Building Regulations Part L1 | Architectural Glazing to New Build Dwellings

Building Regulations are a set of governmental rules and guidelines to ensure all building works in the UK are safe, accessible and limit waste and environmental damage. The installation and specification of architectural glazing in the UK must comply with these regulations. There are slightly different rules for Scotland and Wales.

Approved Document L of the Building Regulations deals with the Conservation of Fuel and Power, ensuring good thermal insulation to all external facades and dictating targets for CO2 emission, thermal efficiency, heating and waste management. Approved Document L was updated in 2022 to merge the approved documents from four to two and to pave the way for the government's Future Homes scheme in 2025.

Approved Document L: Volume 1 covers the building requirements regarding insulation and energy usage for new build private houses (or new dwellings as it is referred to in the document) and works to existing dwellings. This includes the thermal performance requirements of the architectural glazing and considerations for glazing design. Read below for an outline of the building regulations requirements for glazing on your new build house project.

For information about the glazing performance for an extension or renovation read our article Building Regulations Approved Document L and Architectural Glazing to House Extensions or Renovations.

Glossary of terms from Approved Document L

Approved document L uses many acronyms and technical terms that can make trying to read it confusing. Here are a few of the most important terms that relate to the energy efficiency of the glazing on a new build house:

Dwelling = a self-contained unit designed to accommodate a single household

Standard Assessment Procedure (SAP) = the approved procedure for assessing the performance of a new build dwelling.

Target Primary Energy Rate = the maximum primary energy use for the dwelling in a year. This is expressed as kWhPE/(m2,year). It is determined using the Standard Assessment Procedure. This is influenced by the fabric and fuel.

Target Emission Rate = the maximum CO2 emission rate for the dwelling. This is expressed as kgCO2/(m2.year). It is determined using the Standard Assessment Procedure. This is influenced by the fabric and fuel.

Target Fabric Energy Efficiency Rate = the minimum dwelling fabric energy efficiency (kWh/(m2,year)). It is determined using the Standard Assessment Procedure. This is influenced by the fabric of the building.

These are the targets that the new build dwelling must be designed to achieve.

Dwelling Emissions Rate = the dwelling CO2 emission rate (kgCO2/(m2.year)). It is determined using the Standard Assessment Procedure.

Dwelling Fabric Energy Efficiency Rate = kWh/(m2.year). It is determined using the Standard Assessment Procedure.

Dwelling Primary Energy Rate = kWhPE/(m2,year). It is determined using the Standard Assessment Procedure.

These are the actual performance values of the house as built.

A Notional Dwelling = an example building specification that achieves all building requirements of Approved Document L.

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Considerations for the Glazing Specification for New Build Houses

The performance of architectural glazing on a new build house is not simply a statement of performance values.

Building Regulations Part L looks at the balance between the insulation of the building and the energy demands of the building. It strives to ensure the external building envelope is as insulating as possible, whilst balancing this against reducing the energy requirements of the building. All with the aim to get the building as close to zero carbon as possible. (Regulation 25B).

For example:

Limiting the glazing on a project will increase the building’s reliance on artificial lighting, increasing the house's energy demands.

Unconsidered specification of glass without sufficient solar control coatings will increase the building’s energy demands for cooling.

Over glazing might reduce the overall thermal insulation of a building.

In order to achieve the target energy rate of a building, you must achieve a balance between glazing and other building materials.

Approved Document L was updated in 2022. The update is designed so that where a new building is erected, it is a ‘nearly zero-energy building’. This is a stepping stone towards the Future Homes Standard planned to come into effect in 2025.

If the areas of glazing is much less than 20% of the total floor area, some parts of the dwelling may experience poor levels of daylight, resulting in increased use of electric lighting

From Criterion 3 of Approved Document L1A.

Thermal Requirements of a New Build House

There are two ways in which architects can show compliance with Approved Document L Volume 1.

Build a house to match the ‘Notional Dwelling’, using the performance and design parameters listed in the Standard Assessment Procedure.

Build a house with the same or improved performance to the Notional Dwelling, providing evidence that the building achieves the required performance values, ensuring that no single element has a lower performance than those listed in the ‘Limiting Standards’.

While adherence to the Notional Dwelling parameters is a simpler way to achieve compliance, it highly restricts the possible design of the house.

Where architects are designing a bespoke house, the limits on a design from the Notional Dwelling may be prohibitive.

They can therefore use the performance of the Notional Dwelling (at the same size and shape as the actual dwelling) to set the target energy performance for the Actual Dwelling. They can then design a building to achieve these energy performance targets using the ‘Limiting Standards’ for building fabric elements as detailed in Table 4.1 of Building Regulations Approved Document L Volume 1.

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Required Performance of Glazing in Approved Document L Volume 1

If designing a bespoke house, the architectural glazing installed must have a better performance than what is listed in Table 4.1 showing the limiting standards for new dwellings.

