U-values - Revision history

Editor at 10:08, 13 February 2023

2023-02-13T10:08:13Z

← Older revision		Revision as of 10:08, 13 February 2023
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	* Double glazing v triple glazing.		* Double glazing v triple glazing.
	* Emissivity.		* Emissivity.
		+	* Free U-value calculators.
	* g-value.		* g-value.
	* k-value.		* k-value.

Designing Buildings at 07:46, 5 January 2023

2023-01-05T07:46:16Z

← Older revision		Revision as of 07:46, 5 January 2023
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	R-values, which measure thermal resistance rather than thermal transmission, are often described as being the reciprocal of U-values, however, R-values do not include surface heat transfers.		R-values, which measure thermal resistance rather than thermal transmission, are often described as being the reciprocal of U-values, however, R-values do not include surface heat transfers.

−	= ~~Typical~~ values =	+	= What are the U-values of commonly building components? =

−	U-values are measured in watts per square metre per kelvin (W/(m²K)). For example, a ~~[[Double_glazing\|~~double glazed]] window with a U-value of 2.8, for every degree difference in temperature between the inside and outside of the window, 2.8 watts will be transmitted every square metre.	+	U-values are measured in watts per square metre per kelvin (W/(m²K)). For example, a double glazed window with a U-value of 2.8, means that for every degree difference in temperature between the inside and outside of the window, 2.8 watts will be transmitted every square metre.

−	A range of U-values are ~~indicated below for the purposes of comparison only~~:	+	A range of typical U-values are:

	* Solid brick wall: 2 W/(m²K)		* Solid brick wall: 2 W/(m²K)
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	* Solid timber door: 3 W/(m²K).		* Solid timber door: 3 W/(m²K).

−	Part L of the Building Regulations (Conservation of fuel and power) now prevents certain forms of construction by setting limiting standards (i.e. maximum U-values) for ~~[[Building_element\|~~building elements]]. See Limiting fabric parameters for more information.	+	It is important to distinguish between U-values for materials (such as glass), or assemblies (such as windows, which have frames, air gaps, and so on), or elements (such as walls, which may have complex constructions comprising a number of different components).
		+
		+	= What are the maximum U-values allowed? =
		+
		+	Part L of the Building Regulations (Conservation of fuel and power) now prevents certain forms of construction by setting limiting standards (i.e. maximum U-values) for building elements. See Limiting fabric parameters for more information.

	It should be noted however that these are maximum permitted values, the specification for the notional domestic building referred to in Part L1A has considerably lower values, for example:		It should be noted however that these are maximum permitted values, the specification for the notional domestic building referred to in Part L1A has considerably lower values, for example:
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	See Standard Assessment Procedure SAP for more information.		See Standard Assessment Procedure SAP for more information.

−	~~NB: It is important to distinguish between~~ U-values for materials (such as glass), or assemblies (such as windows, which have frames, air gaps, and so on), or elements (such as walls, which may have complex constructions comprising a number of different [[Building_component\|components]]).	+	= How are U-values calculated? =
−		+
−	~~= Calculation~~ =	+

	The U value of an element (in W/(m²K)) can be calculated from sum of the thermal resistances (R-values in m²K/W) of the layers that make up the element plus its inside and outside surface thermal resistances (Ri and Ro).		The U value of an element (in W/(m²K)) can be calculated from sum of the thermal resistances (R-values in m²K/W) of the layers that make up the element plus its inside and outside surface thermal resistances (Ri and Ro).
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	Where the thermal resistance of the layers of the element R = the thickness of each layer / the thermal conductivity of that layer (its k-value or lambda value (λ) in W/(mK)).		Where the thermal resistance of the layers of the element R = the thickness of each layer / the thermal conductivity of that layer (its k-value or lambda value (λ) in W/(mK)).

−	This can become a complicated calculation when there are a large number of layers, ventilated or unventilated cavities are introduced, or the element is inclined. Manufacturers will generally provide U-values for products that they supply. There are also a number of U-value calculators available online ~~(such as the [http://projects.bre.co.uk/uvalues/ BRE U-value calculator], although this is not free)~~.	+	This can become a complicated calculation when there are a large number of layers, ventilated or unventilated cavities are introduced, or the element is inclined. Manufacturers will generally provide U-values for products that they supply. There are also a number of U-value calculators available online.

