VisionVent Control Panel & Rain Sensor

As energy costs rise, homeowners are increasingly recognising rooflights as an effective way to improve energy efficiency.

Whether you are working to tight deadlines, managing a low budget, or simply looking for a reliable, high-quality product that performs, off-the-shelf rooflights are an obvious solution.

Part O of the Building Regulations in England sets out requirements for overheating. It was a new part of the Building Regulations in 2021 and will be intrinsic to the overarching Future Homes Standard due to be introduced this year. Wales and Scotland have their own overheating requirements, albeit the overall aims across the different countries are similar. Limiting the potential for dwellings to overheat is particularly critical as the climate continues to warm. Overheating is not just a comfort issue; it is a health issue and must be addressed as the likelihood of summer heatwaves continues to increase. Rooflights have a role to play in overheating control, especially as the use of mechanical cooling is restricted. What are the requirements of Part O 2021? There is a single requirement to Part O, which states unwanted solar gains should be limited in summer and there should be an adequate means to remove heat from the dwelling. There are two ways to assess overheating risk in dwellings: a simplified approach and dynamic thermal modelling. The simplified approach is generally sufficient for individual homes. It sets maximum limits on glazing areas to prevent excessive solar gains. It also sets minimum limits on ventilation free areas, with the aim of ensuring excess heat is removed via ventilation. Dynamic thermal modelling is carried out in accordance with CIBSE TM59 and is more accurate than the simplified approach. It sets comfort criteria by accounting for various parameters that affect internal temperatures, such as weather data, thermal mass, orientation of the dwelling, occupancy and internal heat gains. Approved Document O makes clear that its purpose is to protect the health and welfare of people within the dwelling. It does not guarantee their comfort. How can rooflights help to achieve Part O compliance? Record-breaking heatwaves in recent years have focused attention on overheating, giving it the same kind of prominence as the effect of cold weather on people’s health. The need to consider our changing climate is leading some planning authorities to ask for overheating to be assessed not just on current weather data, but also weather projections for 2050 and 2080. Dwellings must be able to demonstrate passive cooling strategies that meet the comfort criteria for these predicted future conditions. That is likely to mean increased specification of solar control features on glazing, combined with external shading devices. However, it also expands the role that rooflights can play in helping to achieve comfortable dwellings for the future. Orientation of the building is obviously critical to the likelihood of overheating. East-facing elevations get the morning sun, while south- and west-facing elevations are exposed to the hottest times of day. North-facing elevations, meanwhile, receive no direct sunlight. There is likely to be greater scope for individual dwellings to be designed to maximise the benefits of different orientations, and minimise the drawbacks. That depends on having a relatively unrestricted plot, and little other surrounding development to dictate where and how the dwelling must be positioned. Apartments are often very restricted, sometimes having only a single aspect. Depending on the design of the building overall, larger and more luxurious apartments located at the top of the building might offer multiple aspects. However, the need to accommodate more than one apartment at that level puts limitations on maximising orientation, with each apartment requiring a unique solution based on its different aspects. For both individual dwellings and apartments, specifying rooflights as well as façade glazing increases the options available for controlling solar gains and reducing overheating risk, while still providing high levels of daylight. Since warm air rises, opening rooflights are the most effective way of losing excess heat in conjunction with opening windows to allow fresh replacement air into the building. Positioning rooflights on the opposite side of windows in a dwelling or apartment can help to achieve effective cross ventilation. As well as contributing to fresh air provision, cross ventilation is a passive cooling technique that has long been a feature in hot and humid climates. As we come to terms with living in a warming climate, cross ventilation will be an increasingly important tool for maintaining the health and wellbeing of building occupants. Using rooflights to go beyond the minimum standard of Part O Like all areas of building regulations, Part O only sets out a minimum standard. The option to go beyond the requirements is always available and can be easily justified in this case – we have already seen that Part O doesn’t seek to achieve comfort for the occupants of a dwelling. A frequent criticism of regulations is that requirements in one area don’t necessarily complement the requirements in another area. The typical example is how energy performance requirements have improved, without ventilation requirements improving to the same level. Changes to the regulations are only just beginning to overcome this disconnect, hence the introduction of Part O. Designers and specifiers of prestigious homes and high-end apartments don’t have to wait for the regulations to be completely holistic. They can deliver a joined-up approach now to benefit their clients and add value to their projects. The blank canvas of a new project offers the opportunity to go beyond minimum standards. Project teams now routinely look to the forthcoming Future Homes Standard, and factor in predicted future climate conditions, to benchmark performance now. Rooflights can provide homes with a level and quality of daylight that vertical windows alone struggle to achieve. Perhaps more importantly, they have a significant role to play in helping to mitigate overheating risk, at a time when the regulatory requirement for such mitigation is not fully mature.