Window, Roof Windows, Curtain Walling 1.6 W/m2 
Glazed Door 2.2 W/m2K 
Rooflight 1.6 W/m2K 

All values above show the weighted U value (Uw values).

There is also a requirement to achieve an air permeability rate of no more than 8.0m3/(h.m2) @ 50 Pa and 1.57m3/(h.m2) @ 4 Pa. This equates to Class 2.

When the Uw value for the proposed architectural glazing is input into the Standard Assessment Procedure, the overall building energy performance must meet the target fabric energy efficiency rate. In other words, you have to ensure the whole building envelope hits the target for efficiency.

Using the limiting standards, the energy efficiency of some areas of the building will need to be higher than what is set out in the limiting standards. This could be achieved by improving the performance of any building element, including the glazing. The building envelope must be considered holistically to ensure that the building achieves the required performance.

Architects use approved computer calculation systems to understand the required thermal performance for the architectural glazing in line with their target energy efficiency. It is then up to the specifier to provide an installation that achieves the required performance.

The Glazing Performance in the 'Notional Dwelling'

SAP Appendix R gives full detail of the ‘notional dwelling’ glazing specification. As stated above, this is a prescribed route to achieving the required Target Emission and Target Fabric Energy Efficiency rates. Architects are free to deviate from this specification in order to achieve their design goals as long as the minimum insulation values from Table 4.1 are achieved, and the overall project achieves the target Primary Energy, Target Emission and Target Fabric Energy Efficiency rates.

Overview of notional dwelling performance from Table 1.1 in Building Regulations Approved Document L Volume 1:

Reference value for target setting  
Opening areas (including windows, roof windows, rooflights and doors) Not exceeding a total area of openings of 25% of total floor area 
Semi-glazed Doors (30-60% glazed area)  Uw value 1.0 W/m2K  
Windows and glazed doors (over 60% glazed)  Uw value 1.2 W/m2K. Frame Factor 0.7. Orientation must be same as building 
Roof Windows Uw value 1.2 W/m2K in horizontal position. Use SAP 10 Appendix R to correct in relation to angle.  
Rooflights Uw value 1.7 W/m2K in vertical position. Use SAP 10 Appendix R to correct in relation to angle. 
Air permeability  5.0 m3/hm2 @ 50Pa = Class 3 

More in depth and stringent requirements are listed in SAP Appendix R.

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Glass Porches and Conservatories on a New Build Dwelling

Glass porches and conservatories are exempt from energy efficiency requirements if they:

  • Are at ground level.
  • Are not larger than 30m2 .
  • They are separated from the dwelling by a wall/door/window that adheres to the thermal performance requirements of Document L.
  • The heating from the dwelling doesn’t extend into the porch/conservatory.

If the glass addition complies with all of the above then you do not have to adhere to the U value requirements.

What is the Difference Between a Glass Extension and a Conservatory?

Building Regulations Part L1B for Glazing

If there is not a sufficient thermal barrier (using materials with performances in accordance with Table 4.4) between the conservatory/porch and the dwelling, then you need to design the additional area in line with the requirements of L Volume 1.

 

 

Higher g-values would also compley with the recipe as increasing solar gains reduces the space heat load. However, designers should be aware of the impact of g-value on the risk of overheating and optimise their choice accordingly.

Extract from Table 4 in Building Regulations Approved Document L1A.

New Build Homes in Conservation Areas

If a new build home is in a ‘conservation area designated in accordance with section 69 of the Planning (Listed Buildings and Conservation Areas) Act 1990’ (Approved Document L Volume 1, 2021 edition, paragraph 0.8) there are some exemptions to Approved Document L.

If full adherence to Approved Document L would ‘unacceptably alter the dwellings character or appearance’ then there is flexibility in the compliance with the U values for the glazing.

The building should still be specified to comply with the thermal performance requirements as much as possible, without damaging the character of the conservation area.

Building Regulations advise that the building control body should take the advice of the local authority conservation officer when determining whether the energy efficiency requirements apply to the build and to what extent.

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Front Door by Urban Front, Structural Glazing by IQ Glass

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Thermal Bridging and Architectural Glazing

Once a new build house has been designed and specified, it must also be built to specification and be of high quality. If the house is not built correctly or uses poor quality workmanship/materials, the energy performance of the building will be affected. It may not insulate as designed or may use more energy than expected.

The position of the glazing within the build-up of the insulated wall is important in ensuring the continuity of insulation.

“Windows and doors should be installed in such a way that the thermal integrity of the insulated plane is maintained” (Approved Document L Volume 1, 2021 edition, paragraph 4.15).

This includes:

  • Ensuring minimal tolerance around the window or glass door.
  • Installing the glazing so that it overlaps the inner face of the external leaf to be continuous with the insulation of the external wall.
  • Installing the window or glass door in openings where continuous cavity closers have been used.

