wall chasing

[Stephen]

Hello,

I would like to add some sockets along the lounge wall. Is there a preferred direction for wall chasing? If I chase vertically then that would mean having to lift the floorboards above and drill through joists. OTOH if I chase horizontally along the wall that would save much of the work of floorboard lifting and joist drilling and make it a simpler and quicker job. It would save cable too, as I wouldn't need to keep going up and down. But is it considered bad to chase across a load bearing wall? It won't be a deep chase but still, better safe than sorry?

Thanks in advance, Stephen.

[Stephen]

Sorry, I forgot to add that the lounge floor is thirty year old concrete that even diamond bladed angle grinders won't cut, it's so hard! So I cannot chase up, only down.

[Tim S]

Stephen coughed up some electrons that declared:

Building regs say you may chase horizontally upto 1/6 of the depth of the wall and 1/3 for vertical chases. I tend to interpret this as being 1/6 (1/3) of the brick into the brick which seems perfectly reasonable[1]

That buys you a "free" 10-20mm depth of the plaster.

Many of my chases didn't touch the brick and those that did only went into it by 10mm or so. So not much to worry about.

17th Ed IEE Wiring Regs say horizontal and vertical runs from an accessory are fine too.

HTH

Tim

[1] Unless you subscribe to the School of Structural Plaster like some builders I know...

[Jules]

Ha! Best thing to do having enountered the signs of one of those at work is to glue some structural wallpaper over the top and forget about it ;)

[Jules]

What are you, a man or a mouse? Out with the SDS and chisel bit... ;-)

[js.b1]

I am almost certain AD BR "A" use the word "leaf".

Thus chase limits apply to a 100mm house brick and not overall wall depth. Not surprising as usually the inner leaf is load bearing re roof & floors. Taking even 16% of the entire wall thickness out of the inner leaf would not be pretty.

That limits you to 16mm & 33mm for horizontal & vertical chases into brick respectively, plus 16mm plaster on top. That combined 32mm is sufficient for 20mm & even 25mm round conduit, oval makes it simpler of course. So the limit is pretty immaterial.

If you are in Germany they have about 200mm of PIR insulation now so the issue is how to rescue people & tools lost in the new wilderness. Might just as well dispense with the building and just hot-glue PIR igloos together with a splash of masonry paint. The cost benefit of

65mm (UK) to 200mm (Germany) has a long payback period, something like =A325 saved compared to =A3250 saved - unless the Germans are using 200mm PUR which is inferior to PIR.

[Stephen]

Thanks.

Is there an advantage to vertical chases in that you can leave a bit of slack cable under the floorboards above, whereas with a horizontal chase there is nowhere to hide a spare couple of inches of cable?

[<me9]

Use a 35mm box and there's room enough for a few spare inches.

[John Rumm]

With a straight horizontal run between sockets, its trivial to pull through a new cable if its in conduit, so hardly worth worrying about.

[Stephen]

I had forgotten that. Last time I wanted some floor removed I hired a

10kg breaker. That worked where the angle grinder would not. I see Screwfix sell Erbaurer breakers cheaply, I wonder ;)

[Stephen]

Can you do that? I hadn't realised. I thought the cable had to be as short and neat as possible.

[Stephen]

That's true, I hadn't thought of that. It could be a pain rewiring vertical runs because it would mean lifting boards and dropping wires down the wall, which might not go to plan but you are right, it should be much easier to rewire a horizontal section if too much gets cut off. So are we of the opinion that horizontal runs are best?

Here's a daft question: what should you use to fill the gap around the box? I've always sued plaster but I saw Wickes selling cement and one of the recommended uses was for filling around back boxes but it was also listed as a suggested use for their mortar too. Is any one better than any other?

Finally, I see on the FAQ that there is a tool for removing the insulation from the middle of a section of T&E without cutting the conductors. What is such a tool called and who sells them? I know I don't need one for this job but I just happened to spot it whilst reading the FAQ, which is excellent BTW.

[Tim S]

Stephen coughed up some electrons that declared:

I'm using 35mm boxes as standard, even on lighting, except of course where

47mm is required.

"Good workmanship" is the phrase. If you engineer it so you have the space to loose a bit of slack without straining or crushing things, then it is fine.

But 16mm oval conduit is the answer - cheap as chips, virtually no extra space needed in the chase and the cable can be trivially repulled later if required.

Cheers

Tim

[Tim S]

Stephen coughed up some electrons that declared:

If they involve less cable then they are to be preferred as your voltage drops and earth loop impedances will drop too (both are a Good Thing). But that's an edge case argument unless your circuits are massively long to begin with.

Anything you like.

For little gaps I just wedge polyfilla in. Bigger gaps a bit of bonding or one coat plaster works well. For massive holes or ones on the edge of a wall I sometimes use a bit of 3:1 cement mortar bonded with a cement slurry to ensure that bit won't drop off at an inconvenient moment later.

Something like:

's a different make but most of them work in a similar way. They are very handy if you're doing a lot.

HTH

Tim