Novice Becky

Thanks @Iceverge. There's always more than one way to do things and this forum is great to read about different experiences.

Thanks @nod. Foil wrap sounds quick and straightforward but quite a lot less insulation than the 200mm of PIR suggestion. Thanks @ Redbeard. I didn't quite get the re-plasterboard after VCL. Can you explain please? If I Take off the PIR that's there then there will be the plasterboard exposed. Can I just tape the VCL to the existing plasterboard and timbers and then build up the insulation?

Thanks @Iceverge. Condensation and mould. This has been cured by the MVHR going in in December but it will still be a cold bridge (or cold mountain?)

Any ideas how to insulate my Velux windows? The ceilings below are horizontal with vaulted shafts for the Velux. The bathroom Velux is especially bad. Ignore the orange box attached to bathroom Velux - it's a digital shower processor no longer there Cover what's there with more PIR sheets and tape joins? Would air gaps pose a problem for interstitial condensation? Rip off PIR and start again? Other materials? What thickness of insulation (I know this will depend on thermal conductivity). Thank you.

I'm with @KitchenPotcher on the manky tile grout! I like your Bushboard idea! Possibly cheaper / homemade ideas ... I bought a sheet of roofing zinc (and cut it up) for behind my kitchen sink and range cooker in my kitchen years ago and it worked for 10 years. Cheap and cheerful. Not perfect like stainless steel but was ok for me - tarnished but I seem to recall being able to clean it. I currently have glass splashbacks - I went to local glass shop and got them made to measure with 4 screw holes in the corners. I should have sealed them along the top edge. I also bought some made to measure stainless steel shelves and window ledge (they were actually supposed to be s/steel splashbacks) from https://www.stainlessdirectuk.com/. I'd recommend this company but don't know how pricey it would be if you want a really long splashback. Made to measure and you can choose thickness. My S/steel still looks new after 15 years (when I clean it). I've also used sheets made from recycled plastic bottles from https://smile-plastics.com/samples/ in my bathrooms to avoid grout. Not suitable for behind a hob! But again this stuff seems to be indestructible and still looks new.

Yes it's very exposed to the cold but this machine is supposed to be ok in a cold loft. Vent-Axia said that it doesn't need to be insulated (I could if I wanted but I didn't have to). The machine has polystyrene insulation inside. The manual says -20C to +40C. That's why I didn't build an insulated cupboard for it. The summer could be a problem though. I thought about retrofitting an insulated cupboard for it but I'd have to get it off the wall to insulate behind the machine and then I'd have to alter the metal ducting which seems a bit of a headache!

Thanks @JamesP. That's a useful suggestion. I'm pretty sure they've insulated the VCDs except for the switch/dial bit. If I'd done the insulation myself I would have used 50mm. The installer said no one used 50mm because it's too hard to handle. Has anyone used 50mm instead of 25mm? I was thinking about re-insulating the whole lot to increase the insulation and ensure it's all done properly. I think I had a bad batch of aluminium tape and it's come undone in places and I expect more will come unstuck over time. Do I have to remove the existing insulation rather than go over the top of it? It's foil-backed.

Thanks @JamesP. No stupid questions on this site! There's 5 VCDs on supply and 3 on extract. If you zoom in on the plan you can see them (VCD is in tiny font). You can use them to balance the system instead of twiddling the room valves. More control apparently. They simply increase/decrease the air flow. The installer added them in to the design by BPC. I didn't want to use the more popular plastic ducting because some plastics give me headaches which meant I needed a metal branched system. Glad that people here agree with me on the condensate drain. Will get that sorted - and try to get the machine fixed.

I don't have a thermometer up there but it's cold (30cm of insulation). When there was extreme cold like -7C there was ice under the machine where it had dripped. I had the boiler and hot and cold water tanks in the loft until recently but all the pipes were all lagged and seemed ok. I'll go and grab a max/min thermometer and put it up there - but we don't have any cold spells forecast at the moment.

@JamesP Thanks for looking at this. Your arrow is pointing to a VCD single blade damper (https://www.bpcventilation.com/vcd-in-line-spiral-duct-single-blade-damper) to help with balancing the air flows. There are 7 of them. MVHR layout attached Novice Becky MVHR nov.pdf

Thanks @BotusBuild. OK I will def get the condensate to an internal drain (really irritating that the expert installer ignored me in the first place and then I doubt myself). Your fears are the same as mine! I sent photos to installer to prove it was seriously frozen but obviously they weren't taking any blame for this. VA seemed to think it was all ok and couldn't see any installation errors other than tipping the machine back slightly (installer looked relieved at that news). I'm now not so sure. The date was being weird for a week a while ago and it wouldn't let me or the installer set the date to the correct date. It has since corrected itself. Today when I pressed the momentary boost switch with the installer here it went to 18 hours 11mins! It should be 15 mins. Does that sound like dodgy/damaged pcb?

Thanks @dpmiller. Yes. Yesterday (warm day) it was in humidity-controlled boost all day - even when machine said RH was 61%. Humidity threshold is set to 70%. I read that the machine can go into boost even if it's below the set threshold (70%) if it detects sudden or sharp increases in humidity. But there wasn't a lot going on in the afternoon - just me at home. Surely it should have switched off boost at 61% rather than just slowed down a bit? 14 March Air Temp (C) Time external internal RH % supply speed % extract speed % Mode 13:19 16 20 65 Humidity controlled boost 13:38 17 21 64 54 47 Humidity controlled boost 14:04 17 21 63 54 47 Humidity controlled boost 14:13 17 21 64 55 48 Humidity controlled boost 14:40 16 21 61 51 42 Humidity controlled boost 16:09 14 21 70 61 60 Humidity controlled boost 23:29 12 18 71 20 20 switched to low 8 hrs overnight (88% outdoor) (Zone 1: 22) (Zone 1: 51%) In the evening I discovered some extra pages on the app. See 11:30pm. Internal air temp 18C. How does it even know the room temp is 22C? There's no thermometer or hygrometer/humidistat linked to the machine but it's correct and has been correct each time I look. 18C is quite a lot colder than 22C. Room humidity is 51%? And why is machine humidity much higher 71%? SCRAP THAT - just looked on the app. It says Zone 1 is 25C! It's actually 21C. The sun is shining. Maybe heating up the loft?

Thanks. Do you mean the large steel attenuators? I assumed they weren't insulated because they have insulation inside them. Do the attenuators need insulating?

Thanks @JohnMo. Do you mean dry trap? There wasn't clearance under the machine for a dry trap. I'm lucky I have a trap at all - they are still saying it doesn't really need a trap because it's going straight outside?! Helpful comments - I've been thinking about running the condensate to a bathroom. I've calculated I could get a fall of at least 3.3 degrees to a bathroom. Instructions say min 3 degree fall. Building regs say 5 degrees. Has anyone been ok with a 3 degree fall or do I need a pump or maybe I need to conceal the pipe at ceiling level.

@Conor and @markc a belated thank you for your help! I managed to block up my extract vent holes - first time for everything. The cooker hood one was nasty - the builder years ago had hidden his shoddy job and there was a massive double hole to fill. I stuck some ME508 airtightness tape at the back of the inner leaf, filled with FM330 and then plastered over the top. Now all covered up with a new recirculating cooker hood. Cheated slightly on the brick work outside and happened to find a builder to come and brick up the holes. Thanks again.