I have been asked by a local church group to advise on the possibilities for insulating the roof of their church hall.

I have given them the benefit of my lay person's advice (I've been studying in detail the possibilities for the various different types of insulation for my own projects for many years) but what they really need now is professional assistance from an independent surveyor - not a salesman masquerading as a surveyor whilst working for a firm that fits particular types of insulation.

The building looks somewhat like a Nissen hut but it is not actually a Nissen hut. This is just shorthand to describe the general shape. It has a curved roof (asphalt felt on top) supported by very strong concrete walls.

An internal view of the hall can be found here:

https://parishofbrentford.org.uk/wp-content/uploads/2022/02/st-faiths-parish-of-brentford-playroom-scaled640.jpg

The actual hall is about twice as deep as it appears in this photo.

They are looking at insulating the roof and replacing the original Crittall windows. The roof insulation could be internal or external, but external is likely to be ruled out on cost grounds. As also will be (I strongly suspect) replacing the windows like-for-like as well.

They have been quoted for spray insulation on the underside of the ceiling but I (and several others) have steered them away from this.

The building dates from 1957 and it has an asbestos survey report. There is asbestos in it. For certain the soffits and exterior end elevations are asbestos and it is quite likely (though nobody is certain) that the ceiling panels (that can be seen in the photo) are also asbestos. I have not seen this report personally.

There is a grant available from the local council to assist them with the costs of the insulation work.

Does anybody know of where they might be able to get some professional advice and assistance to take this project forward on a more 'eco' basis please?

The building is in Brentford, West London.

Might actually be a justified case of knock it down. Ideal for a EU grant!

If it was a flat asphalt roof, I'd turn it into a warm roof buy adding insulation board + another layer of waterproofing over the top. I wonder if that may still be possible on the curve using a suitably flexible - and therefore not to thick - insulation board, perhaps cork?

Thanks for all comments so far.

The building is actually in use seven days a week, in particular, by a nursery for 12 hours a day and it is the nursery tenant that has kindled interest in this.

Yes, it is the curve that is the big deal here. It would be so much easier if it were flat or even pitched.

I've a feeling they are going to be out of luck here due to budget constraints.