Cottage Solid Wall Insulation?

[Doug99]

My son moved into a cottage last year and found the past few months extremely cold and difficult to keep warm. All internal walls had been dry lined by previous owner with plasterboard, which sound hollow when tapped which implies no insulation was fitted behind the plasterboard.

What are the options to install wall insulation? A little research online has suggested 'external insulation cladding'. But is there any way of 'filling' the voids behind the boards without their complete removal? Say, with polystyrene beads?

VMT in anticipation - DM

 

[RobinClay]

Sounds just the thing - unless you've ever tried to top-up a bean-bag !

The beads are electro-static, and are very difficult to shift - they cling to everything !

And they will escape if they can, through e.g. power sockets. Fire risk ?

Depending on the area of wall, *I* would probably strip off the plasterboard and re-board with insulated p/bd. P/bd is pretty cheap; and extra battens could be added to make the gap even thicker - existing is probably only an inch. Every inch of insulation is only about half as effective as the previous inch; 4" is probably the limit for cost-effectiveness. Depending, of course, on what material you use.


Or... but probably the expensive option... drill 8mm holes at 3 to 4" centres and squirt in expanded foam. Do it in horizontal rows, so that expansion has taken place when you start the next row. A 750ml can will do one row of 1" gap about 4 to 4.5m long. You will need to establish where the studs and noggins are first - the noggins will probably not line up with their neighbours. It may help to make a cardboard template for drilling the holes, to avoid the timber.


THEN you have the problem of ventilation, condensation and wood rot - is the existing buried timber treated ? Ventilated ? Does the existing skin have a vapour barrier ?

 

[Doug99]

Thanks Robin - Lots of issues to consider!

 

[ajrobb]

Polystyrene and PVC electrical insulation do not mix.

Plasterboard is surprisingly easy to work with. Don't be afraid of ripping it off and replacing it.

Depending on the size of gap behind the plasterboard there are several alternatives:

• less than 20mm - probably have to start again
  20mm - just use foil-backed plasterboard (see below*)
  50, 75 or 100mm - Crown DriTherm

If starting again, there are expensive alternatives like PIR sheets like Celotex GA4000 fixed behind non-treated battens or PIR-backed plasterboard like Kingspan K18 fitted onto treated battens.

*If the gap is 20mm, foil-backed plasterboard has low emissivity and can form a sealed reflective cavity with an R-value of 0.6. This is not enough to comply with Building Control (I think this kicks in if replacing more than 25% of the plaster on a wall). However, it is equivalent to 25mm of mineral wool or 15mm of PIR. It cuts heat loss through a single-brick 9" wall by about 70% and should be enough to prevent condensation.