Extensions with glass roofs: Brilliant ideas for a light-filled addition

kitchen extension with a glass room and view to courtyard
(Image credit: IQ Glass)

Extensions with glass roofs combine the benefit of addition space with an abundance of natural light and views of the sky and garden. 

As with every house extension, you should carefully consider what the new room(s) will be used for — a glass roof designed for a kitchen extension will be different to that designed for a new living room or home office where glare could be an issue, for instance.

Concerns about planning permission, overheating and overlooking should also be addressed before building so take a look below for some great ideas and solutions to extensions with glass roofs. 

Extensions with glass roofs: Where to begin

To begin designing and building an extension with a glass roof you'll need to prepare a clear brief to discuss with your architect. They should be able to navigate your needs and your wants to create something really special. These discussion should include: 

  • what the extension will be used for
  • how big the roof will be and how much glazing you are after
  • your budget for extension costs (structural glazing will cost more than a simple rooflight)
  • the time of day you will use the extension
  • the orientation of your property.

The potential for heat loss and overheating will also need to be considered early on. "As anyone with a conservatory tacked onto the back of their house will attest, simply incorporating a lot of glazing isn't necessarily a recipe for a comfortable interior," explains chartered surveyor Ian Rock, author of the Haynes Extension Manual.

"To make it more challenging, the Building Regulation impose limits on the permitted extent of new windows in extensions. And unless the subject of light is fully considered at the design stage it could have unintended consequences elsewhere in your home."

1. Think about where your extension will be

pink kitchen with glass roof extension and cork flooring

(Image credit: Malcolm Menzies)

Much like positioning a glass extension, where you position an extension with a glass roof will be extremely important. 

A south-facing extension with glazed roof will be drenched in sun for the majority of the day during the summer. However, while that might sound idyllic, depending on how much glazing you include, the space could be too hot during the height of summer. Unless, that is, you've designed in steps to prevent overheating at the design and build stage. 

On the other hand, facing north might not seem like the perfect sun-soaked area you're dreaming of, but this diffused natural light is actually some of the most beautiful and consistent — which is why is is most often used for artist studios and museums. 

Websites like SunCalc.com are extremely helpful in assessing how the sun travels over your home at different times of the year.

2. Plan a glass roof extension around your lifestyle

glass kitchen extension with bifold doors open to garden

(Image credit: Jeremy Phillips)

What you will use your house extension ideas for and, crucially, when, will hugely impact the design of the glass roof. 

If your family like to eat breakfast in the kitchen together before leaving for the day, easterly light will inject the space at the perfect time. Similarly, if you'd like to cosy down and eat dinner in your new extension in the soft evening light, west-facing is the one for you. 

The glass of an extension roof type can be designed to maximise light at a certain time of day, so it pays to give it some thought.

3. Don't forget about overheating

glass and brick extension with modern kitchen

(Image credit: IQ Glass)

Anyone who has spent time in an inefficient conservatory will know that overheating is a real concern for spaces with overhead glass. 

"Internal blinds can reduce the effect of the sun’s heat and different types of glass can also be used to block out the sun," advises energy efficiency expert David Hilton. "Photochromic and thermochromic glass will change colour according to either light intensity or heat intensity and stop certain frequencies of heat entering the internal space."

Structural glazing with steel supports were key to this single storey extension's design but it is the raised brick wall either side of the space that make it really interesting. This design means the sun's glare is reduced, as well as combating overlooking. 

4. Take care to navigate the 25% glazing rule

white house with grey glazed extension

(Image credit: David Barbour)

"Lovers of extended spaces bathed in glorious daylight can sometimes find their best endeavours hamstrung when they come up against the regulations," begins Ian Rock. 

"'Overlooking’ is an important factor that planning applications are judged by, although compromise is often possible. For example, fitting translucent film to glazing can be very effective at allowing light in while restricting visibility out. Windows positioned more than 1.7m above floor level tend to be less contentious, as do upward-facing skylights.

"The general rule is that the area of windows, roof windows and glazed doors must not exceed a maximum of 25% of the extension’s floor area, although this can be increased by an area equivalent to the loss of any original windows or doors that will be covered over by the new extension. 

"The reason for this restriction is simply down to thermal efficiency, since even quite advanced glazing leaks significantly more heat than the equivalent area of walls which need to achieve the stipulated minimum U value target."

If glazed roof ideas for an extension are a non-negotiable for you, you might be able to demonstrate that the efficiency of your extension will surpass that of building regs.

"This can be done by compensating with better insulated walls, roofs and floors along with higher performance glazing that leaks less heat," concludes Ian.

5. Partially glaze the roof an extension

pink and black kitchen with glass roof extension with view to garden

(Image credit: James French Photography)

If your rear extension ideas will be on the larger side, create zones by introducing glazing above set areas. This is particularly helpful for open plan kitchen, living and dining spaces which can suffer from feeling like one large expanse of space. 

The glazed roof of this side extension works particularly well alongside the brick of the kitchen, while the design of the glazing bars draw the eye out towards the garden. It acts as a transitional space between the interior and garden.

6. Play with glass roof pitches

side return extension with glass pitched roof

(Image credit: French + Tye c/o NOTO architects)

The advent of structural glazing has enabled some incredible new designs for roofs and entire glass extension structures. 

This is especially interesting when designing side return extensions where there might appear to be only one basic solution. A glass roof with an interesting pitch can infiltrate the interior spaces with light while creating a beautiful exterior design feature.

This extension project allows the clean lines of a flat roof extension to shine through, but the vaulted 'lean-to' style of the glazed roof echoes traditional terrace extensions. Inside, this interesting glazed roof brings in light and adds height and drama to the space.

glass link extension to cottage with different angles

(Image credit: Dave Burton)

When extending a listed house, planners and conservation officers might require a glass link extension between the original house and a new solid structure. This demarcates the old from the now so there is no confusion between the two. 

This idea has been adapted in this home to create a playful interpretation of the crooked walls of the cottage and converted stables next-door. 

Amy Reeves

Assistant Editor Amy began working for Homebuilding & Renovating in 2018. She has an interest in sustainable building methods and always has her eye on the latest design ideas. Amy has interviewed countless self builders, renovators and extenders about their experiences for Homebuilding & Renovating magazine. She is currently renovating a mid-century home, together with her partner, on a DIY basis, and has recently fitted her own kitchen.