Unlike most window companies who outsource arch bending to third-party specialists, DTW manufactures every arched and curved profile in-house. Our dedicated bending facility houses over £50,000 of specialist machinery, giving us complete control over quality, tolerances, and lead times — with no dependency on external bending houses that can introduce delays, inconsistencies, or communication errors.
Every arch is precision-bent to AutoCAD specifications with a minimum bend radius of 350mm and maximum arc of 6000mm. Whether the project calls for a gentle segmental curve or a tight gothic point, our in-house capability means we can achieve profiles that outsourced bending simply cannot match. Bending tolerances are held to ±1mm across the entire arc length, ensuring glazing rebates remain true and weather seals compress evenly around the full perimeter.
Every arched and curved window project begins with a detailed site survey. Our surveyors capture the exact arch dimensions — rise, span, spring point height, and profile width — and produce AutoCAD drawings for client and planning authority approval. Manufacturing proceeds only once drawings are signed off. Finished windows are delivered to site with all hardware fitted, ready for installation by our own fixing teams or approved contractors. This end-to-end process eliminates the measurement errors that commonly occur when survey, manufacture, and installation are handled by different parties.
Arched head windows are the most commonly specified curved window type — a semi-circular, segmental, or elliptical arch crowning a rectangular window below. They are the defining feature of period properties, heritage renovations, and architecturally distinctive new builds across Surrey and London.
We manufacture arched head windows for listed buildings, conservation areas, churches, and residential properties where the arch profile must match existing fenestration exactly. Each window is produced from AutoCAD drawings based on precise site measurements, ensuring the new arched head matches the original profile in both radius and proportions. Where the original windows have been removed or damaged, we can work from architectural drawings, photographs, or neighbouring examples to reconstruct the correct profile.
Arched head windows are manufactured to the same performance standards as our standard rectangular windows. Thermal performance is governed by glazing specification and system choice: U-values from 1.3 W/m²K are achievable with triple glazing in the Cortizo C-70 system, with 1.4 W/m²K available in double-glazed configurations across all systems. Weather performance is tested to EN 12208 (watertightness) and EN 12210 (wind resistance), with Class 4 watertightness and Class C5 wind resistance available as standard. Security to PAS 24:2022 is available on all casement and tilt-and-turn configurations, and is typically required where the window forms part of the building envelope at ground or first floor level.
Arched head windows are frequently required by conservation officers as a condition of Listed Building Consent or conservation area approval. We produce detailed specification packs — including section drawings, U-value calculations, and RAL finish samples — to support planning applications. Our experience with Surrey and London conservation authorities means we understand what documentation planners require and can produce it promptly.
Gothic arched windows feature the distinctive pointed arch (lancet) that defines ecclesiastical and Gothic Revival architecture. The sharp apex requires tight-radius bending at the crown — a demanding manufacturing process that highlights the precision of our in-house bending capability. The two legs of the arch meet at the apex point with matched radii, creating the characteristic Gothic profile that has defined English religious and academic architecture for centuries.
We supply gothic arched windows for church restorations, ecclesiastical buildings, Gothic Revival properties, and contemporary homes seeking a dramatic architectural feature. The pointed arch profile is produced to exact AutoCAD specifications, with the apex angle and leg radii matched to your original drawings or site measurements. For church projects, we work closely with the Diocesan Advisory Committee (DAC) specification process and can provide drawings and sample sections to support faculty applications.
Gothic arched windows for listed ecclesiastical buildings and heritage properties are frequently subject to faculty jurisdiction or Listed Building Consent. We produce specification drawings compatible with DAC submission requirements and can advise on appropriate glazing specifications for heritage glazing replacements, including those that replicate the visual character of historic leaded lights using slim aluminium astragal bars. Thermally broken aluminium gothic windows achieve U-values from 1.4 W/m²K — a significant improvement over the single-glazed steel or timber windows they typically replace, without compromising the character of the opening.
