YodhrinForge

I know the Party Wall Act does not apply in Scotland and that things are done differently here because that's what every single online search result I get tells me immediately before not saying what those differences are or linking to them and immediately going on to discuss the E&W Party Wall Act in detail. Whether my google-fu is weak or search is just enshittified nonsense now I can't wrestle any more than that out of it. Does anyone happen to know what if any legislation *does* apply here? I have a useless little part of my garden that sits between me and my neighbour's extensions that I'd like to make into an enclosed porch with a mini lean-to conservatory, but that will require at minimum a few bits of silicone sealant on their extension wall(based on both deeds and my own comparative measurements their extension wall is built running *on* the property line, not merely facing up against it) and sticking some butyl tape to their guttering, so while I fully intend to take the idea to them for discussion and come to a reasonable accord rather than just spring it on them as a fait accompli, it'd still be useful to know if I have any legal rights or legs to stand on.

I have this odd little space on my property around the back between my neighbour's existing extension(built up to the property line, so is a party wall) and my own house's existing extension. It serves no real purpose, it's north facing and the ground level is shaded by the extensions so nothing useful will grow there, it's inconvenient to use as a bin store, and it features the downstairs bedroom's only window so regs won't permit a "proper" extension there, it's just generally dead space. My only initial idea was to stick a couple of sheffield stands around there in case any visitors come by bike, but sitting in my little back porch the other evening which unfortunately will be getting demolished to make way for a utility room(and moving that isn't an option since it needs to be in that spot for various reasons) I found I actually quite enjoyed having a sheltered wee space to read and listen to the rain hitting the roof looking out to the garden. The space is about 2.5m wide x 3.6m deep and apart from having to faff with the drainage and guttering(which all needs to be addressed as part of the broader renovation work anyway) it *seems* like it would be a fairly simple extra project since it would only need the roof and frontage, but from attempts to research it I'm finding the "conservatory industry" seems pretty thoroughly geared around a few standard designs all of which are intended to project outwards from a wall rather than be fitted between two existing ones, so I take it I'd be looking at a custom design? Does anyone have experience with rough costs for that sort of thing? Would it be easier to go to a specialist company or could I be better off just getting my existing architect and structural engineer to specify it and order individual components myself? Given I'm in the central belt of scotland and it's north facing it'll have to be triple glazing so that narrows my options.

Yeah I probably will have to drill it in the end, bloody inconvenient though due to the way the extension was done(hipped roof into middle of existing pitched roof so no easy access from the attic, walls inside are tiled and the roof has that really tough popcorn plaster, probably have to go in from outside and then just jam the hole with silicone for the short term). On the plus side your comment made me double check and I was just being dim with the garage - it's single skin on three sides with solid double on the front with the doors in, they just put some lines into the render on the front side so it would resemble the wall of the extension hah.

I'm starting to get into the weeds of detailing with my architect about my renovation and was just wondering if there's a way to determine cavity size without having someone digging into the walls? I suspect I know the answer but might as well check. There's an extension on the back of the house that definitely has some kind of cavity as there are exterior wall vents, exterior leaf is blockwork(it's just painted so is obvious), inner leaf could be brick? Can only barely see it through a tiny hole in the back of the cabinets at floor level - you'd think it would be block as well if the outside was, but there's also a masonry built detached garage that seems to have been put up around the same time as the extension and that's brick inner block outer(although the block outer might just be a facade? there's a layer of engineering brick visible just above the paving slabs and the block layer protrudes out from the top of that by ~30mm or so) so who knows. The approximate thickness of the extension wall is 320mm, the garage wall is 230mm. Trying to decide on relative merits of different insulation systems & materials but it's all so dependent on if there's a cavity and how thick it is.

Re flue liners; the issue there is *air* tight is not necessarily *radon* tight. Radon is capable of diffusing through a lot of materials that can stop air molecules no bother, it's why you're supposed to use a specially rated DPM in known radon areas. It would also - assuming the standard metal option - be putting a huge condensation generator in the middle of a stone wall outside the insulation envelope which doesn't seem great for the health of the wall long-term, as you'd have an air cavity around the pipe where moisture in the wall assembly could evaporate and then a metal tube drawing cool air from the solum space - completely coating the interior of the flue would firstly seal the flue from the wall assembly so water vapour couldn't pass into it from the wall itself, would make condensate less likely in the first place as nothing in there would be cold enough to let significant moisture form out of the air before it was expelled through the chimney, and any that did form could drain back down into the solum rather than being trapped in the air cavity. The Visqueen(or other brands) stuff is designed for exactly this sort of issue it's just normally applied to seal floors or walls rather than the inside of unused flues. At the three access points the measure depth of the cavity between the bottom of the joists and the earthen solum is ~270mm. Re soil gasses; other than maybe radon in a former mining area there's also potentially methane, though that's more common on former waste dumping sites that have been built over, and also just water vapour - you have to be really careful with moisture when renovating these old stone buildings because they were designed to be draughty as hell and have active or residually-hot fireplaces pushing air out through the chimneys pretty much 24/7, so even using the proper vapour-open materials as I will be you have to watch the solum space with so few vents compared to modern structures, soil moisture can elevate the humidity of the space and then you get water condensing around joist-ends and other inconvenient places. Re radon maps & measuring - the maps only report testing that's already been done and most people don't even know radon is a thing they should be testing for. The map data is also not particularly refined - your neighbour a dozen doors down could submit an all-clear result and if that's the only result your whole area could be marked as lowest possible risk, but *your* house could still be sitting on top of a plume of the stuff. You also really have to wait for winter to get proper results, and on top of that results before & after a renovation can be totally different. For my money testing is more something you do to confirm that there isn't an issue *after* you've already done all the mitigations you can within your budget and project scope. And the issue with the recommended methods Mike are they all pretty much assume either old and draughty or modern and airtight, whereas I'll be making an old property airtight(or as close as I can manage) but using vapour-open(and so radon-open) materials to control moisture buildup, so they won't really work in this context because if it stops radon it'll also stop water vapour. Everything about these kinds of renovations is non-standard really.

