Larger Glazing
Accepts double or triple glazed units up to 32mm thick, twice the capacity of the Corporate W20 section.
Crittall Corporate MW40 steel windows were developed as an expansion of the Corporate W20 range, designed to replicate the W20 profile while allowing significantly thicker glass to be specified. Where W20 accepts sealed units up to 16.4mm, MW40 accepts double or triple glazed units up to 32mm. That extra capacity is what the system exists for. It delivers greater sound attenuation on road facing elevations, higher thermal performance where the glazing has to carry it, and improved resistance to air, wind and water on exposed sites, all without widening the sightlines. Shaped frames including arched heads, rakes and curves are manufactured within the range. As a specialist supplier of steel windows since 1935, Lightfoot Windows manages every Corporate MW40 project from initial specification through to survey, manufacture and installation across London, the South East and the Channel Islands.
The features that set the Corporate MW40 range apart for performance driven projects.
Read the MW40 FAQsAccepts double or triple glazed units up to 32mm thick, twice the capacity of the Corporate W20 section.
Pressure equalised frames with high performance double weatherseals for exposed elevations.
Shaped frames are manufactured within the system, from fully welded seamless steel profiles.
Hot dip galvanised and Duralife powder coated in any RAL or BS colour, applied in house.
Corporate MW40 is Crittall’s high performance steel window and door system, developed to replicate the classic Corporate W20 profile while allowing significantly thicker glass to be specified. The result is a window that keeps the slim sightlines Crittall is known for, while offering a step up in thermal and acoustic performance suited to demanding residential and commercial projects alike.
Choose MW40 when the glazing has to do more work than the standard W20 section allows. That usually means an elevation facing a busy road where sound attenuation matters, a site exposed enough that air and water resistance governs, or a thermal target that needs a triple glazed unit to reach. For most period restorations and domestic replacements, Corporate W20 or W20 TE will be the more straightforward specification. We will tell you which of the two suits your openings before you commit to either.
By accepting double or triple glazed units up to 32mm thick, MW40 windows deliver a meaningful improvement in heat retention and sound attenuation over standard steel profiles. Each window is pressure equalised and fitted with high performance double weatherseals, offering superior resistance to air, wind and water. This makes the range a strong choice for busy or exposed locations, including projects near transport corridors, where reducing external noise while retaining an authentic steel aesthetic is a priority.
The Corporate MW40 range offers side, top and bottom hung openers, horizontal and vertical pivoting windows, folding openers and fixed lights, opening in or out. Shaped frames including arched heads, rakes and curves are manufactured within the system. Fixed lights run to a maximum of 3050mm by 3050mm with a perimeter of 9760mm, top hung openers to 1830mm by 1830mm, side hung openers to 1700mm by 1500mm and folding openers to 1525mm by 2440mm.
Every Corporate MW40 frame is fully welded and seamless, flat and square to manufacturing tolerances of plus or minus 1.5mm, with intermediate bars hot tenon riveted. All components are hot dip galvanised after manufacture to BS EN ISO 1461, then finished in Duralife polyester powder coating applied in house. Together these give a life expectancy of over 60 years and keep maintenance down to routine cleaning and periodic inspection. Crittall manufacture under ISO 9001 and ISO 14001.
As a specialist Crittall partner with decades of experience, Lightfoot Windows manages every stage of a Corporate MW40 window project, from initial design consultation and site survey through to manufacture and installation. Our team works closely with architects, designers and homeowners across London, the South East and the Channel Islands to ensure each window is specified correctly and finished to the highest standard.
Browse a selection of Corporate MW40 window installations, supplied and fitted by Lightfoot Windows across heritage and contemporary projects.
Popular Colours
Corporate MW40 frames are finished in Duralife polyester powder coating, applied in house in any RAL or BS colour, or matched to a bespoke reference. Black remains the most requested finish on period properties, with anthracite grey and off white common on new build elevations. The coating sits over a fully galvanised frame, so maintenance stays limited to routine cleaning.
Hardware
Corporate MW40 uses the standard Crittall hardware range, designed to suit both heritage restorations and contemporary elevations. Handles, stays and peg stays are available in a range of finishes, with multi point locking specified where security governs. Because the range is standard across the Crittall systems, replacement parts stay available for the life of the window rather than becoming obsolete.
Here are answers to the questions we are asked most often about the Corporate MW40 window range, to help you specify with confidence.
The appearance is the same. The difference is glass capacity. Corporate W20 accepts sealed units up to 16.4mm, MW40 accepts up to 32mm. That extra capacity is what delivers greater sound attenuation, higher thermal performance and improved resistance to air, wind and water.
MW40 windows accommodate double or triple glazed insulating units up to 32mm thick, giving noticeably higher thermal and sound insulation than the standard W20 profile while keeping the same authentic steel appearance.
The range includes fixed lights, side, top and bottom hung openers, horizontal and vertical pivoting windows and folding openers, opening in or out. Shaped frames including arched heads, rakes and curves are manufactured within the system.
Crittall confirm the system is Part L compliant but do not publish a single U-value figure for MW40, because the achieved value depends on the glazing specification rather than the frame alone. We confirm the figure for your specific unit build at order stage. If you need a published frame U-value on the drawings, the Corporate W20 TE system achieves 1.4 W/m2K.
They can be, but not automatically. Conservation officers usually assess sightlines and glazing bar arrangement rather than the system name, and MW40 holds the same slim sightlines as W20. Where consent requires single glazing or a specific historic profile, MW40 will not be the answer. We advise on this before you submit.
MW40 windows are hot dip galvanised and finished in Duralife polyester powder coating, available in the full range of RAL and BS colours, including the black steel finish associated with Crittall products.