Why is orientation the one decision you can never take back?
Orientation is the only part of a house's energy design that costs nothing on the drawing board and cannot be changed once the building is set out. Insulation can be thickened, windows swapped, a boiler replaced with a heat pump; which way the living room opens stays the same for the life of the house. House siting and orientation on the plot therefore belong in the first hours over the site plan.
Most writing on the subject stops at "put the living spaces on the south". That is half the information, and the other half matters more: south and west behave completely differently, even though both get plenty of sun. Not knowing it is how people glaze a wall facing the afternoon sun, then wonder why the room is uninhabitable in August.
How does the sun's altitude change through the year at our latitude?
Slovakia lies between 47.7 and 49.6 degrees north. At 48.7 degrees, noon solar altitude is about 18 degrees at the winter solstice, 41 at the equinoxes and 65 at the summer solstice. Not an estimate but geometry: 90 degrees minus latitude plus the sun's declination.
Where the sun rises and sets shifts just as much: northeast and northwest in June, southeast and southwest in December. In summer the morning and evening sun therefore sits behind the east and west facades, and around the solstice it briefly touches the north wall. In winter the north facade receives no direct sun, and the whole gain arrives in a narrow arc around south, roughly from nine in the morning to half past three, solar time.
Why does south shade itself while west never will?
A vertical wall collects less of a direct beam the higher the sun climbs. At noon in June, with the sun 65 degrees up, the beam strikes vertical south glazing so obliquely that the wall takes only about 42 percent of its intensity. At noon in December, at 18 degrees, it enters almost perpendicular and the wall uses around 95 percent. Solar heat gains on the south side therefore fall in summer and rise in winter by themselves, before any shading device exists; a roof overhang merely finishes the job.
West gets none of that. In mid July at 17:00 solar time the sun is almost exactly due west at about 25 degrees altitude, so it hits a vertical west facade nearly head on: the wall uses roughly 90 percent of the intensity, in the hours when the air is hottest and the structure has soaked up heat all day. A horizontal overhang can do nothing, because the sun arrives underneath it. That is why the same area of glazing on the west overheats a room that the identical area on the south would not, and why west glazing is the most common single cause of overheating risk in new houses.
Which rooms belong on which side?
Splitting the day zone from the bedrooms follows from when each room needs light and when it must not be given heat.
| Aspect | Character of the sun | Suitable rooms | Main risk |
|---|---|---|---|
| South | High in summer, low in winter | Sitting and dining areas, terrace | Overheating without an overhang, solvable by geometry |
| East | Low morning sun, gone by midday | Kitchen, bedrooms, children's rooms | Summer morning glare, dim afternoons |
| West | Low sun in the hottest hours | Entrance, stairs, garage, store | Highest overheating risk, overhangs do not help |
| North | Diffuse light, direct sun never | Plant room, pantry, WC, study | Zero winter gain, larger windows needed for light |
| Southwest | South and west, afternoon peak | Day zone only with adjustable external shading | Behaves more like west than it appears to |
Why does the long axis of a plan usually run east to west?
Stretching the house east to west enlarges the south and north facades and shrinks the east and west ones: more of the area you can control with an overhang, less of the area you cannot control at all. It also reduces the depth of the plan.
Elongation has a price: every extra metre worsens the compactness factor, the ratio of envelope area to heated volume, and with it the heat loss. The optimum is therefore not a long thin bar but a moderately elongated rectangle.
How many degrees off true south actually matter?
Most plots do not face due south, and there is no point fighting that. Direct beam intensity on a vertical wall falls with the cosine of the deviation from the sun's azimuth: 15 degrees costs about three percent, 20 degrees about six, 30 degrees about thirteen. Up to 15 degrees is irrelevant, and up to 30 degrees simply means sizing the shading differently.
What matters more than the size of the deviation is its direction, and the same asymmetry returns here. Rotating southeast shifts the gains into the morning, when the house has cooled overnight; southwest shifts them onto the top of the daily peak. Twenty degrees east is therefore better for comfort than twenty west, though the annual energy is nearly identical.
How is overhang depth tuned to the height of the glazing?
