Redbeard

In 2022 I paid £3.90 for a radon report from BGS. Among other things it said: Is this property in a radon Affected Area? - No A radon Affected Area is defined as where the radon level in at least one property in every hundred is estimated to exceed the Action Level. The estimated probability of the property being above the Action Level for radon is: 0-1% Guidance for new buildings and extensions to existing properties What is the requirement under Building Regulations for radon protection in new buildings and extensions at the property location? - None BCO accepted this. I did not have to take any measures at all.

Use lime mortar if you are mortaring, and if you are not, have you built a drystone wall before. I have not, but I have worked with enough people who teach it to know that I would not do so without tuition. I am not a retaining wall expert but I should have thought a gravel footing to a retaining wall was asking for it to rotate and fall flat on its face, but then if you mean for example consolidated crushed limestone then it is probably much less of an issue than I foresaw with round washed river gravel.

+1, plus I think we need to know more about the building and the wall build-up (is it already an insulated cavity wall, for exampler? Is it old and retro-filled? Is it new. to Bldg Regs? You may need a vapour control layer in the 'sandwich'.

What is 'it' in this context?

Have you had a look at this? https://www.gov.uk/government/publications/preventing-and-resolving-disputes-in-relation-to-party-walls/the-party-wall-etc-act-1996-explanatory-booklet If not, see what it says about your situation. I think I would have to see a sketch plan and section to understand that, and without understanding it I cannot tell you whether I would accept it or not, I am afraid. I would have a read of the guide and decide whether you feel the works require a PWA. If you do I would suggest you ask your neighbours what they have done about that. If your reading of the guide suggests a PWA is req'd and they say no it doesn't I suggest you send them a link to the guide, or print out the relevant section, and ask them to explain how their interpretation can differ from yours.

After. I had to complete the relevant pro formas. I was client, PD and PC. To the end of that sentence I would add 'without a WUFI calc'. In this particular case I did not have one, but have had them for the same house and same orientation so I was confident to go on past experience in this particular case. My starting-point with IWI is always trying for 100mm unless WUFI says 'no'.

Not sure if that is entirely true. You can still submit a Building Notice (which just says 'in no less than 2 days time from now I propose to start this work. You can come and look, and here's your fee). It works for work you are confident about, but you cannot guarantee that your BC will talk to you about it before you start. In my LA I am fairly confident they will agree with my rationale, even if the U value achieved is slightly worse than the B.Regs target. I don't think the Bldg Notice procedure has changed from what I describe. It hadn't in Oct last year, anyway, when I used 100mm wood-fibre to achieve a U value of around 0.35, against a target of 0.30. Under a Bldg Notice I *have* been asked (where relevant) to provide structural calcs. I *have not* ever been asked for 'proper' dwgs, SAP calcs or WUFI (though I have sometimes offered the latter.

It's not the structural soundness I was worried about - It's the holes in the insulation. Small, yes, but if it has concrete in it it is not insulation.

...and something I forgot to add about the box gutter. It is not just a condensation risk but also a whacking great thermal bridge, even if you mitigate it. Re area-weighted U values: Very roughly: 300 on the flat in eaves and 300 on walls, @lambda 0.044W/mK (U = 0.15W/m2K approx (no allowance made for 'base case' U value, but equally no negative allowance made for bridging thro joists/studs, so assume they cancel out. From https://www.pbctoday.co.uk/news/building-control-news/glazed-home-extensions/93045/ Calculate the overall area-weighted U-Value This calculation can help to show that the area-weighted U-Value of all the elements (walls, floors, roof windows etc) in the extension is not more than that of a similar extension having the same size and shape, but which complies with the minimum U-Value standards for all the walls, floors, roof, and the opening areas as set out in the Approved Document. The area-weighted U-value is given by the following expression: {(U1 x A1) + (U2 x A2) + (U3 x A3) + …)} {(A1 + A2 + A3 + …)} Where: U = the U-Value of the element e.g.: wall U1, roof U2, floor U3 etc. A = the total area of the element (m2) e.g.: wall A1, roof A2, floor A3 etc.

