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GalleryBest Steel Windows Manufacturers: Complete Specification Guide
- 14 January 2026
- News
Steel windows remain among the most durable and aesthetically refined glazing systems available for both residential and commercial properties. With thermal technology advancing rapidly, contemporary steel manufacturers now deliver performance standards previously unattainable. This guide examines leading manufacturers, verified specifications, and performance metrics to help you make informed purchasing decisions.
Why Steel Windows Remain Industry Standard
Steel’s material properties—five times more thermally resistant than aluminium—combined with slim sightline capabilities (as low as 1.125 inches), make steel windows the preferred choice for heritage properties, contemporary architecture, and high-performance buildings. Unlike uPVC or standard aluminium frames, steel retains structural strength at minimal frame depths, enabling larger glass areas and unobstructed views.
The global steel windows market reached USD 2.75 billion in 2024 and is forecast to grow at 5.5% CAGR through 2031, driven by energy efficiency regulations, heritage restoration demand, and commercial architecture trends.
Best-in-Class Range: Crittall Corporate W20 TE® and T60
Corporate W20 TE® – Thermally Enhanced Steel Windows
For projects searching “best steel windows manufacturers” with a focus on energy efficiency, Corporate W20 TE® is a key reason Crittall belongs on the shortlist.
- Whole-window U-values from 1.4 W/m²K using patent-pending thermally enhanced technology, meeting current UK Building Regulations for replacement windows.
- Maintains the original W20 slim sightlines, so you get genuine steel aesthetics, not an imitation system.
- Manufactured from 100% recycled steel and hot-dip galvanised to BS EN 1461 for long-term corrosion protection.
- Co-extruded dual weather seals improve air and water tightness, supporting comfortable indoor environments in exposed locations.
These specifications deliver a blend of aesthetics and performance that many specifiers expect when searching for the best steel windows manufacturers for modern refurbishments and new builds.
T60 – Thermally Broken High-Performance System
T60 is Crittall’s thermally broken system designed for projects where ultra-low U-values and acoustic control are central selection criteria.
- Whole-window U-values as low as 0.8 W/m²K when paired with appropriate high-performance glazing, exceeding standard regulatory requirements and approaching passive-house level performance.
- Uses a high-density polyurethane thermal isolator between inner and outer steel sections to eliminate cold bridging while preserving a traditional steel profile.
- Accepts double and triple glazing up to around 37 mm, enabling advanced acoustic laminated units for sound reduction over 40 dB.
- Tested to EN standards for air permeability, water tightness, and wind resistance, and can be specified to meet security standard EN 16727 and PAS 24 when required.
These thermal and acoustic figures substantiate Crittall’s inclusion among the best steel windows manufacturers for high‑performance residential and commercial projects.
Comparative Performance Metrics
| Specification | Crittall W20 TE | Crittall T60 | Building Regulations (UK) |
|---|---|---|---|
| U-Value | 1.4 W/m²K | 0.8 W/m²K | 1.2 W/m²K minimum |
| Sightline | 1.125 inches | Varies | N/A |
| Material | Recycled steel | Steel | N/A |
| Thermal Break | Patent-pending enhancement | Full thermal break | N/A |
| Glass Thickness | Up to 28mm standard | Up to 32mm | N/A |
| FENSA Certifiable | Yes (UK installations) | Yes (UK installations) | UK standard |
| Lifespan | 60+ years | 60+ years | N/A |
Stunning exterior view showcasing luxury Crittall steel windows and doors on a light stone building, complemented by a manicured garden. Perfect for modern architecture.
Key Specification Criteria for Selection
1. Thermal Performance (U-Values)
UK Building Regulations require minimum U-value of 1.2 W/m²K. Passive House certification demands 0.80 W/m²K or lower. Steel windows with thermally-broken profiles (such as Crittall T60 at 0.8 W/m²K) now meet ultra-low-energy standards without compromising aesthetic appeal.
Modern manufacturing permits integration of thermal breaks within frame profiles, maintaining slim sightlines while achieving performance parity with high-specification aluminium systems.
2. Material & Corrosion Protection
Steel windows require protection against oxidation. BS EN 1461 hot-dip galvanising followed by powder-coat finish provides 60+ year durability in standard environmental conditions. Coastal or high-humidity locations may require additional specification (stainless steel or enhanced protective coatings).
Crittall manufactures 100% recycled steel frames, reducing embodied carbon while maintaining structural performance—a critical specification for LEED, BREEAM, or net-zero energy certifications.
3. Glazing & Acoustic Performance
Contemporary steel frames accommodate advanced glazing systems: triple-glazing, acoustic laminated glass (35-40dB noise reduction), and high-performance low-emissivity coatings.
4. Certifications & Compliance
- FENSA (UK): Required for Building Regulations compliance; available for UK-installed steel windows
- BS EN 1873 (British Standard for steel windows)
- PAS 24 (Security standard for windows/doors)
- Energy Saving Trust accreditation for high-efficiency profiles
Verify that product certifications match your project location and regulatory requirements.
FAQ: Steel Windows Manufacturers
Q: What’s the difference between thermally-broken and non-thermally-broken steel windows?
A: Traditional steel frames (like Crittall’s original W20) conduct heat directly through the metal profile, achieving U-values around 2.0-2.5 W/m²K. Thermally-broken systems (Crittall T60) interrupt heat conduction with insulating materials integrated into the frame profile, reducing U-values to 0.8-1.4 W/m²K—meeting modern energy regulations without compromising strength or aesthetics.
Q: How long do steel windows typically last?
A: Properly maintained steel windows exceed 60 years lifespan. Crittall specifies 60+ year durability. Hot-dip galvanising to BS EN 1461 provides corrosion protection across the frame’s service life. Maintenance requirements (cleaning, occasional repainting in exposed locations) preserve appearance and functionality.
Q: Can steel windows be used in listed buildings?
A: Yes. Original steel windows (particularly Crittall Heritage range) are often required in conservation areas and listed properties to maintain architectural authenticity. Modern thermally-enhanced variants (Crittall W20 TE, T60) replicate original proportions while meeting contemporary building regulations—suitable for planning approval in heritage contexts.
Q: What certifications should I verify before purchasing?
A: UK installations require FENSA certification and compliance with BS EN 1873 (British Standard for steel windows). For energy efficiency, target U-values of 1.2 W/m²K or lower to comply with Building Regulations. Commercial or security-critical applications should specify PAS 24 (security certification). Confirm certifications align with your project location and regulatory jurisdiction.
Q: Are steel windows more expensive than aluminium or uPVC?
A: Yes. Steel windows command premium pricing due to custom fabrication, material costs, and hand-finished craftsmanship. Crittall’s products typically cost 2-3x standard uPVC frames. However, superior longevity (60+ years vs. 20-30 years for uPVC), minimal maintenance, and unmatched aesthetics offset initial investment through lifecycle value.
Selecting Your Steel Windows Manufacturer
Choose Crittall if: You require British-manufactured heritage windows with proven performance, environmental credentials (100% recycled steel), or need FENSA certification for UK projects. Thermally-enhanced ranges (W20 TE, T60) deliver contemporary energy efficiency within traditional aesthetics.
Critical Success Factor: Verify thermal specifications (U-values), local certification requirements, and lead times before committing. Steel windows require 8-12 week fabrication timelines. Engage certified installers experienced with steel framing—poor installation compromises performance regardless of manufacturer quality.
Modern steel window technology now delivers thermal performance equivalent to high-grade aluminium systems while preserving the slim sightlines, strength, and aesthetic refinement that define the material. Specification clarity—particularly U-value requirements and local building codes—ensures you select the optimal manufacturer for your project.