Cold temperatures in 15 year old cavity wall extension!

Hi all,

We moved into our house earlier this year in March, and at the time we obviously had the heating on. However, at times when the heating wasn't on, I noticed that our two storey extension (one large lounge, one hallway with skylight and stairs, and one bedroom) was absolutely freezing compared to the rest of the house (particularly the lounge). One morning before the heating came on, I noted that the Hive thermostat registered 12.6 degrees centigrade in the lounge! As this wasn't an issue for long due to the time of year, we ignored it, but obviously with winter now approaching, I am doing whatever I can to ensure the house is as warm as possible with as little heating as possible. However the extension is just unliveable. The main house itself is 140+ years old (with solid brick walls) and the extension is roughly 15 years old (with cavity walls). The lounge extension is always a minimum of at least 2.5 degrees colder than the rest of the house. In the mornings recently, whilst the main house has been about 17-19 degrees, the lounge extension has been 13-15 degrees.

I have had someone come and check the cavity walls with a camera, and he said the cavity walls have wool board insulation in them (in good condition), and a gap between that and the bricks to ensure damp doesn't transfer across. I know EPS bead and blown wool insulation is used frequently now to completely fill cavity walls, but obviously replacing the current insulation isn't possible without basically taking all the bricks out of the walls. And that wouldn't even necessarily resolve the issue and could obviously potentially cause damp if not done well.

Basically, I'm wondering if anyone can give any advice as to what might be causing the extension to be so cold (although I appreciate it's quite a vague request)? It is north facing so obviously it doesn't get as much solar energy throughout the day, but equally even first thing in the morning the rest of the house is a much more pleasant temperature. The lounge extension has 2.5 exterior walls (half of one of them is covered by the neighbour's own extension), and it has a gable roof covering half of it and the other half is covered by the bedroom extension. I have noticed a few tiny gaps that need sealing around the inside of the windows and patio door. One of my suspicions is the external sealing of the windows isn't right and that somehow draughts from outside are going through the cavity walls through these holes? I've uploaded some photos of the lounge extension (both inside and out) and a couple of others in case it helps build a better picture of the condition of everything: https://mega.nz/folder/NToDyDaY#cncEPM3ujI8fReTmXn-ZJw

I did also have someone come round to do a thermal survey at one point, and on the report he stated that the cavity wall insulation isn't doing it's job at all. Then again, he also used a camera in the wall, and stated it was blown wool insulation and he could see some rubble in the walls, so I'm kind of on the fence with his conclusions! I do have someone coming round on Monday for a third opinion, so I'll see what they say.

I'm a proper amateur when it comes to these things, and I guess I probably don't fully understand it all properly. So really I just want to know if there is anything that I should be looking into here, in terms of fixing the temperature. Should those gaps around the exterior windows and patio doors be filled, and if so with what? Expanding foam?

Apologies for the long post, but I wanted to give as much information as possible!

Thanks in advance.

You haven't said anything about the heating source?

What is the loft insulation?

Is it open plan, or doors left open, so that warm air escapes up the stairwell?

Buy some joss sticks and use them to search for draughts and air escapes. Especially the skylight.

When you put your hand against walls and ceilings do any of them feel cold?

Are the radiators in the extension getting fully hot? And are not undersized?

Is the floor concrete? Or suspended wood with a void beneath?

Is it damp?

Do you know why the brickwork looks rather wet below the DPC?

The first thing to check is whether the heating source in the room is correctly sized to actually heat the room and keep it warm.

And the main consideration is whether the cost of any work is less than the cost of merely turning the heating up a few months off the year.

Deal with excessive draughts and unwanted air loss first - cheapest and quickest! - but your main issue almost certainly comes down to orientation and structural insulation. You've mentioned the cavity walls, which sound poorly insulated but you are stuck with that unless you are up for some fairly major expense. Is there any insulation at all in the floor? If not that will be an issue but, again, at fairly major cost. Finally the loft; probably the easiest and cheapest and is where I would look first. Check what's up there and think about adding to it as much as you can. As advised though, it would be worth comparing cost and disruption against extra heating - or maybe electric underfloor matting in the extension area.

@HaroldFinch

Are you still here?

In hospital with acute hypothermia.

So sorry about the slow response to this thread. Have a two month old baby and am currently on paternity leave with family here, so things are a little hectic! I'll respond to each reply individually. Really appreciate the responses so far.

freddiemercurystwin said:

You haven't said anything about the heating source?

Click to expand...

Apologies that completely slipped my mind! There are two large radiators in the lounge extension so when the heating is on, it should be sufficient to warm the room up. Should I be checking how quickly the temperature drops after the heating goes off?

Whole house is heated by a Worcester Greenstar Ri regular condensing boiler that was apparently installed 5 years ago, so should be pretty efficient.

