Green Building Store is now 21°


Lacuna bi-fold door

Triple glazed timber bi-fold/ foldaside door that meets Part Q security requirements. Suitable for newbuild and retrofit projects.

Suited to

Low and ultra-low energy projects

U value

from 0.9 W/m2k


Tripled glazed as standard

Made in

Denmark by Lacuna

Please note: For Part Q and Secured By Design items, there may be size restrictions. Please get in touch to discuss.

Make your doors unique to you


Customise your new doors with your preferred colours

Frame styles

There's a range of frame options for your doors. Please speak with a member of our team for other options.

Glazing options

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

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

The colours you choose for your 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.

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.

  • Either a window or doorway, any part of which is within 2m vertically of an accessible level surface such as the ground or basement level, or an access balcony, or a window within 2m vertically of a flat or sloping roof (with a pitch of less than 30°) that is within 3.5m of ground level.

  • 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 Lacuna bi-fold doors technical information

Download our technical drawings and UKCA declarations regarding Lacuna bi-fold doors.

Download now

Lacuna bi-fold doors

Take a look at our Lacuna Bi-fold doors for low energy & Passivhaus projects. With low U values and aluminium-clad doors available too, these doors can really enhance the style and design of your project with standard and contemporary designs.

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