Hammertime

Thanks @Mike. I've spoken to a manufacturer and they confirmed the 20mm is mainly for reveals and doesn't have sufficient structural strength. I've had a play with the 9.5mm and 12.5mm plasterboards and I'm thinking the former might have too much possibility for flexing, especially with clay on it. Looks like my choice will be between the 12.5mm plasterboard (cheaper, thinner) and 15mm wood wool (better key, slightly lighter).

Thanks @Beau - good to know how strong the foam bond is. It sounds like the mechanical fixings will just be belt and braces! That sounds a good solution, @Thorfun. I can definitely see the benefits. However, for me, the rooms are so small that I was concerned about losing even more floor space. With the rooms being small, putting corner sockets on the internal reveal rather than the external wall wasn't too much of an issue. Where I did need to put something on the external wall, I either channelled the 50mm PIR or just used two layers of 25mm.

Thank you for this, @Mike - decrement delay is an interesting topic and I considered different approaches when insulating. I'm lucky in that my south facing roof has thick stone tiles which absorb summer heat, but winters are very cold so I decided to instead maximise insulation in the space I had and went with 100mm PIR between rafters and 25mm below. One left-field idea: is there anything to stop me using 20mm wood fibre (rather than wood wool) boards as a plasterboard substitute? I could screw it with washers over the 25mm PIR, then clay plaster it. Very light, and I could get the best of both worlds: high insulation from the PIR and room moisture/thermal buffering from the wood fibre. I realise that you have advised not to worry about moisture with the ceiling, but at 15m2 I thought it might help with window condensation and smoothing out heating peaks and troughs if I can get it to act as a moisture/thermal buffer for the room.

That sounds like a great idea, @torre - I bought some stainless steel washers recently so if I could fit those instead then it would solve my problem. Only issue might be getting the built-in plastic disc off, as I haven't seen any plugs where the disc is separate, but I will keep looking. Thanks @Mike - if so then I could maybe countersink the discs into the insulation for a flat surface to stick the plasterboard on to. But would the foil face of the PIR come away under the pull of the plasterboard if using pu adhesive alone?

Thank you for the replies. As @Mike says (that link was very useful, btw), moisture buffering is less important if ventilation and heating are decent, so perhaps I can use the clay just for aesthetics with a thinner layer as @Russell griffiths suggested. 3mm clay is only 1kg per m2 heavier than gypsum, so 15kg extra overall. ^ This. So it sounds like I'm overthinking it and the 12.5mm plasterboard, clay finish and tree branch light fitting will be fine for weight and better than the 9.5mm? One other thought - is it worth using wood wool board instead? Presumably it has some moisture buffering too which might help if a thinner layer of clay is used. Thanks again.

Thank you both. That could be an option, @Russell griffiths - I've generally tried to avoid running services on those walls eg putting sockets on internal walls where possible. My concern would be that I still need to pierce through the insulation to the thermalite in order to fix the battens and the plasterboard would be on top of those screws, so it's whether the margin of benefit would be worth the extra space lost. @Mattg4321 I decided to go that route partly for cost (it was much cheaper buying them separately) and partly because I can then foam and tape the PIR so the insulation and its foil facing are both continuous, which I thought would be harder with combined insulated plasterboard. There are some plastic plug and pin fixings here on insulationuk that look similar to the Fischer dipk ones, but it specifically says it's not for insulated plasterboard. I wonder why that is? I phoned them and couldn't get a definitive answer. Maybe because the disc is 3mm. If so, could I recess the disc slightly in the plasterboard then scrim over?

Thank you @Russell griffiths for the reply and the reassurance. With everything that needs to be considered in a renovation, it's easy to go down mental cul-de-sacs. You're right, I wouldn't be concerned by people on the roof, but I'd been thinking about creep caused by a long term dead load. The weight difference between 5mm clay and a 3mm gypsum skim across the ceiling is 10 stone; at 10mm, it's 28 stone, so three skinny roofers permanently up there (I suppose they would be skinny if they were stuck on the roof - although it's only a bungalow, so they could jump down...). The light fitting is going to be a branch, so - depending on what turns up - might be a fourth skinny roofer. I think it's got a nice cloudy look to it, but it's also meant to aid with moisture buffering, even at 5-10mm, as well as reduce odours. Don't worry, there's the kitchen, fitting the wetroom, ventilation strategy, flooring, hot water system...I've got plenty to choose from🤣

I've got hollow cavity walls, internal leaf is thermalite. I've stuck 50mm PIR to it with PU adhesive, and I will use the same to attach plasterboard to the PIR, but I think I need some mechanical fixings through to the thermalite too. What would people recommend? - Twistfix make one but it's metal and they say it can cause thermal bridging. - There are hammer-in fixings but again, the only thermal break is a thin piece of plastic and the screw is metal - There are some plastic plugs with fibreglass pins to nail in like the Fischer DIPK, which is probably what I'll use if there's no better option - only problem is the disc heads are about 3mm thick, so skimming over could be an issue. Is there anything more suitable that you know of? Thanks

