Solar transmittance through building fabric (gtot)
Solar heat gain in buildings can be beneficial in the winter, as it reduces the need for heating, but in the summer it can cause overheating.
The total solar heat transmittance into a space is the sum of the solar heat that is transmitted directly through its fabric (such as solar radiation transmitting through glass), and the solar heat that is absorbed by its fabric and then re-emitted into the enclosed space.
Total solar energy transmittance (gtot) relates to the performance of solar protection devices such as blinds and shutters and is the percentage of solar energy incident on the fabric of a blind or shutter that is transmitted to the interior of the building, including both the transmittance of the solar protection device itself and of the glazing.
According to the EN 14501 standard (Blinds and Shutters, Thermal and Visual Comfort, Performance Characteristics and Classification), it is measured on an index of 0 to 1. The closer the fabric’s index is to 0, the more efficient it is at protecting against heat and reducing solar energy; whereas an index of 1 means that all the incident solar radiation is transmitted.
Two methods are used for calculating the gtot of a solar protection device:
- Simplified calculation method: EN ISO 52022-1 (replacing EN 13363-1)
- Detailed calculation method: EN ISO 52022-3 (replacing EN 13363-2)
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
ECA, JIB and JTL back Fabian Society call to invest in skills for a stronger built environment workforce.
Women's Contributions to the Built Environment.
Calls for the delayed Circular Economy Strategy
Over 50 leading businesses, trade associations and professional bodies, including CIAT, and UKGBC sign open letter.
The future workforce: culture change and skill
Under the spotlight at UK Construction Week London.
A landmark moment for postmodern heritage.
A safe energy transition – ECA launches a new Charter
Practical policy actions to speed up low carbon adoption while maintaining installation safety and competency.
Frank Duffy: Researcher and Practitioner
Reflections on achievements and relevance to the wider research and practice communities.
The 2026 Compliance Landscape: Fire doors
Why 'Business as Usual' is a Liability.
Cutting construction carbon footprint by caring for soil
Is construction neglecting one of the planet’s most powerful carbon stores and one of our greatest natural climate allies.
ARCHITECTURE: How's it progressing?
Archiblogger posing questions of a historical and contextual nature.
The roofscape of Hampstead Garden Suburb
Residents, architects and roofers need to understand detailing.
Homes, landlords. tenants and the new housing standards
What will it all mean?
The Architectural Technology podcast: Where it's AT
Catch-up on the latest episodes.
Edmundson Apprentice of the Year award 2026
Entries now open for this Electrical Contractors' Association award.
Traditional blue-grey slate from one of the oldest and largest UK slate quarries down in Cornwall.
There are plenty of sources with the potential to be redeveloped.