Redbeard

Yep, tackle 100% of the floor in 40, 40 and 20% tranches and you may have cracked it! But don't quote me! My justification for spending more than I probably have to on Bldg Notices is to avoid the situation on a subsequent sale where a buyer's solicitor queries BC approval for specific works. If the answer is, or suggests that, that you don't have it they express 'outrage', which can be instantly dispensed with if you drop the price by £x000. I will have in my hand a sheaf of BC approvals and stand my ground.

I was looking for an English source (as the above is from Wales) and found this in https://www.tameside.gov.uk/buildingcontrol/guidancenotes/note24guide1.pdf - it's at the bottom of p.1. It is the first time, as far as I know, that I have ever seen this: For some reason I cannot cut and paste from that pdf. It's at the very bottom of p.1 and begins 'From 9th January 2013... and in summary says "the installation of thermal insulation to suspended floors..." and ends "...is not considered to be controllable under the scope of these regulations". It's not what I have gleaned from other sources, and it obviously hasn't been proof-read!

@saveasteading, I agree it is not totally clear at first sight but I have queried and 'tested' this on many occasions. The impression I am left with is the same as this link suggests: https://www.carmarthenshire.gov.wales/council-services/building-control/building-regulation-applications/thermal-elements-application/ says: "Renovation of a Thermal Element means adding a new layer to a Thermal Element or the replacement of an existing layer. When the renovation is more than 50% of the surface of the individual element or 25% of the total of the building envelope, Building Regulations approval will be required prior to carrying out the work and the Thermal Element may require upgrading to provide more insulation. When assessing this area proportion it should be taken as that of the individual element, not all the elements of that type of building. The area of the element should be interpreted in the context of whether the element is being renovated from inside or outside, e.g. if removing all the plaster finish from the inside of a solid brick wall, the area of the element is the area of external wall in the room. If removing external render, it is the area of the elevation in which that wall sits. The consequence of this change is that much building work, previously exempt from the Building Regulations as it was considered a repair, may now require approval. For example: Replacement of a slate or tiled roof covering even if like for like Re-plastering of a wall Replacement of felt on a flat roof Renewal of a ceiling below a cold loft space External rendering or re-rendering of a wall Renewal of cladding to a dormer Renovation of a ground floor involving replacement of screed or timber decking" Something of even more interest (to the pocket at least) is that my LA used, many years ago, to charge me separately for each thermal element touched, whereas their final position was that one Bldg Notice application covered 1 *or more* thermal elements. Saved me (or rather the client) up to £360 on some jobs. Re netting, it's one of the 'hammocks' I used to use, until I started using breathable membrane which, when taped, not only holds up the quilt but also limits 'wind-wash'.

Yes, you are reading correctly. You are 'renovating a thermal element' (adding or replacing a layer of something which gives on to the 'outside' - the sub-floor void being 'outside' for these purposes). You are unlikely to be picked up on it but yes, the obligation 'kicks in' because it is internal work - thus although it is only part of the ground floor, it is 100 percent *of the floor in the room you are looking at*. Doing it is good (Ecological Building Systems offer this Best Practice advice (https://www.ecologicalbuildingsystems.com/post/best-practice-approach-insulating-suspended-timber-floors?srsltid=AfmBOopVdS5DMUhiXLkltolwyE688i09EDVP0y4fzzJw_IZRi9jJ5hON) and UK gov't offers comprehensive advice too (https://assets.publishing.service.gov.uk/media/5f05d211d3bf7f2be6e0217a/suspended-timber-floors-underfloor-insulation-best-practice.pdf)). To echo other comments 'fluff' is more likely to take up dimensional variations and not fall out.

I would argue the risks of condensation are low if the void above is properly cross-ventilated. Strictly in a roof it's not interstitial, as there are spaces, not interstices (IC would be an unwanted 'filling' in a 'sandwich' of, for example, solid wall and PIR). 50mm minimum vent path, and ensure that the eaves, soffit or fascia vents are of sufficient cross-sectional area (lots of guidance on the web). How many old loft spaces with retrofit insulation and retained ventilation do you see with condensation issues? In my experience it tends to occur when cross-ventilation is compromised. Am I right in thinking that your insulation between rafters is above a habitable room? If not, why go to the significant extra cost compared with laying 300-500mm of cheap stuff on the ceilings of the rooms below? Note that 225 (9") rafters, after the 50mm vent path, will only allow you 175 (7") insulation, which with a fully breathable product such as flexi wood fibre will not give you the B. Regs target value of 0.16W/m2K. I would consider DIY 'Larsen (roof) Trusses', with the rafter as one 'chord', spacers of OSB or ply, and a secondary (?50 x 50) lower chord. Make it as fat as you need, then.

