Gordo

The cold timber deck between EPDM and insulation will be vulnerable to decay there is no doubt. To do this properly their should be a ventilated void between the deck and the insulation in your second option. You have been warned ? impermeable weatherproofing layers are usually laid direct onto rigid insulation from my experience. No issue with walking on insulation doing this?

That explains sprinkler system. Three storey now & open plan GFL so no protected stair. All the same “no one has ever died in a building with a sprinkler system” stands but may not be code compliant.

With a sprinkler system who needs fire doors. No one has EVER died from fire in a building fitted with a sprinkler system.

I wouldn’t recommend timber between insulation and EPDM. It will get damp from condensation and be vulnerable to decay.

Reviews are open to abuse and not trust worthy. Personal recommendation usually best. Or membership of a certification scheme like federation of master builders or such which will step in if unhappy. No guarantee but better than nothing

Charters institute of building or royal institute of chartered surveyors or chartered association of building engineers with a specialised in building surveying. You will pay for their membership but have some comfort in expertise / professionalism

BTW. Don't expect flat roof fitter to do or advise on joinery work or plasterboard, structural or insulation etc. That's not their specialism IE where they make their money. best to get a joiner to price and he can sub in the other trades as necessary. Also that brickwork pier looks way to skinny to be structural sound (unless there's a post in there) but suppose it's lasted this long. All very ropey work

Yeah that all looks like a bit of a bodge job. Wall plate on outer brick leaf vulnerable to decay and No obvious lintel / beam over window to support flat roof joists. Window is doing a fine job of support tho lol. Joking aside it’s Not going to straight forward job to sort that out properly as there is so little depth to work with. Likely a heavy angle iron or channel section (consult a structural engineer) And as Dave said the ventilation is also a problem. Warm deck advice is sound under new weather proofing layer.

Yeah I agree on drainage to floor voids but never gave detailing much thought. I have experience of a few flooded/ponding sub-floors. Especially with the drive towards level access for wheelchairs raising GLs leaving void vulnerable to ponding water. Wouldn’t want to provide a route for vermin and like either or for ingress of ground water. Maybe a untapped gully connected to a BIGT above water line?

What is a “protected solum“ that’s new to me. I assume it is some form of sub-floor drainage arrangement? I would always recommend some drainage of sub-floor voids but haven’t seen any authoritative guidance on subject

I be in favour of leaving a quite a few perpends open for drainage. I recall an extension being built and the ground water was literally squirting out of a perpend when soil was excavated. The original building was a ground bearing slab too. I was amazed. Understand it did so for days after. No damp in the original building either

25mm thick sounds quite thin. I would have considered 38x50mm as a minimum but maybe I’m too conservative. Then again if the battens were broader than 38x 50mm and had two faces planed / regularised down to 25mm and the battens selected for their structural quality ie with minimum notts, shakes parallel grain etc they would likely be fine. A good joiner should select these

I’d second that. 100 blocks per day per block layer. Mind you I have seen footing block work laid with a navy’s shovel in the past so bet they laid a lot more than 100 a day lol I’d say a course or two a day seems near the mark. Day rates are a bit of an open chequebook you have to crack the whip & supervise quality & output

Some 8x2” collar ties bolted to say every 3rd rafter at purlin level should help rafters would help a good bit

That sounds plausible enough upgrade to address sagging ceiling. Don’t think it will help with sagging rafters. Best use liberal wood glue and screw fixings to existing timbers and best avoid or at least keep splicing to end 1/4 of spans (defiantly not in centre). To fix properly to existing timbers the spliced timbers would have to be butt jointed and then spliced with a 2m length of timber I would suggest.

Some flat roofs are designed to be fully submerged in ponded water. I think the idea is to avoid thermal shock on membrane. Never saw it done and don’t think it popular in UK. I would not fret over ponding water on a flat roof it may arguably be beneficial in a smaller scale roof so long as the joints are good.

I would be careful about this solution. 4x2 would still be over spanned and deform. However if it was properly fixed to existing timbers this would be an improvement but still likely be over spanned (would need structural calculation to confirm). Adequate fixings of the two timbers to structurally work together would be problematic. The original structure would be considered sub-standard today, so much better to use new timbers which are much deeper to suit span, but that still leaves the rafters over spanned unless the new ceiling joists are designed to support the struts to rafters. Then the new ceiling joists are likely to be massive IMO

Thought who’s resurrected this old thread. So wasn’t going to comment about the madness of anything other than option 1. Until I got to the feedback. You made the correct choice after listening to all the various opinions and advise offered to you. BS are just guidance for best practice. BC do not enforce BS and as the roof did not contravene the performance requirements of the regulations (the approved documents are not regulations) they could not force you or the builder to do any remedial work. Obviously they would prefer you follow best practice guidance

Yes I realised you ment profiled GRP panels. Yes I guess cosmetically, thermally and for light they would be inferior to multi cell polycarbonate for domestic, but for industrial cladding better IMO.

This was a common enough roof structure back in the day., when times were tight and standards were more of wing and a prayer affair. 3x 2 ceiling joist spanning what looks like say 12’, while also taking the load from struts to rafters lol. You wouldn’t dream of it now. It isn’t likely to fall down just deform more and more over many years. The struts were supposed to go close to a wall but this was poorly interpreted at times as we see. To sort it proper would be expensive ie steel purlins (shims to rafters) with hangers and runners to support the ceilings. I don’t think it practicable to reverse the deformation in rafters but ceiling joists should be quite doable. Then with the addition of hanger & runner the existing ceiling joist spans should be reasonable. I would guess this will be the engineers solution. An alternative would be to fabricate a deep timber lattice beam including the hangers and faced with ply sheeting. Engineers might shy away from this as it would require more structural design on their part but may be my preferred choice.

I would have thought fibreglass would have superior to polycarbonate. Do you mind I ask what’s your thinking

Good practice there. I see this all time at doors. Regular cement screeds should be poured in bays of 14m2 (I think that's the figure maybe its 36m2) with control joints to induce cracks where you'd prefer or saw tracked a couple of days after for same effect.

The outer metal cladding projects the panel to overlap adjoining panel. The double sided tape failed (other issues as well). Only proper remidy was to relay panels with a butyl rubber tape between overlap (seem that tape is a premium option which is often specified)