Bad Airtightness Test Result

[Onoff]

1 minute ago, SteamyTea said:

You buy that off @pocster, wash it thoroughly, in vinegar and carbolic soap.

 

Scored from work for nowt. Thrown out as a bit of random plastic was rattling around inside! 

[TonyT]

I use one of these

https://www.sunrisetools.co.uk/other/dragon-puffer-airflow-indicator-kit.html

[SteamyTea]

2 minutes ago, Onoff said:

 

Scored from work for nowt. Thrown out as a bit of random plastic was rattling around inside! 

If you know the airflow, you can work out your losses.

With the commrcial ones, they have a number of holes of known size and block of a few as the house gets smaller, or more airthight.

I think when @joe90's was done, he had only two holes open (that is the minimum on the kit used), then the fan speed is adjusted to get the pressure difference to 50Pa.

[Onoff]

7 minutes ago, SteamyTea said:

If you know the airflow, you can work out your losses.

With the commrcial ones, they have a number of holes of known size and block of a few as the house gets smaller, or more airthight.

I think when @joe90's was done, he had only two holes open (that is the minimum on the kit used), then the fan speed is adjusted to get the pressure difference to 50Pa.

 

I'm sure a clever bloke could do the maths ?

 

Anyway it's 200mm dia, has a 3 speed motor with a "0.18m3/s nominal flow rate".

 

 

Might do as a positive ventilation fan for Zoot!

[SteamyTea]

1 minute ago, Onoff said:

Might do as a positive ventilation fan for Zoot!

Stick it into his catflap.

[Onoff]

4 minutes ago, SteamyTea said:

Stick it into his catflap.

 

Do you think it would improve his diction and grammar? Gotta love a euphemism! ?

[jack]

1 hour ago, SteamyTea said:

There is a school of thought that is convinced that there are huge radiative losses via glazed areas, "because it radiates to space".

I have never bought into it and always put it down to poor glazing.

 

I'm sure there're higher radiative losses via glass (less with low-e coatings) than walls, but I believe the perception of cold is partly convection-based drafts and partly the colder surface not reflecting back as much of your body heat as the warmer surface of a wall. 

[SteamyTea]

5 minutes ago, jack said:

 

I'm sure there're higher radiative losses via glass (less with low-e coatings) than walls, but I believe the perception of cold is partly convection-based drafts and partly the colder surface not reflecting back as much of your body heat as the warmer surface of a wall. 

There should be, but I think they are so small that we cannot really feel them, so as you say, a perception thing.

 

[AliG]

Further update today. The area around the WC is much improved, so much that I had to turn up the thermostat there. Historically I ran it 2-3C lower than the rest of the house as it was so much colder in that area that if I ran the thermostat at 21C the heating would hardly ever turn off.

 

What is weird is even once all sealed up I could still feel a slight draught in the roof cavity.

 

This got me thinking to the windows and is air coming in around the windows.

 

Now my windows are sealed to the render on the outside, but thinking about it, they are still attached to the cavity behind that, so air can still get in from the cavity. Watching the windows being installed, I was going to ask for them to be taped up, but the builders put plastic sheeting around the frames and taped that up, so I thought they had air tightness sorted. I cannot remember exactly what the detailing was. You can see the plastic poking out in the picture below.

 

Looking at it, I think the plastic is designed stop air getting into the rooms. And indeed we have no draughts anywhere. But what it does not stop is air betting behind the plasterboard.

 

I have been investigating in the gym, as the wall is getting beaten up by gym equipment anyway. If you look at the first IR picture taken on a very cold day, you can see the window reveal is cold, the outside wall which has insulated plasterboard is warmer and then the partition wall which has plasterboard on dabs on a block wall seems have cold air getting behind it.

 

At first I tried sealing up the corner there by pumping foam into the small cavity. This improved but did not fix things. Any I keep thinking where is the air coming from.

 

I pulled out a spotlight and I could feel the air was moving above the ceiling.

 

So as I am already suspicious that there is an issue around the window, I cut a hole in the window reveal

 

What I found was immediately behind the wall I hit the green plastic sheet. This was doing its job of stopping air getting into the room. But immediately I punctured the sheet, I could feel the cold air behind it.

 

The problem is that I think the sheet is sealed to the plasterboard in the reveal not to the block wall. Thus it lets cold air get behind the insulated plasterboard. This air can make its way up into the ceiling void and along behind the insulated board coming out behind the skirting and round the corner behind the non insulated board.

 

I have pumped the area behind the plastic sheet with foam. If this works to stop air getting behind the plasterboard, I will have the simple but laborious job of drilling holes in the window reveals and filling them with foam.

 

I suspect that this has a larger impact on the air tightness test than heating costs. There are no draughts anywhere from behind the plasterboard into rooms that I can feel, other than occasionally at the bottom of the skirting board. Thus the amount cold air getting into rooms under normal circumstances is small. But I am probably heating the air in the cavities constant which will be increasing my costs. When you run the air tightness test the higher pressure involved starts to draw air out under skirting and in other places that are tightly enough fitted to stop normal draughts.

 

As an example of the lack of actual impact on heating costs, the heating has never been on in the gym shown with the cold air behind the plasterboard. There is a UFH manifold in the wardrobe and the heat it generates seems to be more than enough to keep the room warm. Indeed we usually have to open the door when we exercise. Even below 0C outside the temperature in that room stays above 20C.

 

 

 

 

 

 

Edited February 27, 2021 by AliG

[CC45]

sad to read all this - its so much simpler to get this detail right as its going up.  Most trade just don't care unfortunately or believe what they normally do is OK.  I hope you get it sorted.

[ProDave]

On 09/02/2021 at 17:52, Onoff said:

 

So this is a blower rigged to blow air into the house, set in a sealed door or window aperture? The idea being it "pressurises" the internal space? 

 

Silly question maybe but how do you see/feel the draught? Wet finger, bit of paper to blow in the "breeze"?

 

This is what I did.  An old desk fan, a big sheet of cardboard, a lot of duct tape.

A manometer to measure pressure difference between in and out.

Measure air flow passing through the fan with an anemometer to calculate a rough idea of the leakage rate.

 

And go round the house looking and feeling for leaks, I found very few.

 

What was really interesting with the fan going is how the house depressurised, and if you then went and opened a door or window, the massive whoosh of air that came in to make up the pressure difference.

[AliG]

OK, had my retest today.

 

Improved from 7.9 to 5.55.

 

I could probably have done the work to get below 5 given a bit more time and a lot more enthusiasm.

 

The guy said that it was a surprisingly big improvement.

 

From bad to mediocre!

 

I found quite a few largish holes in places that were out of sight. I presume these were the main areas of improvement.

 

I am not convinced it has actually made any material difference to gas usage.

 

The one thing I did conclusively fix was the WC. It was consistently colder than the rest of the house and the heating ran a lot of the time in there during winter. Now the heating runs less than the adjacent hall.

[AliG]

Annoyingly I have managed to do a couple of jobs I didn't get round to before the test was done.

 

There is a shadow gap the whole way round my hall where the glass first floor balustrade is attached. You need to get on a ladder to reach it. I discovered it is not sealed inside the gap. This is also where the stairs were attached and again there was a small gap there that you couldn't see from ground level.

 

I have pushed 15mm foam strip up into the gap and caulked the gap where the stairs are attached. I suspect this alone might have brought the result down to 5 or less. The gap is almost 14m long.

 

Anyway, watch out for shadow gaps when doing air tightness.

 

There are a couple more jobs I can still do. I am pretty confident that had I managed to get these done the result would have been in the 4s.

 

This last job seems to have stopped my doors moving when it is very windy outside. The effect has been gradually diminishing as I have completed jobs.