Air tightness vs ventilation - I’m confused

[DaveG]

Ok so I’ve been on the old home scene for some 5 months so very much still a newbie but I’ve got to ask, does anyone else find it a little confusing that insulation and air tightness is encouraged alongside ventilation units?

I’m sure I must be missing something but it seems as though we’re told to go to extreme lengths to plug all gaps where (fresh, less humid?) air could make its way in to the property, through key holes, under doors and so on, while then being told we need cross flow products which require pulling in fresh air through a vent and extracting indoor moisture back out.

Extraction I totally understand. Get moisture laden air out and replace it with fresh lower humidity air. But a few gaps here and there will act as intake vents am I not mistaken?

Take double glazing for example. You pay top whack for the latest triple glazed argon gas filled unit that’s super duper airtight, then you put a big hole in the frame called a vent that you’ll need to leave open.

Is it just me?

 

[Gothichome]

Dave, I’m a big proponent of old homes being able to breathe. Before extraction fans, the air in our homes was always being changed via drafts and cracks etc. old homes sealed up to tight does not allow this to function naturally. A sealed home will build up moisture and cause all sorts of problems long term there is term for this in modern construction ‘sick homes’. Just control the drafts but do not make the home air tight. Interested in the views of others on this topic.
Ron

 

[a twig]

Air tightness is for modern homes that are designed to be water proof with concrete block, silicon render etc.

By definition such things are not applicable to the houses in this parish. Old houses are not waterproof and allow moisture in so need to allow it out again, which is achieved by breathable finishes and ventilation

 

[stuart45]

The saying for new builds is 'build tight, ventilate right. The idea is that an air tight house is given the exact amount of air changes through mechanical ventilation with heat recovery.
With an older house it's guesswork getting the right balance between getting the correct amount of ventilation and not losing too much heat.
Insulation can stop heat getting to the external walls where it can dry out the brickwork around timber lintels, joist ends in the walls and help prevent the freeze/thaw effect on the brickwork faces.

 

[DaveG]

It just seems so counter intuitive to me to make a building so airtight that you then need to run a system the requires energy to bring air back in.
The only people that seem to win are the people selling air tightness stuff and mhvr. The same people perhaps?
Reminds me of when I used to work in an office that was all glass. Boiling hot, relying on unreliable AC when all you wanted to do was open a window

 

[DaveG]

I’m in the process of opening some fireplaces and my chimneys back up because I’m told that’s what these old buildings need to ventilate but then I’m told my house is going to cost millions of pounds to heat because it’s all being lost up the chimney

 

[a twig]

The difference is if you control the draughts you can use systems like MVHR to keep the heat in while still ventilating.

If the draughts are uncontrolled then yes, you dump all your expensively heated air outside. Hence why if you want low energy bills then a period property isn’t the way

 

[stuart45]

Scandia Hus homes were introduced over here from Sweden about 50 years ago with very air tight highly insulated elements. People living in them said that they could get through most winters with little or no heating.

 

[Gothichome]

I’m in the process of opening some fireplaces and my chimneys back up because I’m told that’s what these old buildings need to ventilate but then I’m told my house is going to cost millions of pounds to heat because it’s all being lost up the chimney

Dave, if your chimneys have dampers you can close the dampers on the fireplaces you aren’t using, if not you can get fireplace doors, antique ones to match your fireplace. A modern solution is a fire place plug, it fits in the flew, also there are inflatable devices that act as plugs or doors. Pretty ugly though.
A quick google search

Vintage Fireplace Doors | Vintage Collection | Stoll Industries

Heavy steel layered with strong distinguished accents give an ageless look to these highly architectural, vintage fireplace doors.

www.stollindustries.com

You can also make your own out of plywood, paint it up pretty for a custom fit

 

[Lacan07]

I’m in the process of opening some fireplaces and my chimneys back up because I’m told that’s what these old buildings need to ventilate but then I’m told my house is going to cost millions of pounds to heat because it’s all being lost up the chimney

First thing to do is put an air brick in the flue at loft level, it will significantly reduce the draw. Then get some flexible wood fibre or some pillows in a sack and plug the entry.

 

[fernicarry]

Its the difference between controlled and uncontrolled ventilation. Old houses have lots of uncontrolled ventilation which makes them uncomfortable because you have air moving around at all levels. Controlled ventilation like trickle vents tries to put the air movement somewhere it won't make you feel uncomfortable. Higher up is generally better rather than having cold air rolling across the floor. If you have sliding sashes you'll know that cracking open the top one lets fresh air in without causing too much of a draft compared to opening the bottom one.

If you get to the point that you have complete control over air movement then you can do MVHR. The HR part relies on the all the air moving in and out via the fan unit so that the heat can be moved from the outgoing air to the incoming air. If you still have a significant amount of air coming in in other ways then you miss out on the HR which will pretty much be the case unless you have done a bare shell style renovation and done a bloody good job of it. Even so trickle extract or PIV are still worth doing to keep the air moving around especially in moisture generating spaces like kitchens and bathrooms.

The philosphy on new builds is that water vapour is completely excluded from the fabric of the building. That's why you have vapour tight layers on the inside and mechanical extraction to remove the vapour produced inside before it can get into the fabric. I very much wonder how successful this is in practice especially for the volume builders as it needs a lot of attention to detail. In any case its unlikely to be appropriate to our buildings so you need to be careful which of the concepts you take from modern construction and materials.

