Airtightness

waqasahmed

Hi

Prior to getting say an MVHR, the house needs to be airtight for maximum efficiency. The house is already well insulated but not sure if it is entirely airtight 

When I look for people who would make it more airtight as well as know what kind of what the current level of airtightness is, I'm not too sure on what kind of person would be able to help with that 

Does anyone know what kind of tradesperson I should look for? 

DougMLancs

Retrofitting a house to improve its airtightness is possible - there’s a decent guide here https://www.eco-home-essentials.co.uk/airtightness.html. To get it at a level where a MVHR system will be really effective though will likely involve vapour membrane installed behind the plaster as well as insulation with all joins taped to form a continuous envelope for the house. You can pay for someone to test your house’s airtightness (about £190) and you’ll get a result in meters cubed per hour. You’ll see an airtightness figure on new build EPCs as an example (generally between 5 and 6 for developers doing the minimum building regs require).

For an MVHR system to work effectively you want a result below 5 meters cubed an hour and ideally below 3 for best results. Research has shown it can be used in more draughty houses (up to 9m3) but the effect is more limited and you’d have to weigh up the cost/benefit. Above 9 and it’s pointless. The Green Building Store has a lot of helpful info on MVHR https://www.greenbuildingstore.co.uk/knowledgebase_category/mvhr-heat-recovery-ventilation/

My Father-in-law made their house almost passivhaus airtight and has MVHR but they almost rebuilt their house. 

Also worth bearing in mind that installing the ducting for MVHR will be disruptive on its own and the physical size of the MVHR unit is substantial (FIL’s one is about 3 times the size of my combi boiler). You also need a meticulous builder experienced in this kind of work as the seal taping takes a lot of attention to detail.

Personally I would improve airtightness where you can (there are quite a few easy wins) but maybe look at other improvements first before MVHR.

waqasahmed

DougMLancs said:

Retrofitting a house to improve its airtightness is possible - there’s a decent guide here https://www.eco-home-essentials.co.uk/airtightness.html. To get it at a level where a MVHR system will be really effective though will likely involve vapour membrane installed behind the plaster as well as insulation with all joins taped to form a continuous envelope for the house. You can pay for someone to test your house’s airtightness (about £190) and you’ll get a result in meters cubed per hour. You’ll see an airtightness figure on new build EPCs as an example (generally between 5 and 6 for developers doing the minimum building regs require).

For an MVHR system to work effectively you want a result below 5 meters cubed an hour and ideally below 3 for best results. Research has shown it can be used in more draughty houses (up to 9m3) but the effect is more limited and you’d have to weigh up the cost/benefit. Above 9 and it’s pointless. The Green Building Store has a lot of helpful info on MVHR https://www.greenbuildingstore.co.uk/knowledgebase_category/mvhr-heat-recovery-ventilation/

My Father-in-law made their house almost passivhaus airtight and has MVHR but they almost rebuilt their house. 

Also worth bearing in mind that installing the ducting for MVHR will be disruptive on its own and the physical size of the MVHR unit is substantial (FIL’s one is about 3 times the size of my combi boiler). You also need a meticulous builder experienced in this kind of work as the seal taping takes a lot of attention to detail.

Personally I would improve airtightness where you can (there are quite a few easy wins) but maybe look at other improvements first before MVHR.

Hi

May I ask what other improvements you're referring to? Also how exactly would someone improve airtightness anyway?

Thanks 

michaels

waqasahmed said:

DougMLancs said:

Retrofitting a house to improve its airtightness is possible - there’s a decent guide here https://www.eco-home-essentials.co.uk/airtightness.html. To get it at a level where a MVHR system will be really effective though will likely involve vapour membrane installed behind the plaster as well as insulation with all joins taped to form a continuous envelope for the house. You can pay for someone to test your house’s airtightness (about £190) and you’ll get a result in meters cubed per hour. You’ll see an airtightness figure on new build EPCs as an example (generally between 5 and 6 for developers doing the minimum building regs require).

For an MVHR system to work effectively you want a result below 5 meters cubed an hour and ideally below 3 for best results. Research has shown it can be used in more draughty houses (up to 9m3) but the effect is more limited and you’d have to weigh up the cost/benefit. Above 9 and it’s pointless. The Green Building Store has a lot of helpful info on MVHR https://www.greenbuildingstore.co.uk/knowledgebase_category/mvhr-heat-recovery-ventilation/

My Father-in-law made their house almost passivhaus airtight and has MVHR but they almost rebuilt their house. 

Also worth bearing in mind that installing the ducting for MVHR will be disruptive on its own and the physical size of the MVHR unit is substantial (FIL’s one is about 3 times the size of my combi boiler). You also need a meticulous builder experienced in this kind of work as the seal taping takes a lot of attention to detail.

Personally I would improve airtightness where you can (there are quite a few easy wins) but maybe look at other improvements first before MVHR.

Hi

May I ask what other improvements you're referring to? Also how exactly would someone improve airtightness anyway?

