Iceverge

@Tom You have my sympathy. It's a rubbish situation to be in. It sounds like you're in need of a more conventional builder. Get some solid detailed plans ready, get in touch with as many of them as you can. Get good references. Pick the best and sign a contract. However you'll have to wait for the good guys and you'll have to pay them. The current bunch probably aren't bad guys. Just a bit boyscoutish. Unwilling to commit to a proper contract. Unable to cost a project properly, and include rates for plant hire etc. Unable to straightforwardly say they've underpriced the project, take the hit on works to date and up the rates for the remainder. Out of interest what factors swing you towards the current builders? Time/cost?

I like it. Can you provision for a ground floor shower or a lift for less mobile occupants. Privacy in the snug might be compromised from the kitchen with the the glazing arrangement. Have you considered overheating with the large ESE window in the kitchen? Expensive and some tricky details, yup, but if you're prepared these can be hurdled. Looking forward to seeing your progress.

What is your exact wall build up at present on site? Are you planning on removing existing cladding? Passive buildings are a wholistic concept. Super insulating your structure is not a panacea. Airtightness, appropriate glazing and shading are all important. Neglecting anyone and you’ll have an underperforming building.

Maybe they’re up to the same tricks by hiding a smaller fantastically hideous house inside.......

You may have a perfectly well functioning system. Have you lived with MVHR before?The air flow volumes are very low. You shouldn’t feel a breeze unless your face is literally beside the vents. Have you checked/changed the filters?

No experience with this., just seen it online. You can defiantly render onto it directly, with breathable plasters and paint ideally,althought you might be ok with conventional materials given the placement in the structure.

20mm wood fiber covered directly with skim?

@Adsibob What about wheelchair visitors?

That's your external moisture barrier. At the moment the moisture from the house can escape between the joints in the kooltherm into the roof and get trapped in there by the sarking which is cold and cause condensation. Carefully taping the joints in the kooltherm should help, No it's an approved detail for permeable roof coverings. In my opinion the membrane is more likely to rip and you'll need to make sure that the builders leave the correct droop under the battens. I'd put it under the counter-battens personally. Given your other two options are having radiators that will be never used or cold rooms I think you're going to have to compromise somewhere. Fair enough. I'd be interested to see some real world pics of those windows when they come. They sound nice. Out of interest where are you planning on running services on the ceilings and walls?

What is your plan for a vapour control layer in the above buildups? I note the membrane is floating between the batten and counter batten in all cases. Why here and not below the counter-batten? As for the heating probably not but impossible to say without knowing the specific situation. If you're doubtful just run pipes anyway for rads. Why double glazed and not triple?

No issues fitting it in. It was obviously the expansion vessel that caused the issue in transit.............

It's a part of the issue, mostly in room in roof designs. It's difficult to get a handle on this without playing with some kind of overheating calculator. The effect of mainly poor glazing choices become more obvious then.

I guess your first buildup was something like this. I calculated a U value of 0.188 and a phase shift (decrement delay) of 6.7hrs. This isn't a great number and may have added to your overheating. A better option for heat protection. Similar U value but a phase shift of 12.8hrs. Notice the much less extreme swing for internal surface temperature in the summer. This makes overheating easier to control. On a cold winters day both roofs will perform the same against the cold. The website I used was. It's worth having a play. https://www.ubakus.com/en/r-value-calculator/? It includes this importance sentence in the blurb there too. "For a proper summer heat protection, materials with a high heat storage capacity should be used, ideally in combination with an outer insulation. In addition, the direct sun exposure through windows must be reduced to an acceptable level by shading means, e.g. outer blinds, roller shutters or sun sails"

Yup. It was just one of the first ones in Googled. Sorry for any confusion.

Out of interest how was the roof insulated in your previous home? Do you know what materials were used as different types of insulations have very different behaviours in heat even with the same u value. Do you have any plans of the house you're proposing to share?

Usually in this scenario it's like this All waste water pipework is run straight down through the concrete base and then horizontally towards the perimeter of the building to an access junction. Is the only reason you're planning to put the slab above the insulation, to allow you the bourgeois pleasures of randomly building concrete blocks whenever and where ever your heart desires?!!! When our place was built all pipes were taken straight down into the middle of the hardcore layer below the DPC with 110mm waste pipe and then outside to an AJ. They were left well proud of the final level of the floor and cut down later. They used normal 90deg bends, I gather these would have been better. They also Tee'd some joints under the floor. In hindsight it would have been more robust to run each drain outside individually. Soil pipe is very cheap. And join them at one of these It would have made it possible to rod every drain properly should they ever get blocked. Do you have your shower trays/formers picked out?

Golden Rule #1.

Worth a read.

Similar topic here a couple of weeks ago.

I did my own design. No rocket science really. I bought some components from BPC and some elsewhere. I would have included rigid silencers in ours as the flexible ones aren't as good I think, my wife can't hear it but I can as our house is very quiet.

I like the aesthetic of the house and it sounds like you've found a lovely plot. The first thing I'd get sorted is the layout. I'd make a dedicated home office. Times suggest they're the future, maybe even two if that's how the household operates. Many of us are stuck having to do video calls from the kitchen table or a bedroom, you don't need to be. It's a large house so there's not much excuse for not having an wet-room en-suite on the ground floor. Nobody wants to go to a care home for the sake of a small bit of shuffling at design stage. It means they can live in their own house when they get old. Much less stress doing it now rather than dealing with adapting the house along with having an illness/frailty. I'd make the utility/ laundry larger. You'll never regret it. Jack and Jill bathrooms are a pain to live with in my experience as well as causing noise issues in the "wee" small hours! I would shuffle the rooms downstairs. All the beautiful daylight will be wasted in the two reception rooms that you will spend little of the day. Once you have that nailed. I'd move onto sorting the energy modelling of your house.

I'm going to take a punt and say the dark grey walls are existing and the light grey are new. Clean sheet design is best opinion. You're going to have to move out either way. You'll have a cheaper, better house. What is the setting of the current building? Are there close neighbours? Is there any nice scenic views? Is there privacy issues from the Street? I notice at the back of the garage there is a hair salon. I'm not sure of officialdoms views on this as it sounds like a commercial venture but maybe it's best labeling it "study" or likewise. Do you intend staying here forever or move in a few years?

What's the primary aim of the policy? CO2 reduction or using electric car batteries as grid storage/stability?

Top tip. Is there a layer of fiberglass in some boards? I guess you would also benefit from the increased heat capacity (with more mass near the room) smoothing temperature swings.

It sounds like a roundabout way of doing things. How thick are your other floor finishes?