I'm a bit concerned about weight on my ceiling and I wondered if there were lightweight alternatives to 12.5mm plasterboard? The ceiling follows the line of the pitched roof (bungalow), which has heavy stone tiles on top. Rafters at 400mm centres. Originally had 12.5mm plasterboard and gypsum skim. I removed this to insulate. I'd like to use clay plaster instead of gypsum, which is both a lot heavier and thicker (5-10mm). I've also got a heavy light fitting I'd like to install. I'm therefore concerned about weight pulling down on the pitched roof, so I thought about lighter boards. Current options over a 15m2 pitched ceiling: - 12.5mm plasterboard: would be 122kg over the 15m2. What was there previously, but I'll now have the added weight of clay plaster and heavier light fitting - 9.5mm: lighter (92kg), but there are mixed opinions about whether this would sag over time? - 15mm Cewood wood wool board: about 105kg. good base for the clay plaster - 12.5mm xps tile backer board: would seem a good option, but issue around fire rating Is there anything else I could use? Or am I overthinking this? Thanks in advance.

That's really interesting. The idea of being able to DIY a TS is attractive, but the chances of running out of hot water with a TS sounds high, unless you're heating and storing it at much higher temperatures, which would be uneconomical in comparison, particularly when relying on the immersion.

Hello! I'm renovating a property and was wondering if you could sense-check my plans (banging my head against research brick walls has knocked all the sense out of me…). I've previously posted a question about solar when I was very early in the process and received very useful feedback. I now wanted to post about the plans more generally. The property: just under 50sqm bungalow, one bed, all electric. Victorian but extensively remodelled in the 90s. It will sometimes be used as a holiday let (hence my concern about energy usage). Might have solar, but would only be a small array if so. Insulation: I'm going as big as I can on this. Roof - upgrading roof areas to between 100-150mm pir as space allows. Walls - three sides are 1990s 50mm hollow cavity, fourth is Victorian solid sandstone c400mm (although altered in parts with modern brick and cement infill). Going to add 50-75mm pir direct to former, taped etc; for the latter, I’m either adding 25mm ventilation gap then pir studwork, or alternatively thermal plaster. Thermal plaster is not as good an insulator, but I’m wondering if this approach might utilise the thermal mass (sorry, I know that’s a controversial phrase) of the wall and help regulate room humidity? Can vapour open and vapour closed be used on different walls in the same room? Heating: I’m taking out the old panel heaters. There is a log burner. Considered: - ASHP would be brilliant, but it's a VERY quiet location. Also, I might just be able to squeeze in a slimline DHW cylinder but any other ASHP equipment would be a real push. - High retention storage heaters might be an option, but I see mixed opinions of how effective they are. I also haven't seen many nice designs. - Tepeo Zeb looks a nice idea, but I'm thinking 10-15 years ahead what happens regarding parts and support if buying from smaller companies. - Offsetting electric usage by heating a slab with electric UFH. I have done some digging (literally) and found my floor buildup is only ~85mm (50mm jablite, 20mm chipboard, tiles), which makes this unfeasible. - Some combination of pump and Willis external immersion heater to run wet ufh - I saw this discussed in other posts but was unsure of feasibility. Currently intending to install oil filled radiators, and electric UFH in the kitchen (~14sqm) and bathroom (~4sqm) as secondary heating. Given the shallow build up, I'm thinking 25mm or 50mm vacuum insulation boards (expensive but hopefully worth it) on the slab to ensure as little heat is lost to the ground below. DHW: I’m taking out the vented direct copper cylinder. Considered: - instantaneous water heaters and electric shower, but would mean paying for electricity when it's used. I started looking at time-shifting energy consumption. - Mixergy tank, but main benefit would be the cylinder learning my water usage then heating required amounts accordingly, which isn't useful for a holiday let. - Sunamp Thermino: a nice idea, but the footprint is similar to a slimline UVC so doesn't actually save much space. Also, the reviews of customer support/reliability seem mixed. If it was able to run heating as well as DHW like the tepeo zeb, that would be more attractive, but I don't think the newer ones do. - Cylinder with integrated ASHP, but runs into the same noise issues as an ASHP. Currently planning to get a 'dumb' direct unvented cylinder as I can more easily upgrade smart thermostats like the Eddi as and when new tech comes out. Planning to oversize the cylinder as far as space allows, so that the on-peak immersion is rarely required, and choose one with good standing heat loss. Hopefully a better shower experience than an electric too. Ventilation: Considered: - MVHR was the original plan; however, the layout - coupled with conflicting advice about whether MVHR can be used with a non-room-sealed log burner - makes this tricky. Currently planning to hit ventilation regs with DMEV in the bathroom, as it’s quiet, and DMVHR in the kitchen. I’ve read negative opinions about the effectiveness of DMHVR, but any help towards heat loss seems beneficial. I'll then get an air tightness test/gas spillage test for the log burner with the extractors running. Zero chance of being too air tight, not least because there are window trickle vents! But better to have it officially confirmed. Does this sound a reasonable plan, or the mad scheme of someone who’s disappeared down too many research rabbit holes and surfaced with the wrong answers? Thanks!

