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.

From the Brink website.... 'The 400 stands for an airflow of 400m³/h' so that would be 100m³ every 15 minutes. I just realised i used the wrong units previously. My fan is moving 100m³/minute.

Then tiling before xmas is a distinct possibility si Thanks Nick. Tiling by early july was the target

'the general level of moisture in the house has an impact on the drying speed of the screed. ' agree, which is why i think the volumne of outside air i am blowing through the kitchen should have a lowering effect on the overall RHI %. Remember that my original question was about the fact that the 'meter box' % goes up again over night when the fans are not running. As Nick suggested i think i will lift and move the test box and see if the behaviour changes.

Its certainly getting out of the house, doors and windows open on the extract side. As i said earlier the fan is moving 100 cfm. That is a large volume of air.

Yes.

And yet all the advice is, 'ventilation is key'

Thanks dude. Throuble is, i followed the instructions. Now i dont know how to get a meaningful figure. It might be that leaving the tester fixed to the floor for more than 24 hours is the issue. Does not say that anywhere though. My fans move 100 cubic feet a minute. Thats twice the kitchen volumne every minute! Ought to be enough. Very confused

Thats not the issue, well it is an issue but not relevant to this question but thank you.

I bought one of the moisture testers from Pro tiler tools. Fix it to the floor and leave it for 24 hours. Easy. I got a reading and then fired up a large fan for the day. Reading %is lower at the end of this, excellent we are moving in the right direction. But the following morning the % RHI is back above 90! Bugger. I have been repeating this for a week now. Am i doing this wrong?

The plaster in our house is smooth like glass, shame to paint it really. Had a few small issues with the frog tape peeling the paint. Even after a mist coat. Probably down to me not leaving the ceilings long enough before wanting to paint the walls.