Glass Extension Guide
Are you looking to create a striking contemporary addition to bring more natural light into your home? Or would you like to improve an inefficient layout and add interest to your home? If so, incorporating a glazed extension could help you to transform your existing home into a highly attractive and light-filled contemporary space.
In this article we seek to provide a guide for Clients considering a glass extension and answer common questions homeowners and aspiring self builders have when considering adding a glass extension to their home.
What are the benefits of adding a glass extension to my home in Scotland?
Adding a glass extension to your home can create an attractive, unique feature that offers many benefits, which can include:
Increased natural light: This is a common and key aspiration for those looking to add an extension to their home. Glazed extensions allow more natural light to enter your home, creating brighter, more inviting and comfortable spaces. The physical and mental wellbeing benefits of exposure to natural light are well documented!
Enhanced connection to the garden: This also a common aspiration for those considering an extension to their home. Extensions which feature abundant glazing inherently create an enhanced visual connection to the garden and beyond, whilst glass sliding doors can also provide an improved physical connection with the outside. For example, when large format glass sliders are in their open position, they can allow the garden to become an extension of the internal space, blurring the boundary between inside and outside.
Bespoke addition to your home: Your architect will design your glass extension to suit your specific needs and also to suit the unique constraints and opportunities offered by your home, meaning that the end product will be a bespoke and attractive addition to your home.
Increased and more efficient living space: Many people make the decision to build an extension due to the need for additional space, or the need to improve an inefficient layout. A glass extension, along with any associated internal alterations, can provide a vastly improved internal layout with increased living accommodation.
Improved levels of natural ventilation: Adequate natural ventilation within your home is important as it will ensure good air quality within the building. An extension which features abundant glazing offers the opportunity to increase the potential for natural ventilation. Natural ventilation can be achieved through opening windows, as well as sliding or conventional pass doors.
Improved thermal performance: A glass extension which is designed by an architect will be designed to comply with the Scottish Domestic Building Regulations, meaning that it will be well insulated and provide your home with a thermally comfortable space.
How much glass can you have in an extension in Scotland?
The amount of glazing that can be achieved in a glass extension depends on the specifics of each project, and is influenced by a number of factors. The Scottish Domestic Building Regulations state that in order to mitigate heat loss, the glazed area (including rooflights) for any extension should be limited to 25% of the floor area, plus the area of any ‘built over’ openings.
There is however an approach that can be adopted whereby the amount of glazing can be increased beyond 25% of the floor area, provided that the thermal performance of other building elements - floor, walls and roof - are increased to compensate for the larger area of glazing. Taylor / Wilson have regularly been able to achieve equivalents of 100% and more glazed areas to extension projects utilising this method and still ensuring the building performs equivalently to the notional building used to calculate the regulatory 25% allowance.
What is the difference between a conservatory and a glass extension?
Conservatories and glazed extensions are similar in that they both involve adding a primarily glazed structure to an existing building. There are however a number of key differences between the two:
Conservatories: Fundamentally, conservatories are standalone and unheated spaces which are separate from the insulated envelope of your home, usually by a set of external grade doors at the connection between house and conservatory. This is because conservatories do not perform thermally to the standards required to be treated as a heated space or part of the insulated envelope of your home. This is not to say that some people haven’t added electric or even plumbed radiators into their conservatory once building control have departed!
When treated as unheated spaces, conservatories are therefore not subject to the same building regulations as extensions in terms of their thermal performance. Although modern conservatories may be built with insulated materials, typically, the large amount of low thermal performance glazing relative to the amount of wall and floor means that they are prone to overheating in the summer and being cold in the winter. Conservatories are conventionally formed of low level masonry walls with wall glazing above and a glazed roof, and are typically added to the side or back of a dwelling with no real connection to the existing internal spaces.