Circular windows — also known as porthole, oculus, or round windows — are striking architectural features for gable ends, stairwells, bathrooms, and feature walls. We manufacture both full-circle and half-round (lunette) windows in fixed and opening configurations, using continuous profile bending through our in-house bending facility.
Full-circle windows require continuous profile bending through 360 degrees — one of the most technically demanding curved window types. Our in-house bending capability handles this in a single operation, ensuring a seamless profile with no visible joints or welding marks. The result is a clean, continuous curve that maintains structural integrity and weather performance around the full circumference.
Circular window diameters range from 400mm to 2000mm as standard, with larger diameters available on request. Glazing is toughened as standard (required by Building Regulations for low-level glazing in domestic premises under Approved Document N), with laminated or acoustic options available. Fixed circular windows achieve U-values from 1.0 W/m²K with triple glazing — excellent performance for a curved window type. Weather performance meets EN 12208 watertightness Class 4. All powder coat finishes are available, including dual-colour options with contrasting inner and outer face colours to suit period or contemporary interiors.
Curved-on-plan windows bend horizontally rather than vertically — creating bowed, bay, and wrap-around glazing that follows the curve of an extension, turret, or circular room. This is specialist work that requires bending of horizontal profiles to match the building radius, rather than the vertical bending used in arched head windows. The geometry is fundamentally different: the profile curves in plan, meaning every horizontal member must be individually bent to a consistent radius, and corner junctions must be precisely mitred to maintain weather performance.
We supply curved-on-plan windows for contemporary extensions, Victorian turret restorations, bow-fronted properties, and architect-designed curved facades. Each installation is manufactured to AutoCAD drawings capturing the exact plan curvature, with all corner intersections detailed to ensure structural continuity and watertight joints.
Curved-on-plan installations require a minimum plan radius of 600mm to maintain profile structural integrity through the horizontal bending process. Larger radii — shallow curves for bow-fronted properties — are more common and can be manufactured to match existing fenestration precisely. Glazing units for curved-on-plan windows are flat panes installed into the curved frame with angled glazing beads that accommodate the facet angle, or, for tighter radii, curved glazing units manufactured to match. Weather performance to EN 12208 Class 4 watertightness is maintained at all curved joints through continuous EPDM seals and compression gaskets. Thermal performance follows the system specification: U-values from 1.4 W/m²K with Smart Systems Alitherm 400, or from 1.3 W/m²K with Cortizo C-70.
Curved-on-plan windows require a more detailed survey than standard rectangular windows. Our surveyors take offset measurements to establish the true plan curvature, verify the structural opening dimensions at multiple heights, and produce a 2D CAD plan drawing for client approval before manufacturing commences. This drawing stage is critical — it allows the architect and client to confirm the window arrangement, sightlines, and glazing bay divisions before any material is committed to production.
We specify three premium aluminium systems for arched and curved window applications, each suited to different architectural requirements. System selection is driven by the project — architectural style, planning authority requirements, thermal targets, and budget all influence the choice.
Steel-look aesthetic with arch-bending capability — the system of choice for heritage properties, conservation areas, and projects requiring an authentic Crittall-style appearance with arched heads. Narrow 32mm sightlines and traditional astragal bar configurations replicate the appearance of original steel windows. The Alitherm Heritage system achieves U-values from 1.4 W/m²K with double glazing and meets PAS 24:2022 security standards. It is frequently specified by conservation officers as an acceptable alternative to original steel windows in conservation areas and listed buildings.
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Versatile casement system that accepts arched heads with clean, contemporary profiles. Dual-colour options, excellent thermal performance (U-values from 1.4 W/m²K with double glazing), and PAS 24:2022 security certification. Weather performance is tested to EN 12208 Class 4 watertightness and EN 12210 Class C5 wind resistance — appropriate for exposed locations across Surrey and London. The Alitherm 400 is the most popular choice for arched windows on modern, transitional, and contemporary properties where a clean, uncluttered profile is required.
