approx cost to correctly insulate roof

[noseall]

It's impossible to fit that vapour barrier on a re roof it's all well and good on a new build or extension

I never said it was. A lack of VCL may or may not be relevant. There may already be one. There may not be a lot of condensation migrating up there at the moment...or there may be in the future.

So put nothing in at all then??

What I said was do it robustly and correctly. If some ape of a roofer rips out 50mm insulation with an air gap and installs 75mm insulation with no air gap, then he stands a chance of making things worse, particularly if he say neglects any other form of mechanical venting.

There are a lot of roofers in the trade who still know very little about the building reg's side of roofing, especially those that learned the trade via site work etc. The reg's side of things is often handled by main contractors or project managers etc. A lack of understanding how condensation works does not help either.

 

[superdon]

Cheers all. He's starting this week so will let you know what happens.