Like any room in your house a garden room has ongoing running costs for heat and light, and a customer recently emailed us to ask “how much do garden rooms cost a year to run?”
There are many factors which will influence the running costs – how big the garden room is, how well insulated the building is, the size and number of windows and doors, the orientation of the building, how much you use the room and the weather conditions.
We could make a guess ourselves that a garden room would cost about the same to heat, cool and power as any living room in your house, so would estimate around £225 per annum, but we thought it would be more beneficial to hear from the garden room suppliers themselves, here are their answers:
Its a tricky one to answer as it depends on so many variables i.e.. size of room, insulation used, amount of doors/window, type of heating, amount of electrical & IT hardware in use, if LED bulbs are installed and how often its used etc. I would not like to give a definitive answer, ours is approx. 30sqm and costs us approx. £300 per annum, it is highly insulated and used daily.
We have recently made a calculation and we think that running costs are no more than £200 per year.
The immediate but no so concise answer is “not very much”. On the cooling side it should be nothing, we normally recommend a 4ft wide 18 inches deep window in the back wall at above filing cabinet height. This then on a hot day, if required, gives a nice gentle cross-flow of air across the room. We all know if we have ever gone in to a fish and chip shop in the summer, the poor staff are in a heat trap if they do not have an openable window behind them as they are then in a hot pocket, a window behind them and a door pinned back or french doors even better, and there is an escape for their hot fumes, without it they do suffer. We often recommend these windows in place of skylights which often leak, these wide but shallow windows never keak and give some balanced light into the room as well as a cross flow of breeze if ever required. Lighting bills in our extra rooms are peanuts as they are warm LED’s using only 3-4 watts each so if we fit 8 which is common, then 4×8=32 divided into 1000 means 250 hrs for one killowatt hour at about 14p so if the lights are all on for 3 hours a day 5 days a week it will take 16 weeks to use 1 kilowatt hour at 14p. Heating if supplied by a decent oil filled radiator with a thermostat and timer would be on a soft setting equalling flat out at 2kw for 2 hours made up of intermittent bursts so that is 28p a day call it 30p a day for heating and lighting x 5 = £1.50 a week. Our ultra green barrel buildings are so over the top with their up to a foot thick insulation sandwiched between 2 double reflective layers of reflective insulation would require even less heating and the angled skylight sides reflecting light into all the room would make the need for the lights never to be on except in winter after dark.
BWB units are built to a U-value of 0.15 with very little thermal mass, therefore the heat required is mainly for the internal air and is a very low requirement. These rooms will slowly warm up through body heat and through the use of electrical items such as televisions, computers and lighting. However, initially to get the temperature up we would recommend a heater is used, which can be set on a thermostat to maintain a comfortable temperature. Based on a 2kw heater being used every hour for 10 minutes each time and lighting mainly in the evenings. We would estimate the running cost at little more than a pound each day the room is used. This is of course subject to the type of heater and lighting required.
Garden Affairs have recently written an article on the running costs of their buildings, here’s a quote:
If you were to scale our usage down to the average 3m x 4m garden room used as an office, with 44mm solid timber walls with roof and floor insulation, used for 40 hours per week, the estimated energy running cost would be about £165 per annum or £13.75 per month. Not a major item on the balance sheet
Read the full article here