Mike

The principle is good - the idea is that it cuts convection within the loft and reduces heat loss (by around 2% to 4%*), although that's only achievable with near-perfect air sealing. In addition to the issues raised above about airtightness at the ceiling level, airtightness below the tiles (and the junction at the eaves and gables) is also vital. The good new is that, also from the study below*, provided you use membranes with very low vapour diffusion resistance then moisture seems very unlikely to be a problem even if there is leakage - you just miss out on the thermal benefits. *Thermal and Moisture Performance of a Sealed Cold-Roof System with a Vapor-Permeable Underlay, by Tuomo T. Ojanen

I used these on my last bath room which was still fine after 10 years. I've used them many times in the past too. AFAIK they're all still fine. But, having seen the damage that can be caused, I no longer take the risk. Reliable alternatives are readily available. Yes and no. Being a hotel, they'd undoubtedly have specified connectors to BS EN 13618 (or it's predecessor - they'd been installed at least 10 years previously). It's more likely a DIYer would ignore that (or not even think of looking for it). However it seems clear that that standard isn't good enough, so to that extent yes, product quality is an issue. However to pick something of higher quality you'd need to evaluate manufacturers' data on the quality and thickness of the brass / rubber / stainless stainless steel braiding that they use, and the resistance to water hammer / temperature / chemicals - if you can find anyone who publishes that.

You can check the regs: https://www.waterregsuk.co.uk/guidance/ :) And, while not a rule, beware of flexible tap connectors:

The downside to flipping the stairs 180° is that, although the dimensions of the dining room (or lounge) remain the same, you loose useful space as you'll have created a virtual corridor through the room, though you may prefer that to a real corridor upstairs. But, of course, you have to make compromises somewhere!

The perimeter of the heated envelope is the best place, in terms of minimising heat loss. Blocking it at both ends could lead to greater condensation (than otherwise) between the blockages. Buanderie wouldn't necessarily be mentioned - utility rooms (with a water supply) fall under the definition of salle d'eau - https://www.batiment-ventilation.fr/outils/faq/dans-larrete-de-mars-1982-quelle-est-la-difference-entre-une-salle-deau-et-une-salle-de-bains-105 (a room other than the kitchen or WC, equipped with a water supply, but without a bath or shower) I'm not an expert on the text (and don't have time to read it!), however it could be because you only tracked down part 1-1-2, or because my memory is wrong (since I have a VMC double-flux). For a more definitive view, polish off your French and ask at the forumconstruire (which comes up with this, and others: https://www.forumconstruire.com/construire/topic-395665-bouche-extraction-buanderie.php)

In France a laundry room does normally have mechanical extract fitted - I think the regs (DTU 68.3) require that - so I'd disable it and probably block the exit from the house in a reversible way, rather than strip everything out and seal it off permanently.

I agree that it's not required while you have that type of dryer.

The Paul/Zehnder ISO-BOX DN160 is much more affordable, as are the filters. Not sure if it's still sold in the UK though - got mine here: https://www.econology.fr/zehnder-comfosystems-caisson-filtrant-isobox-dn-160-filtre-a-pollen.html

Rotate 90°, not 180:

More commonly kitchen or bathroom, but could be utility. You'll need to trace the duct or thread something along it if you want to know. Or test the airflow at the grille - that is, see if a piece of tissue paper 'sticks' to the grille when the fan is on, and falls off if you turn it off. Poor choice of material, in particular. Provided the duct & fan fit together then use either an aluminium foil HVAC tape or, since it won't be running at a high temperature, an airtightness tape such as Pro Clima Tescon Vana.

That's fine, and frequently done these days. Traditionally something like a 225 x 32mm length of timber would be sawn diagonally (in cross section) to create two feather-edge boards that would be nailed to the top of the rafters, fat edge to the centre, thin edge picking up the ends of the tile battens, which is the way I've always done it. Since you have plane tiles on the roof, personally I'd choose to use valley tiles, rather than GRP or lead for the valley.

Catching up with this after some time away, if this is the end of the ridge then it doesn't look good. In the absence of an alternative solution, the top of the rafter should be notched over the beam (or a timber sitting on the beam), so that notch transmits the load from the roof vertically onto the beam. The timber ties beneath the beam are normally there to stop horizontal movement - that is, to keep the notches in their intended place on the beam - not to stop the rafters sliding down towards the wall plates which, they will otherwise tend to do. I would strongly suggest that you get a Structural Engineer involved before proceeding.

To do it properly, add a kerb stone or brick edging along the full length, on a concrete bed and with haunching.

It's an extractor fan (with a 2-year warranty): http://www.panol.fr/product.php?productid=17793 And that tape is not good.

