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There are many legislative factors and Building Regulations to consider when specifying or buying a rooflight or daylight system.

The most efficient means of providing natural daylight is with the use a flat roof glazing system; horizontal glazing provides up to three times more daylight than an equally sized vertical window! Light distribution is also more evenly spread on the vertical than on the horizontal and therefore helps to reduce the likelihood of glare and overheating.

When specifying a rooflight however, there are many other areas for consideration; the use of natural daylight is linked to thermal efficiency and also energy efficiency, fire safety and on-site health and safety are also to be considered when using and working with roof glazing as is acoustic performance and ventilation.

There are number of industry specific guidelines, policies and regulations which are in place to help assist with your design requirements. At JET COX we do our upmost to stay ahead of these Regulations and of any pending changes. JET COX are active members of the National Association of Rooflight Manufacturer (NARM). NARM was established to promote co-operation between member companies, in order to develop and maintain standards and codes of practice – as well as to provide a genuinely authoritative information portal for rooflight specifiers.

For more information, please select the relevant section.

Part L

Thermal Efficiency

The Building Regulations 2010: Conservation of Fuel and Power, Approved Document L

(2010 Edition incorporating further 2010 amendments)

Originally introduced in 2000 to bring about control for the conservation of fuel and power, the latest version came into effect on the 1st October 2010. Further planned updates are scheduled over the forthcoming years.
Approved Document L is divided into four main categories:

The Regulation requires that reasonable provisions should be made to limit heat gains and losses through the fabric of the building. The main change to the 2006 Regulation is largely to the new build sector with much of the focus now on the energy efficiency of the major energy consuming services such as heating and lighting. The revision now requires a calculation on the C0₂ emissions from the actual dwelling.

To comply with the Regulations the Dwelling C0₂Emission Rate (DER) must be no worse than the Target C0₂ Emission Rate (TER). The TER is specified at design stage.

Calculation of the DER must be based on the building as constructed and should incorporate:

  • Any changes made during construction which differ from specification
  • Air permeability – Air permeability is the physical property used to measure airtightness of the building fabric. It is defined as air leakage rate per hour per square metre of envelope area at a test reference pressure differential across the building envelope of 50 Pascal (50 N/m²)

The thermal performance requirements of rooflights can be summarised for each of the categories as follows:

Document L 1A
Section 4.2: Rooflights, 2.00 W/m²K
Air Permeability 10.00 m³/hm² at 50Pa
Document L 1B
Section 4.21: Rooflights, 1.6 W/m²K
Document L 2A
Section 4.32: Rooflights, 2.2 W/m²K
Air Permeability 10.00 m³/hm² at 50Pa
Document L 2B
Section 4.26: Rooflights, 1.8 W/m²K
Section 4.27: Refers to a relaxation in certain classes of building with high internal gains. Here a less demanding ‘U’ Value may be an appropriate way of reducing C0₂ emissions. If this case can be made then a relaxation may be granted and a ‘U’ Value of 2.7 W/m²K must not be exceeded.

Roof ventilators (including smoke extract ventilators) have a maximum ‘U’ Value of 3.5 W/m²K

Fire Safety

The Building Regulations 2010: Fire Safety, Approved Document B

(2006 edition incorporating 2007, 2010 & 2013 amendments)

The UK Regulations for fire safety in buildings are detailed in Document B. There are two sections within the Document which relate directly to Rooflights, and have the following aims:

Section B2 – Internal Fire Spread –

‘to ensure fire spread over the internal linings of buildings is inhibited.

In order to inhibit spread of fire the internal linings shall-

I. adequately resist the spread of flame over their surfaces; and

II. have, if ignited, a rate of heat release or a rate of fire growth, which is reasonable  in the circumstances’

In general, the standards for internal fire spread can be achieved by meeting the requirements of either (British) BS 476

Part 7: Method of test to determine the classification of the surface spread of flame of products or (European) BS EN 13501-1: 2007 Fire classification of construction products and building elements, Part 1- Classification using data from reaction to fire tests. Where  there is no classification for thermoplastic materials under BS 476 Part 7, three other ratings are used; TP(a) Rigid, TP(a) Flexible and TP(b).

Section B4 – External Fire Spread

– ‘to ensure external walls and roofs have adequate resistance to the spread of fire over the external envelope and that spread of fire from one building to another  is restricted.

I. The roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having regard to the use and position of the building.’

In general, the standards for external fire spread can be achieved by meeting the requirements of either BS 476 Part 3 or BS EN 13501 Part 5.