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High-performance curved casement system with U-values from 1.3 W/m²K with double glazing, and from 0.9 W/m²K with triple glazing — making it the system of choice where maximum thermal performance is required in an arched or curved window. The Cortizo C-70 uses a 70mm frame depth with a polyamide thermal break, delivering excellent energy efficiency without compromising on profile aesthetics. Suitable for Passivhaus-influenced projects and schemes where Part L compliance demands the lowest possible U-values in curved window applications.
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Which system? We specify the optimal system based on your project requirements — architectural style, planning constraints, thermal targets, and budget. Contact us to discuss your arched window project.
Our arched window work covers four geometries — segmental (shallow), gothic (pointed apex), semi-circular (half-round), and full-round (oculus) — plus curved-on-plan, where the window curves around the building footprint, not just at the head. All bending is done in-house on our Fom Industrie equipment at our Slough workshop in Berkshire.
Our default specification for arched windows on premium projects. Cor 70 supports arched and curved heads with whole-window U-values from 1.4 W/m²K (double-glazed). Cor 80, the higher-thermal variant, reaches 0.9 W/m²K on triple-glazed configurations. Frame depth 70 mm or 80 mm. Polyamide thermal break. RAL or BS-colour powder coating in-house.
For heritage replacements and conservation-area projects where the arched window needs to read as steel without the cold-bridging. Alitherm Heritage accommodates segmental, gothic, and semi-circular arches with authentic 33 mm slim sightlines. Specified routinely for Edwardian, Georgian, and listed Victorian elevations where the arched window is integral to the historic character.
Technical Specifications
All arched and curved windows can be specified with a range of glass types to meet thermal, acoustic, solar control, privacy, and safety requirements. Our team will recommend the optimal glazing specification for your project during the survey and quotation stage.
Colours & Finishes
DTW aluminium arched and curved windows are available in any RAL colour to any BS/RAL specification, with powder coat applied under Qualicoat-certified conditions for consistent, durable results. Standard lead times apply to the most common specifications; bespoke or dual-colour finishes are available with extended lead times.
Heritage bronze and period-appropriate finishes are frequently specified for arched windows in conservation areas and listed buildings.
A physical colour sample service is available on request. DTW can also match existing powder coat colours using spectrophotometer analysis where replacement or extension work requires continuity with existing frames.
Our arched and curved windows are crafted from high-quality aluminium. This ensures exceptional durability, minimal maintenance, and sleek profiles. The aluminium can be finished in a variety of colours and styles, allowing for customisation to match any architectural design, from traditional to contemporary.
Yes, we offer bespoke solutions for all arched and curved window designs. Using advanced profile bending techniques, we can create windows that fit perfectly with your specified dimensions and styles, including gothic arches, perfect circles, and custom curved shapes.
Absolutely. Our windows are ideal for sympathetic restorations of period properties. We replicate the classic styles of Victorian and Edwardian arched sash windows, ensuring a harmonious blend with traditional architecture while providing modern energy efficiency and security.
Our windows are designed with energy efficiency in mind. The aluminium frames incorporate thermal breaks, and our glazing options offer superior insulation. This combination helps reduce heat loss and can contribute to lower energy bills, making our windows both eco-friendly and cost-effective.
The lead time for our arched and curved windows varies depending on the complexity of the design and current demand. Typically, we aim for a stable turnaround time of 6-8 weeks from order confirmation to delivery, ensuring high-quality craftsmanship and on-time completion.
Explore additional window options from Direct Trade Windows, designed to complement any style and meet diverse functional needs. From sleek modern designs to traditional favourites, discover a range of quality products tailored to elevate your property’s aesthetic and performance.
Arched steel-look doors for heritage and conservation projects.
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Bespoke arched aluminium entrance and bifold doors with in-house bending.
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High-performance aluminium casement windows with thermal breaks and PAS 24 security.
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