Rafters need something to stop them splaying apart, normally a horizontal timber tie. An alternative would be to securely fix them at the ridge to some kind of beam, and that beam would need to support 50% of the weight of the roof. To remove the beam and the ties, the foot of the beams would need to be fixed so they couldn't move, and the wall would need to be strong enough to withstand the sideways load - for example by casting a concrete ring beam. In the drawing above, I can't see how the timbers could be properly secured as drawn, so the carpenter's solution is a good one. To dispense with the RSJ in that situation, the horizontal ties would need designing by a SE.

I can't see an easy solution either. You don't want anything that relies on a gravel board to keep the soil away - it will fill up over time - and a 100mm thick retaining wall 500mm high seems inadequate. Theremoblock insn't intended to be used as a wall and the internal ledge would look odd. I'd also not use cement board cladding that close to the boundary due to the difficulty/impossibility of future maintenance (it's not going to be easy to install it in the first place either); since the houses are brick I'd want a brick external leaf, at least on that side. As @G and J suggests, you'll likely need a structural engineer to come up with something that will work with your foundations. Better to take a pause now and get it right, than build something that could cause problems in the future, not least when you eventually want to sell it, even if you can get it past Building Control.

I agree with the sentiments above - be very wary. Best case is that the cracks are due to poor quality rendering, with re-rendering the solution. If it's entirely crack-free on the inside (and hasn't been freshly painted, and isn't wallpapered, and all other surfaces are sound, flat and appropriately level/vertical), and an SE spots no other significant issues, that may point towards it being mainly a rendering problem. However it's equally possible that there are cracks in in the bricks / blocks beneath, which could be for various reasons, needing anything from repairs to demolition & rebuilding. It seems that there's a filled crack in the older-looking render above the flood light. If that really is an older part of the building, rendered at a separate time to the extension(s), I'd certainly walk away (unless you know that it's not in an area susceptible to subsidence, and you buy with the intention of demolition & rebuilding, at the appropriate price for that). A rather minor point in the context, but that single air vent is inadequate if it's ventilating the floor void.

If pressure washing doesn't work, the next step up would be sandblasting. I'd not paint it.

To add a more rounded picture, MVHR isn't all about cost recovery / return on investment - the same as many kitchens and bathroom suites will never recover their investment. Apart from any cost savings (which can be real), if MVHR is properly specified an installed it can filter the outside air, maintain a healthy internal atmosphere, avoid noise transmission through trickle vents, reduce condensation & mould risk, and avoid blowing warm air out through rattling extractor fans. And probably some other things I've not thought of. As for air-tightness, the Building Regs standards are very unambitious. Passivhaus requires no more than 0.6 air changes per hour under 50pa of pressure, and values as low as 0.2 are possible. However that is only achievable if the architect designs-in adequate airtightness measures, if the various contractors and installers know what they're doing, and if someone is checking the quality of the work and materials used.

Subsidence is a loaded word more commonly taken to mean the dropping of the ground, taking foundations wall and floor with it. If only a localised part the floor has moved that may be why the surveyor didn't want to use the term, even if it has, in linguistic terms, subsided. It could have been the tree. Or maybe poor compaction of the soil or hardcore beneath the floor slab. Maybe there was an old well / bomb shelter / tree root / something else just there. BTW, as I recall, there isn't much clay in Norfork, is there? It wouldn't hurt, and they're not unduly expensive. A structural engineer's survey of the building may be better though, if you want additional reassurance. That depends how keen you are to buy and how competitive the market is. It wasn't necessarily the tree... It's more a case of whether your surveyor has missed anything. If that's really the only fault, and building's been there since 1969, then I'd not worry that much, but my risk aversion may be different to yours. And, budget permitting, I'd be tempted to take up all the ground floors anyway, then insulate them and install underfloor heating.

10mm each way is often used. I prefer 15mm to make sure there's enough space to get a foam gun nozzle in.

'Moisture meters' don't measure moisture, they measure electrical resistance, so no comment on the specific figures. However the presence of the previously mentioned hygroscopic salts would no doubt account for the difference between the inside and the outside of the brick, since they would change the electrical conductivity/resistivity (and be mainly present on the inside). Yes, that does happen. I guess lime mortar would have been used, with as little lime as as the builders could get away with.

Geberit make connectors for back-to-back WCs - https://catalog.geberit-global.com/en-NT/systems/CH3_102113/products. I guess others probably do too.

There is, but below the roof (tiles) - so no scaffolding & no water-tightness to worry about.

Most difficult and expensive is removing the part above the roof. After that, it's normally easy if you have an aptitude for that sort of thing, and can live with the mess for a few days. But if skill and cash are limiting factors, then filing it as previously described is next best (preferably after sweeping it).