Redbeard

See last sentence of Paragraph 3: https://tomspriggs.com/2022-changes-to-the-building-regulations-for-extensions-part-l/ I have not looked specifically but I had not heard anything re consequential improvements for domestic bldgs. I have actually been wishing for years that they did apply! *Now I have had another look, and realise why I had not kept it in mind* Is your house over 1000m2? - (Is anybody's house over 1000m2 except the very very monied few?) "12.1 For an existing dwelling with a total useful floor area of over 1000m2 , additional work may be required to improve the overall energy efficiency of the dwelling if proposed work consists of or includes any of the following. a. An extension. b. Providing any fixed building service in the dwelling for the first time. c. Increasing the capacity of any fixed building service (which does not include doing so on account of renewable technology). Consequential improvements should be carried out to ensure that the dwelling complies with Part L of the Building Regulations, to the extent that they are technically, functionally and economically feasible. 12.2 Technical guidance on consequential improvements is given in Approved Document L, Volume 2: Buildings other than dwellings."

"Did you get retrospective permission?" Not retrospective, no. The Planners told me 'informally' that my proposal did not fall within their interpretation of PD. I applied for PP rather than entering a fray.

"Fun fact, if the ground on which your outbuilding is located is sloped or undulating then you get the benefit of measuring from the highest point. This can mean creating a part-excavated building (as others have mentioned) if you need more head height than would be achieved with a standard 2.5m building on flat ground," Sadly my LA though exactly the opposite. My outbuilding was 4m to the ridge, and 3m at the eaves. It was on a slope, though, so there was a 1m retaining sleeper wall and the eaves height at door level was 2m (and you descends a set of steps to the floor). I tried hard to convince them that they did not, therefore, have to worry their heads about Planning Permission. They disagreed. The measurement, they said, must be from the bottom of the structure, not from the land around it.(It got Planning permission, of course).

?screw-in wall ties, build single skin of brick and then replace the copings that you think you'd have to replace anyway? (Or brick slips? Though I'd be concerned about the adhesive de-bonding in the same way that render might).

I'd contact Illbruck. I did so recently to confirm that FM330 is still a/t when trimmed back (it is) and they were v helpful.

In my limited experience, while £2k/m2 (or 3) might work for a whole house you would not necessarily expect to achieve that for a smaller extension, as you haven't got enough area/volume for economies of scale to work.

What does the condensation risk assessment assume?

You refer to dropping the ceiling. When you insulate from above during re-roofing, you are allowed effectively to 'get away with' an inadequate level of insulation - because that's all that will fit - with the relevant ventilation gap - between the rafters. If you drop the ceilings you have the opportunity to do the full depth - 150mm at present if using PIR, representing a U value of 0.16W/m2K - so you have to do it, unless any get-out clauses (such as lack of headroom above stairs, for example) apply.

Unless something has gone horribly wrong your 3 flues, though they may share a masonry 'home', should be entirely separate, so yes, arguably ventilation still required. The 'beef' I have with flues on an internal or party wall (anything but an external wall, I mean) is that your vent is potentially pulling warm moist air into the redundant flue, and as it nears the cold roof void there is a chance that it will condense. This may then push nasty tarry 'products of combustion' through the plaster, so that apparent 'damp patches' are sometimes not only that, but also contamination. If it's on an outside wall, ventilate externally, but be sure you know which flue you are entering!

Can't really see any reason for going wider than that, particularly since (if I read you correctly) you are backing up with FM330.

How long is a piece of ....tape? Openings are not always perfectly x mm bigger than the frame, so just something within the working range of the chosen tape. Remember that there's an air-tight expansion range, and then there's 'what the tape will expand to', and the two are very different. IIRC there's generally only about 3-4mm in the expansion range. (I have '3-6' and '6 - 10', for example). Ah, did you mean width, not depth? If the former I am not convinced it matters too much.

So area is 72m2, exposed perimeter 25m. P/A ratio = 0.35. Therefore likely base-case U value 0.56W/m2K (R = 1.78m2K/W). On the face of it adding 50mm PIR (R=2.27m2K/W) seems to give a U value of around 0.25 (a pass!), but how it actually performs will depend on a number of factors including whether the B & B floor is ventilated.

Or drop the fan off the ceiling. If it has a duct attached you know it has one (though you do not know where it goes to), and if it doesn't.... If it is the cheap wire-wound plastic duct make sure it does not go up and down (over uneven insulation, for example) or else each dip can become a slime-sump.

Is the fan in a stud wall or a ceiling? Can you see any ducting in the loft? If not, i suggest isolating the supply (or asking a 'trician to do so) and removing the fan to have a look. It sounds as if you suspect that he's just fitted the unit and left it to fill the void with steam. Is that what you think may have happened?

Is there anything wrong with the roof tiles? underfelt is only a second line of defence in case the tiles fail. I would not rush to repair this unless there's a leak. All the growth suggests that the tiles are not young, and it's impossible to tell from a pic. Would I be right in guessing 1960s or 1970s ish?

