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No 3 is what I done. You could use 4mm jacko instead of 6mm to reduce the 'step' to the former when you come to lay mat/tile. Re #1 are there even any addy products approved onto chipboard? Re #2 ditra peel n stick can go on protect but principle of decoupling is somewhat lost in this case i.e. doesn't prevent vertical deflection which is what most people are trying to prevent.

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While you shouldn't accept timber that fails the standard, you have to know what the standard says to know whether what they have sent is acceptable or not - and it does permit some twisiting and bowing (which can add up over a 6m length) as well as other defects that you may find surprising. There's a very brief summary in Section 4 on this page: https://www.site-lynx.co.uk/library/qa-checklists/structural-timber, but you really need to read the full definistions & explanations as set out in the standards (perhaps available at your local library) to successfully argue your case, if there is one, with the Merchant's rep. For higher quality, it's best to choose an engineered product.

They are bent along the crown. You mention posi-joists being straight, but the ones I recently got from a firm in Southampton were far from straight. Where did you source yours from?

I don't know why all of a sudden this is giving me a headache. Our ensuite (about 4m x 1.4m) is 22mm Egger Protect boards over posijoists, I'd say pretty solid, with a fibreglass shower tray former flush level to the Egger boards. We want low wattage electric UFH matting (100w), and then above that will be 12mm marble tiles (600x300 format). It's a small area (7sqm) so cost of materials isn't hugely important. I can see 3 options here: 1) Tile straight onto the Egger Protect - UFH mat goes down, thin layer of self-leveling to smooth over the mat, then tile on top? Seems a bit prone to cracking especially at threshold to shower former, but equally I've tiled bathrooms years ago with nothing more than 6mm ply on more flexible floors and didn't get any cracking. Could run the UFH mat into the shower here as all flush. ETA - could use somehting like the fancy BAL AF Max - apparently does a decent job of decoupling by itself? Would just put a bit of membrane on the join to shower former and tank that to the walls. 2) Decoupling mat - used this downstairs in lots of places, happy with it. My question is do I stick the mat down first, level over it, then decouple and tile, or do I decouple, then level, then mat, then tile? 3) 6mm insulated cement boards - in this case I would just screw them down, then UFH mat, level and tile. Will have to manage the transition to the shower tray, and won't be able to run the UFH mat into the shower. Thoughts? Am I overthinking it and any of the above would work? I did go down a rabbit hole of googling and it seems pretty much every option and scenario is recommended/not recommended by someone. thanks!

For that quantity and length I think you're onto a loser unless you go and hand-pick the timbers. Which way are they bent? FWIW over that length I wouldn't be too bothered by 25mm twist or side bend. If it's a bend up/down i.e. the crown as fitted, then that's more problematic. Not sure on location or how much you're getting them for but after the last couple of projects I wouldn't use anything other than posijoists for something like that. Super straight, regularised, light etc. and for the money a no-brainer.

Hi - I don't know what 'an amendment to warrant' is. We are just finishing up first fix and the poorly-designed stair is a secondary helical stair. We may need to raise an external exit door by 54mm. Does that require this amendment? Did you continue with your architect as PD? Thanks!

Could do cement board topped with vinyl (or similar). Vinyl for waterproofing, cement board for fire. Not sure thats any easier than tiling though.

I do realise that when it comes to timber, you really do need to go through the pack yourself and pick out the best lengths. That's fine fo shorter lengths, but 6.6m lengths won't go on my Berlingo roof rack 😂

@SimonD thank you for your reply, all very useful. I have sent you a DM. Attached are the heat loss and sizing calculations from Daikin. At the time Daikin said they didn't have a 6kW unit available, that they would do the 9kW at the same price and their calculations showed that the 9kW was just as efficient.... with the added benefit of the DHW heating up more quickly due to the greater capacity and having the benefit of a back up heater. Daikin-HSN-Report-32 Easton Town - Reversible cool 9Kw.pdf Daikin-HSN-Report-32 Easton Town - Reversible cool 6Kw.pdf

Try different merchants. Drive round a few. Look for timber merchants as opposed to builders merchants.