In summary

Internal skin:

  • The surface linings of walls and ceiling should normally be rated Class 1 according to BS 476 Part 7
    or Class C-s3,d2 according to BS EN 15301:1
  • The inner layer of a rooflight should either meet that same classification, or achieve TP(a)
  • however, plastic rooflights with at least a Class 3 (BS 467 Part 7), Class D-s3,d2 (BS EN 15301:1) or TP(b) rating may be used in circumstances where the maximum area of each rooflight is less than 5m², with a minimum separation distance between each rooflight of 3m

Outer skin:

  • When used in rooflights, a rigid thermoplastic sheet product made from polycarbonate or from un-plasticised PVC which achieves a Class 1 according to BS 476 Part 7 or Class C-s3,d2 according to BS EN 15301:1 for surface spread of flame can be regarded as having a British AA designation or BROOF (t4) European classification and is therefore acceptable
  • Lower classifications for the outer skin may be acceptable, but only in areas out with 6m from a boundary

Please note that single skin sheet applications must meet the requirements for both the inner lining and outer roof surfaces.

Thermoplastics- Polycarbonate and un-plasticised PVC

Thermoplastic materials; PVC, solid polycarbonate and multiwall polycarbonate, are suitable materials for a wide range of building applications. However, as the material would melt during the testing procedure, they cannot be tested under BS 476 Part 3 or BS EN 15301 Part 5.

UK Building Regulations therefore define an alternative classification for these materials;

  • Polycarbonate or un-plasticised PVC which achieves Class 1, BS 476 Part 7 or Class C-s3,d2, BS EN 15301
    Part 1, can also be classified AA designation or BROOF (t4) classification
  • Multiwall polycarbonate which is rated Class 1, BS 476 Part 7; Polycarbonate ≥3mm thick; and solid PVC (any thickness) are rated TP(a) Rigid
  • Other thermoplastics, not categorised above, can be tested according to BS 2782 and are rated TP(a) Flexible or TP(b)

GRP (Glass Reinforced Polyester)

GRP can be classified to BS 476 Part 3 & Part 7, and to BS EN 15301 Part 1 & Part 5. A variety of grades are available offering alternative fire ratings dependant on application.

TP(a) rigid:

I. Rigid solid pvc sheet

II. Solid (as distinct  from double  or multi-skin) polycarbonate sheet at least 3mm thick

III. Multi-skinned rigid sheet made from unplasticised pvc or polycarbonate which has a Class 1 rating when tested to BS 476-7:1997 or 1971 or 1987; and

IV. Any other rigid thermoplastic product, a specimen of which (at the thickness of the product as put on the market), when tested to BS 2782:1970 as amended in 1974: Method 508A Rate of burning (Labratory method), performs so that the test flame extinguishes before the first mark and the duration of flaming or afterglow does not exceed five seconds following removal of the burner

TP(a) flexible:

Flexible products not more than 1mm thick which comply with the Type C requirements of BS 5867-2:1980 Specification for fabrics for curtains and drapes – Flammability requirements when tested to BS 5438:1989 Methods  of test for flammability of textile fabrics when subjected to a small igniting flame applied to the face or bottom edge of vertically oriented specimens, Test 2, with the flame applied to the surface of the specimens for 5, 15, 20 and 30 seconds respectively, but excluding the cleansing procedure; and


I. Rigid solid polycarbonate sheet products less than 3mm thick, or multiple-skin polycarbonate sheet products which do not qualify as TP(a) by test; or

II. Other products which, when a specimen of the material between 1.5 and 3mm thick is tested in accordance with BS 2782:1970, as amended in 1974: Method  508A, has a rate of burning which does not exceed 50mm/minute.

Non Fragility

Non Fragility ACR[M]001:2005 – ‘Test for Non-Fragility of Profiled Sheet Roof Assemblies’

The original standard arose out of concerns expressed by the Health, Safety and the Environment (HSE) and the roofing industry about the lack of guidance on what is a fragile roof assembly. Its basis is a series of tests, carried out by the HSE, which quantified human impact loads on surfaces.

The Red Book ‘ACR[M]001:2005 defines this test for non-fragility and such a test can be applied to any roof assembly. The test is designed to simulate the fall of a person. It is not a product test but products such as rooflights are tested as part of the roof assembly.

The test defines 3 Classes of Non-Fragility – A, B or C. The classification is dependent on the performance during testing. Most roof constructions (without rooflights) achieve a Class B or Class C, seldom is Class A achieved. As a common rule the rooflight classification should be equal to the classification of the surrounding roof i.e. a roof assembly with no rooflights achieves a Class B and therefore a roof assembly with rooflights should also achieve Class B.
The test in summary…

The roof assembly, in this case the rooflight, is to be tested to the worst case as prescribed by the relevant industry guidance.

The test involves the vertical fall, under gravity, of a 45kg cylindrical sand bag. The sand bag will be dropped from a minimum height of 1200mm measured from the highest surface point of the sample. The response of the sample to the impact will then be judged and recorded. Assuming the sample is intact a second drop will be performed and the result further recorded.

