Bad Airtightness Test Result

[AliG]

Ok. This is embarrassing but here goes.

 

After some considerable time I finally had an airtightness test done today.

 

I wasn’t expecting a great result because it seemed almost impossible to impress upon the builder and architect what was required and working away during the week I just couldn’t be on site enough to see what was being done.

 

Anyway the guy turned up today and we got a number just below 8.

 

I did notice that we had missed dealing 3 of the MVHR vents so maybe the number would have been 7.5 if that was done. We tried sealing them by sealing the MVHR filters but that didn’t work.

 

I was t expecting 1 as a result but expected a lot better than this.

 

The weird thing is that I have sealed most of the obvious draughts and gone around with an IR camera. I keep a very close eye on our gas consumption. Hot water and the pool use 100kWh a day. When the temperature is around 8-11C outside we use 150kWh for heating and at the recent temps of around 3-4C that goes up to 250kWh. This is giving me gas consumption for heating of around 40,000kWh a year so £900. This is less than my last house which was half the size and 15 years old. So by no means high.

 

So considering the gas consumption and no draught issues maybe I shouldn’t worry but we went around to find the worst draughts.

 

A few things surprised me. The walls with stacks  in them got very cold. After he left I check in the loft and the holes in the ceiling were not sealed. They go into a small area of cold loft. The insulation covered them and the loft is not ventilated so I can’t usually feel any air movement up there. But once we depressurised the house air was flowing and getting pulled in around the pipes. I can easily seal this.

 

We also found one gap I had missed sealing in the eaves where there was a gale blowing.

 

The other surprising thing is that we have wooden floors upstairs. When we moved in I checked everywhere for draughts. They were only in a couple of places and I sealed them. But again with the house depressurised it drew cold air through the join in loads of places there has never been an issue.

 

The last big issue I think is two small areas of cold loft off our bedroom. I have been in one of these areas and it is the only place in the house where the top of the cavity is exposed and you can feel wind in the loft. I wonder if air was being drawn through the cavity then into walls and roof spaces connected to these areas. It might have accounted for a massive amount of the rest result. I will speak to the architect on Monday but I suspect that the top of these cavities should be closed irrespective of the impact on the test result.

 

There is also one area where the WC is where I have had the builder take down the ceiling and seal stuff as there very obviously seems to be air getting in behind the walls but I have never beeen able to find the source. This was very obvious when we did the test

 

So I have a poor result but yet heating bills are reasonable and there are no draughts.

 

I will seal the stacks up next week and will have to mastic the skirting to the wooden floors which I had suspected would need done. But I think I need to get those cavities closed, annoyingly there is no access to one of the two areas.
 

Moral of the story is do a test after the shell is built as it is quite difficult to fix now. I suspect I can get down to 4 or 5 but that will be it.

 

 

 

 

[SuperJohnG]

This is good info. And defo helpful advice, you've got to take it in realtive terms though. I'm sure it's a very big house though isn't it? 

 

Also - cost for gas seems off...I just checked my meter and got the following...and I'm with octopus. 

[AliG]

Thanks @SuperJohnG just woken up by a second round of the "thundersnow"

 

Yes, the house is big, it is just under 900sq metres, so the heating bill is very low for its size. We considered buying an old stone built house in Edinburgh before we built this and they were coming out at roughly 6x as much to heat for what were smaller houses.

 

I just renewed my gas at 2.1419p per kWh. Is your system updated with your actual cost of gas, as you are coming out a 3.655p which would be crazy high? Most of the best deals for gas are less than 2.5p per kWh. TBF when gas is this cheap it doesn't necessarily pay to have your house as energy efficient as possible.

 

I also just switched over to having the heating on all night. Previously I was running a 2C setback during the night. In most of the house the temperature wouldn't drop that much during the night so the heating would be off and then rn for a while in the morning to bring it back up to temperature. Having studied the gas usage on this versus a 0.5C setback, gas usage was the same, but there is the added bonus that it is toasty when for example the thunder wakes you up at 2am. I think the 0.5C setback is a good idea as I do like there to be a bit of extra heat for comfort when you wake up, so it is nice to have the heating running then.

