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I'd echo what @ProDave said about PPE. Definitely a full face respirator mask. We did a similar job but from above when replacing floorboards and used Thermafleece (wool) which is way nicer to handle but pricey and hard to cut. Of the rockwools Knauf products like Frametherm do seem the nicest to handle and shed less fibres. Instead of netting, use a breather membrane (and tape it to the wall edges all round, you may need to PVA walls before taping) as that will cut down hugely on draughts. The whole job will be difficult and time consuming but the results are transformative for comfort. Are you sure you have access to all the crawlspace? Our joists were supported at half span by a low wall.

The intention for plant room is that the 12mm green PPB has 18mm hardwood ply board nailed directly to it, then items will be installed into it, with screws going through both. My main concern is if screws are put in and then later removed (items moved), then how do I maintain the airtightness. All of this is, of course, easy to keep an eye on when I’m doing it myself - my concern is once I have the electrician, plumber and others involved who don’t get the significance of ‘its just a screw’. So, how important is it to fuss over this level of detail - am I right to be so picky? (Possibly my ‘default’ approach 🫣)

/board. A few years ago mind...

Thanks all. This is an Edwardian house that is huge. I was surprised that it only has 4 inch deep joists. I’m talking about thermal insulation installed from the crawl space just to be clear. it’s it’s going to be a horrible job, but I think it will pay dividends well I hope it will. No, it’s a case of finding the right material to use as already mentioned I will check out frametherm

Per board or m2? At present my best price for 100mm white eps is just over £15/ board of 2.4 x 1.2.

@ProDave Thank you so much for this suggestion! We had some offcut Medite vent board do the same as it was left to one side. This is absolutely within my ability 😁

Depends on the "STUFF". If it's a 1mm sheet of metal then water and air will get through so special screws have special washers that bind to the thread. A screw into timber might allow damp but not air through...so perhaps a smear of mastic is worthwhile. Yes through wood has been compressed so is tight, but could get damp. If you look at screws into cedar you can see that damp has got in.

Do you mean structurally or thermally? Structurally if they've lasted this long then should be fine. Must have quite a few intermediate walls? Thermally as @ProDave says be a hell of a lot better than nowt. Some modern houses still have 4" in the cavity.

when we were ordering ours, white EPS was £11.57 for a 50mm, vs £13.70 for graphite

When I was screwing into stuff I put a blob of hybrid silicone stuff on the screw. Whether it made any difference who knows? Once a screw is in the wood the wood contracts around the thread, so I doubt there will be any leaks anyway. Ours aluminium faced so used aluminium tape to cover all the staples.

4" will be a lot better than nothing. It will be a miserable job from below you will need full suit and respirator imho. Use something like Frametherm 35, a lot less nasty than most flavours of rockwool style insulation and quite stiff so should push into place and stay there while you get the netting in place.

Where I worked before they built a spiral staircase. The plasterboard was stood against a wall outside and wetted frequently and gradually it curved under it's own weight as it was leaning against a wall. After several days it had got to the approximate bend radius needed so it was brought inside and wetted further and gradually eased into the bend needed. Once to the radius you need you let it dry before you screw it to the wall. That is a job well suited to DIY as it will take time and your own labour is free.

Hello everyone we have recently purchased a bit of a monster Property and taken on a bit more than I can chew however insulation is a priority. The ground floor is a wooden subfloor with about a 70 cm crawlspace. All the joists are 4 inches tall not 6 inches and I wanted to insulate it with Rockwall and netting from below without lifting any floorboards because the floorboards have all been sanded and varnished and I do not want to damage . Kingspan is just not an option. The joists do not run true and the distances between the joists or vary by an inch two besides which getting the material under the floor is virtually impossible Rockwool on the other hand would be a lot more practical to install. I’m just wondering whether the joists being 4 inches are too shallow? Thanks in advance

Ummmm, isn’t that a but too big for a domestic plant room? 😉 Being serious I am sort of facing a similar set of worries. Our airtight layer is our VCL, and we are stapling that up. OK, where we can we are putting the staples on the edge outside the tape so on the non airtight side but still, there are a good few places where the staples pierce the membrane. Where a staple is removed or pulled out we should probably put a bit of tape over it, and that’s ok as none of our membrane will be visible. But your walls will look like they’ve got measles lol Presumably you’ll be painting your the PPB, so can’t you simply fill and paint any screw holes from removed screws? I suspect comments about air gaps in mortar are more relevant as there will be thousands of ‘em and they add up. But I’m sure a grown up will be along shortly to confirm. As for plant room and a service void isn’t it just your preferred aesthetic?

More information on what wall finish you have, and what sort of access panel you want to make.

Useful to be made aware of this sort of detail - TVM. Is sounds like you’re suggesting that all XPS boards are cement-faced, or are you just highlighting the need to check whether they are cement-faced?

