Applying a coat of coloured render over external walls is good way of giving your house a facelift, especially if the current exterior is unattractive, in poor condition, or a mixture of different mismatched materials.
How much will render cost?
External rendering using a sand and cement ‘scratch coat’ and a finer render topcoat, followed by two coats of external masonry paint will cost in the region of £28–£34 per m². Rendering and painting a typical three-bedroom semi-detached house with 80m² of walls would therefore cost £2,240–£2,720.
For a solid walled house or where the cavity is too narrow to apply sufficient levels of insulation you may wish to take this chance to add insulation. In this case an external wall insulation system is usually a better option than insulating internally as no space or architectural detail is lost within the property.
There are many different external wall insulation systems, but most of them are promoted on a supply and fix basis by specialists, so they’re not available to the DIY market.
Applying external insulation with a render finish typically costs £70–£90 per m². A typical three-bedroom semidetached house would require 80m², so it would cost £5,600–£7,200.
Rules and guidelines
Planning permission isn’t often required to apply render, providing the house isn’t listed or in a conservation area, and permitted development rights haven’t been removed (visit planningportal.gov.uk and check with your local authority).
Rendering work on a substantial part of a house must comply with Building Regulations. In an older house it is likely that the walls will have to be insulated. This will mean adding insulation within the cavity or, in the case of solid walls, by applying insulation on the inside or outside face of the external walls. It adds to the cost but reduces fuel bills by up to 40 per cent.
Seven steps to rendering a wall
1. Preparing the walls
Before a building is rendered, the walls should be surveyed, with repairs made to structural defects and any movement stablised, otherwise the render finish is likely to fail. Any new finish is only as good as the wall behind it.
2. External details
External details such as bargeboards will often have to be removed, along with rainwater and soil pipes and other external details such as alarm boxes. Any vents will need to be extended, and sometimes window sills must be extended too. Metal stop and angle beads are then applied around the window and door openings and corners (or the edges of a terraced property) to provide clean edges for the render. The render system can then be applied.
Where external wall insulation is being applied before the render coat, this is usually in the form of rigid boards or slabs. The type of fixing needs to be selected depending on the type of wall — which is either mechanically fixed or glued to the walls.
4. Creating a foundation
A fabric render mesh is then applied over the insulation, bedded into the first base coat layer of render. This mesh acts as a reinforcement against cracking. This is followed by one or two more thin coats of render, usually a primer and a topcoat.
5. Building up the render
Different proprietary systems are built up of different layers, using various forms of insulation, including expanded polystyrene (EPS), mineral fibre (Rock Fibre) and phenolic foam (more expensive but superior performance). Different types of render are also used with external wall insulation systems, depending on the application and the desired finish, including polymer cement, silicone and acrylic.
6. Render finishes
Thin coat render systems are designed to be self-coloured so that they don’t need painting. As well as a choice of colours, different finishes are also available, from very smooth to textured. If you have chosen rendering that needs painting, make sure you choose a weatherproof external paint.
7. Final finishes
Finally, the external rainwater and soil pipes etc. can be reapplied. You can expect the total process to take around three to four weeks.