Redbeard

Thanks @sgt_woulds. I was assuming VCL on sub-base and PIR or similar non-breathable ins'n. Good clarification though re WF.

No idea how I came to answer a 2-year-old post! Nevertheless if anyone is interested in the life of (some) sleepers note that the first '10' above was a misprint. It should read 5 (max) years left.

My first thought was that in a Warm Roof (note the initial capitals) you don't need vents - indeed there isn't anywhere to vent unless you want complete thermal by-pass. Then I wondered if by 'warm roof' you mean insulated between and perhaps also under the rafters, giving you a roof void which is warm (and a heated volume which is greater). A true Warm Roof has all the insulation above the rafters. BUT if you are simply talking about the oversail and the rafter ends then maybe there is some argument for ventilation there. However I have doubts as to whether that air will flow enough to purge the area of vapour. Ventilation generally needs 'ins' AND 'outs'. Diagonally-opposite is always good. If I have completely misunderstood please ignore all of this!

How long are you planning to live there? I had treated softwood sleepers laid to retain approx 700mm soil around 10 years ago. They are noticeably rotting and maybe have 10 years left. I am now 10 years older and wish I had used masonry.

Welcome. I'd suggest dense, breathable insulants such as rigid wood-fibre or cork. You/we will need to try to build up a 'picture' of the 'slightly moist' nature of the marl. Breathable insulants can be a help to breathable walls. They are not an instant solution to wet walls. If this is a conversion, how are the internals finished? Plaster? If so, gypsum or lime? Plasterboard? Is it insulated or not?

Tiles?

How deep do you have to dig? Assuming you maybe need to excavate the connection, take out a 'T' joint and replace a straight section the digging is probably the worst bit. Assuming the drain is circa 100mm you can get sleeves with jubilee clips to span the gap (or 2 smaller sleeves and an infill bit of pipe if it's a wider gap). Cross-posted with @ProDave.

No. I have had a couple of situations where (I cannot remember quite why) I was a little suspicious, and had a sample tested to be on the safe side, but NADIS (no asbestos detected in sample) was the answer.

Do you mean asbestos fibres as 'long hairs'? If so, no. I am not, definitely not, an asbestos expert; just someone who is unlucky enough to have encountered it quite often in the course of my work. Don't forget the PPE when you take your sample!

Check the HSE guidance before you take the sample.

Cut out a small section having sprayed it with shaving foam*, then as the board comes away, spray liberally with water, take sample, send off, box up. I, too, have never seen asbestos fibres as long hairs. I suspect you will find those are from an animal, but until you know it is unlikely to stop you worrying. I have been in this position. Expose a little of the offending material - ever-so-carefully, as explained - send off a sample and get clarity. * The shaving foam is not as ridiculous as it sounds. HSE do, or at least used to (I have not checked lately) have it as a way of containing fibres, particularly for suspected asbestos cement soffits.

If you have already instructed the builder to proceed with the works based on the price given then you have a contract *at that price* and I would argue it's too late. Yes, it sounds like it 'stings', but I think the 'price-change ship' has sailed. Yes, the builder could provide the fabricator's quote but you have a contract at the price you refer to. It will loom big for a while and then something else will crop up, and it will seem 'small beer', possibly while you are sitting in your new extension savouring a small beer...

Too late! @JohnMo has pipped me to it. They could also have been in line with the rafters but the principle is exactly the same. Thanks @JohnMo!

+1. Bite your lip, have patience and put it down to experience. Sorry, I wish I could tell you something you'd rather hear, but @JohnMo is exactly right.

Look up 'Larsen Trusses'. Lightweight 'separating rafters' attached by plywood or softwood 'separators' to the rafters. They are most often used on the outside walls of timber framed buildings to add lots of space for lots of insulation without adding lots of weight. My refurb of my room-in-roof space will use them (effectively a new, thinner, rafter 'dangling' below the existing). I have already drawn it and had it appraised by a structural eng'r to make sure the exg structure will not be overloaded, and it has proved OK. It allows me to use 'friendly' materials (weight included in the submission to SE, of course) rather than PIR. Note that unless you can get solid mountings for your 'under-rafter' in masonry elements all the weight will be on the rafters and any purlins they sit on, so the appraisal is essential. Even if you can get a mounting on masonry it is still a structural alteration so still needs SE 'blessing'.