Post and beam

I had the volume wrong so my calculation would have been nonsense. Area = 479 Vol = 479 Big coincidence Off by a factor of 10 So ACH = 1.4 X 1 = 1.4 Thanks @JohnMo, agrees with your number. confirmation bias? but i am happy with that

The house is a dormer upper floor with some sloping ceilings. These will eat into the calculation, but are then offset by the fact that we have a slightly vaulted ceiling in the dining room. So on balance i think we have slightly less than 4800, but only by about 10 cubic metres. 4800 is a nice round number. Going on a calculation i saw on the intergoogle the surface area divided by the volume gives the SV ratio. 479/ 4790 = .1 Does that look correct? have i got that right?

Hi Kelvin. Is that the ACH then?

If you are having a cold roof then the airtight boundary at the upper floor ceiling will not be provided by them for example. This is a shed load of work. All well and good if you are expecting this but a big suprise if you are not. They dont board the loft or fit the 400mm rockwool either. They just deliver a lorry load of it. Again, fine if you know this. Not so much if you dont.

They do 3 basic types of house the old dormer cottage style like the gransden show house. The georgian style and the much more modern looking things. Even a passive version. I suggest reading their terms very carefully, they have many years experience and de risk everything they say. Whatever target airtightness you end up with remember that they write ' final airtighness is down to' .... others. If you are not taking the full turnkey package then there is so much left to do that will not be done by them that the target is meaningless. It will not be their fault when the target is not reached. I have learnt a great deal while building mine about Potton details and standards.Are you a competent DIYer or a builder yourself? There are things i might be able to help with regarding them. Where are you in the country? Keith

1.4, air permeability of course. i would like to know how that relates to an ACH number. Not a straight forward calculation i know.

Not at the outset no. They filled in the target air tightness box with '1.5-3' and specified MVHR as a consequence. Their chosen supplier was not credible as far as i am concerned. Prior to this i was not really aware of what MVHR was to any meaningful level and thought of it as just another thing i had to pay for. Lots of reading up on the subject quickly brought me to realise its worth. I went with Brink for the parts. What type of house are you talking to them about? 5 is not much of a score for them to aim for as a 'premium' supplier, i think all the major house builders would give you that figure. I am also interested to learn which level of package you are considering from them. Keith

This is why i announced before hand that they were booked. I imagined at least one or two selfbuilders would have been interested. Yeah! dont bank on it. I had to do a LOT of work after the TF frame was left to me as completed. In the kitchen for example i could see daylight ( lots of daylight) out through the open eaves detail. I had no idea 'open' meant quite that open.

House is 70% plaster boarded & plastered, not yet occupied or furnished. Yes the 'goop' did settle on horizontal surfaces. The upper floor is a little tacky. A bit like some pub carpets back in the day. The window sills are the only area of any concern. I told the guys not to bother covering these as they are currently primed MDF and will need sanding and painting anyway. But the goop has not dried to a state where i can brush it off so i think sanding the window sills will be a little more of a sticky task than it might have been.

True, but, disappointing from my point of view. Looking at it another way it means i left them with a lot of improvement to find. So did i do an effective job with all my detailing? It certainly took a shed load of work .

I think the majority of the improvement is from the spray, certainly down to the 2 figure i think. Then the guys entered the house a couple of times with spray foam fine nozzle guns to help where they could see the mist still moving towards cracks. No big obvious issues just lots of tiny movements of air. Guys did say the builders had done a great job on the windows and doors. This made me feel a little better because in this case the 'builders' is me. I taped all windows and doors.

Yes dude

£2k

Results are in. 3.9 as built air permeability prior to Aerobarrier doing their thing. Ended up with a figure of 1.4, so a 63% reduction. The structure surface area was calculated as 479 square metres. I dont know how this would relate to an ACH figure.

Agree totally, my mistake.