The performance of the sample after each of the drop tests will define the classification of the roof assembly.

Sound Ventilation


The Building Regulations 2010: Resistance to the Passage of Sound, Approved Document E
(2003 Edition incorporating 2004 & 2010 amendments)

Approved Document E, which took effect on 1st July 2003, deals with the requirements of Part E of Schedule 1 to the Building Regulations 2010.

The document requires that buildings are designed and constructed to; offer protection against sound from other parts of the building and adjoining buildings; offer protection against sound within a dwelling house, flats and rooms for residential purposes; offer resistance to sound and reverberation in common internal parts of buildings; consider acoustic conditions within schools.

Document E refers to the following key elements of a building when considering sound and reverberation within a property; internal and external walls, floors and stairs.

The sound insulation and acoustic properties of the building materials must then be calculated and factored into the design. Rooflights fall into this category and should perform in accordance with the requirements.

The Building Regulations 2010: Means of Ventilation, Approved Document F
(2010 Edition incorporating further 2010 amendments)

Simply put, ventilation is the removal of ‘stale’ indoor air from a building and its replacement with ‘fresh’ outside air.*
Ventilation is required for one or more of the following purposes:

  • Provision of outside air for breathing
  • Dilution and removal of airborne pollutants, including odours
  • Control of excess humidity (arising from water vapour in the indoor air)
  • Provision of air for fuel-burning appliances (which is covered under Part J of the Building Regulations)

Out with the scope of the Building Regulations, ventilation is also an important consideration in managing thermal control.

It is important at the design stage of a building that emphasis is placed on the ventilation and by what means that ventilation is achievable. There are minimum ventilation requirements within the Approved Document for new, existing, and refurbished buildings.

Rooflights can provide background ventilation, mechanical ventilation and even permanent ventilation.
Specification of a rooflight with means of ventilation will assist in complying with the requirements of Approved Document F.

* It is assumed within the Approved Document that the outside air is of reasonable quality

Health & Safety

Health & Safety Executive; ‘Working on a roof can be dangerous. Falls account for more deaths and serious injuries in construction than anything else and roofers account for 24% – the biggest category of worker by far – of those people who are killed in all falls from height.’

The Construction (Design & Management) Regulations 2007- CDM

CDM was brought in to help eradicate, or at worst reduce, the risk of accidents on site during construction, through to completion and for the life of the building even after use and in demolition. The Regulations are intended to focus attention on planning and management throughout construction projects, from design concept onwards. The aim is for health and safety considerations to be treated as an essential, but normal part of a project’s development – not an afterthought.

The client, the project’s designers, and the contractors, all have a specific duty, a duty of care, a responsibility, to ‘design out’ possible Health & Safety concerns at the earliest possible stage of the process.

Where there is a requirement for rooflights, consideration should be given to; non- fragility; protection surrounds; longevity; durability; and warranty. For information on any of the aforementioned please contact the JET COX Technical Department.


What is condensation?

All air contains a certain amount of invisible water vapour and warm air can ‘carry’ more water vapour. If warm air comes into contact with a cold surface, the air ‘gives up’ its water as droplets on the surface – warm moisture-laden air chills on contact with the cold surface.

There are many ways to reduce condensation.

Factors for consideration are:

  • Reducing moisture production
  • Ventilation
  • Heating
  • Insulation

Use of a Coxdome triple skin dome with an insulated upstand will increase the thermal insulation properties of your rooflight, subsequently increasing the temperature of the internal surface of the rooflight, and therefore removing cold surfaces for the vapour to condense on to.

The provision of ventilation should also be considered when specifying a rooflight. If there is not enough ventilation, moist air will not be able to escape.* JET COX rooflights are available with a number of ventilation options; from permanent ventilation to trickle ventilation, manual opening to electrically operated ventilation with remote control and temperature sensors.

For assistance in specifying your rooflight please contact our Sales or Technical Team.

Things to consider…

Polycarbonate is a hygroscopic material and therefore can attract and absorb moisture from the air. In areas of high humidity it is therefore possible for moisture to penetrate the skins of the polycarbonate domelight; on cooling, this moisture then will condense inside the cavity. This process will likely occur more often in colder periods where there are extremes of temperature internally and externally. The higher the humidity the faster condensation will be visible. Ideally, humidity levels in a house should be between 40%-60%. Where humidity levels exceed 60%, combined with low externally temperatures, there is a likelihood that condensation will occur.

Once humidity levels are restored, however, this condensation dissipates through the breathable seals.

Temperature and humidity levels are beyond the control of JET COX and therefore no guarantees can be given against the formation of condensation on the surface or between the skins of our rooflights.

*Too much ventilation (as draughts) can make condensation worse by making homes harder to heat. But if you seal off all the draughts, then the moist air cannot escape.