What is holding up our retrofit plans? – and advice

Every house is different, but it is still useful to share problems and tips around retrofit – often similar problems keep cropping up. I asked the energy group members what is holding up their plans and we discussed some ways forward. There are common themes. At bottom, we see inconsistency in planning rules and inconsistency in advice from installers. Plus a chronic lack of installers. All this means progress can be very slow but we do believe it is important to keep up the pressure, or nothing will change. If you have more stories and/or advice we would love to hear them.

Some of the problems are due to recent changes in regulations for retrofit. It will take a while for the industry to get used to the requirements of PAS 2035, a framework for approaching whole house retrofit with best practice. Also there are not enough trained retrofit coordinators yet. This can be very frustrating.

(Names have been changed in this article)

Planning permission for EWI – yes you need it but you don’t need to pay a consultant.
If you want to install external wall insulation, you will need planning permission if there is a significant change in external appearance. So if your house is already rendered, you can probably get away without. Or if you are now brick and you intend to use brick slips to cover the insulation and they are a reasonable match, also fine. However, for most of us we need planning permission. Richard told us that he spoke to two planning officers at the council and they both said he needed to submit technical drawings. This would mean (for Richard at least), hiring a consultant to prepare them, at considerable expense. He was quoted £1,200. However, when he complained to his councillor they checked with the department and apparently this is not necessary. You only need to supply:

• A site location plan with the outline in red (you can buy the maps for these online for less than £20 e.g from the planning portal or from UK Planning Maps
• Photo of the property, indicating where there would be render
• Details of the rendering system e.g. product sheet.

Others in the group have put in applications in this way with success. However, non-trivial cases can take a long time to process. This can be a show-stopper if you are relying on a grant scheme that has a limited timespan. So get your planning application in as soon as you can.

Unfortunately, the planning department is under-resourced, and inexperienced staff can give inconsistent responses. This is a problem across the whole country – as described by this article in the Architects Journal . Staff turnover is high (from hearsay, because good planners are quickly poached by consultancies).


Planning on solid wall insulation - you may need floor insulation too.
Sarah was told that, due to rule changes, if you put external wall insulation on a house with suspended floors you must also install floor insulation. This is not always true. Revised standards do require that retrofits should avoid thermal bridges, routes where heat can leak out bypassing the insulation. These heat leaks can lead to cold spots where you could get condensation. Previously, most EWI installations stopped above the damp proof course, which leaves a cold bridge as shown in the diagram. Internal wall insulation poses a similar problem.

Diagram of a cold bridge caused by EWI that stops above the damp proof course.

You might argue this cold bridge is no worse than before, but it is the relative difference in temperature between the warm and the cold areas that matters. The walls have got warmer but the floor has not.

How bad this is for your house depends, amongst other things, on how far the insulation extends below floor level. Best practice would be to extend the insulation below the DPC and into the wall footings. Some installers have always done this. You need a waterproof insulation below the DPC and the DPC itself will be extended through the insulation. Without it there will always be a cold bridge between the outside and the underfloor void. However, even with the added insulation there will still be some heat leakage because you will have air bricks ventilating the underfloor void and letting cold air in. Floor insulation fixes this but adds to cost and can be very disruptive.

It is all a bit of a grey area. Houses vary and no-one should give you firm advice without checking your particular case. The advice from the Transition Cambridge Energy Group was that it is worth asking different installers. You should also bear in mind that when installers are busy they may fob you off with ‘it’s too difficult’ because they do not want the job, not because you cannot do it.


Inconsistent advice from installers
Mike complained that he has got different answers from different installers when asking basic questions such as how to avoid thermal bridging when using a mixture of external and internal insulation. On this particular issue, some say not to worry and some say you should have an overlap of at least 30cm. Who is right? This is an area where the 30cm rule of thumb is probably good enough for most cases…

To check advice you need to buy the standards

… but if you actually want to check yourself, it will cost you £50 to download the standard for calculating thermal bridges and temperature factors from the Building Research Establishment. You can look at the building regulations part L for free but to read the calculation methodology you are required to use you have to pay. It costs another £50 for the U-value calculations (£60 for the calculator but that only runs on Windows, not MACs).

These costs are not huge but they are significant. Competent DIYers can save a lot of money if they do the installation bit themselves, and can often go ahead without grants which removes another barrier. However, they need guidance. These documents (and others) might help. (Should we get them for group members to borrow?)


For heat pump noise, permitted development rules are less strict than full planning.
Installing a heat pump is usually a permitted development but several people we know of have incorporated a heat pump into a larger retrofit which needed planning permission. Unfortunately the rules for noise in planning applications are much more strict than the rules than are used for the permitted development case. Basically, the permitted development rule is based on a typical background noise level but the planning department may require that you actually measure the background noise level at your location. In John’s case, this led to ludicrously severe noise restrictions on the heat pump – the area was so quiet that he would have needed to enclose the heat pump in a sound insulated metal box. The installer was dubious and asked the manufacturer of the heat pump; they refused to give a warranty for the setup.

Heat pumps allowed under permitted development can be challenged if there is a noise nuisance.
The obvious way around this is to keep the heat pump off the application and do it afterwards under permitted development rules. However, if there is a complaint about the noise you may be liable anyway. The planning conditions are based on noise nuisance rules and conforming to permitted development rules is not a defence. So the advice is to be careful about siting your heat pump and be friendly with your neighbours.


We hope these tips help you. If you have other stories or tips do let us know.