Insulation - remove the old?

[Tom Kirk]

Hi,

I'm just about to re-insulate an old state house that has old blow in insulation. Before I put in the new stuff should I remove the old stuff thats there or just put the new on top?

[PC]

Probably not much point in removing existing insulation.
You can get "blanket" type insulation that just rolls over the top of existing.
Or get more insulation blown in.
Have used blown wool before.

http://envirowool.nz/

[Learning]

Got three quotes for insulation and all three said best to add on top of existing.

[sidinz]

Why would you want to muck about doing what is probably a pr!ck of a job?

[Wayne]

Throw it on top - what is there is better than nothing so you get the benefit still, and it would be messy removing the old.

[kslice]

Hi everyone,

I have a question on insulation. I had an assessor come to give a quote and he told me that as there is foil used as roof underlay they cannot install any ceiling insulation.

He explained that it is best practice to not install any insulation products in the roof when there is foil in it as they think condensation will build up and goes into the insulation.

I am going to call a couple of other companies to give quotes but was wondering would anyone know if it is true that condensation can build up in the roof cavity area and absorb into the insulation?

Should the foil be removed and replaced if it is going to cause condensation? There is no leaks as far as I know over the time I have owned the rental.

Thanks.

[Bobsyouruncle]

Sounds like bollocks to me but I ain't a builder.......

[TheFlash]

Yes, ive heard of the problem. Some silver cigarette type paper has a condensation problem and was removed from market a few years back, it was used in the 1980-1990's.

Another issue is thermal bridging which you can lookup.

Basically anywhere there is air - you get water vapour. Water condenses out of the air once the dew point is hit, on the cold side of the roof. This water would be under your tile but on top of the foil - then it tracks back down the foil finding any imperfection, nail holes etc and then drips back onto the ceiling as a puddle giving you a water spot in your ceiling (ive got this problem with a skillion roof).

Another issue ive seen is old mmacerated paper asborbs the water and it dries out. New bats dont seem to asborb water and the water tracks to the edge of the room if the roof is on an angle. Mixing old with new could be a problem.

I would listen to your insulation guy he seems a keeper.

[kslice]

Yes, ive heard of the problem. Some silver cigarette type paper has a condensation problem and was removed from market a few years back, it was used in the 1980-1990's.

Another issue is thermal bridging which you can lookup.

Basically anywhere there is air - you get water vapour. Water condenses out of the air once the dew point is hit, on the cold side of the roof. This water would be under your tile but on top of the foil - then it tracks back down the foil finding any imperfection, nail holes etc and then drips back onto the ceiling as a puddle giving you a water spot in your ceiling (ive got this problem with a skillion roof).

Another issue ive seen is old mmacerated paper asborbs the water and it dries out. New bats dont seem to asborb water and the water tracks to the edge of the room if the roof is on an angle. Mixing old with new could be a problem.

I would listen to your insulation guy he seems a keeper.

Thanks Bob and Flash. This is a block of 3 units that I own and only one did not have the foil so he had a chance to make money on all 3 units but only quoted for 1 unit. Lets see what another company comes back with.

Thanks again.

[Tom Kirk]

Why would you want to muck about doing what is probably a ***** of a job?

I can tell you now I lasted all of about 30 seconds attempting to remove the old. Ended up topping up the whole roof with 4.0R and even a double layer over the main bedroom for about $500 in the end.