@NickfromwalesWhat do you mean 'look'?! (I did spend half a minute looking for the typo in my post though! Got there!)

Messrs Bing and Hornby will be turning in their respective graves! ☺️

Yes, possibly. Permeable substrates leave lots of gaps and have few or no fines. What you describe sounds like 'MOT', which will have compressed, the fines filling in the gaps and leaving a very serviceable not-very-permeable surface. If it was what I think then it never could be permeable enough for a SUDS solution. But I may have misunderstood. Can you give us more detail, please?

I don't disagree with you in principle, but I have just been thwacking hell out of the peripheries of a tiled insulated-plasterboard-and-skim wall in a shower cubicle done about 25-30 years ago - surely provoking potential falling-off if it was going to happen - and all is completely well (I wouldn't do it like that now, but it has obviously survived extremely well).

I searched: "'flashing' for joint between shower tiles and shower tray" and there seem to be the 'shower versions' of a roofing 'undercloak' which, it seems to me, might 'safely' and reliably bridge that gap. I have never used one, but they seem to be what I would be looking for if I had this issue. If the 'lip' of the flashing is a bit wimpy you might have to gun-in some gunge to provide a 'back-stop'. I hope that may help. Edit: Of course many would simply get a (say) 6mm cement-based tile-backer board and screw or stick it on before tiling.

Sorry, I know you wrote 'joists', but I read 'rafters', and was thinking 'hybrid warm roof'. So you are simply putting down insulation in a loft void? If so, and it's not built yet, you can, for a start, design the joist spacing for the roll width. If you truly have 175 joists and the choice of 150 or 200 insulation use the 200 and rip off bits from a spare roll to fill the little gaps between. Then lay 150 over the lot at right angles. Make sure your electricians know you will be insulating over the wiring and they can design cable sizes accordingly (or, better, design cable runs to avoid getting buried.

See

0.15 https://assets.publishing.service.gov.uk/media/69c122a6cfa346b9d4704a55/ADL1_2026.pdf Table 3.2 Limiting U-values for new fabric elements in existing dwellings. And in answer to the 2nd Q: It depends. You'd probably get sign-off from many BCOs on the basis that 0.3/0.044=6.818(R value) and 1/6.818 (U value) = 0.1466(W/m2K). However your description ( conjures up for me a picture of lots of timber to contain the 'above' bit. You can do an area-weighted U value calc (Part L always used to have a guide to doing so - I suspect it still does) by notionally 'lumping together' the timbers into 300 thick 'portions'. If, say, you end up with 2m2 of wood at 300 thick, then your U value calc is for (say, on a 20m2 roof) 18m2 of insulation, and 2m2 of wood. I suspect you could end up slightly over (worse than) the required U value, but possibly no-one will quibble. I have often done area-weighted U value calcs (for my own 'happiness') and I do not think I have ever been asked by a BCO to show them.

In terms of changing the appearance, yes it does. In terms of damaging the property, yes it can. In terms of damaging all properties to which it is applied, no it doesn't. Like all insulation measures it needs care and risk analyses. My guideline is that the end result must not look stupid. If it does, it probably is, and there are probably several more stupidities thrown into the mix. 'Cowboys' never give any discipline a good reputation, but there are good guys out there. I just feel sorry for those who get not-a-good-guy.

Do the circumstances require it to be a permeable sub-base? If so I am not sure MOT will cut the mustard (others on here know more than I). I used between 200 and 400 c40mm crushed limestone, membrane, and finer limestone (but not sand or MOT) as a bedding layer.

... and presumably levy a new charge on you. Would LABC give you anything back? (I don't expect a positive answer!) I am not sure I would actually know where my LA's BC dept 'hung out', and I'd think it v unlikely now that I could actually go and see them. Everything I have done with them for years is by phone or e-mail, apart from visits.

Which ones? I suspect 'put boards' should read PIR boards.

I am not clear what the issue is. Is this a house which you lived in before the works, which has a proven record of noise transfer issues from GF to FF and vice versa? If so do you get the impression it is (a)impact noise which is the main one, or (b)airborne noise. If the former I would not necessarily expect a big change, as much of the 'noise' could be transmitted through the structure via joist pockets. If the latter it may help. If there was not much of a problem anyway why bother? (Unless you are using the insulation for both sound and heat *and* you want to 'thermally compartmentalise' the house).