Paragraph 4.15 also details the importance of detailed drawings for the build. IQ create bespoke technical design drawings to show where our glazing sits within the wall opening. This design phase of the project is essential to understand how the architectural glazing works with the insulation of the rest of the building.

These drawings are also important in ensuring the limitation of thermal bridges within the design. Paragraph 4.17 details the importance of detailed drawings of junctions to reduce thermal bridging.

This design work by IQ is done in conjunction with the architect or principal designer to review the details for approval.

The calculated Dwelling Fabric Energy Efficiency (DFEE) rate must not be greater than the Target Fabric Energy Efficiency (TFEE) rate.

Approved Document L1A, Section 1.4.

Airtightness and Architectural Glazing

As listed in Table 1.1 and 4.4, Approved Document L Volume 1 has requirements for the air permeability of a new build dwelling.

This factor is for the air permeability of the entire building. In order to achieve the required levels, you should ensure that each element of architectural glazing in the house design has a high level of air permeability.

Opening windows and doors are tested for air permeability in accordance with EN 12207. Class 4 is the highest test result possible and indicates the system has been tested with pressures up to 600 Pa. The requirements from Document L Volume 1 are the equivalent of Class 2 or 3.

Useful Reading: Air Permeability in Windows and Doors

This testing standard is not applicable to structural glazing. Fixed structural glazing is instead designed with bespoke fixing details (by the architectural glazier) to ensure the frameless glazing is airtight and built in conjunction with the abutting building finishes.

Paragraph 4.21 details the methods to ensure airtightness to the installation of the window or glass doors. This includes the use of technical design drawings to show the sealing method.

IQ work with the architect or principal designer to detail all the sealing around the glazing during our design phase.

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Architectural Glazing by IQ Glass on RIBA Award Winning Old Fort Road

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Moonstone Contemporary Home with Specialist Glazing by IQ Glass

Maintenance of Architectural Glazing

Approved Document L1A looks at the building as a whole; ensuring the building envelope is insulating but that also running the building uses energy efficiently with the aim to achieve zero carbon status. Part of achieving the required ongoing energy efficiency targets is ensuring that the owner of the dwelling understands how to operate all the fixed building services correctly to maximise efficiency.

One way to ensure this is to provide the homeowner with an O+M (Operations and Maintenance) Manual for the building and all integrated technologies on building completion.

Your architectural glazier should provide the contractor/client with an O+M manual for all the glazing installed on the new build house. This document will include the operation instructions for all architectural glazing. The requirements for this manual are detailed in Approved Document L Volume 1, Section 9, paragraphs 9.1 and 9.2. It should include instructions for the operation and maintenance of;

  • Electrical glazing systems such as heated glass/privacy glass.
  • Solar control glazing (cleaning and maintenance).
  • Automated louvre systems used as solar control methods.
  • Electrically operated windows and doors.
  • Auto opening rooflights.

Providing Evidence of the Thermal Performance of Architectural Glazing

The dwelling primary energy rate, dwelling emission rate and dwelling fabric energy efficiency rate of the building must be calculated to show the actual performance of the ‘as built’ structure. This must be done using the same calculation tool that the target rates were calculated on.

This needs to be done at the design stage (to show compliance before construction begins) and at the completion of construction (to show what has been built complies).

Once the building has been constructed it also needs to undergo a pressure test. The details of this are detailed out in Regulation 43.

The dwelling rates must not exceed the target rates.

All evidence of compliance is then sent to the local building control body before work starts and then again on completion to show compliance.

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Treeside Modern New Build with Specialist Glazing by IQ

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Low Carbon Home Design with Specialist Glazing by IQ Glass

Considerations of Document L with Other Areas of Building Regulations

Approved Document L Volume 1 only considers the thermal insulation and energy efficiency of a building. It is designed to move all homes towards a carbon natural future. However, it cannot act alone.

Architects and specifiers must also consider all other aspects of Building Regulations when designing bespoke homes. Some advice and guidance in Document L seems to contradict other areas of building regs.

For example, under Approved Document L you have to create a building that is highly airtight. But then Approved Document F explains how you must allow for ventilation within a building.

The below other Approved Documents from Building Regulations have cross over with the thermal insulation of the building and energy efficiency and must also be considered.

  • Approved Document F for Ventilation
  • Approved Document O for Overheating
  • Approved Document Q for Security
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What Next?

If you are looking at the glazing specification for a new build house, make sure you speak to one of the experts at IQ.

They will be able to offer advice and guidance to ensure you hit all required building regulation requirements whilst achieving the architectural glazing design you desire.

Visit the contact us page for all the ways in which you can get in touch with the team for specification support or request a quotation.

Rebecca Clayton
Technical Sales

Rebecca is the Communications Director at the IQ Group and has worked in glazing specification for many years. She has a broad range of technical knowledge about all our glazing products and offers technical advice and guidance to architects for specification. Her easy to digest technical advice is often quoted in magazines and publications. You might also recognise her as one of the IQ Glass CPD presenters.

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