JamesP

We were in for 3 years before private BC got pushy. Just go for it. Have a read :

+1 for airtight tape. Worth spending some time and money on covering all holes. https://passivehousesystems.co.uk/shop/airtight-tape/gerband-586/ No comment on "a contractor".

From memory I probably allowed 25mm on each side as I then fitted Pavatex 20mm reveal board around all openings for windows.

@Bramco That is a fab project and build, the flush roof lights very smart. All our triple glazed Velux are on the 1st floor, bedrooms, bathrooms and landing with fitted internal blinds, just about accessible if you are 5'9" +. Would consider solar glass or external blinds and in hindsight have the large fixed window at the gable end opening. 2 in each bedroom to provide some cross ventilation but will be connecting (plumbed in during build) AC to provide proper cooling.

I used EDW for fitting 7 Velux in Tata Standing seam roof. All I can add is take your time with the detail and an extra pair of strong arms for the lift. Have a look at this for starters.

I agree @Roger440. Its a grift, the ultimate pathological altruism.

Have had a quick look and the dpm is mostly cut short next to bottom of sole plate. I would just try and protect soleplate from water splashes, also fitted rodent stainless steel mesh behind cladding. I wrapped the breather membrane underneath the 40mm pavatherm, green. I extended the Cedar 50mm below batten to protect the sole plate. Once board, 2 x batten and cladding fitted probably 75mm proud of render face. Dodgy drawing enclosed. I would not create a pocket where damp could remain in B.

Enclosed a drawing of sole plate detail on my build, not a builder but I brought the 40mm pavatherm flush with the sole plate and lapped the dpc under. Then batten, counter batten and Cedar. I would not leave it exposed. Would bring the medite board level with block and sole plate. Others will have ideas.

With a tray 1200mm is fine as @Kelvin.

Are you using a tray or flush wet room floor? We have overhead rain showers with a wet room walk in shower tray kit, 900mm x 1800mm. Fitted a 1400mm x 1950mm shower screen secured with a horizontal bar at the open end. It works fine and not obtrusive. Anything shorter and water would exit past the screen. I would consider losing the 800mm screen and fitting a 1400mm only. Easy access. Fit 50mm waste if not too late.

I use flexible tile adhesive usually on 6mm or 12mm cement board base. Your existing floor and joists need to be solid.

Quick scan at your drawings. Not dissimilar to our build, as @ProDave make sure you have a ridge beam, try and get 1.5m before roof pitch starts. Make sure Velux are accessible by hand or automate and consider external blinds if possible. Make sure the other bedroom window can open, do not rely on Velux for cross ventilation. I would rotate the kitchen island 90' anti clockwise and change hob to sink. Consider how to address overheating and cooling issues now. Lose the chimney / fireplace for a stove / flue. Spend on airtightness. This bedroom photo is 6.2 metres wide with some built in draws / cupboards. 1.5m to the eaves.

Same spec as your Lindab, 125mm Half round Majestic, 87mm downpipes. Cannot fault it, excellent quality, design and fitting. Just the cost, I have 78 metres of guttering. Your fascia detail looks fine to me in the drawing, all my feather edge on 25mm batten. I had to make a combined fascia / soffit board out of Douglas fir due to the overhang.

@Stones Maybe it does have a fault or I misunderstand the indoor & outdoor temperature settings. I think I should set the indoor temp as low as possible, 16c and the outdoor as high, 20c to enable bypass. The Outdoor Temp screen enables you to choose the minimum outdoor temperature at which the bypass will operate in degrees Centigrade – only displayed when the bypass is fitted.

So 5 years in and think I now understand the summer bypass has minimal effective function in the warmer months. It's 16c outside, it's midnight but the air supplied is at 23c with summer bypass on or off. I naively assumed with the bypass on it would supply the external temperature and have a moderate cooling effect. Is the heat exchanger supplied by the extracts? Help.