Are the top 2 layers (under the rake) stacked or laid? If the latter, why the through-joints? Of course joints should, in practice , be so tight as to be non-existent, but in any case joints are generally staggered. I would be ripping out those 'trimmings'. Yes, I am all for economy, but those are just joints which will not be filled properly (maybe, perhaps...)

It is a long while (happily!) since I had to read the PW (Etc.) Act guidance, but if the wall is built up to the boundary surely the footings go under your land, thus triggering an obligation under PWA. Others will have more recent experience and better memories than I do! As above, I am not sure he can... Anyone got more recent knowledge than me?

In all the jobs I have done or seen with a service void there is usually a VCL immediately behind the battens. Some use 2 battens at 90 degrees so cables can pass up and down as well as side-to-side. Remember that in screwing through (??) the insulation to form a service void you pierce the VCL. Optimists say a hole with a screw in it is not a hole at all. Pessimists gun silicone into the hole and then screw through, giving your screw and airtight (hopefully!) silicone grommet.

That's *really* not a messy cellar! It looks like you can find some space to put your feet. We really need a SE along, but (as a NOT SE) the only comment I would make is that, as drawn, maybe the remaining pier on the RHS is a bit thin?? In reality I suspect that the treads are to some extent cantilevered off the neighbour's wall. We took our stone steps out to aid comprehensive waterproofing. You might also get more useful space if you did that (though it is not for the faint-hearted, and the wall in question was , for me, not a Party Wall. (PWA may be triggered?? - not sure about that.).

"RWA45 insulation slabs achieve Lambda 0.035 W/mK and are available in seven standard thicknesses from 25-100mm, with a density of 45 kg/m3." 'Raw' insulation value (not taking into account anything 'offered' by the structure or 'depleted' by it (joist thermal bridging, for example)) would suggest a U value of around 0.2W/m2K for full fill. I'd also look at making everything (e.g. round the joists and any other penetrations of the 'envelope') as tight as a tight thing in terms not only of 'thermals' but also airborne noise.

You *may* get away with using an extension tube (flexible brewer's/wine-maker' tube is what I have used. I say *may* because the extra length slows the flow and if the first 'hit' is not fast enough nothing sticks and you just end up with a foam floor. It has worked for me, and also it hasn't...

Glad to have been of help. OK, so you have maybe decided to go for the +125mm on the roof (subj to Planning approval). But before you do that... Can you add a dimension for floor to horizontal ceiling (I could draw it and measure it but (a) I am lazy and (b) I have lost my scale rule!). If it would not make things too crazy tight I have in mind a proposal to Bldg Control. For the width of the doorway 50mm PIR between rafters (leaves a 25mm vent gap which I regard as sub-optimal but as you are re-roofing with slate, get a really good membrane and you should be OK for that small area). That gives you a 'tunnel' to enter the room and you don't crack your head. For the rest, 25mm PIR between rafters and 75 below, fixed at wide centres with insulation collars/screws and tightly taped as VCL. Plasterboard fixed directly below (which required you to remember where the rafters are under 75 PIR. For a loss of a further 25mm space, x25 x 50 battens at right angles to rafters over the PIR and adjust centres to suit your chosen boards (I can no longer wrangle 1200 x 2400 so I use 900 x 1800. A very rough calc (unadjusted for the bridging of the rafters) for the main area with the 25 + 75 'sandwich' gives a U value of around 0.22W/m2K. You could propose that to BC as a compromise and quote the section from the Regs in my previous post. Note that even that reduced amount would give you about 9-10 times the insulation value of the un-insulated roof. They *could* ask you to have a SAP calc done to prove that doing it to the full std would have a payback of more than 15 yrs but I have only been required to do that once. Edit: If you decide to go for the 'raise the roof' option be very clear on the design of the box gutter and the box it sits in. I would (could) be concerned about condensation on the bottom and sides of the metal box , wetting the timber box. Maybe consider building the 'under-box' out of Compacfoam or XPS? I would also get a roofer to express an opinion of the 'tails' on the box gutter. I would worry they are potentially too short/not profiled sufficiently.