What are the dimensions of the radiators, and the room, and the windows

Are the radiators double panel

Are the radiators fully hot, all over, top, bottom, sides and middle? Hot means "too hot to hold for long"

HaroldFinch said:

We moved into our house earlier this year in March, and at the time we obviously had the heating on. However, at times when the heating wasn't on, I noticed that our two storey extension (one large lounge, one hallway with skylight and stairs, and one bedroom) was absolutely freezing compared to the rest of the house (particularly the lounge). One morning before the heating came on, I noted that the Hive thermostat registered 12.6 degrees centigrade in the lounge!

Click to expand...

If the heating isn't on and the room is north facing with 2 external walls it is perfectly normal for it to be a bit cooler. Test the room temperature when the heating has been on for a few days.

Bear in mind that the cavity wall insulation is only intended to stop heat escaping. It cannot generate heat in an otherwise cold unheated space.

JohnD said:

What is the loft insulation?

Is it open plan, or doors left open, so that warm air escapes up the stairwell?

Buy some joss sticks and use them to search for draughts and air escapes. Especially the skylight.

When you put your hand against walls and ceilings do any of them feel cold?

Are the radiators in the extension getting fully hot? And are not undersized?

Is the floor concrete? Or suspended wood with a void beneath?

Is it damp?

Do you know why the brickwork looks rather wet below the DPC?

Click to expand...

The loft itself is one big space split into two by rafters - the insulation in the older part of the house is 100mm, and it is 200mm in the extension. The extension has boarding down and the main house has boarding on top of about half of the insulation. I had someone come and quote me yesterday for increasing the insulation - for £660 (roughly 55 square metres of space in total) they said they could put another 200mm of insulation directly on top of all the boarding in the extension and the unboarded parts of the main house, leaving me with the boarded area in the middle that I am currently using for storage. Didn't know you could add insulation on top of existing boarding, but it does make it easier for me to not have to remove my items and the boards themselves.

We generally keep most doors closed (especially the cold extension!), as I'm aware that the hallway and skylight would be a source of heat loss.

I actually have gone round with lit incense and made notes of minor draughts in certain rooms which I will be looking to fix over the coming weeks. But nothing major that I can imagine would cause the levels of cold in the extension.

The walls and ceilings don't feel particularly cold, which was a surprise. I've definitely had colder walls in other houses I've lived in previously.

The radiators are well sized for the space and do get very hot. It does seem to warm up quite quickly, although as I said in the above message, I haven't checked how quickly the room goes back down in temperature once the heating goes off.

Floor is concrete as far as I'm aware, with what I believe as a thin layer of insulation.

No damp from what I can see, which is also a bit of a surprise to be honest!

I did take the photos on a rainy day, but I'm not sure why the lower bricks would be wetter - I'd need to go outside and have another look.

Sorry if my answers haven't been particularly helpful - as you can see I'm an amateur when it comes to this stuff. This is the first house I've ever owned, so I'm trying to ensure it's a warm, safe place for my two month old girl to live in! I appreciate your time on all this.

^woody^ said:

The first thing to check is whether the heating source in the room is correctly sized to actually heat the room and keep it warm.

And the main consideration is whether the cost of any work is less than the cost of merely turning the heating up a few months off the year.

Click to expand...

Yep the heating is definitely sufficient for the space. It definitely heats up quite quickly, but I still need to check if it retains the heat well or not.
I did think about this myself to be honest, regarding the cost of the work vs just having the heating on earlier in the year and potentially for longer each day. If there were one thing that had been earmarked as an issue by the insulation surveyors that I know fixing it would increase the temperature in the extension, then I'd do it. But yeah if it's going to cost a few grand and won't guarantee a result, then the option to heat for longer is probably the wise decision!

I guess my main curiosity comes from the rest of the house (140 years old!) being 3 degrees warmer at all times!

JohnD said:

What are the dimensions of the radiators, and the room, and the windows

Are the radiators double panel

Are the radiators fully hot, all over, top, bottom, sides and middle? Hot means "too hot to hold for long"

Click to expand...

I don't know the exact dimensions of everything, but the radiators are definitely large enough for the space, and they're both double panel and single convector. In terms of your definition of "hot", I would say they are "warm" all over, but I don't think any different to the rest of the radiators throughout the house. I'm guessing that might be due to the flow temperature of the boiler being slightly too low?

wessex101 said:

If the heating isn't on and the room is north facing with 2 external walls it is perfectly normal for it to be a bit cooler. Test the room temperature when the heating has been on for a few days.

Bear in mind that the cavity wall insulation is only intended to stop heat escaping. It cannot generate heat in an otherwise cold unheated space.

Click to expand...

To be honest, what you've said is unfortunately the conclusion I've been slowly coming to given there seem to be no obvious issues with insulation, etc. However, is 13.5 degrees at around 8am really not that unusual in a 15 year old extension in October (with no heating on)? I think my main confusion is that it is 3 degrees colder than the 140 year old solid walls in the rest of the house - my uneducated brain just tells me something must be wrong!