We had cavity ins in our previous house in summer 1981. In the winter of 81-82 our gas bills were unchanged. Initially i was disappointed, but then I realised that 81-82 was the record cold winter AND we had a lodger, who kept her bed-sitting room really hot (previously it had been unheated), so we probably were saving a good 20%. Then we moved, so never got a like for like comparison.

Odbob – could you be more specific about the "botched installation"? Was there anything about it you were unhappy with? (Apart from the obvious perceived payback deficiency?)

Other than for my microgeneration projects I haven’t bothered calculating energy saved in cash terms for insulation projects. I started insulating from the day I moved into my new/old home so I had no baseline. It also depends a little upon your philosophy. My advice would be to be – errr – "philosphical".

It is in the interest of many to accentuate the positive and dis-accentuate the negative. As counterbalance the Royal Institute of Chartered Surveyors in 2006 published the following numbers that might intrigue you:

Cavity wall insulation = £728. Energy saving per year £145. Payback period 5 years
Loft insulation (top up to 250mm) = £755. Energy saving per year £60. Payback period 13 years
Hot water cylinder and pipe work insulation = £761. Energy saving per year £20. Payback period 38 years
Condensing boiler = £2,000. Energy saving per year £52. Payback period 38 years
Installation of full heating controls package = £2,240. Energy saving per year £65. Payback period 34 years
Double glazing = £9,327. Energy saving per year £75. Payback period 124 years

I don’t for one moment intend to imply that we should be less than enthusiastic for these basic measures. These RIC costs seem a tad high to me. "£728" for cavity all insulation? What for? Buckingham Palace?… Payback calculations vary wildly upon your assumptions. One of these assumptions is the price of carbon. My philosophy would be that both the pessimists and optimists are probably wrong. By definition all forecasts are wrong. So expect your calculated numbers to vary from reality. The best numbers I can find for the general case can be found at http://www.cat.org.uk which I would recommend for researchers.

Anyway, I digress… Did something go wrong with your install?

Odbob – yes, I did read the relevant sections of your web site (I think – I admit maybe I have missed something) but it wasn’t clear to me how you knew the job was botched. As you say the insulation is inside your walls. Your site does show a picture that looks like it backs up your belief that the walls are not completely filled. How did you take the photo? How did you know the walls were not completely filled? How did you convince the installer that this was so?

Apologies for labouring this point but THIS is critical to this discussion. I had my walls filled in December 2008 and got messed about. Your experience is pertinent to us all and the performance of cavity wall insulation in general. The installer company did my survey assuming they would do the entire house but the actuall installer turned up and said they could not. Clearly their surveyor ddn’t know what he was talking about. This may have some bearing upon your experience? The installers pointed out that they couldn’t install on the north side of the house due to flint panels. They said it would create "voids". Then then also wanted to access my neighbours’ garage to do the adjoining wall. The neighbours were not in and I was annoyed that the installer didn’t point this out to me in advance. So, in the end, two walls were not done. There was then a debacle about how much I should pay with their head office repeatedly invoicing the wrong amount (but that is a different story).

What intrigues me is the idea of the installers not wishing to create "voids". Why? Isn’t the cavity one big void already? Why are smaller voids important?

Clearly, in your case, you have a void. Clearly your installer accepts they have got voids and attempted to refill them. I find this entire topic quite interesting. If we can all check our walls for voids we could blow a big hole in the industry’s claims. Or prove that they mostly get it right.

Re: photography…. Very cunning method. I wonder just how many of us have this problem? Well, I guess that is why you asked. I wonder if there any useful metrics or rules of thumb?

When our installers came they had to inspect our attic before leaving. It was only a cursory glance before they stapled a small certificate to the bottom of an A frame. I believed that the inspection – although largely worthless – was to ascertain if the cavity filler had over-flowed into the loft space.

I have since found a small amount of the white fluffy filler in the attic suggesting that it (at least in some places) goes up to the roof. Of course this means nothing where there are potential voids and entire walls left undone. One metric may be to check the spacing and height of the holes they drill in the wall? If there is some publically available best practive guides, we could use, then this would be invaluable. As it stands I think we caught out by our own ignorance which might benefit the industry. It is rather like paying to have the oil changed in your car at the main dealer. You have to take their word for it that they actually did it right.

Do we know which industry watchdog has over-sight on the cavity wall filling business? Is there an ombudsman you can go to? Worth a question to the EST and a bit of a Google search. Maybe a TV company who makes programs about bogus and cowboy builders should do an investigation. Maybe there are people who work in the industry (or used to), who are reading this, and can give us some pointers?

I hope and believe that most of these chaps do a good job. But every home is different and we might never know the myriad of ways in which it can go wrong. Without some quality control the Government’s own targets, for such things, will fall way-short. I have heard stories years ago of builders required by Building Regs, to lay out loft insulation, who just bunged the rolls in the attics of new builds and never laid them out. This may well go the same way and doesn’t bode well for all those supposed carbon-neutral homes being built ofter 2016…..

Have you tried http://www.ciga.co.uk the cavity insulation guarantee association. Their website says

"Independent research carried out for the Department of the Environment, Transport and the Regions (DETR) has confirmed that cavity wall insulation is a very reliable process.

Problems are therefore extremely rare, but if they do occur, CIGA has the expertise to ensure that they are swiftly rectified".

The information later on states:-

"If you still feel that the problem is due to the installation, then you should contact the installer, who will inspect and remedy the problem where possible. If the installer is unable to solve the problem, then contact CIGA in writing, stating the problem and the steps you have taken to have the matter resolved.

CIGA will then arrange to investigate the complaint, and where neccessary, ensure that the appropriate remedial work is carried out free of charge. Each Guarantee certificate has a unique number that should be quoted on all correspondence."

I don’t know if that helps, but at least it gives you a chance for redress. Of course, this only works if the installer was registered with CIGA in the first place?

I noticed a short article in last Sunday’s Telegraph that suggested that some people experienced poor value for money from some green investments. The usual Telegraph-fair no doubt. However, of relevance was the mention of a recent "Which?" report on the value of home insulation projects including cavity walls. Might be worth checking it out online if you can find it?

On balance we can’t let one bad experience put people off. But installers have to be responsible as they not only have a moral obligation to the householder, but also an ethical obligation to society as a whole.

I notice that payback figures are becoming slightly more realistic, with Homebase now quoting an average saving on the heat energy bill of £115 per year after cavity fill, quite a significant difference from that quoted to me of £190 per year saving, but still significantly more than my actual saving of £32 per year.
On the question of savings, and my request for someone to prove that cavity fill can save closer to that quoted by these companies, it does not have to be that accurate, just lay out the bills for maybe two years prior to the fill and two years after the fill, and note the difference, this should suffice