Cavity wall insulation

itm2

I am investigating the possibility of having cavity wall insulation installed, and would like to get an idea of the feasibility, risks and likely benefits. The primary motivation is that the house is freezing cold in the winter, and barely gets above 13 degrees even after a couple of hours with the central heating on. We stayed with friends over the holiday period, and were quite taken by how much warmer their house was, even without the heating on (their house was built about 15 years ago).

Our property is a 3-storey semi-detached townhouse, built around 1970. It's in a town location in south west London, and not particularly exposed to wind driven rain. I believe that it has cavity walls (based on looking at the brickwork). Access to the side of the property is not particularly easy, as the side alley is only about 1m wide. This may make it difficult to access the upper floors particularly.

The loft has some existing fibreglass insulation installed (and is mostly boarded over), and is occasionally prone to condensation. I suspect that an insulation upgrade may be a good idea here, too.

The main bathroom has minor condensation issues, but these are easily managed with the extractor fan and window. There is also a minor damp issue behind one of the bedroom cupboards on the top floor. Other than that, no other damp or condensation issues.

We've had issues over the years with leaking gutters causing saturation of brickwork, which in turn has led to internal water ingress into a couple of rooms. As well as replacing the gutters, we've used silicone sealant paint on some of the masonry to prevent a recurrence.

I was wondering whether anyone could offer any advice re:
- whether cavity wall insulation would be feasible, given the access limitations at the side of the house
- how best to assess the risk of damp, condensation or other issues which might result from it
- how much benefit we would expect to see in terms of having a warmer house
- how easy it is to get an impartial survey to advise on the suitability of CWI and loft insulation upgrades for our property.

Teapot55

We managed to get some of that cavity wall insulation that came free - government sponsored? - a few years back. 

It is little grey polystyrene beads - not sure how damaging this is from the point of view of adding plastics to the environment.

The contractors brought ladders and  a small machine and tubes through the house - we are terraced. We said we were not looking to pay for scaffolding - somehow they managed to do it - we thought at the time that the scaffolding thing might have been a ruse but we were never sure. 

There was some sort of hole between the cavity at the back and the small loft above the single-storey part of the house. Fortunately we discovered fairly swiftly that the small loft was full of grey beads and were able to get them to come back and retrieve them. We do occasionally still find the odd grey bead in the kitchen.

Our house is definitely warmer than it was. The upgrade to our double-glazing in our living rooms helped too.

Albermarle

The primary motivation is that the house is freezing cold in the winter, and barely gets above 13 degrees even after a couple of hours with the central heating on. 

Do you mean that the house is empty for periods and when you switch the heating on it does not warm up quickly ( not that unexpected).?

Or that every morning/evening  in cold weather it is still only 13 degrees after you have had the heating on for 2 hours, even though you have the heating on every day ?

What is the boiler make and what is the flow temperature set at ? Are all the radiators fully on ( valves open) ?

itm2

Albermarle said:

The primary motivation is that the house is freezing cold in the winter, and barely gets above 13 degrees even after a couple of hours with the central heating on. 

Do you mean that the house is empty for periods and when you switch the heating on it does not warm up quickly ( not that unexpected).?

Or that every morning/evening  in cold weather it is still only 13 degrees after you have had the heating on for 2 hours, even though you have the heating on every day ?

What is the boiler make and what is the flow temperature set at ? Are all the radiators fully on ( valves open) ?

We tend to have the heating on for a couple of hours in the morning, then a few hours in the evening (off during the day). It's not getting above about 11 degrees in the morning, after 2 hours of heating.
It's a Worcester Bosch 30CDi boiler, with the flow temperature set at 4. All radiators are fully on.

FreeBear

Run the room sizes through this calculator - https://www.stelrad.com/basic-heat-loss-calculator/

I wouldn't be surprised to find your radiators are undersized for the flow temperature. Some useful numbers below if you want to convert the CH numbers to Celsius.

One thing you could try is run the heating continuously until the temperature reaches a comfortable point (say 18°C), and then see if the CH system will maintain it. Try it over a weekend and perhaps crank the boiler up to 5.

