dry lining best option

[pippasdog]

hi any help /advise will be greatly appreciated i am dry lining an existing 9" solid wall on my extension i have used a product called RIW to tank the wall i then intend to insulate using kingspan then dry line on top of that . I know the usual practice is to dot and dab which i intend to do , the problem being the walls are thermalite and i intend to fix kitchen units on the finished wall . i am also aware i can use resin fixings which i have already got .
however what i would like to do is fix a 3" strip of 3/4" ply horizontally along the lengh of the wall using the resin fixing on top of the kingspan for my kitchen units .
The question being what product is best suited to fill the void (3/4")between the plasterboard and the kingspan i know i could use polysterene however i am also aware that pvc cable will react aginst polysterene and i dont wish to go down the route of conduit for my cables .i also dont wish to use timber batterns to fix the plasterboard
thanks again any help greatly

 

[ajrobb]

If the insulation has a low-emissivity coating (e.g. aluminium foil), I'd leave the gap empty as a reflective cavity gives pretty good insulation anyway. I've seen an R value of 0.644 claimed for a 20mm cavity next to Proctor Group's Reflectatherm foil. Just make sure you use a continuous strip of adhesive around the edges to seal the cavity. As you say, I don't think polystyrene and PVC should touch.

I didn't think it was normal to dot-and-dab onto solid walls. Have a look at the Celotex application page. Even with dot-and-dab, I think you should also use some mechanical fixings to hold the plasterboard to the external wall - often a single line of screws half way up the wall.

Yes, maybe you can fix 18mm plywood strips between the insulation and plasterboard. These could be attached to the external wall through the insulation as you say. These can then take the wall units. If you extend the strip along the whole wall, maybe this would also be adequate mechanical fixing for the plasterboard. Plasterboard is supposed to be pretty good at supporting vertical loads, the battens/strips are there to take the horizontal loads. I've seen some kitchen fitters hang wall units just on plasterboard but I couldn't recommend it.

 

[pippasdog]

thanks for your reply ajrobb most helpful, i originally did use battens to support the insulation however the local council building inspector just happened to mention last week about doting and dabbing which i have now done . however i think you are right after reading the link , i have noticed the adhesive appears to have pulled the foil away from the insulation in places, therefore i have gone back to my original plan of using battens ( not to support the insulation its now glued to the wall ) and conduit for the cables and filling in the gap with polystyrene hopefully this should be ok . i thought building inspectors were supposed to know their stuff oh well . thanks again for your advice most appreciatted

 

[PrenticeBoyofDerry]

normal practise when dot'n'dabbing foil backed boards would be to use nailable plugs as a mechanical fix, this would help but not prevent movement, but d'n'd of foil back is not really recommend.

 

[ajrobb]

filling in the gap with polystyrene

Assuming the conductivity of EPS is 0.36 then a 19mm service void filled with EPS would have an R value of 0.528 and this is actually slightly worse than the R value for a reflective cavity of 0.644 (Refletatherm data sheet). So you might not gain anything with the EPS except a headache with PVC cables.