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:
Knauf
Eko Roll Loft Insulation: thermal conductivity (W/m*K) – 0.044, thermal
resistance (m2*K/W) – 4.83
Diall
Loft insulation: thermal resistance (m2*K/W) – 2.27 (also known as R-value)
Roof
area covered with insulation is 9m by 8m = 72 m2.
Original
U-value (W/m2*K). Thermal transmittance, also known as U-value, is the rate of
transfer of heat (in watts) through one square meter of a structure, divided by
the difference in temperature across the structure.
For
poorly insulated roof U-value is 1 W/m2*K. Maximum U-value which cannot be
exceeded required under current Building Regulations is 0.2 W/m2*K, aim is to
go 0.13 W/m2*K (this requires 300mm of the fiberglass insulation).
For our house
heat loss through the poorly insulated rood is: 72m2*1W/m2*K = 72W/K.
Additional
R-value (thermal resistance for 250mm of added insulation) for the loft =
0.250m/0.044 W/m*K= 5.68 m2*K/W
Overall
thermal resistance 5.68 m2*K/W+1 (what it was before) = 6.68 m2*K/W
Overall thermal
conductivity (new U-value) 1/6.68 m2*K/W = 0.15 W/m2*K
Heat
loss through the Insulated Roof = 72m2*0.15 W/m2*K= 10.8 W/K (6-fold
reduction).
In
2016-2017 we spent 972 GBP on natural gas (heating, hot water and cooking).
Although exact hot water consumption could be verified using summer months,
when heating is not required, let’s assume 30% goes to hot water. Remaining 680 GBP is heating bill, another
10% is loss due to ventilation and cold air entering the house, remaining 600
GBP is heating loss.
Approximately
15-20% of heat losses are going through the poorly insulated roof. 600*20% = 120 GBP a year.
The new
heating cost is proportional to the improved U-value 120 GBP*10.8/72 = 18 GBP a
year, or approximately 100 GBP a year in heating consumption.
As
energy prices are raising, I should calculate the savings in the fuel consumption: 1,884 m3 of natural gas for 972 GBP, 100 GBP reduction
in cost, should give annual consumption of 1,690 m3 of natural gas next year.
If the insulation
will last 20 years at the current energy prices and inflation of 3% it will
take me 8 years to get my money back, after which I paid myself at 30 GBP/hr for
the 40 hrs spent on the loft or 1,200 GBP.
I will
be able to confirm that actual energy savings next year. Many people after insulating houses spending
more money on the heating by keeping the house warmer and/or badly down
insulation. In our case I could tell that insulation is working, as for the first-time
upstairs is warmer than downstairs.
Our actual energy consumption in 2016-2017
We consumed
162 kWh/m2 a year of energy (140kWh/m2 is heating and hot water).
Our
monthly payments:
Electricity
- 43 GBP = 516 GBP a year. Actual consumption 576 GBP or 48 a month.
Natural Gas
- 81 GBP = 972 GBP a year. Actual consumption 956 GBP or 80 GBP a month.
Tariffs:
Electricity
– 14.8p a day, 16.56p per kWh, actually paid 18.26p per kWh.
Natural gas
– 14,8p a day, 4.28 p/kWh, actually paid 508 GBP per 1,000m3 or 4.5 per kWh.
Natural Gas:
consumed 1,884 m3 x 1.022640 volume correction 1,927 m3 corrected units
1,927*39.4
calorific value MJ/m3 /3.6 kWh/MJ = 21,086 kWh
Total natural
gas cost = 14.8*365 + 21,086*4.28=54.02+902.48= 956.5 GBP or 80GBP per month.
Electricity:
consumed 3,153 kWh
Total electricity
cost 14.8*365 +3,153*16.56 = 576.16 or 48 GBP per month
Domestic Natural Gas Prices in the UK
With my utility
company in the UK I am paying 508 GBP per 1,000m3 of natural gas to the utility
company, distributing gas. Whole sale market
prices:
In 2017 natural
gas, giant Gazprom is selling natural gas to western europe distributors at $167
per 1,000m3 (125 GBP).
In 2011
Centrica bought 5 billion cubic meters of gas from Norway for 10 years for
$20.5 billion, this is $410 (305 GBP) per 1,000m3.
For
distribution within the UK I am paying between 383-203 GBP more for every 1,000m3
of natural gas on top of the whole sale prices (306% - 67% markup).
Average annual
consumption of electricity per country kWh per dwelling:
|
Norway
|
16,000
|
|
Sweden
|
9,500
|
|
Finland
|
8,500
|
|
France
|
5,000
|
|
Cyprus
|
5,000
|
|
The UK
|
4,200
|
|
Russia
|
4,000
|
|
Germany
|
3,800
|
|
The Netherlands
|
3,200
|
|
We
|
3,153
|
|
Italy
|
2,800
|
Historical energy prices in the UK:
2011 - Gas
20,500 kWh cost £729 GBP and 3,300 kWh electricity cost £424 GBP, total 1153
GBP.
2015 - Average
annual household energy bills (based on fixed consumption of 3,800 kWh per
annum
for electricity and 15,000 kWh per annum for gas - £1,298. The government for
reporting purposes “promotes” energy efficiency, which cost hundreds of pounds,
so the average annual household energy bill would not be so scary. Energy
efficient houses have lower natural gas consumption by 25% (between 2011 and
2015), this disregards the upfront payment and return of 7-8 years on your
investment.
In 2017 the
20,500-kWh gas and 3,300 kWh electricity package is 25% more expensive than in
2011, when actual oil and natural gas prices are lower than in 2011.
EU energy certificate
Estimated
bill from EU energy certificate for our house in 2016 was 1,457 GBP. It was
indicted that by replacing – lightning, boiler and loft insulation potential combined
savings are 600 GBP or 857 GBP a year. We implemented everything before moving in
(apart from loft) and the actual cost was still 1443 GBP per year. Energy
consumption was estimated as 279 kWh/m2 a year, our actual one is 162 kWh/m2.
Where it
went wrong, EU energy certificated estimated us paying 5.2 GBP per kWh/m2 a
year, the actual cost is 8.9 GBP per kWh/m2 a year.
In the
certificate the economic effect (savings) from the additional loft insulation estimated
as 150 GBP a year (my calculation is 100 GBP a year). Before this improvement our
house was so bad that with heating on, temperature on the 1 floor was higher
than on the second floor and we could not raise temperature above 20C on the
second floor, even with heating on all the time. This is changed now.
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