Why choose an Alitherm Heritage Doors


Smarts Heritage Industrial style doors provide a modern, like-for-like replacement for traditional materials, Alitherm Heritage is the ideal solution for projects where planning or design demands dictate the installation of sympathetic materials. Our Crittal heritage profile has a unique slimline look which can be made in any RAL colour.


Heritage Door Replacements

Providing a modern, like-for-like replacement for steel windows. The Alitherm Heritage window range features the slim profiles and sight lines that are associated with traditional steel doors and windows such as critical windows and doors. However, the system’s timeless elegance is also accompanied by the outstanding thermal performance of a modern double glazed aluminium system – each delivering an ‘A’ Energy Rating. Featuring slim, thermally-broken profiles, Alitherm Heritage windows are available in a number of formats to suite any opening in your home or development.

Crittal Style doors internal partition
heritage French doors crittal style

Slimline Heritage Doors

Inspired by the aesthetics of traditional crittal steel windows and doors, Alitherm Heritage features signature slim sightlines and attractive contours making it the ideal choice for heritage building conservation areas where building regulations demand a like-for-like replacement.

Give us a call to discuss any options for your project we will happily assist you 0800 086 2209 

NOW Offering – Heritage Bi fold Doors to Match Alitherm 47 Heritage windows

Our Heritage Bi folding Door is now in full manufacture and is the perfect door to match the alitherm 47 heritage windows. It is thermally efficient and super robust. We believe this is the future for heritage doors. 

critical style bifolding doors

Why choose our SMARTs Heritage Bi folding?


Perfectly Matching the Alitherm 47 Heritage Windows

Our Heritage Bi fold doors is designed and manufactured to be the exact match to our Alitherm 47 heritage windows. The Shape of the sash matches the shape of the alitherm 47 heritage window sash. This means they are perfect match. These door are a lot more robust than the Heritage 47 Doors. Give us a call today to discuss your options.

critical bifolding door
heritage bifolding door slim

Super Slim Interlock Detail – 96mm Glass to Glass

As our bi-folds are manufactured in-house in our purpose built factory in Teesside, we can determine the turnaround time and provide you with a fast, convenient and efficient delivery. So at no extra cost for this premium service, our fleet of transport are ready to deliver your bi-folds anywhere across the UK.


Crittall Lookalike at a Fraction of the Cost

Our Heritage bi fold range of doors are the PERFECT alternative to steel crittall doors. If your want super secure doors along with high energy efficiency and thermal break technology to stop condensation you have found the right product. These doors also come at a fraction of the cost of steel doors.

slim aluminium heritage bifold

Premium Heritage Windows & Doors

Alitherm Heritage Crittall-style windows and doors. Perfect for internal & external.

Let The Light In

Create an elegant and stylish space with our Heritage windows and doors. With beautiful and sleek lines, our windows and doors are a gorgeous feature to add to any home.

Perfect as an interior door or as an interior separation, or externally to create extra light and personality. Our heritage doors are a great modern option, or to upgrade a like for like window where building regulations are in mind.

heritage critical effect French doors


Visoglide Plus Sliding Doors

heritage doors guarantee

Backed By Guarantee

We’ve got you covered. Our products come with a comprehensive 10-year insurance backed warranty to give you ultimate peace of mind.

heritage style windows and doors

With Security In Mind

We’ve got you secured. Ultion locks and multi point locking door straps are provided as standard, and all doors can be certified to PAS24 if required.

High Thermal Efficiency

We’ve got you saving. With excellent thermal efficiency (u-values between 1.4 and 1.8W/m²K) you can keep your home warm and stylish.

slim line aluminium critical windows

Super Slim Sightlines

We’ve got your view in mind. See more of your surroundings thanks to some of the slimmest aluminium sight lines available at just 33mm!

Uniquely Yours

Our Alitherm Heritage windows and doors don’t just come with slim sight lines, durable construction and a secure locking mechanism as standard, they’re also marine grade painted as standard!

We can also tailor our windows or doors to suit your individual needs, specifications and requirements. Choose from a range of configurations and colours, made to measure to make your vision a reality.

Talk to our friendly team today.

powder coated crittal windows


Heritage ‘Crittall-Style’ Windows & Doors

heritage window profile
heritage doors locking ultion
marine grade powder coating heritage windows
energy efficient crittal windows
ultra slim aluminium windows
double glazed crittal windows

Standard Colours

white critical windows and doors
grey critical windows and doors
black critical windows and doors


The range has been designed to combine efficiency, practicality and beauty so there is no need to compromise

Colour options

Stock Colours and all RAL Colours Combinations Available

critical style heritage doors colours
critical style brochure


Click here to request a copy of our free brochure, which is packed full of product information and design ideas.





At Roof Lanterns Online, we know what kind of difference installing quality aluminium windows and doors will make to your home. That’s why we’re always on hand with the products & experience you need.


Safety & Security

heritage French doors
crittal doors high security
Using police approved multi-point locking systems and the UK’s most secure cylinder, we really have your security covered.

Ultion locks feature:

  • Double snap resistance
  • Unique lock-down mode
  • 11 individual pins (twice as many as standard cylinders)
  • Nearly 300,000 key combinations
  • Anti-drill, pick, and bump


Frequently Asked Questions

What is the maximum width or height per sash?

Side hung windows: The maximum width is 700mm, the maximum height per sash is 1400mm.Top hung windows: The maximum width is 1400mm, the maximum height per sash is 1300mm.Doors: The maximum width per sash 900mm, the maximum height is 2100mm.

Can I choose the configuration of my Heritage doors?

Yes! We offer different variations of our heritage doors based on your preference and requirements.

Can I choose what colour my Heritage window or doors will be?

Yes! Our windows and doors come in a choice of variety of colours including standard and non-standard, metallic and Unique Sensations range of textured finishes. These are available as Single / Dual colour, marine quality polyester powder coated.



Application Domestic
Finish Single / Dual colour, marine quality polyester powder coated
Profile Square
Lock Mechanism Ultion (diamond accredited) Cylinder as std.- multi-point locking
Frame depth


Sightlines 59mm
U Value

1.5 w/m2k using a 1.0w/m2k glass unit

Max sash width 900mm
Max sash height 2100mm
British Standards

KM 81580 / PAS 24:2012 / KM81543 / BS4873

Glazing DG 28mm / TG 32mm
Add ons 20mm, 42mm
Bead Internal Only
Cills 85mm, 150mm, 190mm, 225mm, 300mm
Astragal Bar 20mm / 41mm flat bar

British Manufacturer & Supplier

Over 25 years’ experience supplying Aluminium Windows and Doors..

1000’s of door designs

One of the widest selections of doors, colours, finishes and hardware in the UK.

Free UK Delivery

Impressive lead times & fast delivery service throughout the United Kingdom.

Impressive Security Accreditations

PAS24:2016, BM Trada Q-Mark, Secured By Design (SBD), Document Q & Document M.

Raising The Standard