Timber framed buildings and celotex

[dlt27]

Hi all, I have been asked to install new electrics to a wooden lodge / chalet. It is a single storey very large building with a flat roof.
I have a few questions to ask and would be grateful of any answers.
1. Is it ok to wire in Twin and earth or should I be using LSF / LSZH?
2. At the moment it is just cladded on outside with stud walls built. I find out construction of interior walls tomorrow. If it is celotex in walls and in ceiling how do you run the wires. I know some walls are battened off with roofing batten so cables can be run down front of celotex, but what if like I have seen in the past this isn’t the case and celotex is flush with the plasterboard?
3. When running cables in flat roof how do you do it if same scenario as walls and celotex flush with the plasterboard? If I drill holes through neutral point of joist and quarter of the span in flat roof they will be where the celotex is so how can they be run?
4. They’ve asked for spotlights everywhere in celotex so the thermal barrier will be broken. In the past I’ve always asked the builder to ask building inspector and also asked 3 building inspectors myself and they don’t seem to care and say it’s fine. One inspector did say it’s good to put 25mm celotex over the hole cut out for spotlight, but never seen it done!
5. They want about 10 outside lights, but how do I do them because vapour barrier will be broken?
( I will be recommending arc protection to the install).
I like to think I am a good electrician who takes pride in his work, but nowadays nothing seems to be straightforward and I seem to spend my whole life thinking about how I’m going to do the job rather than doing the job!
I just wanted everyone’s honest opinions on what they would do in these scenarios.
Most posts of people I see on the forums tell you what not to do, but don’t help with getting over the hurdle.
Thanks to anyone who takes the time to answer.. much appreciated

 

[SparkySy]

The last wood cabin I did had an air gap about an inch wide in the roof and on the walls so it made it easy to wire. All you can do is see if you can come to some arrangements with the Builder/ carpenter on where the cables will go without being in the cellotex or de-rate the cables accordingly due to the insulation!
For downlights I fitted some 6watt enlite 120mm diameter 12mm thick ones, the only space needed above them is for the driver and a suitable connection box e.g. wagobox lite. They were good fittings and have had no failures like these,

Aurora Slim-Fit Round Low Profile LED Downlight

• Warm white 3000K, cool white 4000K• Pre-wired 500mm 2 core cable• Non dimmable• Average life 25000 hours• 120° beamThe Enlite range of Slim-Fit™ low profile downlights are engineered to deliver superior light output and uniformity utilising the latest edge-lit LED technology. 6W: Diameter...

www.toolstation.com

As for the outside lights all you can really do is seal well around the cable entry with sikaflex or CT1 (can highly recommend both) and keep your fingers crossed
Hope that helps a little
Sy

 

[dlt27]

I suppose they would work on a log cabin, but those lights aren’t fire rated if I remember correctly! Did you use t+e?
Thanks for the reply

 

[Zerax]

Can you speak to the architect ? They should have considered services as part of their design.

 

[SparkySy]

I don't think they are fire rated but does it matter as there is only roof and cellotex above them?
Yes I used standard twin and earth, If the cable is behind plasterboard then it's at least half hour fire rated! the one I did was 9mm ply lined inside and was a bugger to cut out for the lights!

 

[Pretty Mouth]

Flat roofs are often warm deck - the insulation boards are installed above the joists, rather than between/under. Doing it this way removes the need to ventilate the roof space, and means the ceiling void will be empty.

Cold deck roofs, on the other hand, have the insulation between and under the joists. This method of construction has to have a ventilated gap above the insulation, which you could run cables in.

If you have to install downlights in the insulation boards, you can use insulation coverable downlights. After you have cleared enough celotex to fit them, shove a few handfulls of rockwool up there, then fit the downlights. The rockwool will keep the insulation continuous and prevent a cold spot around the lights.

 

[Pretty Mouth]

Also, I personally wouldn't worry about piercing the vapour barrier. Just keep the hole as small as possible, nothing disastrous will happen.

 

[dlt27]

Thank you all for being so honest. When I’ve googled before everybody says you shouldn’t do any of the above, but don’t say how you could do it. I thought it might be warm roof, but not sure so would be easy if it is. I could probably run cables in ventilation space on cold roof, but what about drilling joists as wouldn’t be through the neutral axis.
There isn’t an architect involved.
It is built within the boundaries of an existing property so doesn’t even need planning permission, however it has 2 beds and is the biggest lodge I’ve ever seen.
I will update tomorrow when I know more. This is the drawing they gave me…
Thanks again

 

[dlt27]

Drawing for the lodge…..Thanks

 

[Pretty Mouth]

I could probably run cables in ventilation space on cold roof, but what about drilling joists as wouldn’t be through the neutral axis.

I would drill them in the zones designated for notching.

There will be firring strips on top of the joists to create the fall on the flat roof, so one end of each joist will have an extra 50mm or so of timber on top. Drilling at this end of the joist gives you a better chance of getting the holes 50mm below the top.

 

[DPG]

Surprised something that size didn't need planning permission. Its basically a 2 bed bungalow.