Insulating Solid Brick Wall

[EViS]

One of our home's walls is solid (the remainder are cavity and filled). We are thinking about insulating this solid wall internally and see three options on how to do this however which is the most common solution?

1. Screw battens to the wall and then fix PIR backed plasterboard to these. [Do we risk the battens rotting after some time? What thickness of PIR would be recommended?]

2. Create a stud wall away from the existing solid wall and then insulate this? [Will 100mm mineral wool suffice in between the studs?]

3. Fix PIR backed plasterboard with adhesive. [Would we need to remove the existing plaster which is held firmly, about 1/3rd of it has already come off which does make the walls fairly unlevel?]

 

[joe-90]

I'd go for No. 1

 

[freddiemercurystwin]

No 1 would be best although it is a bit cheaper (if DIY) to use separate PIR insulation and foil backed plasterboard. Use the thickest insulation you can afford (no more than say 70mm though) if you are prepared to lose the space internally. Celotex, Kingspan etc they are all much the same. As long as the external wall is sound there should be no issues with the timber degrading.

 

[EViS]

A couple of questions on this then:

a) Is there any real benefit installing a DPC between the battens and the solid wall (admittedly the screws will pierce the dpc)?

b) I take it that a moisture barrier should be installed between the pir and plasterboard (if we do not opt for plasterboard backed pir)? Installing this between the battens and pir would be counter-productive, correct?

c) Are there any Building Regulations we should (or can) meet which determines the thickness of insulation to install?

 

[freddiemercurystwin]

1) Are the walls damp at all at the moment? If not then there seems little advantage, though it would not do any harm.
2) The foil on the back of foil-backed plasterboard acts as your vapour barrier. If using foil faced insulation then no need for foil-backed plasterboard.
3) If you are renovating more than 25% of the external walls then Building Regs apply and technically you should go through Building Control. You would need to achieve a U Value of 0.30 and to achieve that (assuming you have 9" thick brick walls you would need 72.5mm of PIR insulation.