Glass extensions on the other hand are extensions to the existing insulated envelope of your home and are heated spaces like all other rooms in the building. Although a glass extension may be visually expressed as a standalone architectural element, contrasting old and new, they are designed to be physically connected to the interior space of your home. Glazed extensions are therefore subject to all relevant Scottish Domestic Building Regulations, and as discussed above, must comply with heat-loss regulations to ensure that a comfortable thermal environment is achieved throughout the year. Glass extensions can take many forms, but will be designed by your architect to respond to the specific constraints and opportunities offered by your existing home. An array of options are available for cladding and roofing materials, as well as a range of ways to incorporate large amounts of glazing, such as fixed or opening windows, sliding doors, frameless structural glass and rooflights.
Do I need a set of external grade doors between my glazed addition and the rest of my house?
Since a glass extension which complies with the Scottish Domestic Building Regulations will form part of the insulated envelope of your home, there is no technical requirement for external grade or insulated doors between the extension and the rest of the house. This is a major difference between conservatories and well designed glass extensions. External grade doors between house and extension create a very definite difference and character and prevent the conservatory from integrating well with your home. The reasons for inclusion of external grade doors are the same as the reasons most people who have owned a conservatory complain that it is too hot in summer, too cold in winter and may suffer from condensation. It is a reality that a substantial number of projects of this nature we become involved with propose removal of an existing life expired conservatory.
A well designed glass extension will allow your new space to link into the existing home as part of the open plan (or broken plan) arrangement to suit the requirements of the particular Clients brief, allowing vastly improved usability and quality of the end product when measured against a conservatory.
Why do some conservatories have external grade doors between the house and conservatory?
In contrast to a glazed extension, conservatories are often separated from the rest of the house with external grade / insulated doors. This is because the conservatory itself is an unheated space and the doors ensure that there is no ‘break’ in the insulated envelope of the walls of the house. Conservatories are not designed to allow compliance with the building regulations and are therefore required to be treated as unheated spaces to permit the expansive areas of glass proposed. This similarly allows conservatories to be manufactured from cheaper and lower performing products.
Can my the space be heated from my central heating system?
New living spaces provided by a glazed extension are typically heated via the existing central heating system, since they are designed to form part of the insulated envelope of the building. The size of the new space will however have to be considered; it is possible that an extension with a large floor area may exceed the capacity of an existing boiler and require a new larger boiler to be installed to power the heating system.
Can I have underfloor heating?
Yes, it is possible to have underfloor heating in your glass extension. It does however depend on a number of factors including the design of the floor and the existing heating system. It is also worth considering whether or not underfloor heating will offer value for money, particularly in extensions with smaller floor areas. Greater value for money is typically achieved with underfloor heating over larger floor areas due to greater installation costs when compared to conventional radiators, requirement for an additional manifold and a boiler capable of outputting high and low temperature hot water. In short is is possible to heat a glass extension in any manner you wish and as part of the central heating system.
Glass extension interior, Linlithgow
Interior of highly glazed home extension, Livingston, West Lothian
Do glass extensions require foundations?
Yes, all permanent buildings or structures - including glass extensions - will require adequate foundations to transmit the load of the building elements to the ground safely. Foundations can take many forms, are typically constructed of reinforced concrete and will be designed by your appointed Structural Engineer following an appraisal of the design proposals and inspection of the existing ground conditions.
Do glass extensions require planning permission?
Most extensions to homes will require planning permission, however some proposals may fall under Permitted Development Rights if they meet with the criteria as set out by the Scottish Government. The criteria sets out limits on floor area, distances to boundaries and maximum heights, etc. You can take a look at the Homeowner Permitted Development Rights here.
It is important to remember that even where Permitted Development Rights apply, it will still be necessary to develop a design that meets your requirements and submit architectural drawings which describe the proposals to your local authority in order to obtain a Certificate of Lawfulness, which is a legal document confirming the proposal’s compliance with the permitted development criteria.
