Air Tightness

[richo106]

Hi All

 

At the beginning of our project is was simply to convert a bungalow into a house and then after speaking to few people I became a lot more aware of air tightness and the use of MVHR

 

At the minute the plan is to make the house as airtight as possible and have a MVHR installed. Going triple glazed throughout and a good level of insulation...floor 0.11, ceilings 0.13, walls 0.18

 

We will be adding another floor to our existing bungalow

 

What are the key things to consider and make sure I do when it comes to air tightness?

 

I will be parge coating all my walls before insulating internally/plasterboarding

 

Is it best to get it routinely tested for air tightness at certain parts of the build?

 

And a big question...is it worth it going down the air tightness and MVHR route?

 

Thanks in advance

[joe90]

17 minutes ago, richo106 said:

And a big question...is it worth it going down the air tightness and MVHR route?

Yes, if your insulation is up to a decent level as well.

[SteamyTea]

You have to make sure that your insulation cannot be wind washed.  That would bypass all advantages.

Then you have to consider condensation risk.

 

1 sheet of glass or 3 in the windows does not affect airtightness, it is the seals and joint to the openings that is important.  There is thermal bridging to take into account here.

 

Frequent testing is important if it can be done cheaply.

 

If you get to 1 ACH then MVHR is important.  I think there is a limit where forced ventilation becomes compulsory (<3 ACH?).

 

Can you improve the U-Value the walls and ceilings?  Ceiling especially, walls depend on the total exposed area.

 

 

[richo106]

Unfortunately with our design the only way to improve u values of the walls is internal insulation (already planning to have 50mm PIR in the existing bungalow)

 

Ceilings I can

 

What do you mean by wind washed?

 

The more I look into ACH and MVHR the more I think i could be wasting my time and money trying to achieve it

 

Thanks again

 

 

[jayc89]

17 minutes ago, richo106 said:

Unfortunately with our design the only way to improve u values of the walls is internal insulation (already planning to have 50mm PIR in the existing bungalow)

 

Ceilings I can

 

What do you mean by wind washed?

 

The more I look into ACH and MVHR the more I think i could be wasting my time and money trying to achieve it

 

Thanks again

 

 

 

I'm in a similar boat.

We'll likely reach 0.15 floor, 0.10 loft, but walls will be nearer 0.18, given our size constraints, due to being internal wall insulation. I plan on addressing airtightness as a matter of course when fitting the IWI, however I don't think I can justify a full MVHR system, so will likely replace windows with trickle vents and dMEV in certain rooms for ventilation. Not perfect, but I'm beginning to accept it as a "happy medium" for our property. 

It will significant reduce our energy usage regardless.

[SteamyTea]

22 minutes ago, richo106 said:

What do you mean by wind washed?

If cold outside air can blow around, or though, insulation.  This is a particular problem with mineral wool insulation.

Edited September 8, 2022 by SteamyTea

[jayc89]

17 minutes ago, SteamyTea said:

If cold outside air can blow around, or though, insulation.  This is a particular problem with mineral wool insulation.

 

I guess that's the benefit of parging before fitting insulation to the internal face of brick walls.

[SteamyTea]

2 minutes ago, jayc89 said:

guess that's the benefit of parging before fitting insulation to the internal face of brick walls.

Yes, integral face of the external brickwork.

There are also cavity closers for openings, they need to be fitted well.

[richo106]

Thanks all for the comments

 

I really am stuck in two minds what to do

 

I will still be insulating as much as I can and will be mindful of Air tightness but as I will be renovating/extending and existing bungalow I am thinking to get ACH down to 3 will prove very difficult.

As we are 'off grid'  I will be using ASHP with UFH downstairs and upstairs

 

Similar to Jay I don't know if I can now justify a full MVHR system, this will also negate the reason to have posi joists further saving money

 

Would I now need trickle vents in all new windows and also dMEV extractors in downstairs toilet, bathrooms * 2? What about kitchen extract?

 

I would love some opinions on this and I am now rather confused in what to do 

 

 

[SteamyTea]

9 minutes ago, richo106 said:

I would love some opinions on this and I am now rather confused in what to do 

Have you thermally modelled your house?

 

You can then change things and see what is important and what is not.

 

I find it easier to set a total target energy use for a building, then see what needs to be changed to achieve it.  Using a metric like kWh.m^-2.y^-1 is pretty pointless as it takes no account of the buildings form.

[JohnMo]

Look into humidity controlled MEV and dMEV.  Basically the trickle vent will open and close as required and the fans like wise.  Overall a lower running cost compared to MVHR, no filters, and good energy conservation. Some bedtime reading.

