Green Building Store is now 21°



GBS78 is an ideal choice for low-energy projects, whether simply replacing your windows or specifying for a new home. GBS78 is a cost-effective replacement for retrofits and low-energy newbuild projects. With a choice of designs and styles, this range will enhance your project at a competitive price.

Suited to

Low energy projects

U value

from 0.83 W/m2K

FSC® certified timber

Choice of design and styles

10 year warranty

Opening functions

Choose from two opening functions for your GBS78 window.

Outward opening

A flush casement window hung from the top or side.

U value

0.83 W/m2K

Light transmission value:


Triple unit

Argon fill 44mm


Triple glazed as standard


Outward opening typical maximum sizes: Fixed light: 2500x2500mm, Side hung: 950x1520mm, Top hung: 1300x1650mm.

For sizes beyond this, please speak to a member of our team.

Inward opening

Tilt and turn window options.

U value

0.80 W/m2K

Light transmission value:


Triple unit

Argon fill 44mm


Triple glazed as standard


Inward opening typical maximum sizes: Tilt & turn: 1300 x 2300 mm, Tilt only: 2000 x 950 mm or 1300 x 2300 mm.

For sizes beyond this, please speak to a member of our team

Make your windows unique to you

Frame styles

Customise your new windows with your preferred frame style.


Your windows can be finished in a choice of RAL colours of timber stains.


Customise your new windows with your preferred hardware.

Your windows and doors can be finished in a choice of RAL colours or timber stains.

The colours you choose for your window frames and doors can make a big difference to the impact of your project. All products also have the option of dual colour where one colour is chosen for the outside and one for the inside.

Trickle vents

We promote MVHR when it comes to ventilation, however, if you are unable to accommodate an MVHR system then we can fit conventional trickle vents to your windows. This does affect the thermal performance and airtightness of the window, so please speak to us about ventilation.


Extensions sills protect and maintain windows by directing water away from the window. We have a variety of aluminium extensions sills ranging in size from 25mm to 380mm. We also have profiles available in Acoya timber. All sills can be colour matched to the window.


We offer a range of optional safety features. These include child restrictors to limit the opening of windows. Egress hinges to maximise opening areas of side hung windows for escape. Safety glazing to protect from falling and impact, and lockable handles where required.

We offer a range of glazing options to give you the flexibility you need.

From obscure to transparent, we can offer plenty of choice for window and door glazing. Make your project unique with our various glazing options and glass finishes.


  • Approved Document Q of the Building Regulations for England became mandatory for all new dwellings on 1 October 2016. This means that windows and doors in new dwellings, where Part Q is applicable, will need to be security tested to PAS 24, or equivalent standard.

  • Please contact us for advice on the best range for your project. Or see our summary and overview of the ranges.

  • 21° windows & doors are all made from timber. Our ranges are made from FSC® certified Redwood or Oak. Modern timber finishes are now so durable that, for most applications, we recommend them over aluminium cladding or UPVC.

  • U-Values measure how well heat is transferred by the entire window/ door – the frame, sash and glass – either into or out of the building.  The lower the U-Value number, the better the window or door will keep heat inside a building on a cold day.

Download our GBS-78 technical information

Download our technical drawings and UKCA declarations regarding our GBS-78 windows & doors.

Download now


With FSC® certified timber and low U values, the aluminium clad windows enhance the style and design of your project externally whilst maintaining the warmth and beauty of timber from the inside.

Low U values

Argon-filled triple glazing as standard for comfort and great thermal performance


Dual compression seals ensuring long-term class 4 airtightness

High security

Multipoint locking tested to Secure by Design standard

Certified and quality tested

All of our products are thoroughly tested and quality assured.

FSC Certified Wood

Part Q Compliant

Secured by design

How can we help?

Visit the showrooms

Windows are a big investment, so come and visit our showrooms in Huddersfield and Swindon or catch us at exhibitions around the UK to see our products for yourself.

Request a quote

Tell us about your project, and we'll make sure you get a no-obligation quote from us. Take a step towards a more energy-efficient home today.

Get in touch

We offer a friendly and responsive aftersales service for our windows and door ranges, with a dedicated office and on-the-road aftercare team.

Life changing homes