I sent back a load of C24 timber as it was twisted and pretty curved. They delivered another batch, which apparently was from a fresh pack. But given the date on the timber was August 2025, I am wondering they haven't just sent more rubbish OR that is the quality that you just have to accept these days. I know it's for a flat roof, but this stuff is 6.6m long and some boards have a curve along their length of 25mm and others have considerable twist in them. Is that acceptable, or should C24 be better quality with straighter lengths and less twisting? I am now getting slightly concerned, that cutting the main house roof is the simple part and sourcing 47 lengths of straight 6.6m 8*2 is going to be the tricky part of the task. I am now wondering whether trusses might offer better quality control. Given the roof metal standing seam, I suspect that any flaws will show up more than a tiled roof.? What have others done regarding sourcing timber that for long spans?

Ceramic tiles, job done.

Exactly ! Asking “ how big is it ? “ is a very leading question

So nothing stating MCS, position of heat pump is defined by agreed plans, so that's not moveable. So not many variables left except size of heat pump, which isn't stated on plans. As mentioned above Panasonic are good, a small version of that would be fine. But you don't need a lot of the bits they will want to sell you. Feet, flex hoses, isolation valves and anti freeze valves. I would really consider a direct cylinder. Especially if going for PV and/or battery, so you can make good use of ToU tariffs.

I've just submitted multiple new submissions to get around the upload limit - hopefully they all go to the same person! Had about 150 documents to submit in total - in anticipation of them asking additional questions, I also included: payment receipts, copies of emails with suppliers, photos of materials delivered on site, photos of materials installed etc. Wouldn't have usually bothered but as I've already been put to the back of queue several times due to one sentence enquiries from them, which takes 2 months to climb back up, I thought I'd try to limit their range of things to come back to me on.

Any suggestions / ideas? Only thing I can think of is aluminium checker plate. Ceramic tiles obviously but this is on top of ply flooring.

Had the same problem with our staircase, architect designed it and the staircase company discovered it wouldn’t comply with regs, got it sorted out eventually but needed an amendment to warrant

Installing a number of panel radiators on my project, and unfortunately some of the grounds (within the timber stud walls) for the hanging brackets are in the wrong position. It's my own fault as in a few instances I position the grounds for say a 1000mm wide rad, where a 1200 wide rad is being installed. It can be overcome by opening the wall, installing more grounds and reboarding, reskiming but understandably I want to avoid that. Not keen on radiator support feet either tbh. Does anyone know if brackets with an extra wide wall plate are available as I think that my bridge the offset of ground to radiator hanging lug. Perhaps I could just buy some metal and bend some up myself. Welcome any members ideas of how to overcome this issue?

I don’t know how far along you are or how much tweaking is reqd but I’d get on top of that as soon as possible. A staircase that satisfies the regs may require some structural alterations. Sorry, I’m not up to speed enough to advise on what you should do regarding PD. Good luck.

>>> bringing the double check valve inside the plant room Ah yes, good idea - we had some outside check valves give up last winter.

I don't think there is anything particular in the planning consent, just a heat pump location specified by the architects and to be installed "by specialists". I have seen the kit list from City Plumbing now and they have specified a 6.5Kw heat pump which is too big for my house. I don't think they took into consideration the MVHR. It seems to me the MCS/Heat pump industry is a mess and it is no wonder people who aren't paying attention end up with poor performing systems.

I've found a new circle of reclaim hell - they've requested 30 invoices, all the highest values ones, be uploaded in the claim portal. That would be fine, except the portal only allows a maximum of 20 to be uploaded...

Try submitting a lower demand requirement. We only have single phase here but when I enquired about our supply they offered me a 12KVA single phase supply at a good price. They said anything more they would have to upgrade the transformer. I accepted. So try say a 24KVA 3 phase supply as your requirement? The reality is I have the same cable and same 100A DNO fuse as every other house so could draw the full 23KVA. Nobody would even know.

@Pocster always very kindly provides standard sized ceiling tiles for scale