Okay brief background - property is circa 1900 semi-detaches stone cottage with early-mid 90's extension/attic conversion, slab in the latter suspended timber in the former. Building is getting an EnerPHit-style eco retrofit with all the proper vapour open materials wood fibre yadda yadda. Original plan was for new insulated slab floors with underfloor heating throughout but the project is going through a bit of the old "value engineering" at the moment and my current instinct is to cut down to just the kitchen extension and treat the existing suspended timber floors with a special system that uses a vapour open but windproof membrane to seal the floor structure(allowing them to still dry out to the solum cavity), then wood fibre batts between the joists, then a vapour barrier on top before application of the subfloor. My one reservation about this is it's a former shale oil mining area and so there's a possibility - albeit a small one - of elevated levels of soil gasses and radon. The inhabited space will have MVHR so I'm probably just being paranoid, but I'd rather do too much now when everything's being taken apart anyway than find out come next winter there's an issue and have to dig everything out again. The solid floor plan would have involved a ventilated sump and radon-rated DPM and while I *might* be able to use one of those as the vapour barrier(yet to hear back from architect about it) I still think I'd like to increase the ventilation of the subfloor space as right now there are only three grates(imagine division between the two properties as interlocking L shapes, mine has the narrow front and wide rear so one front vent two at the back). The actual question then: There are two chimney flues originating in the downstairs front & back rooms which I wanted to close up anyway, so I wondered, could extending the flue down into the subfloor space with some ducting and sticking anti-backdraft caps on the chimneys provide extra passive ventilation via stack effect creating a stronger draw on the space? And if that could work, is there a process and what sort of ballpark price could I expect to pay to have the interior of the chimneys coated with something like a Visqueen liquid gas barrier(no point removing any potential radon from the subfloor just to let it diffuse through the completely vapour-open wall buildup into the interior anyway)? I've seen companies that will do a concrete-ceramic spray coating for chimneys with active fireplaces in them, but I've no idea if that sort of equipment would work and if any would be willing to run something else through them.

I'm aware. The Diathonite was planned anyway for the exterior walls inner face, and to be applied thicky both to level, decrease the chances of cracking in future which would compromise the airtight layer, and for its excellent wicking and moisture management properties. And while the cost isn't small, in this plan for the adjoining walls it would be somewhat offset by dropping the inner layer of rigid insulation I had thought to add behind the stud wall. Anyway in the end it's all subject to WUFI/PHPP modelling anyway, I'm just trying to get an idea of how to balance everything optimally.

Having finally found some more detailed reference material, I've amended my buildup again(turns out Diathonite Thermactive has a final density of 250kg/m3 +/- 15%, which is basically double rigid wood fibre, so pushing that from a ~30mm parge/levelling coat to a ~40mm base layer will do both the extra mass and thermal decoupling adequately).

I'd considered using flexible batts, but the wall will be getting coated with some kind of lime-based material anyway as that will form my airtight layer(using enerPHit principles, just not fussed about getting the certification), I also have to be careful about managing dew point and avoiding unintended cavities. How about the pictured; lime parge/adhesive > 20mm rigid wood fibre(thermal break) > stud wall w/ 50mm flexible wood fibre between > clip & rail system > acoustic plasterboard. When it comes to the floors, whichever solution I go with will be carried through the floor as much as possible to achieve continuity of insulation and airtightness, and I was intending to use a sound dampening subfloor for any suspended timber flooring. There's also the benefit that the run of the joists is front-to-back while the neighbouring property is to one side.

