Getting quotes on a new roof.

[JiltedJohnsJulie]

We have a rather leaky roof on our pre-war semi and now have the money for a new roof. I've asked one builder for a quote, he's coming in the new year.

Now I'm wondering what I need to ask when he comes and what to expect. As the house is old, what are our options on insulation?

Any advice at all gratefully received

[OnePlanOnHouzz]

You will need kingspan or similar - think the reg is approx 120mm thick now ?! Could be wrong - it's not in my usual line of work to know ...
will be cosy when it's done though !

[johnd2]

Cheapest insulation is about 270mm of wool, fibreglass or rock wool. Cheap but bulky.
If you want to board it out without losing floor height, celotex/kingspan would be about half the thickness but twice the price to buy. And fitting it is much more labour intensive.
The best solution if you want storage is probably 100mm of wool with about 70mm of celotex on top then chipboard resting on that.
A final option is boarding at rafter (roof tile) level which is better in some ways but can cause unseen condensation in the timbers unless you put the insulation outside (aka warm roof). I'm not sure I'd advise it but it would be an option!
Does any of that make sense?

[JiltedJohnsJulie]

The loft is used as an office, so a thin insulation is going to be better I think. The rafter one sounds ideal, thanks.

[johnd2]

Sorry just to be clear, the rafter one was the one i wouldn't advise. Its very hard to be sure you've eliminated the condensation risk unless you deal with VCLs and polythene sheeting. However if you go for that one anyway, ask the roofer about condensation and report back what he says. Depending what he says depends whether you can trust him with your rafters!

[JiltedJohnsJulie]

Thanks so much john. Useful to know and thanks for your offer of help

[MrCreosote]

When doing the roof, do not let them us felt. Spantech has a half shelf life of 75 years which means, it will take 75 years before it starts to decompos. Felt will only last about 40 years. Hope this is helpful.