Thanks 

I suspect going round your house when it is cold out feeling/using a small length of tissue to spot any draughts around windows, door sans skirtings would be a good place to start.  Our DG doors and windows let in a surprising amount of draughts around the seals, even the relatively new ones (10 years old)

DougMLancs

You posted a list on another thread of a few upgrades you wanted to do so that’s all I meant. An incense stick works well as well. That blog I linked to talks through a lot the improvements but it’s things like draftproofing your doors and loft hatch with brushes/compression seals, sealing around windows and exterior doors, windowsills, pipe work etc. Strips of cork or draftproofing strips under skirting boards and between floorboards. They’re the kind of relatively cheap and effective fixes. They’re also all things that’ll help keep the house warm regardless. After that it depends on the age and construction of your house as to whether you’d get a reasonable result from MVHR at that point. 

My brother in law is trying to retrofit their 1900’s end terrace for MVHR and they’ve been doing internal wall insulation in every room as they can afford it and taping all the joins to form that sealed envelope. Still not ready for it yet though after several years but at least their gas bill is dropping.

waqasahmed

DougMLancs said:

You posted a list on another thread of a few upgrades you wanted to do so that’s all I meant. An incense stick works well as well. That blog I linked to talks through a lot the improvements but it’s things like draftproofing your doors and loft hatch with brushes/compression seals, sealing around windows and exterior doors, windowsills, pipe work etc. Strips of cork or draftproofing strips under skirting boards and between floorboards. They’re the kind of relatively cheap and effective fixes. They’re also all things that’ll help keep the house warm regardless. After that it depends on the age and construction of your house as to whether you’d get a reasonable result from MVHR at that point. 

My brother in law is trying to retrofit their 1900’s end terrace for MVHR and they’ve been doing internal wall insulation in every room as they can afford it and taping all the joins to form that sealed envelope. Still not ready for it yet though after several years but at least their gas bill is dropping.

Thanks. FWIW, my own house was built in 1975. It'd be nice if new houses were built to comply with PassivHaus standards but very few are 

DougMLancs

100% with you on that. They want to build an eco village of them near us which rare but it’s still trying to get through planning so we settled for our 50’s semi

zeupater

Hi

Just to add to what DougMLancs posted .... we spent considerable effort on improving airtightness on our property, but whatever you do on a retrofit you'll find that it soon becomes subject to the laws of diminishing returns .... for example, if your joists are supported by external walls there's likely a huge number of air ingress points from the cavity which would need attention, so unless you're willing to rip up all of the upstairs flooring to gain access to fill the gaps and live with the consequences of lifting & relaying the floors as well as the poor cost/benefit it would return, it'll probably be a case of just hitting the low hanging fruit and accepting that there will be air ingress in a property not specifically designed to be sealed from the outset ....

The way we looked at it was draughtproofing doors, windows, ventilators, holes in ceilings into loft (pipes & light fittings), letterbox etc ... so not only things you can see, but can easily access.

We have the added issue of a log-burner, but that's fed by external air supply delivered below the unit, so effectively an externalised sealed loop from a combustion viewpoint, however, to maintain decent air quality you still need air changes ....

If you're looking at whole house heat recovery ventilation because of moisture related issues then simply addressing the main sources may be more convenient & cheaper ... there are small heat recovery extractors for bathrooms etc which may theoretically be less efficient that the large whole house approach, but are far easier to install and, in addressing the very highest moisture culprits close to source still do a pretty decent job at retaining heat when compared to basic extraction or open windows, especially if running in conjunction with the occasional use of a decent dehumidifier ...

The issue with checking air tightness is the methodology and how it relates to real world conditions .... simply sealing the gap of an open external door and measuring the airflow required to maintain a pressure differential to assess heat-loss based on air changes/hour is logically questionable .... the only time that the induced test conditions occur in the real world is when wind creates pressure differentials, which is only a fraction of the time anyway, so probably insignificant to an extent that such tests overestimate average air changes for an average property by a significant factor .... to support this viewpoint, numerous studies have concluded that there's a large discrepancy between the assessed heat requirements of older housing stock and what they actually consume, whereas in homes built to current building standards the difference is much smaller ... could it be that the assessment of both property cohorts include losses due to airtightness assessments that don't apply except in relatively rare conditions and this is why inefficiencies of older properties are overstated? ... don't know, but logic would suggest that it's a reasonable explanation ..

HTH - Z

paul991

so is  worth getting a smaller mvhr on a self install something like this https://www.bpcventilation.com/airflow-entro-dv250#accordion to remove damp air and provide clean pure air to the dwelling even if a vapour membrane  could never  be fitted to a double glazed insulated  80,s  house

zeupater

paul991 said:

so is  worth getting a smaller mvhr on a self install something like this https://www.bpcventilation.com/airflow-entro-dv250#accordion to remove damp air and provide clean pure air to the dwelling even if a vapour membrane  could never  be fitted to a double glazed insulated  80,s  house

Hi

I was thinking more along the lines of the single room offerings for bathrooms/kitchens etc (such as examples on site you referenced: https://www.bpcventilation.com/heat-recovery/heat-recovery-fans ) where there are smaller options, some of which can simply replace an existing extractor fan whilst still recovering ~2/3 of the heat and not pulling external air into the house through gaps elsewhere ... could offer a much cheaper & easier option for many looking into heat recovery, so at least worth thinking about ...

HTH - Z

paul991

the single room option is  a good idea but unfortunately  for me all the ones i've seen are through the wall  not  the ceiling unless anyone knows better