@ETC, sorry, got that now. I had missed the ref to the lay-up on top of the B & B. That would work quite successfully. Without knowing the house we can't know the perimeter/area ratio, so cannot calc the U value with, say, 50 - 60mm insulation, but it will be a hell of a lot better than it is now.

@ETC, I take it you mean 'work from the existing *first* floor level down'. Of course we don't know the ceiling heights, but losing 200 might be significant.

I have no experience of Scotland but in England it was still OK in 1990 (+) to use 'teeming and ladeling' with Bldg Regs, so you were allowed to get away with not insulating the floor if you (allegedly?) bumped up the wall insulation. I worked for a hsg ass'n at the time and although we used to build our owmn we were outbid on one site and ended up buying the pair of spec-built semis which were built on it. I soon got in the habit of taking off my jacket and one pullover before going in because the house was always at 25+ degrees. Why? Because they were always trying to get warm feet. Never did, really; just sweated from the knees up. Re the suggestion of floating floor the problem is that it puts your stair out of compliance with Bldg Regs unless you have the space to make the bottom stair a 'landing' (can't remember the dimensions)

I worked on a house which had some (but not all) TF 3G sliding sashes. We got 2-and-a-bit m3/m2/hr. Not too unhappy with that. Under test conditions you could hear the seals beginning to 'give' as the tester cranked the fan up. But we still got 2-and-a-bit. Performance vs aesthetics; depends what you want most.

Make one! With a bit of careful thought you are likely to make one which will be much more air-tight and much better insulated than a proprietary one.

Yes, you can definitely use breathable membrane as the 'hammock' and it arguably performs a 'belt-and-braces' function as an 'anti-wind-wash layer'. If you have nothing better to do for the next few hours read these. The BEIS Best practice document is interesting insofar as it is one of a series (IWI, solid floors, suspended floors and rooms-in-the-roof) which were published in (I think) 2022 but (as far as I am aware) barely publicised at all. I may not agree with absolutely everything in them but they have clearly used knowledgeable sources. Seach 'BEIS Best Practice' for the whole bunch. In terms of material it is an expensive option, and it drops bits on you, but in terms of (semi-) rigidity flexible wood-fibre is soooo good. No dropping-out or drooping. Cut 20-30mm oversize, squeeze like a concertina and pop it in. I do 'support' it, as I want a membrane, but I am certain it would stay more-or-less forever without additional support. Under-floor insulation guidance: https://www.gov.uk/government/publications/insulating-suspended-timber-floors-best-practice https://www.greenbuildingstore.co.uk/information-hub/insulating-suspended-timber-floors/ https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors http://www.sofiepelsmakers.com/suspended-timber-ground-floors.html

Splendid, ST! Thank you. The next step is Auto-Crayon-Aided-Design, where the crayon guides itself.🙂 @JohnBishop, ST has depicted my suggestion perfectly. However now I have seen your pictures you need this less than I thought (indeed perhaps not at all if your pics are representative of the situation over the whole eaves). The point of 'my' membrane is to ensure that you cannot block the vent gaps. AFAICS, if they are what I think they are, your black plastic formers do exactly that; if you push the insulation hard against them there still remains airflow. So, message to anyone in future with this issue, if you have nothing to stop the vent path being blocked then mine is a fair idea. If you have plastic formers or similar like @JohnBishop's, you probably don't need my suggestion.

We got under 2.5m3/m2/hr in a refurb of a 19th century house with all sorts of issues and I was a bit disappointed that we did not get better. I would be really disappointed with 5 on a refurb, let alone a new-build. Depending on what the consultant knows about your knowledge I'd have expected simple things like explaining what a solar diverter is, but also looking more broadly at air-tightness, explaining what can be achieved and why you want it, and so on. Does 'finally written...' imply a long wait?

@ProDave said "Get 1m lengths and put nuts on before cutting into 3 or 4 (I'll explain if you go ahead with this). Rod, nuts, washers, angle grinder." Good call. And when you (OP) forget to put the nuts on you'll be off to buy a grinding disc for the angle grinder for 'fine tuning'.

Yes! I do not have pics, I am afraid, as I am one of the world's worst photographers. Basically temporarily clear away the insulation from the eaves. Work out the vertical height (depth) of the insulation you want. cut a piece of breathable membrane which is a bit more than the length of the hypotenuse of that triangle. Lie uncomfortably on your front with your head nearly wedged in the eaves and a staple-gun in one hand and the breathable membrane in the other. Staple to the underside of the rafters tightly, so that as you push the increased-depth insulation up against the membrane the ventilation gap (the gap between the membrane and the underside of the roof covering) remains fully open. If there is a stub of wall to seal the membrane to at the 'bottom of the hypotenuse' then even better. This 'deflector' should allow you to insulate tightly and deeply without risk of getting air-flow between the layers of insulation or compromising the ventilation. I am sure someone with skills in CAD could draw that up in a moment.