Securing cables to PIR

[SuperJohnG]

I've added to 50mm PIR full cover to all my external walls. 

 

How's best to secure cables to the PIR which has an airtightness layer on it? The normal cable clips won't secure it and surely pull out to easily? 

[TonyT]

Are you adding battens for a service batten?

[SuperJohnG]

Just now, TonyT said:

Are you adding battens for a service batten?

Yeah. I will have a service cavity. But only 25mm. So too thin to drill holes in I'd say. Also to make life easier for sparks and to ensure the airtightness membrane isn't damaged using first fix I was going to have battens cut at 450 and 1150mm to leave space for cable runs on recommendation from @ProDave

[LA3222]

Most of the cables will run up and down bud rather than across so I wouldn't worry about the gaps. I did them and wasted a lot of time and effort doing so. As far as tacking the cables, no need. They will.stay put in the 'safe zone' - the cables are fairly rigid to be fair.

Edited July 14, 2022 by LA3222

[TonyT]

A little strip of foil tape will help hold them to the PIR.

 

not a fan of  25mm battens as what happens when you need to fit 47mm deep boxes?

[SuperJohnG]

10 minutes ago, TonyT said:

not a fan of  25mm battens as what happens when you need to fit 47mm deep boxes

I thought I needed deeper but the sparks seem happy with 25mm. I'd put thicker battens but I have an absolute load of 26mm thick roof battens bought during the height of the pandemic. 

[ProDave]

25mm battens and 12mm plasterboard will accommodate 35mm back boxes.

 

[TonyT]

11 minutes ago, ProDave said:

25mm battens and 12mm plasterboard will accommodate 35mm back boxes.

 

Yes but I said 47mm boxes

[ProDave]

3 minutes ago, TonyT said:

Yes but I said 47mm boxes

@SuperJohnG mentioned his spark said 25mm.  I was pointing out 35mm was a much better match to a 25mm void and 12mm plasterboard.

 

Not many things need a 47mm box,  bit if it is just one thing, you could hollow out the PIR locally by 10mm to accommodate it, and still manage to make it air tight with suitable tape or membrane.

[SuperJohnG]

13 minutes ago, ProDave said:

@SuperJohnG mentioned his spark said 25mm.  I was pointing out 35mm was a much better match to a 25mm void and 12mm plasterboard.

 

Not many things need a 47mm box,  bit if it is just one thing, you could hollow out the PIR locally by 10mm to accommodate it, and still manage to make it air tight with suitable tape or membrane.

Yeah 35mm was what they are happy with. Pretty much everything on external walls is main ring or light switches and I only maybe have a few dual switching points. 

 

What's 47mm usually for? Cookers etc? Big cables? 

[TonyT]

Cookers,  

I used them for a few data/aerial points makes live easier for bending radius of cable etc

[Carrerahill]

3 hours ago, SuperJohnG said:

I've added to 50mm PIR full cover to all my external walls. 

 

How's best to secure cables to the PIR which has an airtightness layer on it? The normal cable clips won't secure it and surely pull out to easily? 

Get a length of plastic trunking, cut it into pieces 20-25mm long, stick them to the PIR, cables in, lid on - rudimentary bracket.

 

Another option, which is a bit more commercial house builder spec is to use high impact UPVC conduit glanded in.

 

This is what is on standard notes of most electrical drawings we issue for domestic projects (commercial is a whole different ballgame with proper containment etc.):

 

THE INSTALLATION SHALL BE UNDERTAKEN UTILISING LSF CABLES COMPLYING WITH BS 6004. THE CABLE SHALL BE CLIPPED WITHIN THE CEILING VOID & ROOF SPACE, PROTECTED WITHIN RECESSED DROPS AND ABOVE BY HIGH IMPACT PVC CONDUIT, AND BE INSTALLED WITHIN THE 'SAFE ZONES' PRESCRIBED WITHIN BS:7671. CONTAINMENT SHALL BE FIXED TO THE BUILDING FABRIC IN A NEAT & TIDY MANNER ADHERING TO THE FIXING DISTANCES AND METHODS AS PRESCRIBED WITHIN BS: 7671 AND AS PER THE MANUFACTURERS RECOMMENDATIONS. WITHIN CEILING VOIDS, PLANT ROOMS AND STORAGE SPACES THE INSTALLATIONS SHALL BE SURFACE MOUNTED.

 

In other words, if this was a commercial house builder, we would want to see metal pattress boxes, with conduit glanded in and fixed within the wall to create a cable safe zone - it also helps for pulling cables in the future as it gives a good route up a wall.

 

Usually sockets would be aligned nearer a stud so the conduit can be fastened to the side of a stud. 

 

 

 

 

[JohnMo]

I just added a strip of OSB around the top of external wall (for clipping cables to), then 50mm battons vertically and battens at the top and bottom of the wall horizontally (for fixing plasterboard and skirtings to).