Please help me improve my home insulation.

[wrightwoodwork]

The vapour barrier in the dwarf wall external wall goes on the warm side of the insulation. So insulation between studs then the vapour barrier and plasterboard. The vapour barrier could be foiled back sheets but doesn't need to be could be visqueen and normal plasterboard. Good idea taking the ceiling down. Don't know if you know but the ceiling in the garage to the house has to have 1 hour fire rating can be achieved by double sheeting with normal plasterboard which each layer is rated 1/2 hour or using a single layer of fire rated plasterboard which is rated for 1 hour. The insulation should be pushed up tight to the flooring then straps to hold it up. Don't know if the previous ceiling had been dwanged, but if it has not dwang the perimeter and 1200mm centers it stops the joints cracking from people walking about upstairs. Your ceiling will not need a vapour barrier as it is not a condesation risk. I personally would use the fire board as only need to do a single layer to achieve 1 hour fire rating

 

[Paulrsm]

The vapour barrier in the dwarf wall external wall goes on the warm side of the insulation. So insulation between studs then the vapour barrier and plasterboard. The vapour barrier could be foiled back sheets but doesn't need to be could be visqueen and normal plasterboard.

Sorry, I'm struggling to visualise.
Currently the knee wall is a sheet of plasterboard, not foil backed, followed by rockwool insulation between studs then loft space. So are you saying that the existing plasterboard should have had a foil backing or are you saying that I need to install a vapour barrier within the loft space covering the rockwool. (I assume the foil backing is what we are talking about when we speak of vapour barrier).

Thanks for the help with this.

Paul.

 

[wrightwoodwork]

The plasterboard does not have to be foil backed on all external insulated walls and the knee wall you are referring to is classed as an external wall so as you look plasterboard - vapour barrier - insulation. If you can look behind the plasterboard and pull the Rockwood away you should see a vapour barrier in your situation it should look like a polythene of some kind. If you are struggling to visualize look up any uk supplier like kingspan, cellotex, ecotherm, isoover knauf Rockwood look up the uk site and they will have diagrams of how it is to look and the make up of the walls also look up visqueen vapour barrier. You are half on the right thinking the foil is the vapour barrier if you can see but is not the only way to achieve as long as it is a vapour control system of some kind then it is a vapour barrier. The foil works as vapour barrier by reflecting the cold

 

[ban-all-sheds]

The foil covering is there to keep the inert gas in

Rubbish.

 

[ban-all-sheds]

The foil works as vapour barrier by reflecting the cold

What on earth does that mean?

No, the foil works as a vapour barrier by being a barrier to the passage of vapour.

 

[wrightwoodwork]

It's always been my belief that the foil worked by reflecting the foil worked by reflecting the cold from outside so when the warm air from inside when it touches it does not turn to condensation at the end of the day it is a still a vapour barrier

 

[ban-all-sheds]

No surface can reflect anything which does not reach it, so even if it were possible for "reflecting cold" to exist, the "cold" would have to reach the foil.

Through several cm of insulating foam.

And then somehow, for condensation not to form on the other side of it, that extremely thin layer of aluminium foil would have to not behave like a thin layer of metal, but would have to have an unbelievably low U-value. So low, in fact, that it would call into question the whole point of having the foam.

Please think.

 

[wrightwoodwork]

Not a problem I suppose with foil wrapped building papers that are now used to increase the U value of the walls and that's where confusion come from and I hadn't thought about the insulation

 

[tony1851]

The foil is a 'low-emissivity' surface; its purpose is to reduce radiant heat transfer from the insulant and in so doing improves the U-value of the element
of which the board forms a part.

 

[wrightwoodwork]

That makes sense just before Christmas was fitting a new type (new to me) protec 4000? And it looked a bit like building paper had a foil surface which went to the insulation and black on the outside and then taped. In scotland we have to meet a higher U value and by using this product increased the walls U value to meet current scottish building regs

 

[ban-all-sheds]

The foil is a 'low-emissivity' surface; its purpose is to reduce radiant heat transfer from the insulant and in so doing improves the U-value of the element
of which the board forms a part.

It's on the warm side.

What heat is radiating onto it from the insulation on the cold side?

And if there were any, why would you not want to let it into the room?

 

[stuart45]

It's always been my belief that the foil worked by reflecting the foil worked by reflecting the cold from outside

Cold isn't an energy force. Heat is, so it can be reflected.

 

[tony1851]

What heat is radiating onto it from the insulation on the cold side?

It's not a case of 'heat radiating onto it....from the cold side'.
Remember that the foam in the board will attain a certain temperature. If there was no foil on the cold side, the rough surface of the foam would then emit more radiant heat across the void to the colder side.
The foil on the cold side of the board reduces the emission of radiant heat outwards.

 

[wrightwoodwork]

Then does it radiate the heat back into the room

 

[tony1851]

Then does it radiate the heat back into the room

The foil on the cold side will keep the foam at a slightly higher temperature than otherwise, because of its low emissivity.
This will reduce the heat gradient with the room, thus slowing the transfer of heat to the wall/roof or whatever.