 

It does feel that part of the issue is that there are areas where there are gaps/holes etc covered up by insulation or roofing membrane which isn't airtight. In normal weather, however, these stop cold air flowing, so I don't feel any air movement in the main loft, but when you use the airtightness blower it gets air moving through the roof membrane and through the rock wool into the voids where the stacks are. No harm in sealing where I can but I am not sure how much difference it will make to actual real world gas consumption.

 

A good example os the two spare south facing bedrooms. The heating is never on in these rooms and the temperature never really varies. In fact I can attach the Heatmiser charts for these rooms where you can see the temperature stays in a steady 0.5C range. The warmer room does have a eating manifold in the cupboard which provided a bit of heat. In both rooms when the blower was on you could feel cold air being sucked in under the skirting board. It was a nice cold night so easy to feel. Normally I have never felt this and it seems to have no impact on the temperature, but you can see what happened in one of the rooms where the temperature dropped during the test. Where the pipework comes up through the floor to the manifold, a hole has been made in the slab and it was very draughty, so I will get it sealed.

 

Actually this has now made me realise I can use the Heatmiser charts to see what rooms have issues.What I can see looking at the charts is that the rooms with pipework in them tended to drop around 2C versus around a 1C drop in rooms without pipework and the main issue was the rooms where the pipework leads into the cold roof, so this is the area to get fixed. Bedroom 3 is where the gap in the eaves was found.

 

The thermostats showed a massive drop in the hall and pool, these are the only two thermostats on outside walls, so I suspect a little cold air was getting drawn from the wall messing up the reading. There's a thermostat in the upstairs hall and it didn't show the same drop at all. I have mentioned this before as I had this issue in my last house. In general putting a thermostat on an outside wall is a bad idea unless your house is very well insulated and airtight as the reading will vary much more than the actual room temperature.

 

 

 

 

 

 

Edited December 5, 2020 by AliG

[SteamyTea]

Rather than just using just external temperature as a metric, have you thought of using wind velocity as well.

 

[tonyshouse]

Is it dot and dabbed?  
 

sealing skirtings to floor will still leave draughts in the floor void which can come out behind architraves and other gaps internally. 

[SuperJohnG]

6 hours ago, AliG said:

just renewed my gas at 2.1419p per kWh. Is your system updated with your actual cost of gas, as you are coming out a 3.655p which would be crazy high? Most of the best deals for gas are less than 2.5p per kWh. TBF when gas is this cheap it doesn't necessarily pay to have your house as energy efficient as possible.

Yeah that's updated live costs, I have a gen 2 smart meter.  

 

Its a fully burdened cost and hence includes standing charge.  But gas is it 2.8p /kWh. The standing charge is part of a gas cost regardless as you have to pay it. 

[jamieled]

@AliG although our house is on a much smaller scale to yours I have come to similar conclusions. Our air test was ~3.5m3/m2/hr which was a bit disappointing given the effort we went to in trying to think through airtightness. That said, we don't need a lot of heat to get it to temp and it stays warm for a while. Even on the windiest days I can't find any obvious draughts. So while I may try and work on this a bit more I think I'm at peace with it.

 

Would second the recommendation for others re an air test earlier in the build.

[AliG]

2 hours ago, SteamyTea said:

Rather than just using just external temperature as a metric, have you thought of using wind velocity as well.

 

 

I should have mentioned that, I reckon we use around 10% more gas on a windy day than a calm day, considering that around 40% of gas use is hot water/pool heating then that means heating is costing around 20% more. I am not sure I can get much more accurate a reading than that as the temperature might vary a bit etc, but we do definitely use more heat when it is windy.

 

2 hours ago, tonyshouse said:

Is it dot and dabbed?  
 

sealing skirtings to floor will still leave draughts in the floor void which can come out behind architraves and other gaps internally. 

