Internally insulating solid walls for better U Values

[John D v2.0]

could you stick metal back boxes onto a recessed insulation board with a bit of the pink foam?

Yes but it wouldn't comply with electrical regs, the box needs to be securely fixed. The face plate screws are pulling on the backbox so you'd have to be very sure of the connection, especially when you add on an end user pulling out a plug.
That's why i only went for the approved solution. On the uninsulated internal walls i fixed up a suitable noggin and fixed to that.

appears to be far cheaper to get the insulation and the plasterboard separately.

Yes the added value of fixing the plasterboard costs a lot. Probably due the smaller market which can stand a higher cost to save the labour.

I can get the 50mm celetex boards for just under £20 each. The same in kingspan is approximately £8 a board more. As i will be requiring approximately 30 boards is there any benefit in spending extra money on the kingspan?

No it's exactly the same

 

[padstar]

Yes but it wouldn't comply with electrical regs, the box needs to be securely fixed."

Plasterbaord fixings it is then

 

[Notch7]

So i have been looking at pricing the job for materials and it appears to be far cheaper to get the insulation and the plasterboard separately.

I can get the 50mm celetex boards for just under £20 each. The same in kingspan is approximately £8 a board more. As i will be requiring approximately 30 boards is there any benefit in spending extra money on the kingspan? They appear to do the same thing

Its the same u value. Celetex seem to use a very thin foil, but it does the job.

The easiest method is cover wall in celetex tape all joints. Then screw 50 x 25 vertical battens on, then plasterboard. Double up battens for radiators or use 75 x 25.

 

[JP_]

How long ago did you do it and have you seen any de-bonding from the block work since?

Have you noticed the difference since insulating? If you were to do it again would you bother?

Oldest is 2 years now. No sign of any de-bonding at all. Massive difference - house much warmer. Doing the floors is important too.

could you stick metal back boxes onto a recessed insulation board with a bit of the pink foam?

If you are careful you can cut out 25mm from the 50mm insulation. I had some 25mm boards so I cut it all out, then put in 25mm board, taped it all up with insulation tape, then stuck in the back box. With a 35,, back box, it should sit level with the plasterboard. Solid, no movement, no breaks in vapour barrier, no cold spots.

 

[padstar]

If you are careful you can cut out 25mm from the 50mm insulation. I had some 25mm boards so I cut it all out, then put in 25mm board, taped it all up with insulation tape, then stuck in the back box. With a 35,, back box, it should sit level with the plasterboard. Solid, no movement, no breaks in vapour barrier, no cold spots.

Any mechanical fixing back to the blockwork?

 

[JP_]

Any mechanical fixing back to the blockwork?

No. Glued, and then plaster was up to the box, all pretty solid. But no reason why you can fix to wall if you wanted.

 

[padstar]

Is Celotex acceptable around chimney breasts fi wood burners are to be installed?

 

[padstar]

No. Glued, and then plaster was up to the box, all pretty solid. But no reason why you can fix to wall if you wanted.

Would fixing back to the blockwork cause any form of cold bridging or is this being a bit OTT. Mindful that regs call for back boxes to be secured which i assume will require a mechanical fixing to solid wall.

 

[JP_]

I think OTT. You can always used the plastic boxes that have the plasterboard grabs that slide out - that will be secured to the plasterboard, and can be glue in place too.

 

[padstar]

I would use these but i can find any that you can fit circular conduit to. I want to run all the cable routing within the wall for the spark to pull his cables through so had planned metal boxes with conduit attached

 

[^woody^]

I think OTT. You can always used the plastic boxes that have the plasterboard grabs that slide out - that will be secured to the plasterboard, and can be glue in place too.

And how do these perform in an electrical fire surrounded by Grenfell's favorite type of insulation?

 

[an203888]

And how do these perform in an electrical fire surrounded by Grenfell's favorite type of insulation?

I beleive they should meet BS5733 so long as it doesn't exceed 63A..

 

[IT Minion]

And how do these perform in an electrical fire surrounded by Grenfell's favorite type of insulation?

They're going to use ACM rainscreen panels with polyethylene cores? No? Oh you meant to say the second favourite insulation material. The PIR was fuel in the fire, literally, but it wasn't the principal cause of the disaster.

 

[^woody^]

All fires need fuel

 

[IT Minion]

All fires need fuel

That sounds like the worst charity appeal TV advert ever. Remaining jokes withheld because, well, not really a laughing matter.

I'd class the ACM as more of an accelerant than fuel, although of course accelerants are a subset of fuel.