Earth Notes: KEHS talk: Draughts, Insulation, Ventilation (2024)

Updated 2024-05-21 12:43 GMT.
By Damon Hart-Davis.
Kingston Efficient Homes Show 2024 small talk by Patrick M.
KEHS2024 2 RBK
Patrick M delivering one of the "small talks" at KEHS 2024, helping Kingston householders understand how to make their homes more energy efficient and comfortable without causing damp and condensation issues.

Many thanks to Bob D for for the slides and to Patrick M for delivering the talk on the day!

726s "KEHS2024 draughts insulation ventilation" (captions) Uploaded . Downloads:

So we all want to have warm homes and consume less energy.


I think one of the things perhaps to understand when you're talking about houses,


and I'm talking mostly about houses, not flats, is that they come, I mean,


they're two basic sorts, particularly in Kingston.


They're the houses that were built before the Second World War,


which are one sort of house, so, and there's,


they're houses built after the Second World War, and particularly more recent houses.


So you might have heard the phrases "solid wall construction" and "cavity wall construction".


So the houses that were built before the Second World War are mostly solid walls.


We often call them brick-thick walls, sometimes rendered.


They have raised timber ground floors, so they're lifted off the floor,


and there are air bricks, which ventilate those timbers under the floor.


They used to have single-glazed windows when they were built,


and they have a loft space with a pitch roof.


The other sort of house, which I'm talking about,


which are more recent houses, might have a cavity wall more commonly,


might have solid floors, although they could still have suspended floors,


and might have been built with double glazing,


and they might have some sort of loft insulation.


So there's already a performance gap between those two sorts of houses,


and houses that are being built today are just such a distance away


from those pre-Second World War houses in terms of energy consumption;


it's unbelievable.


So one of the issues, really, that faces us in somewhere like this,


where probably 75% of our stock in Kingston might be before the Second World War,


I'm guessing a bit, but it's quite a lot, anyway, of all we have.


So how are we going to make those houses perform better?


Because it does help if the house performs better,


if it doesn't lose as much energy when energy is becoming more expensive,


and we want to produce it sustainably.


So one of the things everybody looks at, draughts and air movement,


because those are big factors in heat loss.


I think it's, Damon would probably correct me, but I mean,


it's something like 25% of our heat losses.


30% is through ventilation ...


... unplanned ventilation.


So even if you've insulated the walls,


if you've got lots of gaps everywhere,


you're still going to be using a lot of heat.


Of course, as you start to shut up these gaps,


you are keeping moisture within your house,


and that's the root of a lot of the problems we're beginning to see.


You know, we've heard of, I think it's called Abassa's Law,


a little kid who died of a mould in his home,


because when you start to put in double-glazed windows,


you're starting to reduce that airflow.


So the whole issue of draughts / ventilations is very interlinked here.


So in older houses, this diagram just shows,


in older houses we used to have the air, wind brought in air.


There were gaps in the house.


You had chimneys pulling the air out through the house.


That provided a natural circulation of air


and kept moisture levels reasonably low


and kept us cool in summer.


So as we start to...


As we start to put double-glazed windows in,


this is the kind of thing you see,


where that's a double-glazed window.


If you then shut up your fireplace,


which is something you want to do,


I mean, you want to close up your fireplace,


but you've got to pay attention to bringing some fresh air in,


and not letting too much moisture accumulate


to avoid this kind of dampness.


And if you look at pictures of places


which are identified as being damp,


this is often what you see.


And it's not dampness in the way we used to think of it


when it was water coming up through the walls


or rain being driven through the walls.


It's dampness internally.


Because we take showers, we cook,


people sometimes dry washing indoors,


particularly in flats, it's quite a common problem.


And we breathe, and that all creates this sort of difficulty.


So you have to be careful what you're doing.


So this is about ...


This is about where you might want to seal your house up


to try and lose these, to try to stop the loss of heat.


And a very common problem that people are not really very clear about


is when you...


There was a trend for having timber floors,


exposed timber floors in the '70s, I guess.


Lots of people sanded their floors.


I mean, I just mentioned earlier on that the...


There are air bricks on the outside of the house


and there's a continuous passage of air under it.


Well, that is leading to quite a lot of heat loss,


and people sometimes don't appreciate that.


So when you put fitted carpets in,


of course you're sealing off that area


and you are reducing the heat loss through that.


But all these places lose heat and energy.


So... But you can start to do some things.


I would really recommend anybody who's living in a house like this


that's got timber ground floors.


I'm just talking about ground floors here.


First floors are irrelevant because they're already inside the shell.


But ground floors, if you're having your carpet refitted,


it's really worth taking the opportunity to...


I mean, this is disruptive, but it's worth it.


Take all your furniture out of the room.


You've got to take it all out to have it refitted with a carpet anyway.


Lift the floorboards up and put insulation between the floorboards.


And that's... The way these things are done is you can see


that the timber joists are still exposed,


so it's still got air circulation under it,


which stops it rotting because often the underfloor spaces


are a little bit damp.


