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Use this simple cut out guide to work out your ideal insulation thickness for your desired U-Value.

Well done the wrinklies

No idea. Would be OK for windows and doors, but not very good for slab insulation.

Doesnt building control use 15 years as its guide as to insisting on stuff, at least in a retrofit situation?

Now thats a bit of a minefield if ever there was one...............

Or you could not bother and just crack on and fit the insulation. How will anyone ever know? As always, aside from cost, what will the BCO add to this simple excercise? Bear in mind, they may not agree with your proposal and you may need to do more/something different to comply. Once they know work is happening, they know. You cannot have them "unknow".

Go to ChatGPT and type in... "Is it possible for cold air to pass through a double glazed door or window by passing around the sealed double glazed unit i.e. between this unit and the frame it is fitted into ?" When Chat GPT answers and then asks you the frame type etc type in,,, "a upvc frame which has been fitted a few weeks ago and comprises of a french door fitted between 2 outer fixed glazed windows" (And the first 2/3 minutes of this video may be of interest... https://youtu.be/rc5DutkQ0WM

Thanks… that was my gut feeling. Do you think good above both?

Also that heat camera is showing the coldest strips at the bottom edge of the double glazed units i.e. just above the bottom frame where the glazing starts. Could it be that the double glazed units were not a good tight fit into the frame itself, so that you actually have cold air finding it's way through the windows/doors themselves - underneath the base of the double glazed unit - i/e/ between upvc frame and DG unit. Window companies may be ordering in ready made dg units to fit into their frames. They will NOT want the glass to end up too big, so it would seem quite possible for the dg unit to end up on the small size sometimes and perhaps not to fit tightly ? Also there are usually seals between the glass and the frame - are these tightly fitting ? I think it is usual to have a little lee way for heel/toe adjustments, but ultimately the entire door assembly should be perfectly air tight on both sides. If you fart outside you should not notice it inside :0). Maybe you could try some sort of smoke test ? (In my youth I once had to travel around with a fire service chap for a few days as part of a business analysis - the height of his entertainment was taking out a phallic shaped smoke machine which hummed and emitted smoke from the tip to test the smokes. For some reason he thought it amusing to test the smokes in the headmistress office when visiting the girls schools ?!@)

Overlap is probably enough, but taping will guarantee it and keep it in place while insulating/screeding.

Can you show us a pic with a little 'boat' spirit level on the cill so we can see the nature of the fall (or not)? I *seem* to see a fatter mortar bed at the back than at the front, which suggests a fall, but an accurate spirit level will be a better judge than my old eyes. I have used the EWIstore overcills with success.

Can I add in another consideration. From what you have described the complete window/door consists of multiple individual parts: The two fixed side windows with their own frame (presumably pre glazed with double glazing units), the central doors with their frame, and the cill piece itself which the other parts sit onto as a base. Have you carefully checked the vertical and horizontal alignment of these different parts ? If for example the two side windows were fitted to the outer edges of the opening first, but the inner vertical frame edge ended up not being perfectly vertical, then fitting the door frame vertically against it would become a problem. Quite possibly a fitter might then choose to then fit the door frame perfectly vertical regardless. So there would then be a variable gap between the side frame and the door frame - quite possibly tight at the top, but with an increasing gap near the base. This could then be filled with mastic/sealant and appear normal. However there could be an uninsulated gap or path left between the fixed windows and the door frame at the lower part - thereby causing cold bridging problems. In a similar way there could be misalignment and gaps occurring between the cill and the window and door parts fitted onto the cill - again possibly leading to cold gaps between the cill and frame possibly hidden by sealant. I have to say it is a skilled and potentially time consuming task to assemble frames into an opening with precision such that all the verticals are spot on plumb and all the horizontals are spot on plumb level. Doors especially need to be true so they don't swing open/closed of their own accord etc and meet correctly when closed. Anything other than expensive spirit levels are unreliable and can easily be out. Small alignment errors which many tradies might think 'good enough lets go down the pub' might mean installation gaps at the lower part of the frame and between cill and frames. I might be barking up the wrong tree, but get yourself a long expensive known accurate spirit level (or plumb line) and carefully examine whether all the parts of the installation are properly plumb and tightly joined to one another. (It took a second fitting visit to get our alu bifolds right and they sent their crack fitters that were at it until 7pm getting it all just so. And I imagine UPVC frames may show more bendability than aluminium.)

Thank you for your comments. The overlay UFH is a continuation of the existing UFH in the main house, so seemed sensible to carry it through for continuity and levels.

Thanks for the reply. This is an internal stud wall on timber frame build. Raft slab. No dpm under the slab. Will lap up external walls but no bed on internal stud as within the envelope but had wondered about taping to the dpm strip under the stud. Have read that overlap alone is sufficient though hence confusion. ta

Is the image the right way up? Does the concrete have a DPM under? If so I would just lay your new DPM and lap up the wall. If not you may need double sided quality DPC taping.

