Insulated Plasterboard Query.

Southern Comfort

I'm hoping to install some insulated plasterboard in a few rooms in the house. I'm doing walls and ceilings. I'm going to put up the plasterboard myself with a friend who has done similar work before and I'll get a plasterer to finish the job off. Two questions.....

1. Which should be be installed first, the wall or the ceiling board? I'm thinking along the lines of preventing any cold bridging, etc.

2. The ceiling is just standard plasterboard, which I'm not going to take down. What's the thickest insulated plasterboard I could put on the ceiling? (I don't want to pull the ceiling down!) Another friend reckons I should only use the thinnest one which is a total thickness of 27mm. That's Xtratherm Therma Liner.

Thanks.

Carlow52

Re the ceiling, not removing the existing ceiling can cause a problem, depending what is above it, as follows:

The existing skimmed pb is a pretty air tight component.

Secondly the insulated board is going to have a temperature drop across it from room temp to external temp, which is why what is above it is important.

So if the room temp is 21 and the external temp is low enough you will get condensation within the insulation, most lightly on the existing pb and this will create mould etc.

I know u will argue that is the new skimmed pb not airtight: it is to a degree but the drying of the new skim will be a good source of damp for the mould.

Similar considerations apply with the walls.

Slabbing walls with insulation as you propose needs to be done with care..

However dont take my word for it, have a read here of the breaking the mould articles:
http://www.josephlittlearchitects.com/papers.html

Should keep you busy till Euro 2012:D

Re the cold bridging, what I do at wall corners is that if the slab is say 62.5 ie 50 + 12.5 them remove the pb along one board for a width of 62.5, sort of lap joint if u will.

No7

The link given above has some very good information.
In addition make sure you remove the existing finish on the walls back to the blocks. Not doing this will leave gypsum products within the wall that could suffer from any interstitial condensation and allow mould to grow.

As fara s the ceiling boards go why don't you just install more attic insulation?

Pride of Merseyside

Hi carlow 52 u sound like a man in the no!!! im thinking of dry lining my walls. i live in an apartment at the end of the block,my daughters room is very cold and doesnt hold much heat was thinking of using the Gypsum Interior Wall Insulation would i need battons? dont want to make the room much smaller than it already is! room can be quite damp from time to time

Southern Comfort

Carlow52 wrote: »

Re the ceiling, not removing the existing ceiling can cause a problem, depending what is above it, as follows:

The existing skimmed pb is a pretty air tight component.

Secondly the insulated board is going to have a temperature drop across it from room temp to external temp, which is why what is above it is important.

So if the room temp is 21 and the external temp is low enough you will get condensation within the insulation, most lightly on the existing pb and this will create mould etc.

I know u will argue that is the new skimmed pb not airtight: it is to a degree but the drying of the new skim will be a good source of damp for the mould.

Similar considerations apply with the walls.

Slabbing walls with insulation as you propose needs to be done with care..

However dont take my word for it, have a read here of the breaking the mould articles:
http://www.josephlittlearchitects.com/papers.html

Should keep you busy till Euro 2012:D

Re the cold bridging, what I do at wall corners is that if the slab is say 62.5 ie 50 + 12.5 them remove the pb along one board for a width of 62.5, sort of lap joint if u will.

Thanks, Carlow. Great link and good advice.

Southern Comfort

No7 wrote: »

The link given above has some very good information.
In addition make sure you remove the existing finish on the walls back to the blocks. Not doing this will leave gypsum products within the wall that could suffer from any interstitial condensation and allow mould to grow.

As fara s the ceiling boards go why don't you just install more attic insulation?

Hi No7. I'd love to use more attic insulation but, unfortunately, the floor of a converted attic is above a large portion of the ceiling.....

Southern Comfort

Pride of Merseyside wrote: »

Hi carlow 52 u sound like a man in the no!!! im thinking of dry lining my walls. i live in an apartment at the end of the block,my daughters room is very cold and doesnt hold much heat was thinking of using the Gypsum Interior Wall Insulation would i need battons? dont want to make the room much smaller than it already is! room can be quite damp from time to time

For what it's worth, Pride, I recently spoke to an Xtratherm rep. Insulated plasterboard comes in 2 types. the first has a backing which is specially for dabbing and sticking straight onto the wall. The second has a foil back and is for mechanical fitting onto battens.

He told me that the foil backed one will give a lower U-value, if you use the same thickness of insulated plasterboard. However, not using battens would allow you to use a thicker plasterboard so I presume that would give you a better U-value still.

caesarthechimp

Southern Comfort wrote: »

the floor of a converted attic is above a large portion of the ceiling.....

If the attic conversion is in use and heated, there is no point insulating that part of the ceiling.

You won't get significant moisture passing through the polyurethane. Make sure the joints are sealed with mastic, and especially the base of the wall at skirting level. That's how the humidity gets behind the dry liners. If the external walls are exposed to weather, you may have to a apply a paint-on waterproof seal, because they won't have the heat from the house to dry them out.