MJNewton

Thanks everyone for the input - all really useful. Following up on a couple of points: Yes, that's what's concerning me. Even more so that I might screw up a hole and have to perform a repair of some sort. Doing that on a beautifully finished skimmed ceiling would make me weep! It's a bit of a complicated room shape, with a lantern cutout and numerous corners to accommodate, and moving the boards round on my board plan didn't give me many options without resulting in thin slithers or another joint-related problem (e.g. MVHR vent holes) somewhere. The problem join is the bottom row of boards below (where 7 and 8 run alongside 19 and 20) above the worktop beneath. More to the point though; the boards are already up! That's good to hear. As long as the plasterer can cope with it (i.e. it's not a showstopper - just a preference) then I'm a bit more content. I could always bung him £20 or something as a token gesture for any grief these holes cause him!

The question as to whether to cut downlight holes before or after skimming seems such a commonly asked question on the Internet, but with a seemingly 50:50 split response this doesn't sit well with someone like me that prefers a right and a wrong way! I have just finished plasterboarding our new extension ceiling with 12.5mm square edge board on resilient bars at 400mm centres. As my (bad) luck would have it, 3 of the 5 downlights (for worktop task lighting) look like they're going to end up slap bang on unsupported board edges/joins (paper edged of course) and so I am getting nervous about what consequence that might have in terms of causing cracks, either during installation (if I drill the holes after the ceiling has been skimmed) or just long-term due to a compromise of board strength. I was thinking I might cut the holes before I get the boards skimmed then any movement during cutting won't be an issue. I could also then feed some adhesive-backed timber/plasterboard up through the hole and position them across the board edges/joins adjacent to the holes just to give a but more support. Does drilling holes beforehand make life hard for the plasterer? Will it inevitably compromise the finish he can achieve? I did ask him when he quoted (pre-lockdown) and I seem to recall him just saying he prefers no holes - mentioned something about plaster falling out - but I didn't really push him as at that stage I didn't realise I'd be wanting to drill on some joins. I also didn't realise what a maze of joists and resilient bars I'd be up against, and typically how nearly all of my desired downlight positions seem to be really near some sort of obstacle so if I screw up I'd rather do that before it's skimmed (to allow an easy repair) than after. I might be worrying over nothing... I do that. A lot. But if you can honestly tell me a plasterer won't have any issue with five 70mm holes (okay, and three 125mm holes for my MVHR vents too) over a 35m² ceiling that'll set my mind at rest.

I'm sure my wife ponders how best to make my already stressful DIY even more testing. For example, in our new 'family' room (kitchen, diner, lounge) declaring she doesn't want an extractor hood leading eventually to me spending over a grand and 8 months on a retrofit MVHR system. Anyway, I digress... Latest on the list of challenges from the missus is that we are not going for any wall-hung cupboards in the kitchen area... Ordinarily that's where I'd be fitting worktop task lighting, which we're a big fan of, and so instead we're going for GU10 downlights in the ceiling to illuminate the worktops (an L-shape along two perpendicular walls). My question is: how far from the walls should I be fitting them? I have made the assumption that we should be aiming to avoid/reduce shadows from us standing at the worktop, so for a standard 600mm worktop depth that'd presumably put the maximum limit to be 600mm. I'm thinking something less than this would be even better though - perhaps 450mm - 500mm just to be sure we make the most of the light available? What about even less eg slap bang in the middle at 300mm from the walls? I am mindful that the closer the downlights are to the wall the more of a 'cone' shape illumination pattern on the walls, particularly with hard edge LED GU10s. However, I don't anticipate that necessarily being a problem - it might even add to the aesthetics?

Okay, that sounds reassuring. Do you happen to recall any other info on the label eg branding?

Are you able to elaborate on any of that @MikeGrahamT21? We paid for a kitchen from DIY Kitchens a couple of months ago but have yet to specify a manufacturer/delivery date. The worktop was the 'Innova Unique Marble' which, when visiting the showroom, I do recall they said it was exclusively to them (perhaps just by name though?!), but presumably still supplied via Natural Stone Surfaces? I'm wondering it we might be best cancelling the worktop bit of the order (it might end up being done for us when we hit the 'go' button anyway!) and making sure we go for a branded product that has wider availability...

A 3rd for the Titan. I bought it on the assumption it'd be disposable but still represent value for money for the jobs I had to do. Despite several years hard labour (not continuous, admittedly) it still soldiers on.