An overhang of depth D shades a band below it of height D times the tangent of the solar altitude. The whole argument about the "right" overhang depth is that one equation.
| Case (solar noon) | Sun altitude | 0.6 m overhang | 1.0 m overhang | 1.5 m overhang |
|---|---|---|---|---|
| 21 June, south facade | 65 degrees | 1.29 m | 2.14 m | 3.22 m |
| Equinox, south facade | 41 degrees | 0.52 m | 0.87 m | 1.30 m |
| 21 December, south facade | 18 degrees | 0.20 m | 0.33 m | 0.49 m |
| July, 17:00, west facade | 25 degrees | 0.28 m | 0.47 m | 0.70 m |
Glazing 2.4 m tall needs an overhang of about 1.1 m to be fully shaded at noon in June, and that same 1.1 m takes only about 0.36 m off it in December. That pair of numbers is the whole principle of passive solar design. Two caveats apply. Full shading holds around solar noon; two hours later the sun slips underneath. And the equinox row is identical in March and September, though September is hot and March cold, so a fixed overhang always under-shades in late summer. The last row is why the same overhang achieves nothing on a west facade.
Why does external shading beat tinted or low-g glass?
One criterion decides it: can it be switched off in winter? The solar heat gain coefficient, the g-value, is a permanent property of the glass. Glass that removed a third of the heat in July removes it just as reliably in January, when you wanted it. External shading is the only solution that catches the heat before the glass and can be taken away.
| Solution | Where it catches the heat | Seasonal adjustment | Note |
|---|---|---|---|
| Roof overhang, loggia | Outside the glass | Fixed, correct on south only | No operation, useless on west |
| External louvre blinds | Outside the glass | Fully adjustable, retracted in winter | The only device that handles west; needs drives |
| External mesh screen blind | Outside the glass | Adjustable | Keeps the view through, dims the light slightly |
| Low g-value glass | In the glazing | None, applies in January too | Permanently removes winter gain and light |
| Internal blind or curtain | Behind the glass | Adjustable | Fixes glare, not overheating |
| Deciduous tree, planted pergola | Outside the glass | Seasonally correct on its own | Bare branches take some winter sun |
How do you turn solar gain into comfort rather than a peak?
A gain with nowhere to go does not become warmth on a January evening; it becomes an unbearable afternoon. Building orientation therefore needs a pair: thermal mass and night ventilation.
Mass means material in direct contact with the indoor air: exposed concrete, masonry, an anhydrite screed. A concrete slab under a floating floor with insulation on top is not mass as far as the room is concerned, only structure. Mass alone only postpones the problem: with no way to discharge the heat at night, by the third tropical day it is saturated and works against you.
Night ventilation works when the house opens on two different sides or two levels and those openings are secure and insect-screened. A heat recovery unit with a summer bypass is a partial substitute at best; its airflow is small compared with open windows.
What about the shading you do not control?
Terrain, neighbouring buildings and trees can undo good orientation, and it is winter that decides, not summer. At a noon altitude of 18 degrees, an 8 m obstruction throws a shadow roughly 25 m long; the same obstruction in June, at 65 degrees, shades barely 4 m. A neighbour's house whose shadow you never notice in summer can take your entire winter gain.
So I look not only at what stands to the south but at what may be built there under the land use plan. On a north-facing slope the terrain raises the horizon too.
Deciduous trees are the one shading device with the correct seasonal cycle built in and nothing to operate: a leafy canopy in summer, bare branches through the heating season. They are not free, because the branches of a mature tree remove some winter sun even without leaves. If the plot is tight or the obstruction to the south is significant, a daylighting and insolation study is worth commissioning. Under building act 25/2025 Z. z., which has applied since 1 April 2025, the authority can require such an assessment during permitting.
What if the view, the street or the garden is on the wrong side?
This is the most common real conflict, and there is no point pretending orientation always wins. It helps to separate requirements that have merged into one.
- The view and the gain are not the same task. A view is captured with a smaller, precisely placed opening; gain needs area. A framed window to the north plus the main glazing to the south beats one compromise wall of glass.
- The garden can move, the house cannot. If south is towards the street, open the day zone to the street and screen it with a wall, planting, a change of level or a courtyard notch.
- Use the roof. A roof terrace captures south and the view where the ground floor reaches neither.
- If you accept west, pay for it now. The price is adjustable external shading plus workable night ventilation, both in the drawings. Air conditioning will also do the job, but it is a permanent running cost for a decision that was free.
Sometimes a once-in-a-lifetime view, or a plot twelve metres wide, legitimately overrides orientation, and that is fine. What is not is orientation losing by default, because nobody drew where the sun goes.