As you say the front looks difficult for EWI with the incoming power-lines. How would you deal with them? Lots of Red Tape there, I guess. Step-cracks above front GF window (are you happy the original problem has been solved before you 'box it up'?), questionable boundary (? - your porch roof seems to meet a line down from next-door's FF window cill, so is that the boundary?) Where, then, does the fall-pipe go once you have EWI'd? I think your idea to IWI may be less fraught. However if you were to EWI the front... If there is no soffit and you think it would look daft to extend your roof-line only, how do you deal with the EWI projection? 'Industry Standard Capping Details' (bits of bent alu gunged in silicone) have a limited life, particularly if they are of the 'downstand' variety. Measure carefully, outside and in, the height above the window. It is not unknown for EWI to stop before it reaches the height of the ceiling inside, in which case what do you do? If that were left 'un-treated' you could face a strip of mould at the top of the room. Internal 'downstands' can be done. Bring it down well below the line of the top of the EWI. I am probably not alone on here in not regarding 300mm as a huge lot for the loft. Assuming you are not storing stuff in there, and that you are using 'cheap stuff', why not use 400, or even 500mm? You'll only do it once. If you do that you'll probably find the biggest 'shortcoming' is then at the hatch. It's difficult to leave yourself a way in *and* achieve excellent insulation coverage and air-tightness. Get inventive!! I worry about the plan to IWI the gable wall in the garage, certainly at 100mm - with a lot of PIR on a wall giving onto soil. If you look at a Glaser-method condensation risk assessment for PIR (which you can get for free on many manuf'rs' web-sites), and the manufacturer's advice, you'll see that they require you to keep the 'outward path' vapour-open (by removing impermeable treatments inside and/or outside). That's because the VCL on the inside (if indeed it is functioning as a 100% effective VCL) blocks the possibility of any retained moisture in the wall coming back in. As far as I can see, if you block the path inwards, you have no moisture-loss path at all. I may be wrong, though. Enlightenment welcomed! I've written a lot. I hope it is useful - it is certainly meant to be. A lot of 'thinking-through' to do, I reckon. Do come back with Q's and comments. Perhaps ask Nottingham Energy Partnership (0115 985 9057) if they can recommend an assessor. A retrofit assessor course may well increase your knowledge level (of course I don't know how much you already know) but it will not necessarily (AFAIK) give you access to a measured survey model and software, so while it may help you to make a judgement it will not allow you to spit out 'numbers' - running costs, kWh p.a. etc). You can, of course, do that 'long-hand' if you have time, and I bet there are some free access models out there somewhere. Edit: Re EWI - do not automatically think you cannot go below DPC. You do have to think it out carefully and perhaps use different materials but it can be done - down into a French Drain. Caveats re where does the drain exit, have you just dug below the footings, etc., but with care it can be at least considered. I see countless examples where the EWI Co has dutifully avoided bridging the injected DPC which is 150mm at least above internal GFL - leaving a cold bit just behind the 120-year-old skirting...

Hi @Julestools. I don't know what mix was used. That was before my involvement. I am not a lime expert but I think I share your idea that something as rich as 1:2 or even approaching 1:1 might be required. I don't know if having it that rich has any downsides. (Come to think of it I have used lime putty when I want a really creamy mix. Could you do that?). Out of nosiness I note that you are proposing mechanical fix only. I take it this is probably onto existing gypsum plaster. Others (including specialist merchants) disagree, but having gypsum in a 'sandwich' always makes me a bit uncomfortable. I usually strip that off and do a lime parge coat, but then maybe I like making work for myself!!

Hi @flanagaj, I tried to send a private message, but I gather you cannot receive them. Have you intentionally disabled the PM function, or has it just disappeared and is this an issue for Forum mgt?

... and I was just about to write that too. PIR externally amounts, in my view, to a VCL on the wrong side of the 'sandwich' - and I wince every time I see a TV show depicting it. How about rigid wood-fibre with a scratch-coat of lime render before the battens and (?hit-and-miss?) larch?

I know someone who tried to use NHL for the same 'economy' reasons. I think the main problem was using it as the 'adhesive coat' behind the boards. As I recall it simply did not stick at all - not even the 'light tack' afforded by RK70. I don't think he ever tried it on the boards, since he had to buy RK70 for the 'adhesive' coat anyway. Particularly if you are doing it yourself and have not done a lot of plastering I'd recommend RK70. It is so 'forgiving'. Slow, in colder weather, but relatively easy for non-plasterers to pick up.

I think we need a pic of the other end (the end nearest the camera position, where the stairs open up and there is no wall on the L). Likely no problem spanning from wall to wall in the 'distance' of this photo (where the coats are), but then nearer the camera you only have one wall... Is there a 'stub' of wall behind the camera on the LHS so you can bridge across the stair opening?