Question on Wickes Cavity Insulation slabs

[BAGGIES1]

hi,

has anyone tried these?
i'm thinking of using them in wall insulation however the mind boggles when coming to U-value and r-values and the like.

currently i'm looking at a dry lined wall.
the brick will have a DPM and 3x2 battens. then with 9.5 foil backed plasterboard(9.5mm was all wickes did.i'm looking at using 12.5mm std plasterboard to go over top left over from a previous project)

i've been looking at 50mm or 65mm (and poss 30mm high density) insulation slabs.

the thing is my false roof i'm putting in will most likely have 170mm wickes rockwool. in that case will i need to go to far with the wall insulation?

also surely these slabs provide more thermal insulation than stuff like rockwool, right?

i've looked at celotex and kinspan but that is going to go well beyond budget.

any thoughts...i guessing its borderline on the ole building reg questions...

any feedback would be great thx.

 

[Richard C]

Is this an existing room or new extension?

 

[BAGGIES1]

Existing room. Converting 7.5 x 2m outbuilding connected to house in to a kitchen.

 

[Richard C]

In the process of replacing a window with French doors, I ended up ripping out the entire front wall of an existing flat roof extension. I replaced the old 3 inch, inner blockwork with 4 inch & used 70mm cavity bats; the other existing walls have a 50mm cavity & no insulation at all at the moment. I used 9.5 plasterboard (left over from elsewhere) dot & dabbed directly onto the new block wall which is just about to be skimmed. I’ve used 12.5mm foil backed board on the ceiling, fixing this directly over the old boards, mainly to get rid of the grotty Artex but also to give a bit more insulation; the existing flat roof is a warm roof construction with 200mm of Rockwool insulation.

BC were quiet happy with all of this but did come out to inspect the new lintel, cavity closers & insulation. The only difference I can see in your case is that you are converting an outbuilding rather than doing renovation on an existing, habitable room as I am. I’m not sure but you may have to bring the whole lot up to spec with regard to the latest regs! I think current min cavity is 70mm for walls; the level of insulation you propose on the inside should be well within the regs. but 170mm in the roof may not be enough - I think it’s 300mm now. I think you should go talk to BC, better to be safe than sorry!

 

[jono_h]

Thety're looking for 270mm now. 100 or 170 (depending on depth of joist) between joist and then 170 or 100 over the top (at right angles)

But the last advice is sound. Phone BC they'll answer it in a couple of minutes and will be very happy to do so.

 

[BAGGIES1]

Thety're looking for 270mm now. 100 or 170 (depending on depth of joist) between joist and then 170 or 100 over the top (at right angles)

But the last advice is sound. Phone BC they'll answer it in a couple of minutes and will be very happy to do so.

cool...... phoned BC and they said 250mm.
just curious fill over joints - at right angles??

i cant picture that...can you explain further or am i missing the obvious?

 

[Richard C]

Thety're looking for 270mm now. 100 or 170 (depending on depth of joist) between joist and then 170 or 100 over the top (at right angles)

But the last advice is sound. Phone BC they'll answer it in a couple of minutes and will be very happy to do so.

cool...... phoned BC and they said 250mm.
just curious fill over joints - at right angles??

i cant picture that...can you explain further or am i missing the obvious?

That's JOIST not joint! jono is probably referring to a conventional pitch roof with space above the ceiling joists; one layer of insulation is laid between the joists (depending on the joist depth) with the second layer of insulation laid over the top at right angles to the first - total thickness 270mm. In your case, just make sure the false roof has enough space above the joists to accommodate the required insulation thickness; not knowing your circumstances it’s difficult to imaging how you will lay a second layer across the joists if you don’t have access into the roof void! If in doubt go back to BC again & explain, they may offer to accept an alternative solution.

In my case, the original, 60’s roof only had 200mm joists with the flat roof fixed directly to the top of the joists, which is one of the reasons why I decided to fit new 12.5mm foil backed boards over the original ceiling. As it was an existing extension, there was no requirement on me to bring the insulation up to current thickness; just as well as it would have meant a complete re-roof job.

 

[jeds]

BC are quoting requirements for new build. If you are upgrading an existing element the required U-value for a roof is 0.25W/m²K.

200mm mineral wool will provide this easily - in fact 170mm will do it.