System 4-20 window


Aluminium casement window with polyamide thermal break, which can be glazed using internal or external beading. Outward opening casements can be side-hung or top-hung.


Profiles are extruded from aluminium alloy (6060 T6, T5 or T4 to BS EN 12020-2; 2001 / BS 755-9; 2001). Outer frame sections are a minimum of 50 mm deep and incorporate two 20 mm polyamide thermal break sections. Structural profiles are designed so that the maximum deflection of any member will not exceed 1/175 of its span, with no evidence of permanent deformation once the load has been removed.

Joints in outer frame and vent members are formed with 45° mitres, reinforced with extruded aluminium cleats and stainless steel corner braces. Corner joints are secured by pneumatic crimping. Mullions and transoms are secured using stainless steel screws driven into integral screw ports within the sections: additional cruciform cleats are used where required. Joints are sealed using a small gap sealant.

Windows incorporate an internal pressure equalized drainage system with external ‘snap-on’ cover caps.


With suitable glazing, windows can contribute to meeting the requirements of Building Regulations for conservation of heat and power. Consult Metal Technology for recommendations and details.

The windows provide Class IV weathertightness as defined by BS 6375-1 and BS 5368:

  • Air permeability: 600 Pa.
  • Watertightness: 600 Pa.
  • Wind resistance: 2400 Pa.


Lugs and/ or frame anchors used to secure windows to the building structure must accommodate predicted loads and deflection within design tolerances. Generally, fixings must be positioned 150 mm from each corner and each mullion/ transom, and at centres not exceeding 600 mm. Fixing lugs/ straps should be used only where they can be suitably concealed.

Secured by Design:

  • All glazed curtain walling screens, windows, and doors within the ground floor and vulnerable areas are secure by design.
  • All systems installed are tested in line with PAS 24 security standards and certified by a UKAS accredited certification body.

General information


As drawing ___

As schedule ___

Uniclass 2015

Pr_30_59_98_02 Aluminium window unitsPrimary


L10/25 Aluminium windows

L10/330 Aluminium windows

Specification data - Aluminium window units

Product Reference

System 4-20 Polyamide Casement


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As schedule ___

Glazing details

24 mm insulating glass units

26 mm insulating glass units

28 mm insulating glass units

30 mm insulating glass units

32 mm insulating glass units




Glazing method

Factory fitted

Site glazed

Ironmongery/ Accessories

Butt hinges

Friction hinges

Product Options


Maximum opening vent size with friction hinges:

– Top Hung:

  • Height: 1800 mm.
  • Width: 1500 mm.
  • Weight: 75 kg.

– Side Hung:

  • Height: 1600 mm.
  • Width: 835 mm.
  • Weight: 52 kg.

Maximum opening vent size with butt hinges:

– Top Hung:

  • Height: 1800 mm.
  • Width: 1800 mm.
  • Weight: 75 kg.

– Side Hung

  • Height: 1800 mm.
  • Width: 1000 mm.
  • Weight: 52kg.

Configuration and ironmongery may also limit sizes, consult Metal Technology’s technical department for details.


Aluminium sections are polyester powder coated to BS 6496 with the option of different interior and exterior colours; consult Metal Technology for availability of colours and to obtain samples.


Windows can accommodate a range of insulating glass units, and are dry glazed using ‘snap-in’ extruded aluminium beads with colour coded, co-extruded, PVC nitrile, captive ‘E’ gaskets externally and ‘wedge’ gaskets internally. Consult Metal Technology for recommendation and details.

Ironmongery/ Accessories:

Opening vents are hung on a pair of friction hinges or butt hinges, sized to the manufacturer's recommendations, and are fitted with standard push-to-release, lockable, cockspur handles (CA12). Opening vents are fitted with friction restrictors to limit opening depth to 100 mm.

Consult with Metal Technology for recommendations and details of additional ironmongery options.

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