 

It is dot and dabbed (not what I wanted but I was told it would be too difficult to attach all the plasterboard to the Porortherm with screws), luckily the floors are concrete up and downstairs, so there are less paths for cold air. In the main it was coming out under the skirting on outside walls or walls that were attached directly to the outside walls, as you got further from the outside walls it diminished a lot. There was some air coming out from wall lights in the hall, but very small. All the sockets and light fittings seemed fine, however, I did notice that the sprinkler heads in the roof may be an issue, they are just in one room.

 

We did use my FLIR camera to check the walls and ceilings after the blower had been on for 2.5 hours to see how much cold air was being sucked in behind. There were thankfully few issues where so much was being sucked in that the wall was getting cold. They tended to be right in the corner of rooms and not extend out(see pictures). The only exception to this is the kitchen, where even without a blower test I had noted that the corners of the square bays were cold above the ceiling using the IR camera before. This time the ceiling started to cool down and you could see the strapping.

 

Here is the offending soil stack inside a wall in an ensuite, taken from both sides. As I say this has never been an issue. When I went up into the loft I had to remove a few hundred mils of rock wool to actually find the hold in the ceiling, so it may be that cold air doesn't get in at normal pressure levels. Also the cold isn't showing up over a large distance inside the wall, so it may be that air was getting drawn into the stack via plug holes and not actually via the roof.

 

I suspect that in the kitchen I need to drill small hols in the corners of the ceiling and inject a little  foam up behind the strapping if I can to seal the corners. I have been hoping not to have to do it as it will be messy.

[Mr Punter]

Was the test for SAP compliance and if so, what is the target number?

[AliG]

The target number was 4. I think though that we only need the 10 BC maximum. I have not had this confirmed yet.

[Mr Punter]

Even if you pass it may be worth spending a day or so plugging any gaps with foam or tape or OSB.

 

It is annoying when you have plasterboard on dabs.  You can get SAP to treat the space between plasterboard and wall as a low-e gap, which add to insulation.  The reality is that mostly it allows cold outside air to freely circulate.

[AliG]

37 minutes ago, Mr Punter said:

Even if you pass it may be worth spending a day or so plugging any gaps with foam or tape or OSB.

I will be, sadly I think it will take me more than a day.

 

I am happy to do most DIY jobs but I do hate stuff where things stick to my hands such as working with foam and mastic.

 

I have a bit of touch up painting to do, so I am going to try and get this done all together. I will make a room by room list of areas to target.

 

The guy doing the test thought there was a problem in one quite specific area near where we found the gap at the eaves that was letting cold air straight in from the loft. There was an area where I found I cold get my phone in and see the underside of the roof which was exposed and uninsulated or sealed. I asked the builders to fix it and they plasterboarded the area. However, I don't think they sealed the area first, so the air was getting sucked in behind the plasterboard and then able to get in behind the wall in that area. I need to remove the plasterboard and have a look. Luckily it is inside the eaves storage so it hasn't been taped or plastered, I just need to take the screws out.

 

[A_L]

1 hour ago, AliG said:

The target number was 4. I think though that we only need the 10 BC maximum. I have not had this confirmed yet.

 

https://www.gov.scot/publications/building-standards-2017-domestic/6-energy/62-building-insulation-envelope/

 

Quote

6.2.4 Limiting uncontrolled air infiltration

 

The infiltration rate used for the TER calculation is 7m³/h.m² @ 50 Pa (see clause 6.1.2). Whilst no backstop value is set for uncontrolled infiltration, it is recommended that buildings are designed to achieve a value of 10m³/h.m² @ 50 Pa or better to allow a balanced approach to managing building heat loss.

 

The downside is the CO₂  difference between 4 & 8 on your DER which has to be less than the TER. If your insulation is better than the minimum it should not be a problem.

[AliG]

4 hours ago, SuperJohnG said:

Yeah that's updated live costs, I have a gen 2 smart meter.  

 

Its a fully burdened cost and hence includes standing charge.  But gas is it 2.8p /kWh. The standing charge is part of a gas cost regardless as you have to pay it. 