Structural floor loadings for walk on glass rooflights should be stated as Uniform Distributed Load (UDL) and Concentrated Load. Although you should expect a manufacturer or supplier to confirm what loadings the glass is designed to withstand, you should not expect them to provide information on the loadings themselves; this remains the responsibility of the specifier. For example, if you are working on a scheme that involves a glazed floor section in a commercial shopping centre, you must provide the loadings that are relevant to this specific application in accordance with British Standards. The supplier will then ensure that the glass provided will meet those demands. In order to establish what these loadings might be you should refer to BS EN 1991-1-1:2002, Eurocode 1: Actions on structures which covers General actions, densities, self-weight, and imposed loads for buildings. Further information regarding UK specific loadings can be found in the UK National Annex to Eurocode 1 (NA to BS EN 1991-1-1-1:2002). The loadings for any glass rooflight designed for deliberate foot traffic will depend on building type and specific use, but typically you might expect to see load capacities of the following magnitude: Domestic applications Uniformly distributed load (UDL) from 1.5kN/m2 Concentrated load from 2.0kN Commercial applications Uniformly distributed load (UDL) 4.0kN/m2 Concentrated load 3.6kN Heavy duty commercial applications Uniformly distributed load (UDL) 5.0kN/m2 Concentrated load 4.5kN Glass specifications for walk on rooflights For walk on specification rooflights the outer pane of glass should always be both toughened and laminated. It should be specifically designed for the pane size and method of support. The outer pane will vary dependant on intended use and will usually comprise of two or more leaves laminated together; occasionally an additional sacrificial layer of annealed glass is used on the surface. The increased thickness of this type of glass results in a heavier product when compared with non-walk on rooflights and consideration should be given to the supporting roof structure and site logistics. Weights may typically range from 95 kg/m2 – 110 kg/m2. You might also be interested to read our post on the difference between non fragile and walk on glass and anti-slip walk on glass. To find our more about specifying rooflights book a CPD which would be delivered by a member of our expert technical team.

The benefits of specifying rooflights and roof windows are clear: they provide high levels of natural light, they can be wonderful sources of ventilation, and they contribute to the thermal comfort of a building. Roof windows and rooflights also provide an aesthetically pleasing addition to the external appearance of a property. But what else should you consider to ensure the specification runs smoothly once it gets to site? Roof windows and rooflights are generally easy to install, but knowing what to expect can help to ensure things go smoothly. We have exclusive insights from Clarkson Builders about how to ensure proper specification and keep work on-site progressing as expected. Here are the things they recommend specifiers should be aware of: Window size Roof windows and rooflights come in an array of shapes and sizes, and choosing the right dimensions for your project is critical. The ‘standard’ for roof windows is 900x600mm, and these are installed between rafters at 600mm centres. Other common sizes are 980x980mm and 900x1200mm – the latter is designed to fit in a double-rafter space. They can also be provided in much larger sizes – for example, the Glazing Vision Pitchglaze Roof Window stocked on rooflights.com can measure up to 3000x1000mm. Structural support The most effective way of supporting a roof window is to use double trimmers for horizontal support and double rafters for vertical support. Double hangers are placed in each corner, and single hangers are located around connected rafters. The double supports comprise two pieces of rafter timber with 600mm centres (either C16 or C24 between 100x50mm or 225x50mm, depending on specification and structural calculations). The rafters should be fixed together with bulldog timber connectors and M12 bolts. When fixing the timber, the head of the bolt should be recessed on the side of the wood to which the rooflight will be fixed. Otherwise, it could protrude into the area beneath the glazing. As with all structural requirements, relevant calculations should be carried out by a qualified structural engineer. Preparing the window aperture Remember that the size of the window aperture may not be the size of the window itself. The actual requirements will depend on the individual roof window, so be sure to consult your desired manufacturer early in the planning stages. When preparing the rafters, consider how elements like the insulation sarking and the ends of the battens will be supported. The roofing underlay should be folded back and fixed appropriately. Other elements will also need to be added to the roof, such as tilting fillets, battens and flashing. Out-of-plane rooflights will also require the construction of an upstand. Site delivery and storage Take time to consider how rooflights and roof windows will get to site – and once there, how will the units be stored to ensure they aren’t damaged. In addition, don’t underestimate the weight of a roof window. A small, 750x750mm laminated rooflight weighs just over 31kg, and the units can reach more than 150kg, depending on the size and type of glazing. Heavier units should also be assessed in terms of Health and Safety. Mechanical assistance should be utilised for moving the roof windows around the site safely. Getting the roof window or rooflight onto the roof In most cases, construction materials are delivered ‘to the kerb’, and this is the case for rooflights and roof windows. Unless you have a particularly obliging driver, you will need to work out how to get the unit onto the roof. As discussed in the previous section, roof windows can be very heavy and lifting them in a way that avoids damage or injury will require careful planning. It could also incur extra costs – you may need to hire lifting equipment for bulky units, or for hard-to-access locations. Instructions and tools Many roof windows come with an installation guide that actually covers multiple products – and those products can look very similar while having slightly different fixings and flashings. If these instructions aren’t followed correctly, it could impact the installation process and how the roof window or rooflight performs. Be sure to check the instructions to ensure that the installation team has the right tools. Depending on the manufacturer, special drill bits may be required. For example, Velux windows use a screw that uses a T20 drill bit that’s commonly used for day-to-day work on building sites. Tiling around roof windows Roof windows are usually found on pitched roofs (unlike roof lights, typically found on flat roofs). When tiling around roof windows, it’s important to ensure that the bottom tile is not too close to the window, as the flashing cannot be installed correctly. The best way to plan the tile gauge is to measure from the bottom of the roof, as this allows for the best finish and helps to ensure the roof window performance isn’t compromised. When using pantiles (these are usually made from concrete but may also be clay in heritage projects), be sure to chamfer the top of the bold roll beneath the window. This should all be explained in the instruction manual, which should outline the distances to install your battens to the sides, top and bottom of the window. With so much to think about, it’s easy to see why it’s so important to look beyond appearance and performance of a building element at the specification stage. If you have any questions or concerns about a product you’re specifying, it’s a good idea to get answers and advice as soon as possible from the manufacturer.

