Iceverge

Apart from this bit. Like @Kelvin says. Our PHPP predicts 2625kWh/m2/Annum at the moment. If I put the limiting values in for Air permeability and ditch the MVHR it goes to 7525kWh. It really is the lowest hanging fruit. Far more so than super insulation.

Passive or "Passive". About 2 years ago, at a stag party, I was looking forward to an in depth chat about thermal bridging with and airtightness details with a man who introduced himself as a passive house self builder. Imagine my dismay when I learned he had double glazing, hadn't done an airtightness test, had no idea what insulation levels were at. Turned out his living room was almost unliveable with all the glazing for most of the year. Too hot or too cold.

Excellent. Can we see the finished cavity? Do you think it would work with celluose?

It may be a case of fiddling with the door to get it snuggly fitting soby adjusting the hinges and latches. I wish wish wish someone made doors with fridge door style magnetic seals. Then the cheapest crappiest buckled door would still seal perfectly everytime .

I've used TF 100, cheap and plasticky, and TF400, top notch in my opinion. Better than Tyvek, is TF200 closer to 100 or 400?

Looks like the rain runs down and is directed into the channel here and cannot escape. Can it follow the route of my arrows to any external drainage holes? Are they blocked?

@minty Sorry I think I(we) might have git a bit bogged down here in an effort to assist. Shortest answer I have to solve your problem. 1. Stop any water leaks from outside or inside. ( Roofs, windows, doors, pipes, shower trays, washing machines etc etc) 2. Replace the bathroom fan with this. You can DIY it or pay an electrician. 3. Make the house hotter by leaving the rads on. 4. Give it time.

It's just a way of heating the air. Like an electric rad but costs about 4 times cheaper to run. Your mould is caused by poor ventilation. You need to tackle this first.

I'd be cautious with the unit you buy as those optimised only for cooling may not work efficiently when heating. I bought a Daikin FTXM25R. I will update IF I EVER MANAGE TO GETTING AROUND INSTALLING IT.

Probably not enough, You need 2x windows open to get a decent cross flow. The trouble is then that the house gets cold and they get closed. This needs to be on 24/7 a max power. Take this out and replace with one of these. As mentioned above, it runs continuously and ramps up when the humidity does. and sucks out all the damp air. Costs about 1/20th of what a dehumidifier does to run.

I think I improved that marginally.

47x42mm is what I've used. You can nailgun them then, if that's any use to you. Also 50mm mineral wool insulation is readily available, I wouldn't object to wider mind you.

What was the final wall build up you chose?

Interesting. I've seen it mentioned but invariably people opt for something like woodfiber or (shudders at the thought) badly fitted PIR. Is it dear? I'm guessing a wet plaster layer is your airtighess then? Does the barn need an internal timber frame to support the first floor?

If you're near passivhaus levels then an GSHP is the worst choice you could make. It'll never pay itself back. In fact for all but the cheapest ASHPs restive heating can be competitive for a very low energy house. What are the specs of your walls etc? Do you have a proposed build-up?

Firstly Welcome welcome! Congratulations on the planning. Secondly STOP! Hit the brakes for a minute. Please post the spec sheet of the build and some de-identified drawings. I can already see a £10k saving from your first post. I suspect collectively the "hub" can save you much more. Thirdly, be realistic with your budget and labour. You have a young family, time is precious with them. Overcommitting yourself financially and in terms of time will make the build miserable and home life strained. Good luck!

Will give that a spin with a cuppa later. Cheers.

Yup. I've turned it off for a while to see what happens.

Upstairs looks very logical apart from the lack of south facing windows but since they're bedrooms it's probably not worth the effort of changing them . It depends how far you want to go with extensions etc and what your budget is, and what your needs are? Pics will help too. Without any more info I would consider something like this.

I'm going to reach to the top shelf and pull down this dusty old tome of a thread. We recently spent about a week away. Before I left I tripped all the switches in the consumer unit except the MVHR, the blower for the bio cycle water treatment unit, the borehole pump and the fridge. Our average load of electricity was 245w since we left!!!! To put that in context Thats over 2 MWh annually or about 2/3 of our annual heat demand.

There's lots of things going on with house construction. Unfortunately there are loads of snake oil salesmen and manufacturers sales claims being treated as science. Most people rely completely on gut feeling. Amusingly this covers the entire spectrum of building types. Starting with the guy with the reflective wrap around sunglasses. " It was first used by NASA don't you know, ,researched in zero gravity, AI and smart watch connected. It will predict the hot water demand using quantum computing" In the middle there is the trusty local builder, "my dad did it this way like his father before him, hammer a 2 X in there and an bit of mortar and she'll be right." "Stick with what you know" At the other end is the hairshirt hippy. "Straw bales and reclaimed beachwood, gotta let it breath MAN" "Align the floorboards to the energy lines MAN". "WiFi gives you cancer MAN". Of course they're all right........and they're all wrong. It's a roll of the dice really........ They rely on belief and faith and it if works for them, I've no objection. However I would be wary about spending my cash on what someone else "believes". @Carly Lawson if you believe that durisol is the most environmentally friendly choice (I don't know BTW) and having that feeling is enough for you, then go for it. However, if you want to actually build the lowest environmentally impactful house then that's a different thing.

I would rather eat a breeze block than use rigid boards in a cavity wall.

It's an elegant structure that.

How about this.

With 100mm insulation and 150mm blocks you're at 250mm. Why not just build a full fill cavity wall with batt insulation? Alternatively a TF garage with an insulated inner stud and block external leaf.