When is single skin blockwork acceptable?

Single skin blockwork (100mm or 140mm) is suitable for: internal non-load-bearing partitions, garden and boundary walls up to 2m (with piers), single-storey outbuildings and garages, retaining walls (with engineering design), and below-ground foundation walls. Single skin is not suitable for external walls of habitable buildings due to thermal and weather resistance requirements.

What does a double skin cavity wall consist of?

A standard UK cavity wall consists of an outer leaf (typically 100mm dense or facing blockwork/brick), a cavity (typically 50-150mm, partially or fully filled with insulation), and an inner leaf (typically 100mm aerated blockwork). The two leaves are connected with wall ties at specified centres. Total wall thickness is typically 275-375mm depending on cavity width.

How much more does double skin cost?

A single skin 100mm block wall costs approximately £40-60/m² for materials and labour. A full cavity wall with insulation costs approximately £100-160/m². The cavity wall is roughly 2-3 times more expensive but provides weather protection, thermal insulation (meeting Part L), structural stability for multi-storey buildings, and sound insulation.

What foundation does each wall type need?

Single skin walls need a foundation width approximately 3 times the wall thickness — so a 100mm wall needs a 300mm wide strip foundation. Double skin cavity walls need 450-600mm wide strip foundations depending on soil conditions and building height. Cavity wall foundations are wider and use more concrete, adding to the cost difference. Approved Document A Table 10 gives minimum foundation widths.

Can I build a habitable room with single skin walls?

Not for external walls in England and Wales. Building Regulations require external walls of habitable buildings to meet Part L thermal requirements (typically U-value 0.26 W/m²K for new build), Part C weather resistance, Part E sound insulation (party walls), and structural requirements. A 100mm single skin wall cannot practically achieve these. Single skin is only used for external walls in certain agricultural and non-habitable buildings.

Single vs Double Skin Blockwork — UK

Compare single skin blockwork walls with double skin (cavity) blockwork for UK construction, covering structural capacity, thermal performance and cost.

Side-by-Side Comparison

Feature	Single Skin (100mm)	Double Skin Cavity
Wall thickness	100mm	275-375mm
Material + labour cost	£40-60/m²	£100-160/m²
Thermal performance	Poor (no insulation cavity)	Good (meets Part L)
Weather resistance	Poor — rain penetration	Good — cavity drains water
Structural height	Limited — single storey	Multi-storey capable
Foundation width	300mm minimum	450-600mm
Sound insulation	Limited	Good (meets Part E)
Building Regs habitable	No (external walls)	Yes

When Single Skin Is Appropriate

Internal partition walls (non-load-bearing)
Garden and boundary walls
Single-storey garages and outbuildings
Foundation walls below ground
Agricultural buildings exempt from Part L

When Double Skin Cavity Is Required

External walls of all habitable buildings
Multi-storey construction
Party walls between dwellings (Part E and Part B)
Any wall needing to meet Part L thermal standards
Exposed locations requiring weather protection

Related Calculators

Use the Block Calculator for block quantities, or the Foundation Calculator for foundation sizing.

How We Calculate This

Frequently Asked Questions

Last updated: April 2026

All calculations are estimates. Verify with your supplier.

Single vs Double Skin Blockwork — UK

Side-by-Side Comparison

When Single Skin Is Appropriate

When Double Skin Cavity Is Required

Related Calculators

How We Calculate This

Frequently Asked Questions

Related Calculators

Composite vs Timber Decking

Render vs Plaster

Copper vs Plastic Pipe

Brick vs Block Walls