300-year-old lime rendered Cornish cottage restoration and extension by Jonathan Tuckey Design Studio. Photo by James Brittain.
Render is a common exterior finish used on traditional and contemporary homes in the UK.
In traditional buildings, it’s often used as the defining material, adorning all exterior walls. For contemporary projects, it can also be used as the predominant material for a modernist-inspired aesthetic or complemented by other materials to create added robustness and visual appeal.
With so many types of render available, you may be finding it hard to know where to begin. In this architect’s guide, we provide advice on which types of render are suitable for different types of buildings, planning permission, maintenance, cost, and more.
For inspiration, check out our article below.
READ: House Rendering Ideas: Architect-Designed Inspiration
House rendering, or external render, refers to durable plasters applied over a base layer to protect walls from the weather, serve as a decorative covering, or hide coarse masonry. Traditionally, it’s a mix of lime, sand, and water, with origins dating back to around 7,000 BCE.
Georgian stucco became popular during the Georgian period (1714-1830) and continued into the Regency period (1811-1820), was designed to imitate ashlar stone. It typically consists of non-hydraulic lime, sand, and other materials like brick dust or marble dust for different textures.
By the Victorian era (1837-1901), materials like Portland cement and hydraulic lime were introduced, bringing increased strength and reduced setting times.
Sand-cement render, widely used throughout the 20th Century, consists of Portland cement, sharp sand, and plasticizers, though it’s inflexible and prone to cracking.
Today, there are a wide variety of render systems to choose from including monocouche, a pre-coloured single-coat render offering flexibility and durability, and cork render, made from cork aggregates and natural hydraulic lime, providing breathability and sustainability.
Cement render painted pale pink, Isokon Building, Wells Coates, 1933. Restored by Avanti Architects, 2004. Photo by The Modern House. Render was commonly used by modernist architects to create smooth, clean surfaces that emphasised simplicity and geometric forms.
While render protects walls from weather, it shouldn't be used to fix existing damp issues on unrendered walls. Address underlying causes first, such as damaged roofs, broken guttering, and inadequate surface drainage.
For homes with existing rendered walls, cracks and defects can lead to penetrating damp. Make like-for-like repairs where appropriate, and consider repointing the brickwork before reapplying render.
For older buildings, if sand and cement render has been used to patch or replace original render, it may be necessary to remove this and apply breathable lime render instead. Sand and cement render can trap moisture, leading to damp issues from interstitial condensation.
External renders fall into two main categories: permeable and impermeable. Permeable, breathable renders are recommended for older buildings to allow moisture to escape, maintaining structural integrity and avoiding damp. Impermeable renders act as a moisture barrier and are suited for modern construction.
Microfibre cement can be applied externally on walls and roofs to create a highly durable, contemporary surface. Seabreeze by RXX Architects. Photo by Richard Chivers.
Lime render is traditionally applied in three coats – scratch, float, and finishing coat – with a metal trowel. Comprised of coarse aggregates, the scratch is about 10-15 millimetres thick, which is keyed with a scratch comb, ready for the next layer. The float coat is about 10 millimetres thick. When it has dried to a malleable, putty-like consistency, it is worked with a wooden float to smooth out inconsistencies and remove air bubbles and then scratched lightly for the finish coat. The finish coat is decorative, normally about 6 millimetres thick and made with a fine aggregate to produce a smoother, flatter finish.
Lime render can also have a textured or rough cast finish. Harling, common in Scotland, provides greater protection in wetter climates.
It is important to allow sufficient time for each coat to dry before applying the next. The recommended drying time for lime render is 1 day per millimetre. Until the render has adequately cured, it should be protected with hessian sheeting.
Non-hydraulic lime requires knocking up - the process of kneading, beating, ramming, and chopping the materials together with a wooden stick - and cherishing - the process of moisture control undertaken during the curing process to prevent shrinking.
Modern sand cement renders are often applied in just two layers, a scratch coat and a top coat.
Thin coat renders, including silicone renders and fine natural hydraulic lime dry mortar, regularly used to finish external wall insulation, are applied in two passes to a total thickness of about 3 millimetres.
Monocouche renders are installed as a single render coat, usually about 15 millimetres thick, either by trowel or pumped mechanically.
Microfibre cement is applied by hand trowel only to a thickness of as little as 2-3 millimetres.
Lime render heritage installation by David Sleight Conservation.
