Natural light. The source of energy that’s essential for so many processes in our bodies. An influencer on our mood and free source of light and heat. If we’re not careful, however, it’s an extreme source of discomfort from overheting or glare. So, in the built environment, what does good daylight/sunlight design mean? Designing with the sun means getting the geometry right to harness useful solar energy and block unwanted solar gains for interior and exterior spaces around buildings, throughout the year.
INTERIOR: Let’s start inside. Good natural lighting is high on the list of what people look for in a home. So, here are the ingredients for getting it right.
Orientation. Keep the main axis running East-West-ish, so the building is facing within 30 degrees of south. Main living areas should be on this facade.
Window position: keep them high in the wall to throw light as far into the room as possible. Horizontal windows disperse light around a room and function better than vertical ones, all things considered (e.g. ventilation, view, desirable solar gain…). The height of the window influences the distance into the room at which good daylight can be achieved.
Floor plans should be limited by the rule of thumb for room depth: good daylight will be achieved at a distance into the room of 2 times the window head height for an unobstructed window e.g. if the window head is 2.5m, the daylight will be sufficient up to 5m into the room.
Window size: affects heat loss and useful solar gain, view and ventilation and really depends on the individual building and its surroundings. 25% of the facade is a reasonable stating point.
Glazing type: We ask a lot of the glass in our windows. We want it to keep heat in sometimes and block it’s arrival at others; it needs to let us see out and illuminate the room. The glazing’s g-value tells us how much solar heat it lets through. It’s different from it’s visible light transmission (VLT) which tells us how much light reaches inside. Low g-values are promoted to guard against overheating. However, we need glass to allow in useful heat gains in winter and there is now extensive research showing the importance to human health of some of the wavelemgths this glass may cut out. Broadly speaking, the more pains of glass, the better for heat loss but the more good wavelengths are cut out. The industry is just waking up to this so for now, choose a glass with g=0.5 or 0.6 and visible light transmission of 0.7.
EXTERIOR: use of water features and planting (such as green roofs, green walls, trees and shrubs) can lower local indoor and outdoor temperatures and ease the urban heat island effect. These strategies work best alongside building‑level measures that limit solar gain.
Solar Absorption or Albedo: extensive dark, hard surfaces should be avoided because their low albedo means they absorb more solar radiation and raise surrounding air temperatures. Re-radiation of heat from hard surfaces can be the main source of overheating in urban spaces.
Spacing: if developing a group of buildings, use the rule of thumb for: ows a distance of 1,5 times the building height reduce heights to the south to preserve solar access further north where the tallest buildings should be.
Shading: South-facing windows not shaded by their surroundings will need horizontal shading to cut out high-angle summer sun but let in much-appreciated winter sun. Rule of thumb for overhang length: half the height of the window. East and West facing glazing needs vertical shading to block highly penetrating, direct low angle summer sun, Where shading is needed, use external, moveable shading (see here)
Courtyards: lower heights in the south is important for courtyards which also need gaps to ensure some winter sun gets through and the interior isn’t in shade all year round. Use deciduous tree to the north of courtyard spaces to create deliberate summer shade and coolth.
Balconies should be the sticky-outy type and staggered up the facade, not one above another.
Playgrounds: make sure that sun will fall on them during colder weather. Deliberately create shady areas (several small ones is better than one big one), Ideally, consider tree planting which will create dense shade as it matures. Do not, repeat DO NOT use hard surfacing. Ideally, the hole area willprovide access to dirt on the floor but particularly ensure that the ground spaces receiving sun in the summer are shaded in summer. The recommended guidance is for at least 50% of the playground to receive direct sun on the equinox (not counting trees) but more is better. Double check the solar access for 9-3 on a winter weekend when it’s likely to be used.
Gardens: again, at least half the space should receive sun on the equinox but gardeners will thank you for more. Plant for shade and water retention
Planting: trees can be used to offer additional shading for buildings and public spaces. Deciduous species provide summer shade but allow winter solar gains once the leaves have fallen. Select species for drought resistance canopy cover, canopy density and crown height over 3m. Groups of trees are better than one. If you’re aiming to reduce the temperature of an area (e.g. playground or neighbourhood block) significantly, the canopy coverage needs to be 30-50%