Redbeard

What's the roof made of, and how well is the base-rail fixed to the base? If the whole structure is not crazy heavy/wobbly a few jacks in sequence might get things level, allow a course of blocks and give the edge restraint for an insulated concrete (or not concrete) floor. Not as simple as 'leaving it be', but potentially not as complicated as one might think.

One can never guarantee what an individual BCO will think or do, but I'd expect concern, yes.

Depends on how 'in situ' you mean. Cutting down onto the lead - no, unless you can slid something 'un-cuttable' underneath, between tile and lead. Dust extraction/suppression, perhaps easier on a bench on the ground, and no lead to cut/ruin. (I'm not a roofer either!).

I'd use a structural engineer, 'cause you're only wanting to do it once. Where will the insulation be? Even if you use PIR will there be enough height left once you have come down a minimum of 162mm? (162mm assumes 25 PIR between rafters, 125 under, 25 battens and 12mm pl'bd - all taped to within an inch of its life, of course. I'd strongly encourage you not to skimp on the insulation even if you are I am assuming the insulation will be at sloping ceiling level, otherwise you'll be very cold in there.

Assuming you are planning to insulate as well I would consider a floating floor - level out over the tiles with a sloppy screed, then DPM, insulation, T&G OSB and final floor. Suspended timber floors, when they already exist, can be a real pain to insulate in terms of moisture issues arising, so if you haven't got one, why build one?!

Controlled ventilation = known cross-sectional area of air in and out, as against uncontrolled - the aggregate of all the gaps in the structure. Seal up the gaps and rule out the uncontrolled, at the same time bringing in controlled ventilation. It may be overkill for a garage but I am a great fan (sorry!) of small fixed vents and slow-running decentralised mechanical extract fans (or one, in your case, probably). The slow-speed extract of the fan is used to pull fresh air *in* via trickle vents or similar. Just relying on the wind blowing in and out of the right holes is a bit haphazard.

I cannot remember the name of the arrangement, but you could offer to lodge the 2nd 50% with an intermediary party, payable on satisfactory completion. Personally I'd be happier for that to be 45% and 5% held a further 6 months, but I would not fall out with anyone over that.

Agree with Conor, but I'd also look at the Party Wall Act to see if that is relevant here. I vaguely remember reference to 'party structures' and wonder if that could be relevant to an alley. Although it is the nearest 'outside' you may not have an automatic right to go via the alley. Though v likely less convenient, how feasible would it be to dig a trench under the floor to get out to the rear (or front, if that's where the manhole is)?

Confused! Where is the balustrade going to sit? Fixing through the lead to a sturdy timber (???) underneath the lead? The EPDM appears to fall down to the lead, and the lead rises to the tiles. Are you planning a pond? I think we'd have to know more about the alu section (and how and where the installer would intend to fit it - or does he expect 'others' to fit it?) before we could comment about its suitability. I hope there's a hell of a lot of packers close to each other under that bottom rail, or is the whole unit hanging on the sides? Looks v strange to me.

I had been about to suggest you commission your own SE inspection and report, but then they can treat that as biased if they so wish. I would say let them get their report done, and as @MikeGrahamT21 said: So even if they do suggest a reduction it may be relatively small, and more for 'just to be on the safe side' work rather than for serious 'structural stuff'. And if they really want it that isn't going to put them off. I'd just roll with it for now. (If I were 'diagnosing' more the pic I'd really like to see is of the area immediately below the area shown in te pic - so below the mineral wool.

Thanks for the list @Vijay. My biggest concern is the anxiety and irritation that it's causing you. That may govern how much you try to speed it (them) up.

Appreciating that this is an evolving issue, do you wish to share the list of 'works set out above'?

Not an awful idea but edge restraint is critical, and that restraint must hold the sub-base and the grit-sand, not just the blocks, otherwise the sand just runs out and the blocks droop.

If you want to dot 'i's and cross 't's it may be worth asking Celotex (or the tool on Celotex's web-site) to do an interstitial condensation risk analysis (or someone on here who uses Ubakus - I am sorry, I don't) of that lay-up. If I am understanding it right you are describing a 'hybrid warm roof', with some insulation between the rafters and some above (with membrane, counter-battens and slate battens above that). The 'probably-get-it-right-without-doing calcs' rule of thumb is that two-thirds of the insulation value should be *above* the rafters and one-third between. You have the opposite, if I understood right. The theory is that, if you have it the wrong way round, there is a potential risk of interstitial condensation at the 'interface', because the 100mm is doing its job of keeping the heat away from the interface. Do it the other way, 50mm between and 100 above, and enough heat escapes thro the 50mm to keep the interface above the interstitial condensation threshold. That's the 'rule of thumb'. Much better is a calc.

