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
The Home Energy Model and its wrappers
From SAP to HEM, EPC for MEES and FHS assessment wrappers.
Future Homes Standard Essentials launched
Future Homes Hub launches new campaign to help the homebuilding sector prepare for the implementation of new building standards.
Building Safety recap February, 2026
Our regular run-down of key building safety related events of the month.
Planning reform: draft NPPF and industry responses.
Last chance to comment on proposed changes to the NPPF.
A Regency palace of colour and sensation. Book review.
Delayed, derailed and devalued
How the UK’s planning crisis is undermining British manufacturing.
How much does it cost to build a house?
A brief run down of key considerations from a London based practice.
The need for a National construction careers campaign
Highlighted by CIOB to cut unemployment, reduce skills gap and deliver on housing and infrastructure ambitions.
AI-Driven automation; reducing time, enhancing compliance
Sustainability; not just compliance but rethinking design, material selection, and the supply chains to support them.
Climate Resilience and Adaptation In the Built Environment
New CIOB Technical Information Sheet by Colin Booth, Professor of Smart and Sustainable Infrastructure.
Turning Enquiries into Profitable Construction Projects
Founder of Develop Coaching and author of Building Your Future; Greg Wilkes shares his insights.
IHBC Signpost: Poetry from concrete
Scotland’s fascinating historic concrete and brutalist architecture with the Engine Shed.
Demonstrating that apprenticeships work for business, people and Scotland’s economy.
Scottish parents prioritise construction and apprenticeships
CIOB data released for Scottish Apprenticeship Week shows construction as top potential career path.
From a Green to a White Paper and the proposal of a General Safety Requirement for construction products.
Creativity, conservation and craft at Barley Studio. Book review.
The challenge as PFI agreements come to an end
How construction deals with inherited assets built under long-term contracts.
Skills plan for engineering and building services
Comprehensive industry report highlights persistent skills challenges across the sector.
Choosing the right design team for a D&B Contract
An architect explains the nature and needs of working within this common procurement route.
Statement from the Interim Chief Construction Advisor
Thouria Istephan; Architect and inquiry panel member outlines ongoing work, priorities and next steps.