Decrement delay
The term ‘decrement delay’ refers to the time it takes for heat to pass through an element of a building (such as an external wall or roof). Typically this is taken to be the delay in hours between the peak temperature of the outer surface of the element on a summer day and the resulting peak temperature of the internal surface.
This concept reflects increasing awareness that the thermal behaviour of buildings is dynamic, rather than static, and that thermal mass, as well as thermal insulation, has a significant impact on the energy efficiency of a building. For example, two buildings with identical U-values may perform very differently depending on their decrement delay, with a longer delay likely to reduce peak loads on building services systems.
Materials with a low lambda value (sometimes referred to as thermal conductivity or k-value), high specific heat capacity and high density will tend to have a high decrement delay.
The term ‘decrement factor’ refers to the amount by which conditions are moderated by an element of a building. So in the case of the peak temperature on the outer surface of a building on a summer day, this would be the amount by which the peak is reduced by the time it reaches the inner surface. It is expressed as the ratio between the internal surface cyclic temperature variation compared to the external surface.
To reduce summer overheating, a low decrement factor is required, and a decrement delay of 6 to 12 hours.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
ECA Industry Awards 2024 shortlist revealed
22 leading businesses from across the electrotechnical and engineering services sector.
Government unveils Skills England strategy
Skills England to transform opportunities and drive growth.
New Government Hub for York Given Planning Green Light
For up to 2,600 civil servants, due for completion by 2028.
Construction Skills Certification Scheme cards
July update on Professionally Qualified and Academically Qualified Person Cards.
BSRIA Briefing 2024, November 22
Sustainable Futures: Redefining Retrofit for Net Zero Living.
The CLC on driving competency in the retrofit sector
Previously published roadmap on skills for net zero.
The first labour government King's speech in fifteen years
Construction industry reactions, support and some concern.
CIOB Retrofit of Buildings Technical Information Sheet
What retrofit is, the approach to be taken and processes to be followed.
Adapting Historic Buildings for Energy and Carbon Efficiency
Historic England advice note 18, free download published.
10 retrofit projects revisited 10 years after completion.
Information orders, building liability orders and SPVs
Key BSA terms and how they impact special purpose vehicles.
Listed despite problems with its design.
Zen and the art of cycling exploration.
Design Council Homes Taskforce launched
To support government 1.5 million homes target within UK climate commitments.