Do the training and become a registered installer. You don't actually have to work as one, just be on the list. I found myself a registered installer for a couple of companies mainly by dint of buying their stuff. Fills you with confidence, doesn't it?!

@Neverfinished, could you please post the dwg again with dimensions, so we can see what the pinch-points are? I am particularly unsure of how the 1.72m headroom 'kicks in'. Is it because the stair comes up under the sloping roof? Is there so much more headroom in the room itself that you could fit insulation under the rafters? Your statement below suggests not:

What is the plan for insulation in that rear monopitch roof? If, for example, you are trying to use something 'friendly' (and perhaps to achieve a'better than Regs U value) whether below rafters as a cold roof or above them as a warm one, you may find yourself 'fighting' with either the GF windows on the inside or the FF windows if the insulation is above the rafters.

I realise complexity makes £/m2 costs a bit meaningless, but my GBS (21 Degrees) 3G wins came out at about £735/m2 supply only in 2022/23. (Tried to send you a PM re another firm but apparently you cannot receive messages...)

I fear wood-fibre etc. *will* 'break the bank', at least compared to the costs of PIR. Don't get me wrong, it is exactly what I propose to use in the refurb of my rooms-in-the-roof, but mine is a steep-pitched roof with plenty of headroom. My 'sandwich' is proposed to be: 20mm rigid WF (lambda 0.044W/mK) between 75mm rafters leaving the recommended 50mm (well, 55 here, but Gov't guidance says 50) ventilation path. 225mm flexi WF (lambda 0.039W/mK) in Larsen Trusses, and 20mm WF again as plaster carrier. This sounds like it would take a lot of space which you have not got, and it *will* cost plenty. For me this is the right thing to do and I will shut my eyes and scrimp on other things to achieve it. Unless you use PIR (and I am certainly not trying to persuade you to) even your +5" on top will not get you a compliant U value. There are some get-out clauses in the Regs. See pp 25 and 26 of 'Part L': https://assets.publishing.service.gov.uk/media/662a2e3e55e1582b6ca7e592/Approved_Document_L__Conservation_of_fuel_and_power__Volume_1_Dwellings__2021_edition_incorporating_2023_amendments.pdf And try to get a word with a Building Control officer. Depending on staffing levels they can be hard to pin down, but as well as ensuring compliance with the regs they also have to be realists. I think if you are trying to get an area-weighted U value of 0.15 with such limited space in or under the rafters you might find that you are trying to get more insulation in the eaves voids than they will physically contain! Fairly certain Planning permission would be required to lift the roof but, importantly, if you are using WF or similar, 5" will not be enough - see my lay-up referred to above. Also, as Warm roofs are typically done with rigid material, the weight of rigid WF @ 140-180kg/m3 would, I think, break your roof! Flexi is, I think, about 55kg/m3. I am running out of stamina tonight but have a look at this and fire back further Q's and I'll try to help if I can.

When you say 'running out' I take it you mean running downhill to the dormer cheek. Am I right? I can see that )possibly) on the 1st pic (RHS) but not sure if I can see it on LHS, or whether I am just convincing myself I can! I am generally fairly pernickety, and I would not, I think, have picked up on that. How often will you stand and look at it? If it will annoy you forever, change it. If you can programme your eyes and brain to 'ignore', live with it. Ah, I have just read again and seen: Hmm, maybe my advice above won't help then. I *suppose* you could basically eye it up, decide on what would look right to you, decide the adjustment required for the eaves course, alter the battens accordingly and go from there. I cannot think of a more 'scientific' way. If that helps a little, good. If it doesn't, sorry.

If you are really 'taking off the roof' why not try to get a structural design which includes removing that cross-timber and providing alternative strengthening? Have you got a structural engineer? Have you been through Building Control? Is Planning Permission required?

BC won't like it, nor will they like the fact that you are not using permeable paving, I think. Are you getting Planning Permission? Has the would-be contractor done a percolation test? If a soakaway does not soakaway it's just called a. And it can also soak away too fast. That's not good (or allowed, I think)

What for? Footings, lintels etc. @Tony L, did you not need a structural engineer? A long time ago the architects I worked with did their own SE, but from quite a long while ago they started using consultant SEs.