Which way should a conservatory face?
Conservatories have a reputation for being too hot in summer and too cold in winter, and most are both. The direction one faces decides when the heat arrives and how bad the winter is. The roof decides how much of either you get, and it matters more.
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What each direction gets
We modelled a typical conservatory against the back of a house: 4 m wide, 3 m deep, glazed 1.5 m above a low wall on three sides, with a glass roof at 20°. For each direction it could face, we added up the sunlight falling on its glass through a cloudless day in London:
| Faces | 21 June | 21 December | June sunlight after 3 pm |
|---|---|---|---|
| North | 76 kWh | 11 kWh | 41% |
| East | 127 kWh | 26 kWh | 11% |
| South-east | 148 kWh | 47 kWh | 9% |
| South | 157 kWh | 51 kWh | 28% |
| South-west | 147 kWh | 47 kWh | 48% |
| West | 127 kWh | 26 kWh | 57% |
Direct and diffuse sunlight striking the glass on a clear day at latitude 51.5°N, with the house blocking any sun from behind. This is light arriving, not heat retained, and real weather cuts both columns, especially December. Compare the rows with each other rather than reading the absolute figures.
Two things stand out. In summer the spread is modest: an east- or west-facing conservatory still gets about four-fifths of the sunlight a south-facing one does. In winter the spread is large: south gets twice what east or west gets and nearly five times what north gets.
It is when, not how much
The peak intensity barely changes with direction either. At its sunniest moment on a June day, a south-, south-east-, south-west-, east- or west-facing conservatory is taking in almost exactly the same amount of sunlight. What differs is the time of day it happens.
That is the real reason west-facing conservatories have the worst reputation. More than half their June sunlight arrives after 3 pm. By then the outside air is at its warmest, the frame and floor have been warming since midday, and people want to sit in the room. An east-facing conservatory gets a similar total, but more than four-fifths of it before 1 pm, while the air is still cool. By late afternoon it is in the house's shade.
The rule of thumb. Morning sun warms a room you are not using yet. Afternoon sun heats a room that is already warm. If you want to use a conservatory on summer evenings, east beats west, even though they get the same amount of sun.
Direction by direction
- South: the best all-rounder, if the roof is dealt with. It gets the most winter sun of any direction, which is what makes a conservatory usable from October to March. In summer the midday sun is high, so most of it lands on the roof rather than coming in through the walls. That makes a south-facing conservatory unusually easy to fix by shading or insulating the roof.
- South-west and west: the hot ones. A west-facing conservatory gets only half of south's winter sun but takes in most of its summer sun in the afternoon and evening. That late sun is low, so it comes straight through the side and front glass, where roof blinds do nothing. This orientation needs vertical shading as well as roof shading.
- South-east and east: the easiest to live with. They are bright, warm breakfast rooms that have cooled down by the evening. South-east gets nearly as much winter sun as south, so it is the pick if the choice is open.
- North: a summer room. It is not dark in summer. It gets half of south's June sunlight, including long low sun late on a summer evening, when the sun sets well north of west. In December it gets almost none, so it is expensive to heat. Its steady, glare-free light is why artists' studios traditionally face north.
Further north the summer figures barely change and the winter ones fall. In Edinburgh a south-facing conservatory gets about a third less sun than in London on the shortest day, and a north-facing one gets less than a quarter of what faces south.
The roof matters more than the direction
In our model the roof takes 60–65% of all the June sunlight, whichever way the conservatory faces. Moving a conservatory from south to east cuts its summer sunlight by about a fifth. Making the roof solid instead of glass cuts it by nearly two-thirds.
That is why solid and tiled replacement roofs are so effective in summer. There is a cost, though: the roof takes about half the winter sun too, so a solid roof also halves the winter warmth and noticeably darkens the room. A roof light or two, or solar-control glass in place of clear glass, is the middle route: most of the summer benefit while keeping some winter light.
Keeping it usable
- Shade outside the glass, not inside. An internal blind stops the glare, but the heat is already inside the room. External awnings, shades over the roof or a pergola stop sunlight before it passes through the glass, and are much more effective.
- Vent high as well as low. Hot air collects under the roof. Roof vents, or high-level windows at the ridge, let it out; opening only the doors at floor level leaves the hottest air where it is.
- Use plants to the west. A deciduous tree or climber on the west side blocks summer afternoon sun and lets winter light through once the leaves drop.
- Keep the doors to the house. A door between the conservatory and the house keeps summer heat and winter cold out of the rest of the home. In the UK, keeping the conservatory thermally separate from the house is usually part of what exempts it from Building Regulations, so check with your local building control before removing those doors.
Check your own house
The figures above are for a free-standing back wall under an open sky. A real conservatory is shaded by the house next door, a garage, a boundary wall or a tree, often in exactly the afternoon hours that decide whether it overheats. Your house also almost certainly faces somewhere between the compass points.
Start by finding the exact bearing of the wall the conservatory will stand against. Then use the sun path tool to see, for your address and any date, which hours the sun spends in front of that wall and how high it is. The room tool shows where that light actually falls through a window.
In the southern hemisphere, swap north and south throughout: north is the best all-rounder, and south-facing conservatories are the cold ones.