Although my house is not particularly good, I can raise the temperature by 1°C per hour, and maintaining it at 19°C only needs a 10-15 minute burn every couple of hours. Overnight, the temperature will drop by a couple of degrees depending on how cold it is outside.

I'm not convinced that cavity insulation makes that much difference in a lot of older properties - I certainly didn't notice any change when mine was done (but it is only cavity on the lower half). Putting down ~300mm of loft insulation, fitting Low-e double glazing, and killing cold draughts have all helped.

Worcester Bosch CH numbers to Celsius.

Min - 40°C

  1  -  47°C

  2  -  53°C

  3  -  61°C

  4  -  68°C

  5  -  74°C

  6  -  80°C

Max - 82°C

EssexExile

In this weather our house wouldn't get above 13° after 2 hours, even with cavity insulation.

itm2

I tried the calculator at https://www.stelrad.com/basic-heat-loss-calculator/ - thanks. Using the info for the main bedroom  (which is one of the most important for us), it looks as if the existing radiator should be fine, in that room at least 
It's interesting that some people see little or no benefits from CWI, whereas others see an immediately noticeable improvement. I guess there are alot of other contributing factors. I read somewhere that around 70% of heat loss in a typical house is through the roof, so loft insulation needs to be factored in. We have double glazing throughout - and triple glazing in the main bedroom - so I don't see much scope for improvement there. 
It would be good to get a genuinely impartial assessment of the situation, but that may be difficult from a company that is trying to sell to us (

Albermarle

EssexExile said:

In this weather our house wouldn't get above 13° after 2 hours, even with cavity insulation.

I think it can be a bit of a mystery why some houses are more difficult to keep warm than others. I live in a one hundred year old house with solid walls ( apart from where it has been extended) and mainly quite old double glazing. Even this morning ( zero degrees ) after two hours with the central heating on then quite cosy in most rooms, and for sure above 13 degrees even in the largish hallway and kitchen.
Boiler flow temperature set at around 62 degrees.
The heating is on and off for most of the day so I think that helps.

FreeBear

itm2 said: It would be good to get a genuinely impartial assessment of the situation, but that may be difficult from a company that is trying to sell to us (

It may well pay to have a thermograohic survey done whilst it is ruddy freezing out there. One may cost £300 or so, but will help to identify where the major heat losses are, and you can then target your efforts more effectively. Some councils run a thermal camera loan scheme (either directly, or through a charity), so would be worth checking before paying someone. Although, paying someone for a survey should also elicit advice on what to do to improve matters.

itm2

FreeBear said:

itm2 said: It would be good to get a genuinely impartial assessment of the situation, but that may be difficult from a company that is trying to sell to us (

It may well pay to have a thermograohic survey done whilst it is ruddy freezing out there. One may cost £300 or so, but will help to identify where the major heat losses are, and you can then target your efforts more effectively. Some councils run a thermal camera loan scheme (either directly, or through a charity), so would be worth checking before paying someone. Although, paying someone for a survey should also elicit advice on what to do to improve matters.

That's a good idea. I just did a quick check and my local council doesn't have a loan scheme. My energy company (Octopus) does, but it's now closed for 2023/24 so I've added my name to the waiting list for 2024/25.
It looks like you can pay anything from £200 to £4,000 to buy one. I have no idea how much you'd need to pay to get one that would be fit for this sort of job. I also don't know whether an untrained person like myself would be able to draw sensible conclusions from it, in terms of identifying the most effective ways to reduce heat loss.
Has anyone had any experience of DIY thermal imaging prior to a home insulation project?

Chickereeeee

We had our 1920s house (50mm clear cavities) filled with eps beads last autumn. It has made a huge difference to the feel of the house. Much more uniform warmth, cupboards attached to exterior walls are warmer, and bills reduced. A 1970s house is likely to have larger cavities (good) but may also have partial-fill insulation installed when it was built (bad). Get a bead injection company to come around and give you a quote. Make sure they inspect ALL your cavities with a borescope,  not just one.