Insulating attic roof – please give me your advice

[fluffedup]

I’m thinking of getting the attic boarded out and the roof insulated – not the floor of the attic, but the roof itself, giving an insulated loft space that will be better for storage and could be used as a quiet reading / study space. I’ve read that it’s called a warm loft.

This is more difficult than just boarding out and insulating the floor of the attic (cold loft) since you have to be careful not to create damp in the roof, and the building inspector has to be involved.

The roof is not high enough to allow conversion to a proper room with enough height to stand up in, so it would not ever meet the building control requirements for a proper room, not without adding a complete new, higher, roof. (I am in England.) That’s fine as I only want an extra storage area but I don’t want the stuff stored up there to be damaged by damp or extremes of temperature. I would also want to add a velux window.

I am worried that the cost may make this idea unfeasible. The house is detached with a footprint of 8m by 6m but of course the usable attic space would be much less because of the eaves.

Has anyone else done this and what would be your advice?

We also want to get the roof tiles replaced and have found someone to do this, but should the boarding out / insulation be done before the new roof tiles are added, or after, or does it not matter?

Insulation between rafters and under
Ensure an air gap is maintained in order to prevent moisture being trapped and rotting the rafters.
You do not need to replace tiles in tandem. The two jobs are separate.

Thank you @DrPrunesqualer

I've been doing some googling - if you are going to replace the roof tiles, as I plan to do, you can put a breathable membrane and insulation over the rafters before replacing the roof tiles. Then put more insulation between and around the rafters. Apparently you can end up with your roof better insulated than your walls.

I need to find a local firm that know what they are doing as this could go horribly wrong if moisture got trapped. I also need an idea of the costs.

If you put insulation above the rafters you will raise the roof level
This will have a knock on effect in terms of cost and work with the fascia, soffit and guttering/downpipes also needing to be upgraded

Id stick to insulation between the existing rafters as a minimum and under if you have to head height in the loft
as detail above