Passive solar design: Direct solar gain


Needs highly efficient thermal glazing or supplementary shuttering to prevent heat loss.

‘Direct Gain’ is the most basic form of solar gain. Solar energy enters through south-facing glazing and is absorbed by thermal mass incorporated into the floor and walls. Heat is stored in the thermal mass during the day and later released during the night into the living space. This re-radiation of collected heat can maintain a comfortable temperature during cool nights and can extend through several cloudy days without ‘recharging’.



• Up to 75% of the solar energy striking the glass is converted into thermal energy.

• Solar radiation can provide a significant proportion of a buildings heating requirements.

• The area of glazing is determined in response to the duration and severity of winter temperatures; the building size; and the amount of interior thermal mass. A correct balance between these factors must be established in order to avoid large daily temperature fluctuations that could result in overheating, even in winter.

• Though solar energy is most effectively absorbed by direct radiation, convective air currents can transmit energy to areas of mass that are not directly illuminated by the sun.

• Comfort in a living space is improved if mass is evenly distributed. Increasing the surface area reduces the incidence of localised hot and cold spots.

• The location and sizing of glazing is also dependent upon the building layout and types of spaces eg., frequently used spaces vs. infrequently used spaces.

• Since the absorption of solar energy is most effective through direct radiation, careful planning of the building is required. Direct absorption from south facing glazing implies that walls and floor need to be close to the source. With façade glazing only, the heated room is restricted to a relatively shallow depth, typically no more than 1.5 x the height of the glazing. 



• By using clerestories and roof lights, the depth of penetration of solar radiation can be extended further into the building so to allow for a deeper plan. A secondary benefit is the extra daylight provided to reduce the need for artificial lighting.

• A clerestorey roof angle should be approximately the same angle as the sun at the time of the winter solstice.



• Solar Architecture in Cool Climates, Porteous with MacGregor, Earthscan, 2005
• Sustainable Solar Housing, Hastings and Wall, Earthscan, 2007
• Solar House, Galloway, Architectural Press, 2004
• The Whole House Book, Borer and Harris, CAT, 2005
• EcoHouse 2, Roaf et al, Elsevier, 2003

Further information

• BSRIA: Building Services Research and Information Association (
• CIBSE: Chartered Institute of Building Services Engineers (




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