Redbeard

Have you read the gov't's guide to the PWA? https://www.gov.uk/government/publications/preventing-and-resolving-disputes-in-relation-to-party-walls/the-party-wall-etc-act-1996-explanatory-booklet This may (or, I accept, may not) answer your Qs. (Was typing the above when @joe90 replied). If your new retaining wall is entirely separate from the party wall and will not in any way interfere with that wall's foundation you *may* be able to argue that these are not works to, or affecting, a party wall. But I am not sure we have enough info. It seems that the party wall is built well above the level of your yard with its footing well above the level of your yard, possibly meaning that if you were to take down your 'retaining wall' which is entirely on your land you would be removing support from the party wall. That sounds like something which affects a party wall.

I don't know the Permitted Dev'p't rules in Scotland, but I do know that you could construct a timber-framed garden room and achieve far, far better insulation and air-tightness standards than a bog-standard static caravan. Yes, you can improve upon the 'standard standards' of a caravan, but as that would effectively involve building a better-insulated structure around it, surely better to build that structure without the impediment of a caravan...

Yes I don't know, because I do not know what the designer had in mind. One assumes either that it is an incomplete dwg - there is nothing shown above the firrings - or, as you surmise, the OSB is in the wrong place. I always like a howling gale on the top side of a cold roof, although I have seen designs for apparently unventilated, fully-Warmcel-filled roofs, which seem to work OK. As that is drawn I cannot tell whether the 'air gap' has ins and outs (cross-ventilation) anyway. Has the detail been drawn by a company specialising in Warmcel-ins'd roofs? Warm roofs are theoretically much better, I feel, but the scope for poor execution due to misunderstanding the concept can be significant. If you get someone who is really good at insulated cold flat roofs you *may* get a better job than asking them to do a warm roof that they have never done before. Is it really a full-depth thermal bridge, or is the tail of the arrow masking a 'mitigating' piece of insulation? Certainly it wants to be 'cloaked' as best it can.

Can you offer some clarification, as the pictures and the words seem to say different things to me? I don't understand Where is the boundary line on that pic? Are the garage roofs in the foreground (Green Mineral felt)? What is the sloping mineral felt roof - is that part of the neighbour's garage, or of yours, or of something else? I cannot see an obvious 300mm gap, but maybe it's just the camera angle. Is the gap you are talking about on the L of the lead flashing, just past the brickwork return on the taller building element? Assuming the garages are not new, are you saying that there has never been a 'rainwater strategy' up to now other tan it falling off the edge? How long has that been the case for?

+1 to Gloomsbury! Wonderful belly-laugh sort of humour.

I cannot see how deep any 'dinges' are but if it were me I'd be tempted to try a bag or 2 of thin-coat EWI-type render. Goes on easily (you can use a toothed trowel as a depth guide if you want, and effectively do it in 2 'half-coats'). Let the first half stiffen up a little then 'fill in the valleys'.

What's the round thing we can see at the bottom? You'd expect a side, not a bottom entry, but wd be nice to know what it is. It is perhaps likely that if you cannot find an inflow and outflow pipe that it is redundant, but although we are perhaps assuming that that is the invert (bottom) that we can see, are we sure? We had the Water Authority out to one, which they declared redundant. They were interested. Did you ask your water auth'y if they would visit? Yes, they don't maintain it, but that need not necessarily mean it has nothing to do with drainage. No-one can really confirm anything based on that pic, I think. The lack of any 'ins' and 'outs' suggests it is not used/cannot be 'live' *as mains drainage*, but that's only a suggestion from afar!

Yes...

I worry about those puppies! Maybe that's where the dog('s)-leg comes in...

+1 to @joe90. It worked for me. You have to be OK with the admin, but it can be kept v simple. I only ever used spreadsheets, not 'accounts packages'. Only difference to @joe90's sugg'n is that my prices were always stated to be estimates, not quotes. Not that the customer necessarily sees the difference, but if unforeseen complication leads to a higher end-price you can point back to 'estimate'. In reality, reasonably often my final bill was less than the estimate.

Although you have highlighted (?highlit?) the area the pic is not clear enough for me to see what the issue is which you are referring to. Perhaps the top-coat/paint has flaked off the render at the jct with the tiles. Is that what you mean?

Ideally you want a dynamic condensation risk assessment such as WUFI. This will tell you whether the added insulation will make the plank/membrane 'interface' cold enough for condensation to occur in worst-case circs. A 'rule of thumb' (which seems sensible but I cannot prove or disprove) is that if you do mix insulation between and above the rafters then two-thirds of the R value should be above the rafters and a max of one-third below. If my quick maths when I saw your post last night was correct that's a max of 100 -110mm of, for example, flexi wood-fibre with a lambda value of 0.039W/mK. Your glass wool may have a lambda value of 0.044, so a bit more thickness may be OK. But definitely using WUFI to 'prove' it is the better path.

Via the trickle vents and undercuts referred to. The dMEV units are the extract/'pull' which pull fresh air in via the trickle vents.

Not quite an answer to your Q but I always try to achieve more-or-less the same U value for all elements of rooms-in-roofs, so never mind that stud *walls* only need 0.3. I look to achieve 0.16 or less over the entire envelope (apart from the windows which are not very see-through at 0.16!)

That was my first thought, and if it's the sort of thing I have in mind (and had a few years of schooling in) I would have some doubt as to how it would stand up to a rigorous structural assessment. I take it you have already done a trawl through the local SEs? While you may not find someone who specialises in timber buildings (and old ones at that) a generalist with a portfolio including timber buildings and an interest in a challenge might be prepared at least to have an initial look. I like the idea of pulling the 'Local Charity' strings and looking for pro bono or reduced fee work as well.

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.