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Yep. Currently have large expanses of glass on both, but should be reasonably shaded in the summer. Won't really know until we get to live in the place, but hopefully soon

My PHPP is using "GB0013a-Hemsby"

I agree, PHPP is a model, not a crystal ball. It remains the best tool I could find to test the combined impact of all the fabric choices I made. I have very little south-facing glazing so solar gain is a smaller problem than it might be. My last house was similar and in the extreme heat of last year it stayed bearable inside, but only if I vented the house at night and buttoned it up in the day.

Haha. Maybe, but not expecting to need AC. If the PHPP calcs are correct then the house will only exceed 25°C for a few days a year.

My Zehnder Q350 can be configured to turn on the supply or extract, or both (normal balanced mode). I wonder if I'll get a good cooling result if I use Home Assistant at dusk to switch the MVHR to supply only, chill the slab and also open all the Velux. Then, before dawn close the windows and switch the MVHR to balanced mode with summer bypass. Thoughts?

Yep, not counting on it.

That's my plan for the days where the PHPP predicts overheating: crack open the electric velux windows to create some passive stack cooling.

Nope. Hoping the MVHR will help. Otherwise I’ll be opening the three roof lights for passive cooling at night.

Yep, I heard that. Where do you think I need to watch for dew forming? Pipes above the slab, or on the floor tiles?

My house is near-passive (0.12 walls, 0.1 ceilings. 0.08 slab, MVHR, triple glazed but sub-optimal solar gain). I've installed UFH in the ground floor slab but the 4kW ASHP is not on yet. Installing electric UFH mats and electric towel rads in bathrooms, otherwise nothing else. I can run the ASHP in cooling mode if summer heat is a problem. Had very high humidity after plastering (85% @ 12ºC) so brought in some dehumidifiers running 24x7 and a 3kW fan heater running for 6 hours a day to get the house up to 18ºC and 55% RH. Turning on the MVHR helped. I'm very hopeful now that I'm more than covered for my space heating needs.

Apologies yet again. I won’t be able to join you. Paid work getting in the way but unfortunately necessary to keep the project on track. On a positive note, plastering underway and kitchen onsite

Sorry, not me. Got to be in the City that afternoon.

Oh, I’m so sorry Geoff. I hate to think of you waiting but admire the commitment. I know I didn’t commit either way but had hoped to come. Unfortunately could not make it.

Yes, mostly excellent. Got a few snags to iron out with the slider (they didn’t install the soft closer and it has paint issues) and with the French doors (not locking quite as well as expected). Their snagging team should be onsite next week to resolve.

Finally cleared the mountain of soil in my garden.