−	Calculation methods for U-values appropriate for demonstrating compliance with the building regulations are based on standards developed by the European Committee for Standardisation (CEN) and the International Organisation for Standardisation (ISO) and published as British Standards~~. See Conventions for U-value calculations (2006 edition) BR 443~~.	+	Calculation methods for U-values appropriate for demonstrating compliance with the building regulations are based on standards developed by the European Committee for Standardisation (CEN) and the International Organisation for Standardisation (ISO) and published as British Standards.

−	Whilst U-values are still used in the Building Regulations to set limiting standards for the elements of a ~~[[Building_fabric\|~~building's fabric]], the overall thermal performance of buildings is now assessed using more complex modelling procedures.	+	Whilst U-values are still used in the Building Regulations to set limiting standards for the elements of a building's fabric, the overall thermal performance of buildings is now assessed using more complex modelling procedures.

−	For non-domestic buildings, the Simplified Building Energy Model (SBEM) developed by the BRE for the Department for Communities and Local Government, determines the energy performance of a proposed building by comparing its annual energy use with that of a comparable notional building~~. SBEM can be downloaded from the [http://www.ncm.bre.co.uk/ National Calculation Methodology website]~~.	+	For non-domestic buildings, the Simplified Building Energy Model (SBEM) developed by the BRE for the Department for Communities and Local Government, determines the energy performance of a proposed building by comparing its annual energy use with that of a comparable notional building.

−	For dwellings, energy performance is assessed using the ~~Government's [http://www.bre.co.uk/sap2009/~~ Standard Assessment Procedure] (SAP).	+	For dwellings, energy performance is assessed using the Standard Assessment Procedure (SAP).

	NB: Whilst U-values and methods of modelling the thermal performance of buildings are invaluable in setting standards and providing a means of comparing alternative solutions, they are simplifications of reality, and performance in use rarely matches that which was predicted. Poor workmanship can result in reduced thermal resistance, as can poor detailing and the presence of water in insulating materials. See Insulation specification and performance gap for more information.		NB: Whilst U-values and methods of modelling the thermal performance of buildings are invaluable in setting standards and providing a means of comparing alternative solutions, they are simplifications of reality, and performance in use rarely matches that which was predicted. Poor workmanship can result in reduced thermal resistance, as can poor detailing and the presence of water in insulating materials. See Insulation specification and performance gap for more information.
−
−	NB: The building regulations now require that 'consequential improvements' are carried out on certain non-domestic buildings when they are extended or altered in order to bring the entire building more into line with the requirements of Part L of the Building Regulations. See Consequential improvements for more information.

	= Related articles on Designing Buildings =		= Related articles on Designing Buildings =
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	* Building performance.		* Building performance.
	* Cavity wall insulation.		* Cavity wall insulation.
−	* Co-heating test.
	* Conduction.		* Conduction.
−	* Conductor.
	* Conventions for calculating linear thermal transmittance and temperature factors.		* Conventions for calculating linear thermal transmittance and temperature factors.
	* Conventions for U-value calculations (BR443 2e 2019).		* Conventions for U-value calculations (BR443 2e 2019).
−	* Computational fluid dynamics.
−	* Double glazing.
	* Double glazing v triple glazing.		* Double glazing v triple glazing.
	* Emissivity.		* Emissivity.
−	* Fabric first investigation into net zero for existing buildings.
−	* Floor insulation.
−	* Flue insulation and air tightness requirements.
	* g-value.		* g-value.
	* k-value.		* k-value.
	* Heat loss.		* Heat loss.
	* Heat transfer.		* Heat transfer.
−	* Home design prospects under the Future Homes Standard.	+	* Insulation.
−	* Insulation ~~specification~~.	+
	* Limiting fabric parameters.		* Limiting fabric parameters.
−	* PA ratio.
	* R-value.		* R-value.
−	* Roof insulation.
−	* Shading coefficient.
−	* Solar heat gain coefficient.
−	* Solid wall insulation.
	* Standard Assessment Procedure SAP.		* Standard Assessment Procedure SAP.
−	* The effects of subframe systems on the overall thermal performance of external rainscreen walls.
	* Thermal admittance.		* Thermal admittance.
	* Thermal bridge.		* Thermal bridge.
−	* Thermal bridging and the Future Homes Standard.
−	* Thermal imaging of the building fabric in the net zero world.
	* Thermal mass.		* Thermal mass.
	* Thermal resistance.		* Thermal resistance.
−	* Thermographic survey.
−	* Triple glazing.
	* U-value conventions in practice: Worked examples using BR 443.		* U-value conventions in practice: Worked examples using BR 443.
	* U-What?		* U-What?
	* What do design professionals need to know about U-value calculation conventions?		* What do design professionals need to know about U-value calculation conventions?
−	* Zero carbon homes.
−	* Zero carbon non-domestic buildings.

