How to calculate economic return on loft insulation? Projected vs. Actual.

It has been one year, since I calculated and invested into the loft insulation.

      At the time I spent about 750 GBP and 5 days to put the insulation up in the loft (including cleaning it and teak oil application to the beams and joists to protect them). I also estimated that 20% of the heat loses were going through the roof.

     The actual natural gas consumption in 2016-2017 was 24,500 kWh (at 4.28p per kWh + 14.80p standing charge a day) or 1,104 GBP a year. 

Since I installed the loft insulation 2017-2018 consumption was 16,400 kWh (at 4,46p per kWh + 19.18p per day) or 8,100 kWh less (30% reduction) at the cost of 760 GBP.  This is a saving of 344 GBP a year.

    This means that I will get my money back in just over 2 years.  I overpaid my  utility company by 500 GBP so far. Only after I contacted them, they bothered to cancel couple of the monthly payments to reduce their debt to me.

    The natural gas prices went by 5% up in the UK last year, making them among the most expensive in western europe. No wonder that the propaganda encourages people do not heat their homes, including leaving some of the rooms unheated and keeping others at 61F (16C) in the winter.  

How to calculate economic return on loft insulation and energy consumption in developed world

    When we bought out house loft insulation had only 25 mm loft insulation thickness, with recommended 275-300 mm of fiberglass.  I decided to do put some more, while also use it as an opportunity to clean up the dusty loft (no storage there).

With the current insulation in winter our second floor was colder than first floor due to roof loft heating losses. Additionally, I was encouraged by perceived saving due to improved insulation.

      How to calculate economic effect from insulating your loft and any potential energy savings?

Previous insulation – 25 mm, new – 275 mm.  I decided to use mineral fiberglass insulation, although if I do it again I would use more expensive natural wool. Advantages of natural wool: it absorbs condensed water and then evaporates it, traps any gases and contamination (i.e. breathes), does not loses thickness when gets wet with condensed water.  Disadvantage: more expensive, perhaps more flammable.

Materials I used for the loft insulation:

Diall Loft insulation – 23 rolls - 290 GBP -3m2 per pack, coverage - 68m2.

Gardman Bubble Greenhouse Insulation - 6 rolls - 99 GBP (as a vapour barrier).

Knauf Eko Roll Loft Insulation – 14 rolls - 280 GBP – 5.5m2 per pack – coverage - 77m2.

Loft Vent Trays (plastic) – 40 pieces – 60 GBP.

Total cost:  730 GBP or 10.2 GBP/m2

      Additionally, I used this as an opportunity to apply some teak oil to the joists and the roof beams, to preserve and protect them - 20 L at 160 GBP. No installer will do that for you, unless you specifically ask and pay.

All together it took 5 days ~ 7-8 hrs each or 40 hrs.

 How I calculated the economic effect and return on the loft insulation: