Portscatho House

Chimney window design in Cornwall

Chimney window design in Cornwall is a defining element of the renovation and extension of Portscatho House, an Arts and Crafts coastal home near Portscatho. IQ Glass worked with Coal Architects and contractor KPK to deliver a glazing package comprising a three-metre-high marine-grade chimney window, bespoke arched windows, aluminium casement windows and doors, and ultra-slim sliding glass doors.

The new double-storey wing accommodates a master bedroom and bathroom, while a separate entrance link connects the new accommodation with the original house. Each glazed element was developed to reinforce the vertical forms and shaped openings of the existing architecture while improving daylight, garden access and views across the coastal setting.

Project Partners

Coal Architects

Location

Truro, UK
Arched windows to modern annexe with chimney window design
Portscatho House chimney window design glazed extension
Glazed extension to Cornish home with chimney window design
Cornish home extension with chimney window design

Chimney window design in Cornwall for an Arts and Crafts extension

The design challenge was to add a substantial new wing to an Arts and Crafts house without weakening the architectural character of the original building. The existing property is defined by tall chimneys and shaped openings, so the extension needed to reference those proportions rather than rely on a standard arrangement of rectangular windows.

The new two-storey volume has a footprint of 9.3m by 5.1m and contains the principal bedroom and bathroom. Its glazing had to introduce daylight across both levels while maintaining a clear relationship with the vertical geometry of the existing house.

A three-metre-high window was therefore incorporated into a chimney-like form at the centre of the bathroom. Bespoke arched windows respond to the shaped architecture elsewhere, while the entrance link and rear sliding doors provide a more minimal glazed connection between the original house, new wing and gardens.

The exposed coastal site introduced additional requirements for wind resistance, marine durability and solar control, all of which had to be resolved without adding visually heavy framing to the new elevations.

Three-metre chimney window engineered for coastal wind loads

The chimney window is positioned on the central axis of the bathroom, introducing a tall shaft of daylight above the bath while referencing the scale and proportions of the original chimneys. At three metres high, the window becomes part of the architecture of the extension rather than a conventional opening inserted into the elevation.

Its glazing specification was developed for the exposed coastal location, with a design wind load of 1,250 Pa and marine-grade glazing selected to support long-term performance. This allowed the vertical aperture to remain visually clear while responding to the environmental demands of the site.

Bespoke arched glazing and three-panel sliding doors

The shaped windows were custom manufactured to follow the arched openings within the new wing, allowing the glazing to reinforce the architectural geometry rather than interrupt it with standard rectangular frames. Aluminium casement windows and doors were installed elsewhere to provide controlled ventilation and practical access.

The new entrance link measures approximately 2.4m by 2.3m and establishes the connection between the original house and the extension. At the rear of the link, three-metre-high ultra-slim sliding glass doors comprise one fixed pane and two sliding panels. The large glazed opening connects the reinterpreted Arts and Crafts architecture with the surrounding gardens while maintaining minimal frame lines across the elevation.

Chimney window design to contemporary extension
Sliding glass doors to modern extension
Frameless arched windows to Portscatho House with chimney window design
Chimney window

Performance considerations

The performance strategy for the chimney window design in Cornwall was shaped by coastal wind exposure, solar gain and the scale of the glazed openings. The three-metre chimney window was engineered for a design wind load of 1,250 Pa, with a marine-grade glazing specification selected for the exposed environment.

Solar control coatings were applied to glazing on the south-west-facing elevations to reduce excessive heat gain and glare while retaining daylight and outward views. The opening casement windows provide controlled natural ventilation, while the tall sliding doors allow the entrance link and adjoining spaces to be opened more extensively to the gardens.

The slim sliding system combines large glass panels with tested air, water and wind performance. Its reduced sightlines support the architectural requirement for minimal framing, while the fixed and moving panels retain clear garden views when the doors are closed.

Together, the chimney window, arched glazing, casement openings and sliding elevation provide a coordinated response to daylight, ventilation, coastal exposure and the distinctive geometry of the original house.

Technical details

  • Chimney window glazing: approximately 3m high; engineered for a design wind load of 1,250 Pa; marine-grade glazing specified for the exposed coastal location
  • Slim framed sliding doors: one fixed pane with two sliding panels; project height approximately 3m; 21mm sightline; glass thickness 26mm to 32mm; max tested sliding pane 8.5m², up to 4m high and 500kg; typical Uw greater than 1.1 W/m²K; Air Class 4 / Driving rain Class 7A / Wind Class C4/B5; PAS 24 security
  • Bespoke window package: custom arched windows with aluminium casement windows and doors used throughout; solar control coatings applied to south-west-facing glazing
  • Project geometry: double-storey extension footprint approximately 9.3m × 5.1m; entrance link footprint approximately 2.4m × 2.3m

Portscatho House demonstrates how chimney window design in Cornwall can reinterpret the vertical forms of an Arts and Crafts building while meeting the wind, solar and durability requirements of an exposed coastal site. This approach is well suited to architects and specifiers working on heritage-led extensions where shaped glazing, tall structural openings and minimal sliding systems must respond directly to the original architecture.

To discuss a comparable coastal extension, contact IQ Glass for technical advice on chimney window glazing, bespoke arched windows, slim sliding door configurations and marine-grade specification.

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