If the design for your glass extension does not meet the criteria for permitted development rights, it will be necessary to submit an application for planning permission. Architectural design information which describes the nature of the proposals are then assessed by the Local Authority to ensure that there are no planning related issues, such as overlooking or overshadowing neighbours. If compliant, the Local Authority will issue Planning Permission. Home extension projects are typically assessed within 8 weeks by a local authority planning department. We have a success rate in excess of 95% obtaining permissions for domestic projects over a period now approaching 10 years.
I own a listed home, can I add a glass extension?
Yes, it is possible to add a glass extension to a listed home. Listed buildings are however protected by law and are considered to be of special architectural or historical interest, meaning that Listed Building Consent approval is required for any alterations and extensions as well as Planning Permission.
Proposed extensions to listed homes will be subject to a more stringent level of assessment by the Local Authority planning department due to the legally protected nature of the existing building. Design proposals will be required to convey a high level of sensitivity to and understanding of the architectural elements which contribute to the listing of the property, meaning that your architect will require the specific skills and knowledge to design a scheme which is appropriate for the sensitive setting. Taylor / Wilson carry RIAS Conservation Accreditation and are experienced and highly skilled in working with listed buildings.
I live in a Conservation Area, can I add a glass extension to my home?
Yes, it is possible to add a glass extension to a home which is located within a Conservation Area. Similarly to Listed Buildings, Conservation Areas are designated by Local Authorities in order to protect and preserve the character and appearance of an area of special architectural or historic interest. Planning Permission will be required for your glass extension, as Permitted Development Rights do not apply in Conservation Areas.
As with an extension to a Listed property, design proposals to homes within Conservation Areas will be required to demonstrate a thorough understanding of and sensitivity to the elements which contribute to the character and appearance of the Conservation Area. As mentioned above, Andrew is an RIAS Conservation Accreditated architects and therefore possess the necessary skills and knowledge to create design proposals which are appropriate for highly sensitive statutory contexts.
Will it be cold?
A glass extension which is competently designed to comply with the Scottish Domestic Building Regulations will be well insulated and provide a comfortable thermal environment throughout the year. Well designed glass extensions will not suffer from the same issues as conservatories. Whilst this is true if your objectives are to design a highly energy efficient extension it is a reality that glazing, no matter how high specification will always have a higher heatloss than insulated wall or roof.
How much does all of this cost?
The cost of a glass extension can vary greatly depending on a wide range of factors. The size of the extension, the design of the structure, the amount and specification of glazing, and the current market conditions are just a few of the factors that can all contribute to the cost of a glass extension.
Glass is always one of the defining elements of a building or extension, and typically one of the most expensive. The specification of the glass can have a significant impact on the construction cost. For example, large expanses of frameless structural glazing will be significantly more expensive than conventional UPVC framed windows; and 3-metre tall aluminium framed sliding glass doors with a high U-value (thermal performance) will be significantly more expensive than 2.1m tall timber framed windows with less requirement for thermal performance.
Simply put, the cost of a highly glazed extension will be greater than a more ubiquitous extension, but it will also be of greater appeal and may add more value, uniqueness and personality to your home.
Glass extension to a Linlithgow home.
What about a glazed roof?
It is possible to have a glazed roof in your extension, the decision depends on personal taste, what function the extension will be used for, and whether a fully glazed roof is appropriate for the setting. A fully glazed roof can be a very striking and attractive feature to add to your home, but there are a few things to consider:
Privacy: A fully glazed roof will limit the amount of privacy offered to the space, and it would be good to consider if this is potentially going to cause an issue. If your house is looked onto by neighbouring properties, it may not be the best solution for your extension.
Cost: Having a fully glazed roof will also significantly increase the overall amount of glazing, which in turn increases the level of thermal performance required from the glazing; both of which could have a sizeable impact on cost.
If you feel that a fully glazed roof isn’t quite what you would like for your glass extension, there is the option to feature rooflights into the design of the roof for your extension, whether that be a flat or pitched roof. There are many different types of rooflights available on the market, and these can be incorporated into the design to significantly increase the amount of natural light entering the new space, while maintaining privacy and being more cost effective.
