Inter-War Property Restoration Guide: 1919–1939 Houses in North London

Introduction

The inter-war period — from the end of the First World War in 1918 to the outbreak of the Second in 1939 — saw the largest wave of domestic construction in Britain's history. Suburban north London was transformed during these two decades as the Underground extensions opened new territories to commuter housing, and millions of semi-detached and detached houses were built to accommodate London's rapidly expanding population.

Inter-war houses have their own distinct architectural character, construction system and set of planning considerations. This guide covers the key aspects of restoring, extending and improving properties from this period.

Recognising Inter-War Architecture

The archetypal inter-war house in north London is the 1930s semi-detached — but the period encompasses a range of styles and scales:

• The suburban semi: Two storeys, hipped or gabled roof, bay window to the ground floor, cavity brick construction, integral or detached garage. Commonly in Neo-Georgian, Tudorbethan or Moderne styles.
• Tudorbethan: Mock-Tudor influences — half-timbering (usually applied rather than structural), leaded-light casement windows, steep gables, clay tile hanging and prominent chimney stacks.
• Neo-Georgian: Formal, symmetrical facades with sash windows, brick or render, dentil cornices and classical door surrounds.
• Art Deco and Moderne: Flat or low-pitched roofs, metal Crittall windows, smooth render finishes, curved bays and angular geometric detailing — less common in domestic architecture but found in some north London suburbs.
• Garden suburb housing: The planned garden suburb tradition continued from the Edwardian period — Hampstead Garden Suburb (Barnet) is the outstanding north London example, with Arts and Crafts influenced houses designed by Parker, Unwin, Lutyens and others.

Construction Characteristics of Inter-War Houses

Inter-war houses have a fundamentally different construction system from pre-1919 buildings:

• Cavity brick walls: From around 1920 onward, the cavity wall replaced the solid wall as standard domestic construction. The cavity was originally left unfilled (providing a degree of insulation and preventing damp transfer). Modern thermal improvement often involves filling the cavity with insulation.
• Concrete ground floors: More widespread from the 1930s, replacing the suspended timber ground floor of Victorian construction.
• Timber upper floors: Suspended timber joists continue to be used for upper floors throughout the inter-war period.
• Roof structure: Cut timber roofs with rafters, purlins and ridge board, typically covered with concrete or clay plain tiles or interlocking tiles.
• Crittall windows: Steel-framed casement windows are characteristic of many inter-war houses, particularly those in the Moderne or Art Deco tradition. These are now considered significant heritage features and replacing them with modern double-glazed units requires careful consideration.

Planning Considerations for Inter-War Properties

Conservation Areas and Designated Estates

Some collections of inter-war housing have conservation area designation or are covered by specific planning policies protecting their character. Hampstead Garden Suburb is the most significant north London example — a conservation area covering one of England's finest planned suburbs, where all works are subject to the strict control of the Hampstead Garden Suburb Trust alongside Barnet Council.

In Hampstead Garden Suburb, Article 4 Directions remove virtually all permitted development rights and works must conform to Barnet's conservation area policies and the Trust's design guidance.

Standard Permitted Development Areas

In areas without conservation area designation or Article 4 Directions, inter-war houses generally benefit from full permitted development rights, allowing single-storey rear extensions and loft conversions without planning permission in many cases.

Restoration of Inter-War Features

Crittall Windows

Original steel Crittall windows from the inter-war period can be refurbished, re-glazed with modern double-glazed units (where the frame size allows) or replaced with new steel-framed equivalents. Modern Crittall manufacture has continued, making faithful replacement possible. Aluminium copies are generally considered inferior and may be refused in conservation areas.

Clay Tile Hanging and External Render

Tile-hung gables and smooth render finishes are characteristic of many inter-war houses. Replacing cement render with lime-based render is generally recommended for older inter-war properties, as cement render can trap moisture.

Original Fireplaces and Joinery

Inter-war houses often retain distinctive fireplace surrounds — typically in a simplified classical, Tudor or Art Deco style. Original joinery including staircase balusters, skirtings and picture rails should be retained and repaired wherever possible.

Extending Inter-War Houses

Inter-war houses are among the most extension-friendly building types:

• Cavity brick construction can be tied into easily with new extension walls
• Generous rear gardens allow rear extensions without compromising amenity
• Hipped roofs convert well to gable-ended dormers via hip-to-gable conversions
• Side passages (common on semis) can be incorporated into side extensions

In conservation areas, extensions must respond to the character of the original building in materials, scale and form.

Thermal Improvement

Inter-war cavity walls can be improved thermally by injecting cavity fill insulation. However, this should be done carefully — poorly applied cavity fill can bridge the cavity and allow water to cross to the inner leaf, causing damp problems. A building surveyor should assess the condition of the cavity before any fill is applied. Part L of the Building Regulations requires new extensions to meet minimum thermal performance standards regardless of the existing house's performance.

Conclusion

Inter-war houses represent excellent value for north London homeowners seeking generous space with good extension potential. Their construction is well understood, their materials are generally available, and the planning environment is broadly accommodating outside conservation areas. Restoring their original character — retaining Crittall windows, original fireplaces and distinctive external features — adds both charm and, increasingly, market value. The right architect will help you balance sympathetic restoration with effective modernisation.