

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#2432749 4-Mar-2020 19:32

mdooher:

simple job, anyone with 2 brain cells to rub together can do it. One thing, do not split the insulation and sandwich it around electrical cables...that is a big no no, unless you want all your circuits de-rated for being "fully surrounded in thermal insulation (you don't)

Funnily enough having the circuits pushed to the outside or inside of the wall framing if it's standard 90mm framing makes the wiring technically illegally placed because it needs to have 50mm gap around it on a finished wall (as in be in the center of the wall) -- All jobs I've done and been back after insulation has gone in they have split the insulation around the cable. This is why derating to 16A for 2.5mm TPS circuits came into effect a few years ago (instead of standardised 20A)

mdooher

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#2432894 5-Mar-2020 08:04

snnet:

mdooher:

simple job, anyone with 2 brain cells to rub together can do it. One thing, do not split the insulation and sandwich it around electrical cables...that is a big no no, unless you want all your circuits de-rated for being "fully surrounded in thermal insulation (you don't)

Funnily enough having the circuits pushed to the outside or inside of the wall framing if it's standard 90mm framing makes the wiring technically illegally placed because it needs to have 50mm gap around it on a finished wall (as in be in the center of the wall) -- All jobs I've done and been back after insulation has gone in they have split the insulation around the cable. This is why derating to 16A for 2.5mm TPS circuits came into effect a few years ago (instead of standardised 20A)

interesting: the 50mm thing is only relevant if the cable is fixed or restrained within the cavity, so where the cable goes through the stud, not in the cavity. (same reason you can't just put a notch in the stud.Basically if it can move out of the way when someone puts a fixing in to hang a picture) it is fine

as for the de-rating, if it fully surrounded in thermal insulation it would need to be de-rated to 15A, not 16 so you would need a 10A breaker

This de-rating all circuits thing was doing the rounds a few years back because someone who should have known better tried to get everyone to panic.

Matthew

Paul1977

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#2432934 5-Mar-2020 09:11

You guys are confusing me!

When I put in the insulation, what should I be doing where there are electrical cables?

rogercruse

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#2432935 5-Mar-2020 09:16

How much are you really saving by doing this yourself?

mdooher

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#2432952 5-Mar-2020 09:47

Paul1977:

You guys are confusing me!

When I put in the insulation, what should I be doing where there are electrical cables?

usually you will have one side of the wall lined already.. in which case just tuck the insulation behind them, it helps hold the insulation in place while you work. The only thing not to do is the sandwich the cable between two layers

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Paul1977

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#2432953 5-Mar-2020 09:51

rogercruse:

How much are you really saving by doing this yourself?

I'm not sure exactly, but we are hitting the limit of our budget and the builder has assured us it is dead easy to do. I just want to make sure we get it right first go as to not cause any hold ups if we need to fixed some of it.

Paul1977

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#2432961 5-Mar-2020 09:57

mdooher:

Paul1977:

You guys are confusing me!

When I put in the insulation, what should I be doing where there are electrical cables?

usually you will have one side of the wall lined already.. in which case just tuck the insulation behind them, it helps hold the insulation in place while you work. The only thing not to do is the sandwich the cable between two layers

I'm not sure that one side will be lined already. The schedule had the gib fixers coming in and banging it all out pretty quickly. I assumed we'd be doing it all after the pre-wire and pre-pipe, but before any gib fixing.

rogercruse

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#2432984 5-Mar-2020 10:41

Paul1977: ...we are hitting the limit of our budget...

I know what you mean about budgets. We're also having a house built and hoping to move in before Easter. I think we passed our original budget about six months ago and we're about to past our latest budget fairly soon...

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#2433448 5-Mar-2020 23:17

mdf:
and a proper respirator mask, not just woven paper.

Those may be tricky to find in the current climate.

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