It sounds like it must be regional as all my local Wickes round here (North Wiltshire) have plenty of drywall adhesive in stock. Plasterboard too but granted little plaster.

Great, thanks everyone!

Ah, yes, okay - will take a look. Found this stuff which might work too described as a cut-to-size washable mesh filter (for extractor hoods):

Would that be good for grease? I was under the impression carbon has really small pathways hence why it's good for trapping smells?

Does anyone know of grease filter that I could put inside my kitchen MVHR extract vent? Ideally one that would sit inside the 125mm duct so I can keep the current terminal. Rather than bespoke item I wondered if I could just use some generic filter media of some sort, cut to a round shape and shoved up inside?

Slight correction: it was actually a ply deck (the OSB was used below the insulation).

There was an 18mm OSB deck and he put matting just over the joints.

Good question; it doesn't seem to be all that widely available when I looked around for where I might get it from in future. I know my roofer got his from Raven Roofing Supplies although there's no mention of it on their website (which is odd as they do training courses for it too). I'd get it from there as they's local but I'd suggest others contact Eagle Insulations as they are the UK distributor I think.

Yes, all fine thanks. It's only been 18 months though so maybe a bit early to comment on longevity which is probably what really matters. It's been really tested though over the past year with the rain, and the fall isn't the best (builder made an error with the firrings.... grrr - still winds me up) so if there was an issue I'm sure I'd have seen it now. I'd definitely use it again - easy to apply (a roofer did mine but next time I'd DIY) regardless of complexity if surface/upstands/etc, no seams, tough yet elastic etc. The only things that do bother me about it is 1) hardly anyone else seems to use it (the manufacturer told me they sell very little to the UK compared to other countries and, for what it's worth, stating that the UK market does tend to hold on to its traditional building methods so it's been a tough market to break in to), and 2) I do wonder if Desmopol is all that different from those 'quick fix in a can' paint-on roof repairs that even the manufacturers state are for temporary use only. That said, Desmopol does have a BBE certificate and comes with a 15yr (or is it 25?) guarantee that can be extended 5yrs at a time by an additional coat over the old one every 10(?) years so I'm as confident as I would be for any flat roof covering I think. Here's a pic (of the roof lantern really but's got most of the roof in) after around a year:

I was going to ask if that was a euphemism but as I read on then wondered if it was true so decided it was insensitive to joke about. Got to the end and realised it was a wind up but I'd be lying if I said you didn't have me for a minute!

Is there a BR requirement for maximum ventilation? If not then just whack the system up to full and measure the flow rates to ensure the minimums are met and done with it. I doubt there's a need for a balancing for BR compliance too.

I think you might be expecting too much from MVHR - particularly a single room one - in terms of their ability to cool (or heat) a room. With the limited heat capacity of air coupled with the relatively slow flow rates that's not their raison d'être. View them more for their cost-effective air freshening and dehumidifying qualities and you can't go far wrong. Don't get me wrong; MVHR can really help keep a closed-up room/house fresh and in some circumstances they can have a slight active cooling effect (ironically when the summer bypass isn't active and the outside air is warmer than inside) and we do feel what could well be a psychological cooling effect from ours with that constant flow of 'fresh' air, particularly on warm still summer evenings/nights. To summarise: MVHR isn't the same as air conditioning, if that's more what you're after?

Ah okay. The ones I've been looking at (Integral Evofire) are sealed by the bezel on the ceiling side and have a piece of glass over the bulb. I guess they use different methods by the sounds of it.

If the fittings are fire rated aren't they already airtight (sufficiently so for what's required here at least)?

I've used both the red Airflow Airflex Pro and green Blauberg semi-rigid ducting and whilst they were nominally the same in terms of size and interchangeability the former was more flexible and felt like a better quality product.

Thanks everyone. One less job on my list... ?

I could just do that. I always like to get things ready for tradesmen so they can just jump straight in to what I'm employing them to do. It's a big room though and not too many holes so he'd probably have done them before I'd even got the kettle boiled.

Interesting about spray foam. I did consider that but wondered if it might be considered a bodge? It's a 'done thing' then? Would it still resist knocks without cracking?

I shall be getting a plasterer in to skim some previously dot-and-dabbed walls and as I've made quite a few holes where sockets have been removed, new cables routed etc, was wondering what plaster I could use to fill these prior to him doing hia bit? Maximum depth is around 40mm. Noting the difficulty getting plaster at the moment are there any viable alternatives? Or does anyone have any idea how long it'll take for supply to recover?