Render, EWI or Brick Slip?
How to Choose and What Each Will Cost Per m2

When it comes to external wall finishes, builders and clients are increasingly faced with a choice between three main options: traditional render, external wall insulation (EWI) systems and brick slips. Each has its place, but understanding the cost, performance and installation implications of each is essential before you specify.

Traditional Render

Render is the most established external finish and the one most builders are comfortable specifying and applying. It is applied directly to masonry, blockwork or sand-cement render boards and can be finished in a range of textures from smooth to scraped or roughcast.

Types of render

• Sand and cement render - the traditional two or three coat system, applied wet. Labour-intensive but durable and well understood.
• Monocouche render - single-coat through-coloured render applied at 15-20mm. Fast to apply, minimal cracking risk, wide colour range.
• Silicone render - thin coat finish applied over a base coat, highly flexible and breathable. Popular on EWI systems.
• Acrylic render - polymer-modified finish, very durable and comes pre-mixed. Less breathable than silicone.

Typical material cost per m2

• Sand and cement render: £8-15/m2 materials only
• Monocouche: £18-28/m2 materials only
• Silicone thin coat (over base): £20-35/m2 materials only

Best suited for

New build masonry, block extensions, and properties where adding insulation thickness to the external wall is not required or appropriate.

External Wall Insulation (EWI)

EWI systems add a layer of insulation board to the outside of the existing wall, then finish with a reinforced base coat and thin coat render. They are increasingly popular on retrofit projects where cavity or internal insulation is not viable.

How EWI works

An EWI system typically consists of:

1. Insulation board (EPS, mineral wool or phenolic) mechanically fixed and/or adhesively bonded to the wall
2. Reinforcement base coat with embedded fibreglass mesh
3. Primer
4. Decorative thin coat render (silicone or acrylic)

Typical material cost per m2

• EPS (expanded polystyrene) system: £35-55/m2 materials only
• Mineral wool system: £50-75/m2 materials only
• Phenolic board system: £65-100/m2 materials only

Key considerations

• EWI adds 80-200mm to the external wall thickness - impacts window reveals, eaves details, and boundary clearances
• Requires planning permission on some properties (especially listed buildings or conservation areas)
• All detailing must be correct - poorly detailed EWI can trap moisture and cause serious damage
• Labour cost is significantly higher than render alone - typical installed cost is £80-140/m2 including labour

Best suited for

Solid wall retrofit insulation, buildings where improving U-value is a priority, and projects where external appearance needs to change (the render finish can be any colour or texture).

Brick Slips

Brick slips are thin veneers of fired clay (typically 15-25mm thick) that replicate the appearance of full brickwork when fixed to a substrate. They offer a brick aesthetic without the structural load or thickness of full brickwork.

Installation methods

• Adhesive bedded - slips bonded directly to render board or masonry with a flexible tile adhesive, then pointed
• Rail system - pre-panelled slips on a mechanical fixing rail, suitable for rainscreen applications
• EWI brick slip finish - slips bonded to EWI base coat for a brick-look insulated system

Typical material cost per m2

• Standard adhesive-bedded brick slips: £45-70/m2 materials only (slips, adhesive, pointing mortar)
• Premium or handmade slips: £80-130/m2 materials only
• Rail system: £90-150/m2 materials only

Key considerations

• Pointing quality is critical - poorly pointed brick slip work looks obviously fake
• Movement joints must be incorporated correctly or the system will crack
• Not all brick slips are frost resistant - check the specification for exposed external use
• Detailing at corners, sills and heads is more complex than standard render

Best suited for

Contemporary extensions where a brick look is required but full masonry is too heavy or too slow. Also popular for internal feature walls and for matching brick appearance to an existing building without structural brickwork.

Comparison Summary