Protecting wiring

In what way? PVC is pretty resistant. Some plastics will leach out the plasticiser, but I suspect in that case it's probably better not to do anything which moves the wiring.

I've read about this problem many times. I'm prepared to replace the wiring if it's damaged. Since most wiring in NZ houses touches building paper I guess I'll just put building paper between the wiring and foam.

If in direct contact with electricity cables, polystyrene insulation can cause the coating on the cables to harden and crack, creating a fire or electrical safety risk. To avoid this, polystyrene insulation must not get into direct contact with any PVC coated cables. They should be separated using self-adhesive paper, polyethylene or polypropylene tape between the PVC and polystyrene, or by installing the cables through conduits."

"Foam" is not usually polystyrene, at least not in the UK. Simon.

Well my foam is polystyrene.

OK so I've got the roof off. Here's a photo of the wiring to the light in the middle of the ceiling.

But why did the wire sink into the foam? It's a short lighting circuit to a single socket in the ceiling. At most it would have had a 100 watt bulb in it, and for the last 5 years, a 20 watt CFL. So, less than half an amp melts the foam.

It's a chemical reaction between the polystyrene and the cable, not heat that caused that.

OK that's probably it. Look's like I'll be taking the rest of the house apart.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember sm_jamieson saying something like:

It's very common - as Aerobord, etc.