	= External references =		= External references =

Designing Buildings at 07:39, 5 January 2023

2023-01-05T07:39:56Z

← Older revision		Revision as of 07:39, 5 January 2023
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	[[File:U-value.jpg\|link=File:U-value.jpg]]		[[File:U-value.jpg\|link=File:U-value.jpg]]

−	= ~~Introduction~~ =	+	= What are U-values? =

−	U-values (sometimes referred to as heat transfer coefficients or thermal transmittances) are ~~used to~~ measure how effective elements of a building's fabric are as insulators. That is, ~~how effective~~ they ~~are at preventing~~ heat from transmitting between the inside and the outside of a building.	+	U-values (sometimes referred to as heat transfer coefficients or thermal transmittances) are a measure of how effective the elements of a building's fabric are as insulators. That is, the degree to which they prevent heat from transmitting between the inside and the outside of a building.
−		+
−	[[R-value\|R-values]], which measure [[Thermal_resistance\|thermal resistance]] rather than thermal transmission, are often described as being the reciprocal of U-values, however, [[R-value\|R-values]] do not include surface heat transfers.	+

	The lower the U-value of an element of a building's fabric, the more slowly heat is able to transmit through it, and so the better it performs as an insulator.		The lower the U-value of an element of a building's fabric, the more slowly heat is able to transmit through it, and so the better it performs as an insulator.

−	Very broadly, the better (i.e. lower) the U-value of a building's fabric, the less energy is required to maintain comfortable conditions inside the building.	+	Very broadly, the better (i.e. lower) the U-value of a building's fabric, the less energy is required to maintain comfortable conditions inside the building. As energy prices increase, and there is greater awareness of sustainability, performance measures such as U-values have become more important, and building standards (such as the Building Regulations) have required that lower and lower U-values are achieved. This has required changes in the design of buildings, both in the use of materials (such as insulation), the make-up of the building elements (such as cavity walls and double glazing), and the overall make up of a building's fabric (for example, reducing the proportion of glazing).
		+
		+	= What is the difference between a U-value and an R-values? =

−	~~As energy prices increase, and there is greater awareness of sustainability, performance measures such as U~~-values ~~have become more important~~, ~~and building standards (such~~ as the ~~[[Building_regulations\|Building Regulations]]) have required that lower and lower~~ U-values ~~are achieved. This has required changes in the design of buildings~~, ~~both in the use of materials (such as [[Insulation\|insulation]])~~, ~~the make~~-up of the [[Building_element\|building elements]] (such as [[Cavity_wall\|cavity walls]] and [[Double_glazing\|double glazing]]), and the overall make up of a building's fabric (for example, reducing the proportion of [[Glazing\|glazing]]).	+	R-values, which measure thermal resistance rather than thermal transmission, are often described as being the reciprocal of U-values, however, R-values do not include surface heat transfers.

	= Typical values =		= Typical values =

Designing Buildings at 08:28, 7 October 2022

2022-10-07T08:28:07Z

← Older revision		Revision as of 08:28, 7 October 2022
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	NB: The building regulations now require that 'consequential improvements' are carried out on certain non-domestic buildings when they are extended or altered in order to bring the entire building more into line with the requirements of Part L of the Building Regulations. See Consequential improvements for more information.		NB: The building regulations now require that 'consequential improvements' are carried out on certain non-domestic buildings when they are extended or altered in order to bring the entire building more into line with the requirements of Part L of the Building Regulations. See Consequential improvements for more information.
−
−	~~{{:Velux_cta_setup\|DBWCTA0012}}~~

	= Related articles on Designing Buildings =		= Related articles on Designing Buildings =
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	* [http://www.bre.co.uk/sap2009/ Standard Assessment Procedure].		* [http://www.bre.co.uk/sap2009/ Standard Assessment Procedure].

