Thatch roof spaces

[flyingsparks]

Ok, so have a job coming up soon of rewiring a thatched roof space. Lighting only.
In the past I have either

-used swa, with a galv box above each light/switch drop and feeding the cable through the back of the box.

-used FP cable

-used PVC conduit

I have never used Ali tube cable (or seen it for that matter)

I can't decide the best route to take. Swa is ok but time consuming. not sure if FP is compliant or not? PVC conduit is again time consuming.
Not sure how cost of Ali tube compares?

Any thoughts, what do you do?

 

[Taylortwocities]

Eh? What's wrong with normal T&E?
There's no more risk using that in a thatched building than anywhere else, providing the cable is planned properly.

 

[sparkwright]

Last time I did a thatched cottage attic, it was deemed acceptable to use PVC twin, then board the loft floor completely with chipboard flooring - with only the loft light in galv conduit.

This was years ago, with rodent damage in mind.

Seems a bit misguided now, as rodent damage could still occur.

 

[bernardgreen]

It would be sensible to ask the insurance company what they will accept.

In my thatched cottage the potential for hassle with the insurance company was avoided by not putting any electrical wiring in the area under the thatch. It means using up-lighters and table lamps which look better ( in my opinion ) than pendant lamps.

 

[stillp]

I have a friend with a thatched cottage, whose insurance company insisted on Pyro.

 

[bernardgreen]

I am aware of a claim on the insurance for a non fire related incident of damage to a thatched roof. The claim was not paid in full as the wiring in the loft was found to not meet the insurance company's requirement.

Also check with what tools can be used in the loft. Some power tools are banned, angle grinders and anything that might make sparks. You may be required to have a fire extinguisher with you while working in the loft.

 

[flyingsparks]

The cables need to be protected from rodent damage but also I have heard protected from mechanical damage during re thatching (that I find hard to believe tho tbh)
I guess all insurance company's will vary what they want. So what would one put on an EICR if cables are found to be normal twin and earth without mechanical protection?

 

[Taylortwocities]

I guess all insurance company's will vary what they want. So what would one put on an EICR if cables are found to be normal twin and earth without mechanical protection?

If you are doing an EICR, surely your job is to report any deviations from BS7671? T&E will comply assuming its installed correctly.

 

[RF Lighting]

There is a regulation which requires installations to be protected from the external influence of flora and fauna.

I'd say that T&E in a thatched roof does not comply, and from a none regs point of view, certainly is far from ideal.

I've never worked on a thatched property, but I have worked in places where wiring has been damaged by mice, rats, squirrels and even wild rabbits.

I've found both pyro and steel conduit stops the problem completely. I'd imagine SWA would do the same, but it's sheath still makes it susceptable to attack, even though it's unlikely they'll penetrate to the live conductors.

I don't think FP200 would be good enough to either guarantee it'll prevent an attack, or fail safe if it is attacked.

I have never used ali-tube cable but from what I understand it's not much different from FP200.

What ever you do will be labour intensive. If it were my design I'd wire the switches by looping the feed and neutral in twin and earth going up the walls from under the floorboards below, and then use either steel conduit or pyro up the wall into the loft to the light.

This way you'll only need to thread and bend the conduit once per light or make off two pyro ends per light which should help reduce both material and labour costs.

I understand that RCD protection is also required for wiring in thatched roof voids, but it can be upto 500mA. Not sure if this still applies when using metallic containment though.

 

[bernardgreen]

Fire is the biggest concern in all thatched roofs. Any source of ignition is excluded from the loft space, that includes power tools and ( with some insurers ) inspection lamps without shatter proof protection of the lamp.

Dry thatched material dropping from the inside of the roof and laying on the ceiling below is like tinder and will ignite very easily.

The use of metal conduit or copper sheathed such as pyro earthed by a PME system has been seen creating a risk should the PME "earth" come into contact with something at true ground potential.

 

[RF Lighting]

I think that's taking your PME paranoia to a whole new level

 

[bernardgreen]

I think that's taking your PME paranoia to a whole new level

It is not my paranoia.... It was information from one of the thatched roof owners associations I contacted when buying this cottage. Some thatched roof owners are a bit paranoid but much of the advice has been formulated from experience of many owners over many decades.

In my opinion the risk of ignition by sparks between PME earthed metal and true ground earthed items at roof level is practically zero. That said there is a very large area of wire mesh on damp straw ( or reed ) on thick damp walls so current from "earth" to ground could be significant. Enough to make some insurers consider it

Ignition by a spark from a stone mason chiselling a stone in the loft is more likely.

Some thatch fires have smouldered for days un-noticed before being detected. One started smouldering in the loft when a defective chimney heated the dry inner layer of thatch. Many hours after the fire in the grate was out the increasing smell of smoke was noticed and the Fire Brigade called. The roof was saved.