Part L of the Building Regulations in England sets out requirements for the conservation of fuel and power, or energy efficiency as it might be more commonly termed. The current version is Part L 2021, which is expected to be replaced by a new version later this year as part of the overarching Future Homes Standard. Wales and Scotland have their own energy efficiency requirements. High standards of building fabric performance, supported by low U-values and a good standard of airtightness, are essential for meeting current or future regulations in all parts of the UK. Rooflights are part of the building fabric, and so must play their part in delivering energy efficiency as part of overall building performance. What are the requirements of Part L 2021? As Approved Document L volume 1 says, “A new dwelling must be built to a minimum standard of energy performance.” To assess that performance, the dwelling’s specification is compared to that of a theoretical dwelling, called the notional dwelling. The calculation method for making the assessment is the Standard Assessment Procedure, or SAP. The actual dwelling must meet or exceed the targets set by the notional dwelling in the following areas. Primary energy rate Carbon dioxide emission rate Fabric energy efficiency rate The first two are influenced by both the building fabric and the fuel used within the dwelling. The fabric energy efficiency rate is defined entirely by the building fabric. As we are talking about rooflights, which are part of the building fabric, we won’t be discussing heating systems, different fuel types and building services in this blog post. How can rooflights help to achieve Part L compliance? What does meeting the requirements of Part L look like in practice? Generally speaking, dwellings need to aim for well-insulated and reasonably airtight building fabric. Doing so reduces thermal transmittance and keeps the leakage of warm air to a minimum. Glazing of any type must play its role within the building fabric performance, while acknowledging that it doesn’t perform as well as the surrounding construction in terms of U-values. Ideally, the U-value of windows and rooflights should be as low as possible. This is particularly important to minimise thermal bridging, where the rooflight sits within the roof build-up. Failing to address thermal bridging risks undoing all the intended performance goals for the dwelling. Rooflights must be installed within the surrounding roof, without creating a break in the thermal envelope and causing significant thermal bridging. For the first time, Part L 2021 introduced a requirement for photographic evidence to demonstrate that details were being installed in accordance with the intended design. This effort to reduce the difference between what is designed and what is built on site – known as the performance gap – is vital to ensuring that dwellings do not consume more energy and emit more carbon than anticipated. Using rooflights to go beyond the minimum standard of Part L We’ve already acknowledged that Part L only sets out a minimum standard. The option to go beyond the requirements is always available and can be considered preferable. A frequent criticism of national building regulations, especially in recent years, is that the requirements in one area don’t complement the requirements in another area. The most common example of this issue is how levels of insulation and airtightness have increased, without a corresponding improvement in rates to maintain indoor air quality and reduce. Changes to the regulations are only just beginning to overcome this disconnect. Designers and specifiers of prestigious homes and high-end apartments have it within their power to think holistically and deliver a joined-up approach that benefits their clients and adds value to their projects. The blank canvas of a new project offers the opportunity to deliver more than the minimum standards required by building regulations. Project teams now routinely look to the promised and predicted climatic conditions decades down the line, to benchmark performance now. Rooflights have always played an important role in homes. They can provide a level and quality of daylight that façade glazing alone struggles to replicate. And better levels of natural light are good for the health and wellbeing of building occupants and can reduce reliance on artificial lighting – thereby saving energy.