Should of added if low temp system and/or you do cooling you also add biocide and chemistry should match your inhibitor.

You are still comparing overall thickness though (I know you had a (expletive deleted) up are limited on thickness). What you need to do is pick a U-Value (i.e. 1.2 W/m².K) and compare the prices to achieve that, not compare prices to fill the gap up. Not if you had made that decision in 2015, 6 years before our energy prices doubled.

Argh I’m overthinking this so could do with some advice. Here’s a photo of my internal stud wall with dpm strips underneath. I was going to lift up the thicker black dpm and lay my floor dpm with double sided tape between the 2 but thinking now that it’s probably better to lay the floor dpm over both? I’m also unsure whether taping is needed or the overlap is sufficient? Paused mid job to think over a brew so any advice greatly appreciated. 👍☕️ @nod@Nickfromwales @saveasteading

'Renovation of a thermal element' is 'adding or replacing a layer'. The 50% is *of the relevant thermal element in the room you are in*, so if there are 2 external walls and you IWI them both, you have done 100%, so definitely BC approval required. Theoretically if you did 49%, 49% and 2% in separate tranches you could arguably do it 'outside the Regs'. However when questions are asked when you come to sell the purchaser or their solicitor may not understand the 'letter of the law' under which you carried out the works, and may ask for an indemnity of a Regularisation Certificate. Your walls and ceiling to unheated space would be treated separately if done at separate times, but for counting purposes the 2 external walls are 100% of the wall area and the ceiling is 100% of the ceiling area. I always get BCO approval even for IWI of 1 external wall since, if and when I sell, I would want to be able to wave the completion cert in front of the person who was trying to find reasons to reduce the price. 200mm of wool will not reach the 0.16 U value for compliance (Edit: It might, just, if the exg 200mm was 'extra special' sheep's wool with a (lower-than-mainstream-sheep's wool) lambda of 0.035W/mK) but if it was done at a time when 200mm did 'cut the mustard' then as you are not adding a layer or replacing a layer (the pl'bd) you do not *have* to add anything. I would if I were replacing the ceiling (and of course arguably at that stage you have to stump up the £180 or whatever (may have changed since last I did one) for a Building Notice).

If it's not a building of historical interest (listed) and you are doing insulation internally and externally, not sure why anyone needs to be involved. Photograph everything good for future reference. Only thing other than the above, if the wall is currently breathable keep it that way, so add mineral wool wood fibre etc not PIR. I would be adding another 150mm on top of that.

Hi all, I'd like to ask a 'general' question about adding internal insulation to ONLY the 2 external-facing walls of a bedroom in my victorian terrace, with regard to what Building Control are likely to require of me, etc. These 2 walls amount to precisely 49.1% of the total 4-walls area of the room. I read somewhere that if an upgrade is below 50% then B.C.don't need to be involved, and thus I wouldn't need to meet U-value requirements etc! Or, do things need to be looked at more holistically & the whole room taken into consideration - for instance - the ceiling was, some years ago re- boarded (but not yet skimmed!) so would B.C. add this in as part of my upgrade (& thus becomes >50%)? I've no plan to add more insulation to the ceiling but there's an existing 200mm of wool atop in the loft space, brought up to Regs & without having to apply to BC ! Also, to ask opinions of folk on here about whether its worth all the 'faff' of obtaining B.C. consent for these smallish, almost DIY projects - For myself I'm keen to comply since, when I eventually sell (10+ yrs hence) I believe a search is made, for the sale documents, to ascertain if home improvements/works legitimately comply with Regs. But it seems to me the public commonly are quite blasé about the whole matter, + some tradesmen 'forget' to apply on behalf of client, on small jobs at least. This 'delinquent' attitude seems quite common to me. Am I right this comes back to bite the house-owner eventually? Any comments much appreciated.

It's the tiles that they complain about.

Cutting. I've just been discussing it with the guy likely to be doing it . He likes the latest and best tools. But for this he says a coarse cut handsaw and a big bench. He is up for the challenge of tiny waste figures if I predraw the best use by room.

@flanagaj I presume you won’t be attempting to access the garage from within the house? And if not, why are you planning an ‘attached’ garage and not ‘detached’? Detached would be a whole lot easier I suspect.

Ok so the issue is where the higher garage founds meets the lower house. The ground must slope down to the house in this area so you also need to think about drainage and the visuals. You don't want to be looking at exposed concrete. I would expect a standard stepped foundation a few feet along the garage wall away from the house depending on how the ground rises. Some engineered bricks might be needed where partly burried? Check ground levels carefully to avoid the wall of the house accidentally becoming a retaining wall. I agree an SE needed to design how the garage floor slab abuts the house.