Is there any reason you want to stay with Octopus? I just switch every year to the lowest tariff. Have never had an issue with any provider. Sometimes i even switch more often if I get a better deal.

 

You could probably save about 10% on your electricity and 20% on your gas by switching. 

[SuperJohnG]

3 hours ago, AliG said:

Is there any reason you want to stay with Octopus? I just switch every year to the lowest tariff. Have never had an issue with any provider. Sometimes i even switch more often if I get a better deal.

 

You could probably save about 10% on your electricity and 20% on your gas by switching. 

I always switch every year with Uswitch. But hadn't in the last year as octopus was still coming back the best deal. Maybe need to check again. 

[Vijay]

My only experience with Octopus was them being quite deceitful. I gave them my usage figures and they gave me a higher price. They then asked what I was paying a month, which they they said they could beat. When I questioned that, it turned out the reason they would beat my monthly charges, was by reducing the usage figures - so basically I would end up in debt if I used the same energy. Very wrong of them to try and fool people!!!

[ProDave]

1 minute ago, Vijay said:

My only experience with Octopus was them being quite deceitful. I gave them my usage figures and they gave me a higher price. They then asked what I was paying a month, which they they said they could beat. When I questioned that, it turned out the reason they would beat my monthly charges, was by reducing the usage figures - so basically I would end up in debt if I used the same energy. Very wrong of them to try and fool people!!!

Until just over a week ago I would have recommended Octopus.  But they have just put the prices on my variable tariff up by over 10%. I have not heard anything in the news to say wholesale electricity prices have risen 10% lately.  And the only fixed tariffs they offer are no different to their variable tariff.  So sad to say time for that battle of switching suppliers. A task I hate because all I want is the different electricity supppliers listed in order of pence per kWh but nothing is that simple on the comparison websites who pull the dirty tricks you mention.

[Oz07]

At 900 quid to heat your mansion a year I wouldn't worry too much. As long as it is comfortable. Deal with the obvious stuff as much as possible then enjoy the house.

 

As has been discussed before people don't value energy efficiency too much. You can see why when even if they saved your whole heating bill of 900, you'd be relaxing in the pool while they would be overheating!

[tonyshouse]

I don’t value energy efficiency as it doesn’t do what people think it says on the tin, it says nothing about how much or little is used.

 

I much prefer energy use reduction - using less that is what it should say on the tin so why not say it! 

[Oz07]

I've just looked at my meter I don't know how you heat that place so reasonably! It just goes to show the diminishing returns on this eco lark. I got an air score of just over 1, installed mvhr and I've just done my numbers. Ok it's a lot less than 900 for the heating and hot water but the difference isn't going to make me rich. I remember being sceptical about all this year's ago. People like Jeremy were convinced energy costs would rise. I always thought the govt would step in and keep costs down due to the rubbish housing stock we have and people would be bankrupted. Dont get me wrong I enjoy having a comfortable place but is it that much more comfortable than my last place which conformed to part L but didn't exceed in any way, not so sure. All this is making me think life is too short and I'd like an indoor pool! Ha. 

[Oz07]

I get about 68kw per m2 if I take readings from August to now, should include an even amount of no heating and heating months. Also includes hot water

[Oz07]

That 68 kWh would be for the whole year btw

Yours is 44 kWh but only for heating?

Is my maths off or is my mvhr system not recovering any heat!?

[tonyshouse]

Are we talking kWh/m2/year ? 

[Ferdinand]

A very interesting thread - thank-you.

 

@AliG I've enjoyed reading your story - remember that you can get Smoke Pencils if you want to trace draughts.

And I like the typo:

 

On 05/12/2020 at 02:46, AliG said:

The warmer room does have a eating manifold in the cupboard

 

That makes me think you have a private anchorite (walled-in hermit) in the wall of your spare bedroom ?.

 

Ferdinand

 

[Oz07]

54 minutes ago, tonyshouse said:

Are we talking kWh/m2/year ? 

I am yes 

Including heating, hot water and cooking on the hob