Historic lime renders were either self-coloured with different sands or decorated with lime wash or breathable paint.
Limewash, typically applied in 4 coats, is not particularly durable and requires redecorating every 5 years, on average. Alternatively, Silicate paints, hard-wearing, yet still highly breathable, offer a longer life expectancy, require fewer coats, and are generally more water repellent. They are available in many colours and can be RAL colour matched. Through-coloured renders may be repainted with silicate paint or other breathable paints.
Lime render should only be decorated once fully cured to avoid trapping moisture in the wall, usually around 3 months after the application.
Avoid standard exterior paints as they will compromise the render’s permeability.
If you have Georgian stucco, follow your local authority heritage guidelines for the redecoration of the front elevation, often including windows, doors, walls, and other architectural features. Guidance usually requires Georgian stucco to be painted with lime wash or breathable paints, typically in Magnolia or Soft White colours – a late 19th Century interpretation.
The Georgian Group, The Victorian Society and Historic England are also good resources for advice on heritage matters.
Sand-cement renders can be finished with any high-quality exterior paint, though the durability of the paint is limited by the render’s tendency to crack over time.
Monocouche and microfibre cement renders are through-coloured and do not require additional decoration.
Bright yellow rendered house extension by Uncommon Works.
External wall insulation (EWI) systems combine insulation layers and thin top coat renders to provide a contemporary exterior finish. EWI systems can be vapour permeable using materials like wood fibre or cork, or vapour closed using plastic foam insulation for maximum thermal performance. Combined with thin coat silicone renders, they create a very durable, thermally efficient, and modern rendered façade. Always consult an architect for advice and installation.
READ: External Wall Insulation: A Guide To Retrofitting Homes
The longevity of a render depends on the climate, exposure, installation quality, and maintenance. Modern render systems typically last between 20-30 years before replacement, though well-maintained lime renders can last a lifetime. All renders require periodic cleaning or redecorating to remain in good condition.
Rendering costs vary based on the size and complexity of your property and your location. Here are rough estimates per square metre for the UK:
When compiling estimates, remember to include additional costs like scaffolding, waste removal, and access requirements.
Render can be combined with other materials such as brickwork, providing added durability and aesthetic appeal. Consideration must be given to where the two materials will meet to avoid cracking and staining. Proper planning and the advice of skilled residential architects will be invaluable in achieving the best results.
New build house with brickwork and monocouche render by Stanton Williams Architects. Photo by Jack Hobhouse.
Rendering may fall under permitted development, meaning planning permission is not required if the materials used are of a similar appearance to the existing building. However, planning permission is required for listed buildings, properties in conservation areas, and where Permitted Development rights do not apply. It’s always advisable to apply for a Certificate of Lawfulness to confirm that proposed works fall under Permitted Development.
Consult Permitted Development Rights for Householders Technical Guidance, September 2019 for more information.
Like-for-like repairs or the application of uninsulated render typically do not require Building Regulations approval. However, if the render is combined with external wall insulation and affects more than 50% of the wall or 25% of the building, it is necessary to notify Building Control.
House rendering can be carried out under the Competent Person Scheme, making the process more efficient.
Other approvals that may be required include listed building consent, party wall, and oversail licences.
When compared to most other facing building materials, house rendering is a relatively quick method of achieving a visually appealing exterior. However, like all building materials, there are advantages and disadvantages that need to be considered.
Pros
Cons
Crisp, contemporary white silicone render by McGonigle McGrath. Photo by Aidan McGrath.
The render you choose will depend on the type of wall construction.
Generally, hydraulic lime render is ideal for many residential projects, offering superior environmental credentials and breathability compared to sand and cement render.
Historic properties should be repaired with like-for-like materials. Do not apply render to high quality facing materials such as historic brickwork or stone. It will ruin the integrity of the building and create unnecessary maintenance.
For contemporary aesthetics, monocouche or microfibre cement renders are ideal.
If you live in a home with low-quality facing brickwork and want to improve its aesthetics and energy efficiency, consider EWI with a render finish.
The information provided in this article is intended for general guidance and educational purposes. For specific expert advice for your project, appoint an architect featured on Designs in Detail.
About the author
Aron Coates, an architect with over two decades of experience, draws upon a wealth of residential architectural expertise, encompassing projects ranging from the restoration of historic structures to the design of contemporary homes.
