Nickfromwales

Chaps. AC or MVHR?

Yes. It’s quite common practice amongst the Chinese stuff. Typically you’ll have a master unit that provides the 50hz metronome to the slave units, linked by the AC signal or a cat 5 cable. Been a good while since I dipped my toes into this stuff, so I expect a lot of the more reputable industry standard manufacturers are also ‘parallel capable’ by now.

Why cable tray? Lots of expense and faff. All round patent band is fine for bunching and laying, and clips are less time consuming than hundreds of cable ties. Seems a massive ball-ache and cost for very little practical return? You’ll need spacers behind the trays to get cable ties in / out, so further projection outwards too. Rows of 38x 25 and 38x 16mm trunking would be quick and simple, using the self adhesive to lay these out and then a few mechanical fixings to corners and joints where you’ll be pulling on them.

Kind of contradictory? Easier said when you’re in the industry but when we’re advising first time, novice self builders then what should we actually be saying here? Cautious approach, manage risk, appoint liability, measure twice, cut once.

Don’t bother with a duct. Sharp sand or pea shingle below / above. 👍🫡

That’s only true if you’ve gone for a single thickness raft, on good ground, and with MUCH thicker concrete. That’s when you can say the loads will be spread out, so what is your actual foundation detail? Point loads are almost unavoidable, unless it’s a small dwelling, they just become less of an issue with one beefy slab. One of the one’s I’m on currently (MBC PH TF + passiv raft) had to have 2 sizeable pads installed under the EPS level, to take the posts (x2) used to break up the weight of the ridge beam. People don’t use terminology well, as raft can mean a few different methods for that one discipline. An SE is absolutely necessary, please don’t assume otherwise

Not if you’re renting to build.

In winter they’ll have masses of cold air infiltration and bump their heating bills up.

You, sir, are correct. I now routinely dissuade anyone from 'diverting' excess PV as these days it's either going into a battery or they're getting paid for the less complex method of selling and buying back. KISS at its finest. Hoooooooooooooooooooooooooooooooowever....... I would like to interject. In terms of promoting longevity for ones ASHP, I suggest that my clients use the ASHP at dawn, and again at dusk for recharging the DHW, and only topping up at midday off the grid, via the immersion, if it is at all necessary. I dislike the idea of having the ASHP jump from a relaxed state of cooling to a panic state of DHW recharging, and the subsequent downturn in COP. I like to look holistically at how the M&E is presented at the design and concept stage, but furthermore, how long the homeowner will have a reliable system that doesn't need replacement prior to it delivering a ROI. Most ASHP's don't come with a warranty longer than 7 years, which is pretty crap, gas boilers around 10 max, so anything simple that can stave off a premature replacement of a bit of kit in the multiples of thousands, is a worthwhile pursuit imho. Kicks the beloved BUS grant saving into touch if you need to replace these any sooner than expected.

Usually PV would sort that, or just a midday blast on the immersion heater, direct from the grid, so the cooling can just plod on in the background.

They get it all year round. We don’t .

Agreed, but it’s a little like being imprisoned by the sun, and also that’ll be on the handful of nice days where you want to be able to look out of those lovely (and very expensive) glazed elevations, to the views outdoors. In the villa we stayed at in Faro (Portugal) there were a few days where dropping all the external shutters was necessary, as well as AC running, but it was horrible to sacrifice the views. For those current projects I’m on, we’re using solar reflective glazing, and the blinds etc will only be needed for privacy. The AC on these will only react to a slight rise in temps, and will have very little to do, so it won’t be a cure it’ll be a prevention.

Depends on whether the one without had trickle vents? You know me and my impartiality lol. “Resistance is futile” 🤣

Sorry, but this is barking mad. They're not "nice to have", they are a B Regs mandated requirement in an airtight house. AC just recirculates the same air in the same space, it doesn't dump heat or moisture or stink to outdoors. If someone has made an airtight home and doesn't install MVHR, or worse that they have installed it but don't use it, then they must be nuts.

Are you cooling the GF slab with the ASHP? I guess you intend to retro-fit the downstairs ones if you deem that necessary?

Getting the cellulose pumped isn’t cheap either. It’s good, but rockwool + DIY will be more cost effective.

It’s Friday. Let’s settle this at the pub!

It’s all about blame / risk / return visits and arguing over who’s part of the install or kit is to blame. Good luck, but I’d walk away from that job every day of the week.

Nor will the MVHR.

Hello! Sorry, this fell through the net. Are you DIY’ing or getting it supplied and laid by a contractor? Dry S&C mix is fine, but at 60mm you’re close to the thinnest I’d do that at tbh. This sounds like a candidate for Cemfloor tbh, eg a liquid screed. If you’re going for resin atop then I’d avoid gypsum (Anhydrite) as there’s a laitence that needs to be removed (like a scum on the surface when cured) which nothing will stick to. Do Clockwork cover your area? https://www.clockworkscreed.co.uk Very good for price and quality, and they mix on site to the exact qty you need.

Just about to write this, the builder is clueless. For my current 2 clients new builds I’ve recommended A2A AC for the 4 FF bedrooms, and ASHP + wet UFH in-slab (both insulated rafts) and MVHR in both; airtightness will be <0.6ACH for each (I’ll likely get these below 0.4 as I’m a freak when it comes to airtightness). If you go for airtight, then add another £2.5k and just get AeroBarrier in to treat the place, and it’ll be the best money you spend. Airtightness trumps insulation every time, as ventilation heat loss is huge compared to fabric heat loss. Stop the air infiltration, recover the heat, and enjoy an extremely comfortable, and cheap to run home. AC is the luxury, MVHR is a necessity (as you’ve said you’re going airtight you don’t have a choice!!!!”); hence your builder is giving you shoddy advice that he’s picked up in the pub. 👎

Ask him how underpinning works.

If the blocks are installed and left to fully set, you can hard pack and shim with zero issues. Done Christ knows how many knock through jobs over time.

Can’t argue with an 8 week turnkey house!!

I'm working in Cambridge next week. Are you saying to leave my thermal budgie-smugglers at home?