Decrement Delay Decrement Factor (Jargon Buster) G#14043

GBE Jargon Buster Collection A49 brm 061215

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Decrement Delay & Decrement Factor (Jargon Buster)

Decrement Delay Decrement Factor (Jargon Buster)

GBE Jargon Buster

Words & Phrases



Refers to the time it takes for heat generated by the sun, to transfer from the outside to the inside of the building envelope and affect the internal conditions. (EESC ’11)

Decrement delay is essential in the design of lightweight (non-masonry) timber or metal frame building’s walls and roofs.
See: Thermal Lag, Decrement Factor
(GBE BRM ’12 – ’16)


The time taken (measured in hours) for heat to transfer between opposite surfaces of a material.

Insulation with a high decrement factor can be used to limit solar over-heating in particularly warm climate conditions.
For example, installing cellulose as a roofing insulation will likely slow-down the heat transfer from a sun-heated roof surface, through to the inside by around 7 hours – or by evening time by which time the sun has set and its heat source is removed.

(GreenSpec AEP ’09 & NGS BRM ’12 & GBE BRM ’16)
See: Decrement Delay, Thermal lag,
(GBE BRM ’12)


Insulation materials offering a high decrement ‘factor’ include:

  • Wood fibre insulation board (11.3 hr);
  • Cork
  • Cellulose fibre (7.3 hr),
  • Cellular glass

whereas materials with a low decrement factor would include:

  • Low-density mineral fibre (3.7 hr)
  • Low density foamed/extruded/expanded plastics polyurethane/ polystyrene (2 hr).

the very lowest include:

  • Vacuum Insulated Panels (VIPs) (0 hr)

(GreenSpec AEP ’09 & NGS BRM ’12 & GBE BRM ’16)

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Information sources:

  • EESC ’11
  • GreenSpec AEP ’09
  • NGS BRM ’12
  • GBE BRM ’16

Relevance to Environmental Construction

  • Healthy
  • Environmental
  • Resourceful
  • Appropriate
  • Competent
  • Effective
  • Yardstick




© GBE NGS ASWS BrianSpecMan aka Brian Murphy
13th December 2016

Decrement Delay Decrement Factor (Jargon Buster)

 GBE JargonBusterCollection A49brm061215

© GBE NGS ASWS BrianSpecMan aka Brian Murphy
13th December 2016

Decrement Delay Decrement Factor (Jargon Buster)
See Also:

GBE Jargon Buster

Jargon Buster Themes G#1333 N#1320

Insulation/Decrement List

  • Attic
  • Attic Insulation
  • Cellular Extruded Clay Block
  • Cellular Glass
  • Cellulose Fibre Fake
  • Cement Particleboard
  • Conduction Thermal Insulation
  • Cork
  • Decrement Delay (Jargon Buster) G#14043
  • Decrement Factor (Jargon Buster) G#14043
  • External Insulated Render Systems (EIRS)
  • k value
  • Loft
  • Loft Insulation
  • Masonry
  • Metal Cladding
  • Overheating
  • Rainscreen Cladding
  • Radiant Thermal Insulation
  • Raised storage/access systems
  • R value
  • Single Aspect
  • Steel Frame
  • Squashed Insulation
  • Structural Insulation Panel System (SIPS)
  • Thermal Break (Jargon Buster) G#9357
  • Thermal Bridge (Jargon Buster) G#9351
  • Thermal Bypass
  • Thermal Flanking
  • Thermal Insulation
  • Thermal Lag
  • Thermal Mass
  • Timber Frame
  • Top Storey
  • U Value
  • U Value Envelope
  • Wind Wash (Jargon Buster) G#14021
  • Wood Fibre Thermal Insulation

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GBE Issue Papers

GBE Links

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  • Raised Storage/Access platform
  • Loft Insulation U value calculator
  • Support thermal bridge Psi calculator

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  • Generic Material Properties

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Robust Specification Work Sections

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© GBE NGS ASWS BrianSpecMan aka Brian Murphy
13th December 2016 – 14th December 2016


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  • Solvax says:

    I think the content of this article is not correct.
    There are to aspects:
    – time lag or phase shift, which is named decrement delay in this article
    – decrement factor, which is the change in amplitude of the temperature curve

    Furthermore these values are dependent of thickness. This is not even a linear calculation.
    So you cannot just say that the delay is “2 hours” for a certain material.

    • BrianSpecMan says:

      This refers to a definition on GreenSpec website.
      I did not say it.
      Refer it to GreenSpec website.
      Whilst it is not explicit….
      I have assumed this is based in providing sufficient insulation to meet U value requirements.
      With the added bonus of decrement delay.

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