Underfloor Foil Insulation Removal

[John the builder]

https://www.building.govt.nz/assets/...lation-ban.pdf

the ban only applies to repair and installation. Foil to rigid panels is of as staples not used to fix.

It is a silly ban really...this is the first time that the provision was used and frankly is more about stopping idiot installers than the actual method (the provision is supposed to protect buildings from poor methods rather than the idiots
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polystyrene is not considered combustible as it self extinguishes when removed from fire source

[AlexL]

Personally not keen on Expol - it cant be in contact with PVC wiring and generally polystyrene burns quite well.. Never used pinkbatts underfloor before, but the ceiling and wall types tends to sag over time. I do like greenstuf - it doesnt itch your skin or throat when installing it. Also a fan of Mammoth medium density underfloor insulation - it fits snug, so no need for staples, straps etc.

[JimNic]

Also what is everyone's opinion on the type of underfloor insulation?
Expol kind of material or PinkBats/Greenstuff?

[JimNic]

This is what it currently looks like, our building inspector guy said its like that all over, possible due to the reno when re-plumbing and rewiring so its not doing its job at the moment to keep heat in

[John the builder]

The foil draped and would most certainly bunch up if you put batts or similar on top of it.

it doesnt matter that foil bunches but it needs an air space which the batt provides. The small air gap above the foil also increases efficiency as it creates another insulation space

[Meehole]

I was just trying to clarify if it was something that HAD to be done (a regulatory (or something) requirement) or just a recommended practise (recommended by someone).

I'm with JTB on the worth of the foil - it would add a little to, but subtract nothing from, the efficiency of the new insulation given that the new insulation is about trapping warm air and I can't see how a bit of foil could detract from that.

I'm no technical expert and cannot recall the reason for not having 2 types of insulation together, those being existing foil and batts/greenstuff together other than being told the foil reduces efficiency. I'm not sure where the trapped warm air would be as batts or similar are placed hard up under the bottom of the floor and then they are moulded over and stapled to the side of the joists. The foil draped and would most certainly bunch up if you put batts or similar on top of it.

[Wayne]

Like I said I was told when I worked at Right House selling insulation and heat pumps to advise the client that the foil had to be removed as it reduced the efficiency if having floor insulation installed over it.
Hubby is a builder and had an insulation business many years ago, he was the one doing the work on the property and that was what he thought was best practice as well.
However you do what you want Wayne. I'm only telling others of my experiences and what I know. Feel free to offer yours.

I was just trying to clarify if it was something that HAD to be done (a regulatory (or something) requirement) or just a recommended practise (recommended by someone).

I'm with JTB on the worth of the foil - it would add a little to, but subtract nothing from, the efficiency of the new insulation given that the new insulation is about trapping warm air and I can't see how a bit of foil could detract from that.

[Meehole]

So is that really a 'it's a good idea to remove' rather than 'you have to'??

Like I said I was told when I worked at Right House selling insulation and heat pumps to advise the client that the foil had to be removed as it reduced the efficiency if having floor insulation installed over it.
Hubby is a builder and had an insulation business many years ago, he was the one doing the work on the property and that was what he thought was best practice as well.
However you do what you want Wayne. I'm only telling others of my experiences and what I know. Feel free to offer yours.

[Wayne]

Oh well we followed my advice and removed the draping foil before installing Greenstuff.

So is that really a 'it's a good idea to remove' rather than 'you have to'??

[Meehole]

Oh well we followed my advice and removed the draping foil before installing Greenstuff.

[John the builder]

foil acts to reflect radiant heat. Batts and the like create a still airspace. Foil works in combination with other materials to create an overall thermal insulation.

The draped foil formed a air gap where heat was reflected back into but not very efficient. Not worth doing but if it is there leave it do a job?

[Wayne]

Interesting -one says you have to remove and another says you don't.
MBIE doesn't say you can't - they say you can't add as new or repair.

[Meehole]

people were killed installing the foil and stapling through live wires. This livened up the foil and was deadly

That web site suggests that existing foil could be live? Is that possible? but get a friendly electrical to check
Leave the foil in place It adds to the thermal efficiency (but only a little). Place the new insulation under it between joists. It is exempt work under schedule 1

The foil is draped so installing insulation over top of it will also cause it to scrunch up. Also when I worked for Right House selling insulation and heat pumps we were advised that the foil had to be removed as it reduced thermal efficiency. Very confusing.

[John the builder]

people were killed installing the foil and stapling through live wires. This livened up the foil and was deadly

That web site suggests that existing foil could be live? Is that possible? but get a friendly electrical to check
Leave the foil in place It adds to the thermal efficiency (but only a little). Place the new insulation under it between joists. It is exempt work under schedule 1

[Keithw]

First thing I would ask is, are you talking about actual foil insulation? or the building paper foil between the floor joists and floor boards (which shouldnt be removed)..
.

you raise an important point that for me is very much a matter of misconception / lack of knowledge.
Foil insulation is obviously very different from foil backed builders paper

Foil backed building paper

foil insulation

foil bonded to fibre insulation