...or a nice place to visit...

I don't know, but I want that word!

I'm not sure what the permanent solution would be. Permanent removal of the soil on the neighbour's land would require construction of another retaining wall at right-angles (and it'd need to be a hell of a lot more chunky than those slabs to meet Regs) and it would have exposed their footing wall. Subject to a structural assessment of that exposure, back-filling with pea-gravel might help the 'moisture management' but, like any French drain it becomes a maintenance liability in terms of potential 'silting'. This can be mitigated by layers of horticultural membrane, though. To get a really good idea of what is going on you really need to see in your neighbour's sub-floor void. If their 'arrangement' (solum - 'soil' under the suspended floor - about 300mm below joists, AFAICS) is the same as yours then their solum is against your back-room wall because of the height of the 'step' (the flagstone 'retainers'), so your chances of that bit of wall being, and staying, dry are poor. Interim solution for the rotten joist is simply not to 'pocket' it in the wall. Build a 'footing' out of your solum and sit the joist (protected by a DPC) on that.

I think your theory that the damp in the corner is being 'transmitted' via the neighbour's masonry is a good one. All of the 'solutions' which come to mind immediately are compromises rather than true solutions. I shall ponder a bit more.

Assuming your SE's spec and dwgs were submitted to BC at application stage then what was drawn and spec'd is what BCO will expect to see, not a not-as-specified alternative enacted by the builder. Is the builder in possession of the SE spec and dwgs? If not what went wrong and (come to think of it) if yes, what went wrong? Unless you can get your SE to say it's OK. (Which, given that... "Our structural engineer is not happy and says he will not stand behind it." does not seem likely) you arguably have to call a halt to all works forthwith until the builder has either re-done as per SE spec or come up with a proposal which, though different from SE's spec, will satisfy that SE and *get you BC sign-off*. (Arguably contractor should be liable for extra SE costs if incurred, too). All of this is a hell of a lot easier to say than to get done, and can be very much depend om personalities, so I wish you very good luck.

I have one very like that, and the price was exactly that. The quality is awful, but I expected that for £30! The thread was 'cut' (cast??) so badly that the paddle, when fitted, had about 30-50mm 'slop' at the 'business end (got round that by using the old but higher-quality paddle off my old mixer). The cable-entry 'grommet' is glued only (or un-glued now) - It does not have a groove, so now it's off there is little to stop strain on the elec connections. When it finally dies it will be either that or a burnt-out motor, whichever comes first. I only bought such a cheap one as I am no longer contracting and thought my use would be very sporadic. If it goes wrong it entirely serves me right for being a skinflint. It *will* mix concrete, but it doesn't like it, and it's a big strain on your back if your back feels strain. 1 jumbo bucket, 2/3 full, fine. 2, you're getting tired and irritated. 3 or more, or a more regular requirement to mix concrete, buy a second-hand Belle. (And yes, the bucket will spin, so you also have to use your ankles to 'pin' the bucket, hence not something to do regularly!

I think we need to know more about this before we express any opinion as to whether 25mm will make any significant difference. What is the width of the cavity? (So that we can work out, at least roughly, what the U value might have been intended to be.) What went wrong? You say full fill, so there is no *intentional* ventilation to the cavity. What about 'unintentional'?

"4) Outbuildings are not permitted development forward of the principal elevation of the original house. The term original house means the house as it was first built or as it stood on 1 July 1948 (if it was built before that date)" Castle-style porch?

So the builder has left a 100mm ventilation gap?! Guess you don't need to worry too much about the ventilation, provided he has built adequate 'ins' and 'outs'. Was the instruction to the builder clear? "Build me an extension which meets Bldg Regs ", for example? If so.... I like to have something to at least 'cloak' the thermal bridge of the rafters, so how about pull down the ceiling, add 50mm between and 25mm below the rafters (U val probably less than 0.13W/m2K compared with Bldg Regs target of 0.16. Then you know you have surpassed the Regs req't. Then you ask the builder to pay for re-boarding and plastering. By the way, It definitely isn't. In come circs the BCO might agree to accept it, but that just means you are getting away with more heat-loss than you should have. Not good.

Go for your own TP. Effectively you have already told us why you need to. One fewer thing to bite you in the future.

Thanks ST, I knew you'd know. I stand corrected. I somehow had in mind that XPS was OK. The rest stands, though!