Windows & doors FAQs

Please complete our online quote form

Yes, all our products meet class 4 for airtightness which is the highest class. Our products have been used in the most airtight home in the UK with an air test result of 0.041 @ 50pascals. View more on the Passivhaus Trust website.

Yes, we do! Our fitting service operates throughout the UK.

Yes, we have a showroom in Huddersfield and a permanent exhibition at National Self Build & Renovation Centre, Swindon. Find out more about visiting our showrooms.

We do exhibit at a number of events throughout the year covering a wide geographical area, making it easier for customers to see our high performance triple glazed timber windows first hand.

21 Degrees 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.

All our products are triple glazed as standard. We were one of the first companies in the UK to fully move away from double glazing.  

In addition to our triple glazed timber windows and doors, 21 Degrees offers a wide range of products and services,  including advanced MVHR heat recovery ventilation, specialist airtightness & insulation products, and consultancy.

We provide up to 10 years warranty on our range of timber window and doors. Speak to our team to find out more.

Green Building Store was set up in 1995, under the name Environmental Construction Products. We changed our name to 21 Degrees in 2024.

Please ring us on 01484 463336 for advice on the best range for your project. See our summary and overview of the ranges.

Yes, we quote colour matched extension cills as standard and can supply cills ranging from 25mm right up to 400mm. We have end caps to suit all different wall types and cladding materials.

Our ranges can be inward or outward opening.

Yes, all our entrance doors, double doors and lift and slide doors have a part M compliant wheelchair accessible threshold option. Should you need a stepped threshold we can also provide a solution for this.

Yes, all of doors meet PAS24 and our Entrance doors, Double doors and lift and slide doors are tested to Secure by design (SBD) which satisfies Approved document Q of the building regulations and PAS24. SBD uses live police data to ensure it is providing protection against the most modern break in techniques. This takes our products beyond standard security testing. 

We have some standard design ideas but our doors are bespoke so we can modify the designs to suit your project. Please discuss with one of the team.  

21 Degrees windows and doors are available in the RAL classic range and we also have a selection of natural wood stains to choose from. On the inside we can use Farrow and Ball colours. All our products can be dual colour.

Yes, we have a range of handle choices in assorted designs and colours. If you have seen a different handle, send us a link and we can check its compatible with our windows.

Yes, please specify this when requesting a quote.

Both, all of our windows are available in inward or outward opening.

Do you have bespoke sizes? Yes, all our windows are bespoke sized to suit your project. We can do all shapes and sizes within reason so please speak to us about your requirements.  

21 Degrees windows and doors can be made Part Q compliant, please specify this when requesting a quote and our estimators can use your elevations and floor plans to ensure we comply with Part Q.

21 Degrees windows have an option to be SBD compliant, please specify this when requesting a quote.

Yes, unlike most of our competitors we can increase frame profile sizes to help with installation detailing. We are often asked to increase frame thickness which allows for extra insulation to overlap to create better psi values. Please speak to one of our team.  

Yes, our windows are tested to Secure by design (SBD) which satisfies Approved document Q of the building regulations and PAS24. SBD uses live police data to ensure it is providing protection against the most modern break in techniques. This takes our products beyond standard security testing. 

Yes, our Lift & Slide Doors have Class 4 airtightness with optional SBD/ Part Q security.

Yes, we can include cat-flaps in fully glazed doors. Please note that the cat flap would be at least 300mm from floor level. Our doors all achieve the highest level of airtightness at Class 4, but adding a cat flap would obviously affect this. Cat flaps are not advised for Passivhaus builds unless you use a specialist Passivhaus-suitable cat-flap, which we can advise on.

You can download these on our technical pages.

• Windows technical information

• Doors technical information

• MVHR technical information

Or find out more with our technical resources

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.

Yes, we supply PHPP data on our windows and doors for those needing the information for Passivhaus projects. You can download our PHPP10 file on our technical page.

Quadruple glazing is not energy or cost optimal in the UK climate zone.  Although the thermal transmission is reduced, so is the solar gain.  So on balance, this gives worse performance for the building at a significantly increased cost.  Triple glazing is at the ‘sweet spot’ of optimal energy balance while satisfying our need for warm inner surfaces to meet Passivhaus comfort criteria. In colder climates, quadruple glazing is required for optimal energy balance and warm inner surfaces.

Yes, we have an in-house installation team who will work anywhere in the country. They have decades of experience and have worked on all property types from Passivhaus and low energy builds to deep retrofits and standard replacement projects. Find out more.

Yes, our team are FENSA registered and are audited every year.

Yes, we do.

Yes, we do.

Yes, our team have lots of experience with handling large units and we have access to specialist lifting equipment and plant hire.

Yes, wherever possible and always on new build and retrofit projects we will supply and install airtightness tapes. For replacement projects where internal finishes will remain, we will talk through the options with you.

Yes, we have a dedicated aftersales team with 2 full time office staff and a team on the road. The team have decades of experience along with useful documents, guides and videos available.

Yes, these are sent out with each order.

Yes, please contact the team.

Yes, please see our Installation & aftercare page for windows and here for doors.

Yes, we use 3 star Brisant ULTION cylinders and our hardware is all multi point locking.