The physical decoupling occurs in the decoupling system I mentioned, one of the polymer mount & channel type systems for fixing your plasterboard to, the insulation layers are for thermal performance and mass(rigid wood fiber has a similar or better kg/m3 than the best acoustic-rated rockwool and I'm using it on my exterior wall interior facings for insulation anyway). I'll be stripping all exterior and adjoining walls to the masonry to add vapour open airtightness, insulation and, for the adjoining walls, soundproofing. Here's a shitty MSpaint of what I've been discussing with the architect. Top to bottom on the buildup is existing wall, lime adhesive, wood fibre, stud wall, decoupling system, acoustic plasterboard. The variations are just different thicknesses of wood fibre(top to bottom 80mm, 40+40 between studs, same, and 20+40 between studs) and sizes & layouts of CLS(top two 38x63, bottom two 38x98), which I end up with will depend on space constraints of the final designs and what the structural engineer wants. Second one down seems the best compromise of depth, mass, & thermal performance to me. Oh and for clarity I say excessive because the existing wall is two rows of brick in a circa 1900 stone building, so you already have to pretty much be *trying* to be loud to annoy each other, I just figure that since I'm pulling everything down for airtightness & insulation work anyway I might as well see how I can tweak it to maximise acoustic performance too.

There are a few decent calculators out there online that let you get a very rough ballpark u-value for whatever your wall buildups are going to be, I'm wondering if there's anything similar for wall buildups designed for acoustic mitigation? I'm a big fan of over-designing rather than dancing on thin margins so I'm less interested in the exact precise values for a specific actual wall than I am in whether the general buildups I'm considering(current lead contender is existing brick partition wall>40mm rigid wood fibre boards with adhesive & hammer fixings, CLS stud wall in contact with previous, further 40mm wood fibre depth between studs bonded to initial insulation layer, then some kind of decoupling system with acoustic plasterboard mounted to it) will be sufficiently excessive.

I'll remember to remember that tip thanks No this is me going back & forth with my architect trying to find something with the right balance of cost, risk, time, DIY-ability, and likelihood of getting past BCO/planning/whinging council conservation officers. As for the service cavity: it's more convenient, future repairs/modifications are easier, and it lets me use the plasterboard approach which for me will be a lot cheaper as I can do it myself. I'll ask the architect about the model, and the other suggestions received thanks to all. Just to be clear neither of the alternatives actually have been modelled for this property and only the latter(clayboard & clay plaster) has been used(and modelled) by the architect before, the membrane solution was something the architect got back from a potential "eco" building supply place we were considering using for the raw materials, and I wanted to see if there was a way to stick with my original plan before faffing about running more models.

I refer to it that way mostly because most of the youtube tutorials I found were yanks and they rarely do anything else by all accounts, whereas all you hear about on UK property shows when I was growing up was plastering. Anyway, I appreciate the link but that's actually one of the things I read that encouraged me that plasterboard would work in the first place. Unfortunately the modelling of my intended buildup says that even the small additional resistance of gypsum board over clay or similar is enough to cause a slow accumulation of moisture in the wall over time even with fully vapour open paint used internally, so I'm not sure what to believe except that if the modelling is right then in a few years time I'll have to rip out all the work I'd done and do it again so it seems safer to look for alternatives.

Still trying to figure out the specifics of my eco retrofit of a circa 1900 stone cottage, but I've been slightly buggered by the WUFI modelling. Based on what I'd read previously I believed taped & jointed - American style - thin gypsum plasterboard with vapour open paint would be sufficient to allow the internal wood fibre insulation and the stone wall to breathe properly, but Computer Says No apparently. Previously planned buildup was external lime harling > original stonework > up-to 30mm Diathonite levelling & airtight layer > 100mm rigid wood fibre > ~40mm stud wall to create service cavity with spaces infilled with flexible wood fibre > 12mm plasterboard > clay paint, however the modelling suggests this would accumulate moisture over time despite proper MVHR to manage internal humidity - slowly, but in a few years or certainly a decade or two I'd be having issues. The two suggested alternatives suck for different reasons; either adding an Intello membrane between the rigid wood fibre and the stud wall, but this would require dropping the flexible wood fibre filling out the spaces in the stud wall which is a noticeable reduction in u-value; or switching to clayboard with clay plastering for the interior instead of plasterboard, which has sufficient permeability to avoid the buildup issue but uses up a bit more internal space given it's thicker and would require me to fork out for a specialist plasterer to do the mesh-reinforced binder coat and the skimmed finish coat, which ain't cheap. I found *one* company offering what appear to be lime-based plasterboard substitutes designed to be very vapour open but still work pretty much exactly like common gypsum board, but they're only just starting to roll out the product and aren't selling to the public yet, and I can't imagine that a small house renovation will get through their application process to be a demo project(not to mention that as it's brand new there's no track record to look at, could be a complete dud in practice). Are they genuinely the first to come up with such a thing? Standard plasterboard was appealing exactly because with the tape & joint method I could do it myself and achieve pretty nice results for just material costs, while still maximising insulation, so any alternative that let me do something similar would be ideal.

I have to replicate the appearance, not the exact scale. There were bigger iceboxes and smaller ones, that one just happened to have the right layout and relative proportions to illustrate the point. Also, it's not a massive household, if we could manage with a regular freestanding fridgefreezer - and we could - I'm pretty sure we'd be fine with a larger freezer, a slightly smaller fridge, and an extra minifridge. It might end up rivalling one of those American style monstrosities in size once the cabinet is built but we have no need of that kind of capacity. Could we maybe possibly start with the assumption that I'm not a total numpty with no idea how much space he needs and circle back to the questions asked?