Return to list

Green Deal or No Deal Part 3: Number Crunching

Bruno Girin

May 22, 2013

Following part 1 and part 2, I received the official assessment a while back. Here is a quick analysis of the content and subsequent research on my part.

Basic Numbers

The Green Deal assessment I received is a 5 page PDF document. The very first thing that it tells me is that my current situation could be worse:

So my household consumes less than the typical household. This is probably due to my habits rather than the building being energy efficient: I am out during the day, I tend to switch lights off when I'm not in a room and will put a fleece on when it's a bit chilly rather than switch on the heating. The side effect of this, as the rest of the document attests, is that my saving potential is lower than average.


The document then contains two tables: one is a list of improvements recommended by the assessor, the second is a list of improvements recommended by the EPC. They are both the same list with slightly different numbers:

Recommended byEstimated costEstimated annual savingsMaximum Green Deal repayments in year 1
The Assessor £25,830 - £47,620 £202 £450
The EPC £25,830 - £47,620 £262 £567

The first interesting piece of information is that both recommendations have the same cost but the EPC claims a higher annual saving. Then in both cases, it looks like the Green Deal repayment is actually higher than the savings. It's a maximum figure and the assessment very clearly states that it could be less but the way it's worded is very confusing and doesn't give me any confidence that the golden rule of the Green Deal whereby repayments should be lower or equal to savings can actually be met.

I've asked for additional clarification on this point from the assessor and so far have not received anything.

Return on Investment

Another way to look at it is to look at the return on investment should I want to finance all this. The idea is that if I were to do everything that I have had recommended, the savings on my bills should make it worthwhile. In order to evaluate that, I decided to use the EPC numbers that show slightly higher savings and calculate the number of years it would take me to get my money back from the investment based on such savings. The numbers are not very encouraging:

ImprovementsEstimated costEstimated annual savingsEstimated ROI in years
Increase loft insulation to 270 mm £100 - £350 £25.00 4.0 - 14.0
High performance external doors £2,000 £10.00 200.0
Solar photovoltaic panels, 2.5 kWp £9,000 - £14,000 £80.00 112.5 - 175.0
Internal or external wall insulation £4,000 - £14,000 £47.00 85.1 - 297.9
Floor insulation £800 - £1,200 £17.00 47.1 - 70.6
Draught proofing £80 - £120 £4.00 20.0 - 30.0
Low energy lighting for all fixed outlets £20 £12.00 1.7
Heating controls (room thermostat) £350 - £450 £11.00 31.8 - 40.9
Replace boiler with new condensing boiler £2,200 - £3,000 £39.00 56.4 - 76.9
Solar water heating £4,000 - £6,000 £9.00 444.4 - 666.7
Replace single glazed windows with low-E double glazing £3,300 - £6,500 £8.00 412.5 - 812.5
Total £25,850 - £47,640 £262.00 98.7 - 181.8

If I were to consider that a reasonable ROI is to get my money back within the term of my mortgage and considering I have 23 years left on said mortgage, the only improvements worth doing are loft insulation, low energy lighting and at a push draught proofing, all of which I can do without any financial help. Everything else is not worth considering from a simple economic standpoint. I particularly like the cool 812.5 years ROI on double glazing.

Now, if we assume that we're not in it to save money but we're in it to save the planet or we just want to live in more comfortable homes, a lot of those measures make sense, in particular anything that insulates the building. Therefore, I did a bit of additional research on two of the measures in the list to see how well reality matched the assessment.

Floor Insulation

One improvement that I was quite keen on doing was floor insulation on the ground floor. The reason for that is that I can feel the cold coming through the floor in winter. So even if the ROI is not fantastic, the added comfort would make it worth it. Knowing that floor insulation can vary widely depending on the type of floor I decided to get a quote from a company that had experience in doing this. The builders came in and had a look. As my floor is a suspended floor, the process to insulate it is:

  • Remove all skirting boards,
  • Lift the floor,
  • Insulate between the joists,
  • Put the floor back down (replacing damaged slats if any),
  • Re-fit the skirting boards,
  • Repair any plaster damage resulting from removing the skirting boards,
  • Sand and varnish the floor.

This for a cool total price of £11,233.95. Slightly more than the maximum £1,200.00 suggested by the assessment and the EPC. Of course I could decide to insulate above the floor and lay down laminate on top but considering that this floor is original and one of the most striking features in the property, it would feel wrong to hide it. The answer to that conundrum is that I would be better off doing that work at the same time as other work that I want to do in the house and that would require the floor to be sanded and varnished too.

Solid Wall Insulation

The other improvement I did investigate further was solid wall insulation. Having done a thermal survey of my house last year, I know that I lose heat via the walls more than I do via the double glazed windows (the two remaining single glazed windows are another matter entirely) as demonstrated by this infra-red picture:

So it looks like insulating the walls could result in an improvement in comfort and it's one of the measures in the Green Deal that I qualify for. Where it becomes complicated is that I have a few constraints:

  • The outside brickwork of the building is quite characteristic so I would prefer to have internal insulation rather than external, which means I'd want a material that would minimise the thickness of the insulation and therefore the amount of space lost inside the house;
  • The bay windows are shaped as real circular arcs, which means that any off the shelf insulation that comes in rigid panels won't work.

The ideal answer to both constraints seems to be the Spacetherm Blanket, an interesting product that uses aerogel. Of course that doesn't come cheap and I'm not sure to what extent the Green Deal is flexible in terms of using non-standard materials and techniques.

The result of all this is that I will get started with some of the energy efficiency improvements that my house needs outside of the Green Deal context but will defer some of them in order to plan them better.

Tags:   advice