Air tightness, breathability and insulation are interlinked. Insulation isn't much good without some degree of air tightness. Its like walking around in a gale with your jacket unzipped, you'll probably still be cold not matter the tog value of the jacket. But air tightness can reduce breathability if its done wrong. I'd go so far as to say you want air _exclusion_ in the fabric of the building. Avoid little gaps and voids where air can sit and condense water vapour onto elements like joist ends especially as those elements may now be cooler than they previously were due to less heat leakage from inside.

If you are opening up a fireplace and putting a stove in then there will be a register plate closing off the bottom of the flue which greatly reduces air movement up the chimney. We're reinstating a fireplace for the same reasons, to ensure its ventilated and to put some heat into the wall from time to time. I'm also making the room more air tight by putting a breather membrane under the floorboards and also insulating the walls that have been stripped. Time will tell if I made it better or worse...

 

[Cubist]

This discussion, whilst interesting from a technical knowledge exchange point of view, seems to be entirely out of kilter with my understanding of the typical mindset of Period Home Owners.

Surely, the cold bracing draughts around our ankles and the dithering and shivering at every exit from the bath or shower are some of the very things that appeal to the SadoMasochistic tendencies we all obviously share?

 

[larry]

It just seems so counter intuitive to me to make a building so airtight that you then need to run a system the requires energy to bring air back in.
The only people that seem to win are the people selling air tightness stuff and mhvr. The same people perhaps?
Reminds me of when I used to work in an office that was all glass. Boiling hot, relying on unreliable AC when all you wanted to do was open a window

The benefit is that if designed right and built right energy costs can be almost nil or negligible to heat your house... Passivhauses might be heatable with a hoover, or the dishwasher. The cost is the need for mechanical ventilation, but a heat recovery system costs very little to run.

We have an old house but I have put an MVHR system in. I appreciate there are mixed views as to whether it's worth it but we absolutely love it. No mouldy bathrooms, and the roast lamb smell from a Sunday lunch disappears in no time. Step out the shower and the mirror is clear in a few minutes.

 

[larry]

Actually I say I have an old house, but compared to some on here ...

It's got solid walls, though!!

 

[Lacan07]

The benefit is that if designed right and built right energy costs can be almost nil or negligible to heat your house... Passivhauses might be heatable with a hoover, or the dishwasher. The cost is the need for mechanical ventilation, but a heat recovery system costs very little to run.

We have an old house but I have put an MVHR system in. I appreciate there are mixed views as to whether it's worth it but we absolutely love it. No mouldy bathrooms, and the roast lamb smell from a Sunday lunch disappears in no time. Step out the shower and the mirror is clear in a few minutes.

Indeed, this is a good option for new builds but not so much for old houses with solid brick walls. From my limited understanding MHRV only really works well (in heat recovery) when the spaces are well insulated and super air tight, something you could never really do in an older house with breathable insulation.

 

[Flyfisher]

This discussion, whilst interesting from a technical knowledge exchange point of view, seems to be entirely out of kilter with my understanding of the typical mindset of Period Home Owners.

Surely, the cold bracing draughts around our ankles and the dithering and shivering at every exit from the bath or shower are some of the very things that appeal to the SadoMasochistic tendencies we all obviously share?

I was beginning to think we're the only ones here to keep a duvet on the sofas in the winter months and sleep with the bedroom window open all year around

While I deny having SadoMasochistic tendencies, I don't feel the need to keep the entire house at Tee-Shirts-And-Shorts temperatures and am perfectly happy to wear sensible clothes during the colder months, ie thicker socks, pullovers and even thermal undies in the more extreme weather. That's not to say the house is completely unheated (well, except a few rooms when we have no house guests) but a background temperature of around 15-16c seems reasonable with a wood stove taking occupied rooms to a more comfortable 20-21c means I don't need a second mortgage for the heating bills.

Electric blankets are essential, of course, and there's little so luxurious as stripping off in a cold bedroom before diving into lovely warm bed at the end of a long day

As for the shivering at every exit from the bath or shower, has no one heard the 'Just One Thing' programme by dear old Dr Michael Mosely (RIP) about the health benefits of a minute or two under a cold shower. I can't quite bring myself to go that far, but a cold bathroom seems likely to be the next best thing!

 

[larry]

Indeed, this is a good option for new builds but not so much for old houses with solid brick walls. From my limited understanding MHRV only really works well (in heat recovery) when the spaces are well insulated and super air tight, something you could never really do in an older house with breathable insulation.

I'm sure you're right, but there's an undeniable benefit in reducing heat loss from not having to keep the blooming window open every time you have a shower...!

We've reduced yearly gas kWh from approx 28000kwh to 9500kwh through wood fibre + smart TRVs+ MVHR + wearing more jumpers... Can't tell you which has caused the biggest difference but it's nice having a warmer house!!!

 

[Cubist]

As for the shivering at every exit from the bath or shower, has no one heard the 'Just One Thing' programme by dear old Dr Michael Mosely (RIP) about the health benefits of a minute or two under a cold shower. I can't quite bring myself to go that far, but a cold bathroom seems likely to be the next best thing!

And exactly how is that, Not a SadoMasochistic practice?

 

[Flyfisher]

And exactly how is that, Not a SadoMasochistic practice?

Doesn't it have to have an element of pleasure to quality?

 

[Cubist]

Doesn't it have to have an element of pleasure to quality?

So no pleasure involved in getting out of that freezing shower? Methinks I would be glad the agonies were over and singing because the icy stinging was over and relief as new warmth overcame it.