Thank you all so much for your great advice. @Nick Thomas - I hadn't realised I'd need to combine the capacities of the main inverter and the inverter on the AC coupled batteries for G98/99 approval. This is also relevant to my question of whether to oversize the inverter; just for preventing those times when the inverter becomes a bottleneck (eg all appliances on, or a future large battery charging at limited off-peak times), it would create a far more complicated application process. I'll ask the quoting company about EPS with either DC and AC coupled batteries. As you say, maybe marginal benefit, but in the countryside where power cuts do happen, it would be useful to both power a battery from the solar array and power the property from the battery. I will take on board your SolaX experience and ask for a different brand. Are there any you recommend? GivEnergy seem decent (and the company has the Octopus tie-in), and I've read Fronius are too. @sharpener - yes, it would be electric ufh. I don't have gas (100% electric), and space is probably too tight for an ashp cylinder. I've been reading the other forum threads with interest. @JamesPa- After reading your example usage breakdown I think, for my size of solar array, I need to shift my thinking. I'd been viewing battery storage as a mixture between off peak grid storage and topping up with my own (potentially meagre) trickle of solar, and trying to cover a large percentage of my energy usage like that. But actually maybe I need to view any solar production as an added bonus for now and think more widely about timeshifting energy purchase. Battery storage is only one option, and maybe not the go-to option either. I like the idea of storing excess solar in DHW, but I'm already considering removing the immersion cylinder to save space, and replace it with an instantaneous water heater, because space is at a premium. I'm also probably not getting an ashp for the same reason. Instead, I wonder if I could view the electric ufh not as an expensive luxury, but as a thermal store. It's not on-demand heating, so if done correctly, I wonder if it would be possible to heat it from the grid only at the lowest off-peak rates (directly, rather than via a battery), with the aim of maintaining a low comfortable temperature, and then top up the room temperature when needed with a log burner or a boost of more instantaneous heat such as IR panels. This would then time-shift a large percentage of my heating, without having to buy a battery. And if left at a low-ish temperature, I could leave it to sort itself out year-round. For all other electricity usage, I can then use my own production to give a little helping hand, with any excess sold to the grid; and in the future if desired, I could get a battery to store it instead, with the 5-7kwh mentioned by @sharpener and @JamesPa being an achievable size given that heating would be covered with the off-peak ufh and only requiring a top-up. I don't know if all of that's technically possible or if I'm being wishful; I will also need to speak to underfloor heating companies to discuss minimum insulation and concrete thickness etc. Also, I'd have to ensure it was possible to tie all this into a Hive-style app. Each item I read about comes with its own app, but it wouldn't be great having five different apps on your phone independently running different pieces of the puzzle. One other thought lurking at the back of my mind is that all the timeshifting of energy usage is entirely dependent on the electricity companies offering decent off peak rates, and it's in their power to take it away if it suits them as more people get electric cars or timeshift their energy purchase.

Hello! I'm installing a 3.7kwh solar array for a small property, and I'm wondering about whether to add battery storage now or wait to see how the system runs first. Which one I decide on will determine whether it's a DC coupled battery and hybrid inverter (installing at the same time as the solar array) or AC coupled battery (retrofitted to the array). From reading up about AC Vs DC coupled, people seem to love one or the other, but I'm struggling to see much difference. - AC is less efficient, but only by a few percent so not worth worrying about - A hybrid inverter might become incompatible with future batteries as manufacturers bring out new ranges, whereas AC coupled batteries have their own inverter and so any brand can be added to any standard inverter at a later date Is this correct? I read something about one not being able to feed back to the grid, but I don't think that's right. If those are the only differences, I might be better off waiting to see how the system runs then adding AC coupled later if required. A couple of other questions: 1) I've been offered a SolaX inverter. Does anyone have any experience with these? The online reviews look pretty awful and I'd prefer paying a little more for a reliable brand. 2) Should I oversize the inverter to anticipate future battery installation? I've been quoted for a 3.3kw inverter, but eg underfloor heating would probably pull double that by itself and so a 3.3kw inverter would limit the benefit of a large battery system in the future 3) If I did get a battery, what size would be good? I've been recommended 5.12kw, but it seems to me this would hardly touch the sides with winter energy usage, even in a small one bedroom house. Thank you for any replies and advice!