Put it and then put insulation in between,


and that will help to reduce your heat loss


before you put your carpet back on.


I mean, modern houses all have pre-insulated ground floors.


Yeah. I suppose you might not recognize it,


but when you take the floorboards up on your floor,


that's what you see. You see this pattern of floor joists.


The thing is that the cavity walls,


your house either has a cavity wall or it doesn't.


And there are probably relatively few houses in Kingston


that have cavity walls.


So that is not an option for a lot of people in Kingston to do this.


So there are a couple of options if you haven't got a cavity wall.


One is internal wall insulation and one is external wall insulation.


So just starting with internal wall insulation,


that's where you're adding some kind of insulating material


on the inside of the walls.


And there are some... I mean, there are some problems with this.


I mean, it's quite expensive to do.


It's quite disruptive.


And you have to be careful about where...


You can create a situation where you get condensation inside that wall.


So condensation occurs.


So you've got the warm side of the room where he is.


Then the temperature is dropping through the wall


to the temperature it is outside.


And if you allow moist air to pass through that construction,


it will condense somewhere in the middle of that.


So you've got to... If you're not careful.


If you're not careful, yes. So it's got to be done quite carefully.


And the other problem with this, obviously,


is you've got mouldings in a Victorian house.


You have to replace those.


But you can do it and it can be made to work.


There are some other problems with cold... with joists and things.


Anyway, so it's tricky.


And this is why, in a way, people are not doing this so much.


It's better to do what you can do reasonably easily in a way


and then have an air source heat pump,


which, if we're all worried about the climate,


is what's really going to make the difference.


So that's the external option.


Now, I mean, there are quite a lot of rendered houses in Kingston,


and that is an option for them.


And it is quite a good system because it does...


It makes the whole...


It is putting a tea cozy round the house, really,


and it will reduce it.


But that is quite an expensive thing to do.


But it's not hundreds of thousands to do that.


I mean, I think that's more like 25...


This is the thing that most people do,


and it is the thing that you should all do.


And if somebody says to you, they've insulated their loft,


if you look at the depth that they're talking about here,


because the depth has risen and risen and risen


since I've been working on buildings.


So it used to be 100 millimetres


and we're now at nearly 300 millimetres.


So it is well worth everybody making sure that your loft is properly insulated,


because that's an easy thing to do.


I mean, I say it's easy, because it isn't that easy,


because we all fill our lofts full of a load of rubbish.


And then you've got to...


If you want to put that rubbish back,


you've actually got to build a platform on top of it


to let the insulation run under the top.


But it is still, relatively speaking, the easiest thing to do.


So well worth considering.


Now, the other thing to understand is that the physics of houses


is relatively simple, but you ventilate.


That space under your roof, you really want to ventilate,


because moist air will rise up through your ceilings.


And I talked about moisture condensing.


What you do with the roof, where it rises through the loft,


you have to keep it ventilated so that that moisture will be dispelled.


If you close up all your eaves and seal everything off,


and that can be a problem with some sorts of insulation system,


the thing won't perform properly.


But I mean, most traditional houses have eaves ventilation.


If you go up in your roof space,


you can often feel a bit of air movement, and that's a good thing.


That's what you want, provided your insulation is at ceiling level.


That's just repeating that.


And that's talking...


This is a trickier problem to insulate


where you're following a line in the ceiling,


and you haven't got a big depth.


And there are various solutions to that.


You can actually put the insulation on the outside of the roof,


or you have to keep a ventilated void on the other side of that,


again, to dispel the moisture.


Or you can go for trying to completely seal it from the inside.


But it has to be carefully thought through.


And that's a bit more of a discussion.


This is how you prevent the condensation of the roof space


by bringing the air in at the eaves.


Now, the other thing to talk about is...


So when you've done all this, if you do a lot of sealing up,


then the question is,


how do you make sure that you don't get this condensation


I've been talking about?


So the building regulations has some solutions to that.


So when you...


They ask you to put...


There are various ways of doing it.


One way of doing it is to put what we call "trickle vents" in your windows.


So if you look at...


when people have replaced their windows,


you'll often see these little grilles at the top with a sort of flick,


so you can have them open or shut.


And that's what that's about.


That's supposed to be providing a little bit of fresh air into the home.


And then they're also building regulations


for having fans in your bathroom and your kitchen.


Again, that's another place.


That's where you're generating the moisture,


because you want to get that out of the room.


A more sophisticated approach


and what happens in new buildings now is something called...


is a system where you actually extract the air


and you pass it through a heat exchanger somewhere in the building,


maybe in the loft or in a hallway.


And that preheats air coming in,


so that's an even more efficient way to do it.


But what's particularly dangerous is if you don't do any of those,


if you put in double glazing,


you seal up your chimneys


and you seal up all the ... draught proof the doors,


and then you don't do anything else about ventilation,


you are in danger of getting condensation in the building.

Show Notes

Recorded with the Zoom H1n, stereo 48ksps, sitting on the desk at the front of the drama room near the speaker.

~2492 words.