Thanks - once the battens are in place and give the final radius I was thinking about getting a board to test out options. I hadn’t been aware of the tile backer board for this purpose (just had it recommended for going under electric UFH mats, but wondering if it’s really needed there - that’s a different matter entirely). I’m wondering if the cuts/scoring can be made in the other boards (20mm is very deep).

Hopefully I’m overthinking this, but having read about the impact of small gaps in mortar on airtightness I just want to check… Situation: Timber frame build. Internal face of stud wall is Pro Passive Board. Intello airtight membrane used to lap joints and maintain airtight layer where PPB won’t fit. Timber frame company has a proven reputation for achieving better than 0.6ACH. They will install PPB & service battens, that’s where we pick it up from. Plant room: This is the first area where I will be installing 18mm ply throughout to give us a solid fixing for all the equipment that goes in here. I’m thinking that we can do away with the need for a service void here because all the wiring, piping, ducting etc is going to be on show anyway. I’m very keen to see how others have done their plant room fit-out. My questions are: 1. Should I still keep a service void in the plant room? (Why?) 2. When screwing through and into the PPB (which would be the case with/without a service void), this will pierce the airtight green coating on the PPB - will this affect the ACH performance? 3. There will inevitably be cases where screws are put in and then taken out, having gone through into the PPB layer. Will this affect the PPB? How significant can these piercings impact the air tightness performance? Photo for interest. This is ‘the big one’.

Hi All, first time poster, so greetings! I was wondering if there was any insurmountable reasons why roof a lantern cannot be installed directly onto a cavity wall with a wall plate, coping or some other such capping. To provide a little more context the query - I have the conservatory in image 1. that is now 21 years old, therefore at/approaching the end of its service life. To that end I was thinking about the viability of organising a design to increase the height of the dwarf walls , introduce aluminium heritage doors to the front elevation in a designed goal post frame, all to receive a roof lantern with blue glass which seem to be available in the required size and more economically priced than a replacement conservatory roof, bespoke aluminium roof bar equivalents. Only over seen image 2 that looks something like what I envisage in terms of the roof. Any thoughts would be welcome Note. BC and planning considerations are secondary at this point. Have had initial conversations with both that suggest that some iteration of what I would like to do (which is to retain and reuse the foundations walls and slab of the existing conservatory to create something more robust and aesthetically pleasing still with a glazed roof) will be allowable if supported with the right calcs, foundation tests etc etc.

The cement faced xps board required a specific primer before skimming.

You can get 6mm board, that might be flexible enough to form a radius, alternatively, if you can get a plasterer that would be happy to skim over xps backer board, then you can buy the stuff that is prepped for strange shapes and curves… https://www.amazon.co.uk/Thermopanel-Waterproof-Resistant-Install-Bathroom/dp/B07RZV1XCR/ref=asc_df_B07RZV1XCR?mcid=5c31f7c6a9a731dcb14df90763ba078c&tag=googshopuk-21&linkCode=df0&hvadid=697339313975&hvpos=&hvnetw=g&hvrand=1902209021199673924&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=1006886&hvtargid=pla-943033153117&psc=1&hvocijid=1902209021199673924-B07RZV1XCR-&hvexpln=0&gad_source=1

I had two different lads do two rooms both I wasn’t happy with the finish. in the end I had a recommendation from a lad on here, I used the bloke he recommended and he has since gone on and done another buildhub members house. £4 a metre gets you a site plasterer, smash and dash lots of work for the decorators. mine came in around £6 when I added it up, I could see an awkward layout or high ceilings costing a bit more. I seam to recall a conversation with him about £10 a metre for high quality pain in the arse stuff.

It's BASF so not likely to be untrue. I've found a thing saying the eps nodules work identically, being bubbles of air, but the conduction route over the bubbles' convoluted path is less conductive because infra red gets mirrored back whence it came. Hmmm. Anyway its quoted insulation is 10 % better than white eps, but I think the publushed cost is double, and I wouldn't expect so much discount.

I asked AI got this answer when asking about graphite embedded in EPS insulation Value is added because the "air space" required for graphite to reflect radiant heat is actually located inside the material itself, not as a separate external gap between the insulation and the concrete. 1. Internal Reflection Within Micro-Cells Graphite insulation, specifically Graphite EPS (GPS), is composed of individual closed-cell beads. Even when tightly embedded in or under concrete: The "Air Space" is Internal: Each bead contains millions of microscopic trapped air pockets. Infrared Mirroring: The graphite particles are infused into the walls of these tiny internal cells. As radiant heat attempts to travel through the board, it hits these graphite "mirrors" and is reflected back and forth hundreds of times within the cellular structure. No External Gap Needed: Because this reflection happens at a microscopic level inside the insulation board, the board can be in direct, "intimate" contact with concrete without losing its reflective benefits. 2. Physical and Efficiency Gains Even without an external air gap, graphite adds measurable value over standard white insulation in concrete applications:

I'd have to check the facts but I recall that there was more than one factor, one being that a fire test sample was 'adapted' to perform better.