How do I ensure privacy?
There are various ways in which privacy can be obtained in a glazed extension. The overall amount of glazing will have a big impact on the sense of privacy within the space. As discussed above, an extension which is fully glazed may provide a striking and contemporary addition to your home, but will likely not offer a high level of privacy! Here are a few different ways in which privacy can be provided through intelligent design solutions:
Covered outdoor space: Extensions can be designed to incorporate a canopy or covered terrace area which offers and intermediate zone where occupants can sit under cover, while also limiting the view in from neighbouring properties. These can also incorporate flanking or fin walls to assist in providing privacy
Blinds: The roof or ceiling of your glass extension can be designed by your architect to incorporate an integrated zone to house blinds that stay neatly out of view when in the open position. The blinds can then be raised or lowered to control the amount of privacy you require at any given time.
Opaque glazing: It is possible to include selected areas of opaque or frosted glazing to provide privacy in certain areas of the space. For example; where there is a requirement for natural light, but also where you do not wish for there to be a view into your home from the street or a neighbouring property.
Landscaping: Trees, plants, shrubs and bushes can be incorporated into the landscape design to create a natural barrier between your glazed extension and the surrounding context.
How do I keep my the space cool in summer time?
A glazed extension which is designed to comply with the Scottish Domestic Building Regulations, in particular those regulations relating to levels of insulation and heat-loss, will ensure a comfortable thermal environment in summer as well as in winter.
The purpose of insulation is to control the transfer of heat. Ensuring the correct amount of insulation in the building elements not only keeps heat in during winter months, but also reduces heat gain in the warmer summer months.
Ensuring adequate natural ventilation can also help to ensure your space feels comfortable during summer months, as well as incorporating external shading devices such as overhangs, brise-soleil or blinds into the design of the extension. Many glass extensions incorporate large sliding glazed doors which can be opened during warmer months to allow air to circulate freely.
What are the best ways to incorporate artificial lighting?
Artificial lighting can be incorporated into the design for your glazed extension in a number of ways, and your architect will be able to suggest some of the best ways to do this. The type of lighting most suitable will largely be determined by the design of the roof and ceiling, and it is of course down to personal taste! Here are a few different options to consider:
Pendant lights: Lights which are hung from the ceiling and can create a feature in the space. They are ubiquitous in homes across the country, but they may not be ideal in spaces with lower ceiling heights.
Recessed downlights: These are incorporated into the ceiling itself and provide a clean aesthetic. They are suitable in all types of spaces since they are essentially flush with the ceiling.
Wall lights: Lights which are mounted to the wall to provide accent lighting and can be placed to highlight specific areas of your space.
Task lights: Can be placed in specific areas of your extension to provide localised areas of muted lighting which will typically create a homely environment.
Concealed LED lighting: The ceiling can be designed to incorporate concealed areas of lighting which accommodate LED lights to provide subtle and ambient lighting to the space.
Smart lighting: There are a number of lighting brands which offer ‘smart lighting’ options, which allow the colour and level of LED lights to be controlled via an app on your mobile device. It is also possible to set timers or routines, such as for lights to be activated at dusk. Smart lighting can come in the form of bulbs, lighting strips, or lamps and pendant feature lights.
What are the innovations available in glazing systems?
The glazing marketplace is continually innovating to provide better insulated, more sustainable and more attractive products for the residential sector. Here are a few other specialist types of product which are available:
Smart glass: Also known as switchable glass, it utilises an electric current to change the glass from translucent to opaque, allowing the amount of light and privacy to be controlled at the flick of a switch.
Solar glass: This type of glazing incorporates solar cells into the glass to generate electricity in the same way that solar panels do. This is an emerging product and technology which is not yet widely adopted.
Self-cleaning glass: The glass is finished with a special coating that enables the breaking down of dirt when exposed to direct sunlight and subsequent rainfall, reducing the overall need for cleaning and maintenance.
