NEW INSTALLATION in TIMBER FRAMED HOUSE

[speedster]

Hi all,

Just been to look at a new timber framed house to give a quote for new electrical installation.

I have wired and rewired many houses, but a timber framed one is new to me.

I have two queries.

Firstly, on the outer walls hich have solid insulation,there is a gap big enough to get cables between the slab (cellotex) type insulation and the inner plasterboard wall surface. Will these cables need to be derated (though they will be in free air and touching the inner surface of the plasterboard) ?.

On the inner stud walls,(100mm between inner plasterboard surfaces) insulation is approx 50mm thick.

Again, does cable need to be derated ?

Second question is about protection of cables in walls.

Will they need to be 50mm from outer surface of plasterboard ? (All circuits will have rcd protection).

Thanks for any advice.

Speedster.

 

[Zeespark]

Add 12mm for the thickness of plaster board, is there alot of difference in the cable calcs at worst?

AndyGuinness

 

[ProDave]

I do timber frame all the time, normal method up here, and no, as long as the cable is not burried in the insulation then no problem.

Tell the owner however not to skimp on insulation. I take it that's a 150mm frame. Up here it's normal to have at least 100mm if not 125mm insulation, leaving just a 25mm gap for services.

If he only fits 50mm now, he WILL regret it. The house will be so much warmer and cheaper to heat if he does the job properly now.

 

[speedster]

Hi, Thanks to you both for your replies.

So, just to make sure I've got it right.

There's a 10mm gap between the outer wall insulation (cellotex) and the inner surface of the plasterboard, so thats not a problem ?

Secondly, as long as there if free space inside the inner stud walls (i.e. the cables are not completely enclosed with insulation) then I don't need to derate the cables ?

By the way, the outer insulation (Kingspan) is about 150mm thick.

Best regards,

Speedster.

 

[ProDave]

Perhaps a diagram of the wall make up might help.

Normally the timber frame is 150mm thick. You fill most of it with insulation then the plasterboard on top.

You mention inner and outer. You say the outer is 150mm of insulation. Are you then adding another layer of insulation and counterbattens before plasterboarding?

As long as the cables are not sandwiched between two layers of insulation I don't see a problem.

P.S Celotex and Kingspan are different trade names for the same type of insulation.

 

[speedster]

Hi Dave. Thanks for your replies.

You've answered my questions.

Regarding the wall thicknesses. The OUTER frame walls are about 150mm thick and have Kingspan insulation in them, and thats all. It looks like there will be about a 10mm gap between the kingspan and the inner surface of the plasterboard. Enough room for the cables.

The INNER stud walls look to be around 100 mm thick (without the plasterboard). I have to check with the builder what thickness insulation will be going into the walls.I did see some lying around and it looks like 50-75 thick mm.

Speedster.

 

[ProDave]

I'm still slightly confused.

When you say INNER walls, are you just talking about the walls that separate one room from another? (internal walls) If so it's only normal to put insulation around bathrooms, and perhaps between adjoining bedrooms mainly for soundproofing.

If so the partition walls are normally 100mm if load bearing, but can be 75mm if not load bearing.

Beware that sometimes the internal walls are sometimes covered on one side with OSB or plywood before the plasterboard for wind bracing. When that is done, you need to know where your accessories are going and cut a clearance hole in the OSB or plywood, so you can then cut the correct size hole in the plasterboard for the accessory.

Once you get used to it, timber frame is a nice building method. No chasing out to do. Just ensure you have a good selection of sharp wood bits for your drill.

One builder I work for takes it one step further. The outside walls are 100% filled with insulation and covered with an air tight membrane to completely seal the house. They then counterbatten with 50mm horizontal battens as a service void, onto which the plasterboard is fixed.

Also get yourself a good load of protector plates. You will be drilling the frame members close to the surface. These are metal plates to nail over any timber you have drilled for a cable to ensure the plasterboard screws don't go through your cable.

 

[speedster]

Thanks again Dave,

Yes I did mean partition walls.

I hadn't thought about the osb boarding, but I did notice it in several places.

Also,I wondered about protecting the cables through noggins and timbers,and you've mentioned the metal plates.

Do you make them up out of sheet steel, or can you buy them ready made (are they galvanised) ?

If you can buy 'em who sells them ?

Sorry about all these questions, but if I do the job, I want to make sure it's done properly !!

Best wishes,

Speedster.

 

[ProDave]

Protecta plates Protecta Safe Plate Pack of 20 | Screwfix.com

You don't even need nails. They have sharp bits bent over that you just hammer into the timber

 

[speedster]

Good on you Dave,

I go to Screwfix every other day ! I'll get some in.

Regards.

Speedster.

 

[Doc Hudson]

Or TLC have two different sizes. Safe Plate Joist Cover - Protects Hidden Wires and Pipes

Doc H.