How much sun will this flat get? Orientation, floor and street width in Spain

Every flat looks bright in a September viewing at noon. You'll be living there at 4pm on a Tuesday in January too, working from home, with the building across the street in the way.

This works anywhere in mainland Spain. The worked examples use Barcelona's Eixample, and the Madrid numbers sit next to Barcelona's.

The winter sun is low

Barcelona sits at about 41,4° north, Madrid at about 40,4°.

	Barcelona	Madrid
Sun height at noon, around 21 December	about 25°	about 26°
Sun height at noon, around 21 June	about 72°	about 73°
Daylight, around 21 December	about 9 h 10 min	about 9 h 17 min
Daylight, around 21 June	about 15 h 10 min	about 15 h 3 min

Barcelona's sun heights are calculated for 41,39° N, and Madrid's are from timeofsunrise.com. Day lengths are from sunrise-sunset.org (Barcelona, Madrid) and timeofsunrise.com; sources differ by a few minutes.

Madrid is a degree further south, so its winter sun is slightly higher. It's also further west in the same time zone, so the sun peaks later by the clock: around 1:15pm in late December and 2:15pm in late June, halfway between sunrise and sunset. Elsewhere in Spain the pattern is the same: the further south, the higher the winter sun.

In summer the sun is high enough to clear almost any street. In winter it isn't, so orientation, floor and street width decide how much of it you get.

The Eixample: which side of the block?

The Eixample grid runs parallel and perpendicular to the sea, which turns it about 45° from north. Ildefons Cerdà did this on purpose, so that every façade would get direct sun at some point in the day, for health, light and ventilation (Cerdà Plan, Barcelona Metròpolis). Streets are 20 m wide, and blocks 113,3 m a side.

Façade faces	In local terms	Winter sun	Summer sun
South-east	The mar (sea) side	Sunrise to early afternoon	Sunrise to mid-afternoon
South-west	The Llobregat side	Mid-morning to sunset	Late morning to sunset, and hot in the afternoon
North-east	The Besòs side	Almost none	Early morning
North-west	The muntanya (mountain) side	Almost none	Late afternoon and evening

Barcelonians already give directions this way: mar, muntanya, Besòs, Llobregat. It's also the quickest way to place a flat when an agent says it faces "mar" or "muntanya".

The winter sun rises at about 122° (east-south-east) and sets at about 238°. So north-east and north-west façades catch only a few low-angle minutes at either end of a winter day, usually blocked by the buildings opposite. These azimuths are calculated for Barcelona's latitude. Madrid's differ by less than a degree, so outside Barcelona the table still holds if you read it by compass direction.

Floor and street width: a rule you can do on a napkin

At noon in late December, a façade facing the sun gets direct light above roughly:

height of the building opposite − (street width × 0,47)

0,47 is the tangent of Barcelona's 25° winter sun. In Madrid use 0,49 (the tangent of 26°); the answer barely changes. For any other town, use the tangent of its own noon sun in late December.

Street	Building opposite	Direct noon sun above about…
Eixample street, 20 m	21 m	11,6 m for a façade facing due south. About 7,7 m for a typical Eixample façade (SE or SW), because the sun comes in at an angle
Old-town street, 6 m	18 m	15,2 m: top floors only

At roughly 3 m per floor that's about the second or third floor in the Eixample case, and only the top floor on the narrow street. Treat these as rough guides. The rule assumes a long, straight street, flat ground and noon only.

Some streets in Ciutat Vella are barely wider than a corridor. Carrer de les Mosques is about 2 m (Metròpoli). A first-floor flat there may never see direct sun in winter.

How to check before you buy

1. Find the orientation with your phone's compass at the window, or the floor plan's north arrow. In the Eixample, work out which side of the block you're on.
2. Look across the street. How tall is the building opposite, and how wide is the street?
3. Visit twice, once late in the afternoon, ideally on a grey day. Sunny noon viewings flatter everything.
4. Use a sun-path tool. Sites like SunCalc show the sun's path for any date and address.
5. Ask about interior rooms. In the Eixample, rooms facing the block's inner courtyard (interior) can be quieter and sometimes brighter than street-facing (exterior) ones, depending on the floor.

Why there's no official map for this

The public solar maps cover roofs, not façades. Barcelona Regional's metropolitan solar map shows solar-panel potential building by building, but only for roofs (Barcelona Regional). So does Spain's national viewer (IGN). Catalan habitability rules require windows of at least 1/8 of a room's floor area in new homes, but set no minimum hours of sun (COAC), so a flat can be perfectly legal and still dark.