Atamate_SDAR+Paper+2019+(1).pdf

[Radian]

I must fit some sort of active shutter to an extractor fan in our downstairs loo. I was puzzling over a uniform layer of dark grey dust on the lid of the toilet cistern when it dawned on me that the day before I'd been in the garden sanding a painted picnic table!

[JohnMo]

MEV and dMEV run 24/7, so not sure you need a shutter.  Do the same in the kitchen and cooker hood set up to recycle.

Edited September 8, 2022 by JohnMo
Add kitchen bit

[richo106]

1 hour ago, SteamyTea said:

Have you thermally modelled your house?

 

You can then change things and see what is important and what is not.

 

I find it easier to set a total target energy use for a building, then see what needs to be changed to achieve it.  Using a metric like kWh.m^-2.y^-1 is pretty pointless as it takes no account of the buildings form.

No I have not thermally modelled my house...I will work through the spreadsheet today and see what I can play with.

 

[Radian]

12 minutes ago, JohnMo said:

MEV and dMEV run 24/7, so not sure you need a shutter. 

It'd have to be fairly powerful to keep the wind out! The actual fan is OK as is, the usual type operated by the light switch - but modified by me to use a 140mm PC case fan after going through a series of noisy expelairs! Almost imperceptible now, instead of something that sounded like a food mixer.

[richo106]

I thought I had all this planned out....how wrong I was haha. Back to the drawing board

 

My thoughts have now turned to saving my money on the MVHR and potentially use some of that money increase insulation

 

I will still try to make as air tight as possible but with the original bungalow and large glass oak front section I think it will very very hard to get down to the ACH level required to make the MVHR cost effective/worthwhile

 

Will my windows now need trickle vents in? I am looking into other ventilation options (dMEV)

 

As i will be having an ASHP I do want it as low cost to run as possible but within reason weighing up budget etc..

 

 

[JohnMo]

dMEV are silent also, not the same as a normal bathroom fan.  A few watts to run each.

[JohnMo]

You don't have to have trickle vents, things like this are also available from various manufacturers

 

https://www.aereco.co.uk/products/air-inlets-uk/eht/

 

https://www.bpdstore.co.uk/glidevale-energy-saver-humidity-sensitive-trickle-ventilator/p/182

Edited September 8, 2022 by JohnMo
Added second link

[richo106]

https://www.bpcventilation.com/extractor-fans/c-mev/vent-axia

 

Would something like this work?

 

Thanks again

[JohnMo]

Would work, but

 

Something like this would be much better or something from Duco or passivent

 

https://www.ventilationland.co.uk/product/44535/itho-daalderop-cve-s-s-co2-optima-inside-package-hp-415-m-h-plus-build-in-rv-humidity-sensor-and-co2-sensor-plus-4-ventilation-valves-plus-auto-rf-control-perilex-plug.html

 

Then you just demand controlled inlet and you are good to go.

[richo106]

I have spoken to passivent and they recommended there sister company Glidevale and their fully passive iPSV system

 

As you can tell I am new to this area of ventilation so trying to learn which would be best

 

Thanks again

[richo106]

On 08/09/2022 at 09:59, SteamyTea said:

Have you thermally modelled your house?

 

You can then change things and see what is important and what is not.

 

I find it easier to set a total target energy use for a building, then see what needs to be changed to achieve it.  Using a metric like kWh.m^-2.y^-1 is pretty pointless as it takes no account of the buildings form.

I have completed the excel sheet linked (very good sheet) however I haven't got a ACH target. Speaking to a friend in the 'know' he says I could possible get to  ACH 3. Is this easily achievable?

[SteamyTea]

Just now, richo106 said:

Speaking to a friend in the 'know' he says I could possible get to  ACH 3. Is this easily achievable?

Achievable, but if that is easy is another matter.

 

What you can do is play with the ACH figure and find out what sort of ventilation is worthwhile.

Don't forget you can get single room heat recovery units.

[richo106]

I have done some scenarios with MVHR at 0% and 85% and ACH at 7 and 3. Obviously a massive difference but would there be another system that would help total heat loss instead of MVHR? What other benefits do MVHR give?

 

What are peoples thoughts of the scenarios i have done?

 

Thanks again, really appreciate the replies

Total House Heat Loss - Scenarios.docx

[SteamyTea]

9 minutes ago, richo106 said:

would there be another system that would help total heat loss instead of MVHR

Not really, it is just physics.

MVHR gives you controlled ventilation, and to a certain extent, controls humidity, while also recovering energy.

Mechanical ventilation does the same, but without the heat recovery.

 

You can, if you want, just pump external air into the building and hope that there are enough, evenly spaced, leaks that the system works.

 

I am currently improving my airtightness, in my already good house. For ventilation I will, for this winter, just open a window.