−	~~[[Category:Articles_needing_more_work]]~~ [[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Standard]] [[Category:Planning_permission]] [[Category:Policy]] [[Category:Client_procedures]]	+	[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Standard]] [[Category:Planning_permission]] [[Category:Policy]] [[Category:Client_procedures]]

Editor at 03:22, 22 July 2022

2022-07-22T03:22:00Z

← Older revision		Revision as of 03:22, 22 July 2022
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	* [http://www.bre.co.uk/sap2009/ Standard Assessment Procedure].		* [http://www.bre.co.uk/sap2009/ Standard Assessment Procedure].

−	[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Standard]] [[Category:Planning_permission]] [[Category:Policy]] [[Category:Client_procedures]]	+	[[Category:Articles_needing_more_work]] [[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Standard]] [[Category:Planning_permission]] [[Category:Policy]] [[Category:Client_procedures]]

90.251.56.38 at 21:38, 13 December 2021

2021-12-13T21:38:58Z

← Older revision		Revision as of 21:38, 13 December 2021
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	* Double glazing: 1.2 to 3.7 W/(m²K) depending on type.		* Double glazing: 1.2 to 3.7 W/(m²K) depending on type.
	* Triple glazing below: 1 W/(m²K).		* Triple glazing below: 1 W/(m²K).
−	* Solid timber door: 3 W/(m²K). h	+	* Solid timber door: 3 W/(m²K).

	Part L of the Building Regulations (Conservation of fuel and power) now prevents certain forms of construction by setting limiting standards (i.e. maximum U-values) for [[Building_element\|building elements]]. See Limiting fabric parameters for more information.		Part L of the Building Regulations (Conservation of fuel and power) now prevents certain forms of construction by setting limiting standards (i.e. maximum U-values) for [[Building_element\|building elements]]. See Limiting fabric parameters for more information.

90.251.56.38 at 21:37, 13 December 2021

2021-12-13T21:37:00Z

← Older revision		Revision as of 21:37, 13 December 2021
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	* Double glazing: 1.2 to 3.7 W/(m²K) depending on type.		* Double glazing: 1.2 to 3.7 W/(m²K) depending on type.
	* Triple glazing below: 1 W/(m²K).		* Triple glazing below: 1 W/(m²K).
−	* Solid timber door: 3 W/(m²K).	+	* Solid timber door: 3 W/(m²K). h

	Part L of the Building Regulations (Conservation of fuel and power) now prevents certain forms of construction by setting limiting standards (i.e. maximum U-values) for [[Building_element\|building elements]]. See Limiting fabric parameters for more information.		Part L of the Building Regulations (Conservation of fuel and power) now prevents certain forms of construction by setting limiting standards (i.e. maximum U-values) for [[Building_element\|building elements]]. See Limiting fabric parameters for more information.

Editor at 11:38, 17 November 2021

2021-11-17T11:38:09Z

← Older revision		Revision as of 11:38, 17 November 2021
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	{{:Velux_cta_setup\|DBWCTA0012}}		{{:Velux_cta_setup\|DBWCTA0012}}

−	= Related articles on Designing Buildings ~~Wiki~~ =	+	= Related articles on Designing Buildings =

	* Air tightness in buildings.		* Air tightness in buildings.
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	* U-value conventions in practice: Worked examples using BR 443.		* U-value conventions in practice: Worked examples using BR 443.
	* U-What?		* U-What?
		+	* What do design professionals need to know about U-value calculation conventions?
	* Zero carbon homes.		* Zero carbon homes.
	* Zero carbon non-domestic buildings.		* Zero carbon non-domestic buildings.

Editor at 10:45, 23 September 2021

2021-09-23T10:45:10Z

← Older revision		Revision as of 10:45, 23 September 2021
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	* Solid wall insulation.		* Solid wall insulation.
	* Standard Assessment Procedure SAP.		* Standard Assessment Procedure SAP.
		+	* The effects of subframe systems on the overall thermal performance of external rainscreen walls.
	* Thermal admittance.		* Thermal admittance.
	* Thermal bridge.		* Thermal bridge.

Editor at 11:07, 19 July 2021

2021-07-19T11:07:08Z

← Older revision		Revision as of 11:07, 19 July 2021
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	* Thermal bridge.		* Thermal bridge.
	* Thermal bridging and the Future Homes Standard.		* Thermal bridging and the Future Homes Standard.
		+	* Thermal imaging of the building fabric in the net zero world.
	* Thermal mass.		* Thermal mass.
	* Thermal resistance.		* Thermal resistance.