The Conservatory: Eco Saint Or Eco Sinner?

The ideal way to reduce your fuel bills, or a leaky glass box that heats up the skies? We go in search of the answer to the great conservatory conundrum…

Passive solar sunspace, ecoarc

 Conservatories are terribly popular in this country. And it’s not surprising.

As well as helping to eke out the Great British summer, a conservatory is seen as a cheap way to extend your home and add value to your property.

But what about the impact on the environment?

A recent eco-living booklet attached to Grand Designs Magazine warns that the conservatory is a very bad idea:

“When heated, a three-sided conservatory (with glazed roof and three exposed sides) can double the energy use of a three-bed semi”.

Yikes! That sounds worse than owning a Hummer.  But hang on – how, then, do you explain all those eco homes with acres of sun-capturing glass?

They look suspiciously like conservatories. And as such they prompt the question: is it possible to have one that won’t melt the icecaps and turn you into an eco-pariah? One that might even reduce your carbon footprint?

We went in search of an answer. Here’s what we discovered…

Eco Saint: The Case For 

Ecos Homes Great Bow Yard

 The eco credentials of conservatories (AKA sunspaces, in the green building world) are impressive.

Most new eco homes are built with some kind of south-facing conservatory to allow the building to utilise passive solar heating.

Stunning floor-to-ceiling examples of this are the sunspaces on the Ecos Homes Great Bow Yard development. There’s also an impressive passive solar conservatory on the Earthship in Brighton.

How do they work? Located on the south face they look great and give the inhabitants a bit of inside-outside space to enjoy, but they are also positioned and designed to improve the environmental performance of the houses.

Well-designed conservatories, such as these, are effective in two principle ways.

Earthship Brighton 

 1. They act as a buffer, or draught excluder, between inside and outside.

2. They trap the sun’s heat and use thermal mass (such as a heavy stone, conrete or brick floor) to warm up the home and reduce the amount of fuel we need to use.

In order to work efficiently these sunny spaces can be controlled by doors, vents and louvers, according to the weather, to direct warm air into the house in winter, and keep the heat down in the summer.

The Great Bow Yard sunspaces are, of course, very state of the art. But even suburban-styled conservatories can help to reduce our carbon emissions and keep our fuel bills down by up to 20 per cent.

Sounds great. But here’s what has been labelled the ‘conservatory paradox’.

Eco Sinner: The Case Against 

Traditional conservatory

 It used to be generally believed that, for the reasons given above, conservatories were a great way to reduce household energy consumption.

But this relied on the assumption that they are used as they were intended, only when it’s warm enough, between spring and autumn.

However, a survey in 1993 found that 91 per cent of respondents heated their conservatories and 50 per cent of those said they did so regularly.

And more recent research shows even more owners using their conservatory all year round, coping with temperature fluctuations by installing heating, and even air conditioning.

Ironically, while a well-designed, properly-used conservatory will reduce energy consumption by a significant amount, findings from building research group, the Building Research Establishment (BRE) show that, when heated, a conservatory can double the energy use of a three-bed semi.

The Solution
So what’s the solution? Here’s a quick run through the main issues to keep in mind if you want an eco friendly sunspace:
1. Solar Orientation: The usual advice is not to bother unless your garden is south, south-east, or south-west facing. 

However, it’s worth consulting an expert on this. Julian Brooks, a sustainable development consultant at Brooks Devlin is, in fact, in the process of putting a conservatory on his own home, despite the fact that it faces north.

“It will catch the easterly morning sun and in the west in the evening,” says Julian. “Any conservatory in the height of summer is too hot if it’s not shaded, so there’s no reason not to do it.”

2. Keep It Separate, Not Integral: Conservatories are designed to fit onto the outside of a house, not be an integral part.

Julian Brooks says that you won’t find a knocked through conservatory to be a cheap option once the bills start coming in.  “You’ll be going down a dead end in energy-efficiency terms by losing a wall that has better thermal performance.

“Even triple glazing has a U-value of 0.8, compared to 0.35 for a wall, but triple glazing a conservatory would be extremely expensive.”

If you really have to open up your living space to the conservatory, external quality folding doors that can be closed throughout winter may be a reasonable compromise.

3. No Heaters, Please! It’s impossible to efficiently insulate a mostly glazed building, and, says Julian, if you fit a heater you may as well leave the door open because your hot air will quickly escape into the garden anyway.

Plus, even with a heater, your conservatory probably won’t be warm enough to sit in comfortably all winter.  Just don’t do it, is the advice. “Heating a conservatory is so inefficient that it won’t pay you back in any way.”

4. Thermal Mass: Include plenty of ‘thermal mass’ to store the heat gained for longer. A stone, tiled or brick floor works well because it will absorb and slowly release heat during the evening.

5. Airflow: Make sure that there is a means of drawing warmed air into the house. Airflow is hard to predict, however, so adjustable vents between the conservatory and the house may need help from a small electric fan at times.

6. Keep Cool: Include a system to prevent overheating during the summer. The best way to keep cool is external blinds, wooden shutters or sun canopies, like those used by shops.

As the goal is to stop the glass heating up in the first place, blinds that fit in-between the double-glazing are less efficient, but better than internal blinds.

Nikki Sheehan


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