The exterior of your annexe is the first thing people see, so it is vital that the first impression produces an impression that you can be proud of.

Choosing a product that’s durable and long-lasting and maintenance free is the ideal solution.There’s a host of options available for your annexe including:

• Wood
• Modified Timber
• Metal
• Fibre Cement
• PVCu

Wood
Wood cladding has been a popular choice for annexes for many years. Different species of timber means there are varies options in terms of colour and graining, life span and the amount of upkeep they require. Ideally, you want minimal maintenance, and a durable, rot-resistant material.

Dimensional strength is also key, as some species are more prone to swelling and shrinkage than others. Many types of timber don’t need to be treated prior to installation, but bear in mind that they will inevitably weather to a silvery hue after several years. As Wood is a natural product, so it will react with its environment and will require some maintenance over the years.

UV degradation and moisture absorption will affect its appearance, and it could develop a patchy weathered look with uneven changes. The amount of sunshine an elevation gets, in addition to architectural features such as overhangs, can contribute to this variation.

Some treatments, are available such as Sioo, that will create an evenly weathered appearance at an accelerated rate. This means that regardless of the property’s level of UV exposure, the cladding will age at the same rate, resulting in a consistent tone. Any finish you do apply will wear over time, so boards will require re-coating – exactly how often depends on the qualities of the wood, how exposed the building is and the design of the annexe.

Species like Western Red cedar, which is classed as durable, have natural properties that make it suitable for external use without a preservative treatment, Cedar offers a life span of 40-60 years.

Larch is another softwood suitable for this application, providing you use the heartwood. Siberian varieties can offer a longer life span of 50+ years than their European counterparts.

Hardwoods like oak and sweet chestnut are even more hardwearing and you can expect a service span of 40-60 years from each, but they can be expensive. Oak is more prone to natural movement than other hardwoods, so should be a kiln-dried version to allow a moisture content of 15%-25% prior to installation.

Other species offering a shorter life span of 25-30 years are varieties like, spruce, pine and fir which all require preservative treatment to render them suitable for use externally. They are usually impregnated with chemicals that have preservative properties to boost their durability. As a result, they’re less likely to be considered a low-maintenance form of cladding for your annexe.

Modified Timber
Modern manufacturing techniques mean that some woods can be chemically or thermally altered to boost their stability, durability and resistance to rot. For example, products like Accoya and Kebony are equal with some tropical hardwoods in terms of how hardwearing they are. Chemical modification enhances the timbers durability by reducing its ability to absorb water.

Accoya is becoming increasingly popular for striking exterior finishes. The wood undergoes an acetylation process to increase its dimensional stability. Swelling and shrinkage is reduced by 75% or more compared to untreated wood products, and overall upkeep costs are generally low and infrequent.

The product offers a minimum service life of 50 years. It is usually given an opaque finish to provide the desired visual effect and facilitate even weathering. The improved stability means the top coat can potentially last longer than with natural timber products, which should make for less frequent treatments and reduced upkeep costs.

Created from a variety of softwoods, including Southern Yellow and Monterey pine, Kebony is another chemically-modified option that undergoes an eco-friendly process to boost its durability and dimensional stability. It doesn’t require any treatment beyond normal cleaning, and you can expect a service span of 30 years or more.

A variety of thermally-modified timbers is available, such as Brimstone cladding. Production involves heating wood above 200°C in the absence of oxygen. This causes permanent chemical and structural changes. The outcome is superior durability, better stability and more consistent weathering. The life span is considered to be around 40+ years.

Fibre Cement
It was developed as a low-maintenance alternative to timber, and is available in an extensive range of colours and finishes. During the manufacturing process, cement is added to a mix of cellulose, fillers, fibres and water to create pliable, wet sheets. These are rolled and flattened to remove excess moisture. At this stage, the material is formed into smaller tiles or large panels.

Scuffs are less visible on through-coloured sheets which gives it an advantage from a maintenance point of view. Painted varieties are also available, and products will be coated with a water-based or acrylic top layer to increase their resistance to the elements. Thanks to this treatment, fibre-cement cladding has a low water-absorption rate. The cement binding agent also means it will not rust or rot.

Expect a service life of approximately 40 years from this kind of covering and very little upkeep is required beyond a yearly clean.

Metal
Steel, aluminium, copper and zinc are the main options. As well as being durable and versatile, it’s low-maintenance, quick to fit.

Thanks to modern production techniques, materials can be pre-aged and coated to maintain the original shiny finish or supplied painted and powder-coated. These treatments mean that most metal solutions are fairly low-maintenance, though it’s a good idea to clean the surface annually.

Typically, steel coverings are supplied with a protective layer of zinc or zinc-aluminium alloy on their surface for a hardy finish. They offer a life span of approximately 35 years, whereas the surface of aluminium cladding will naturally oxidise to produce a robust protective layer that means it will last 40+ years.

Zinc can achieve a service life of 50 years or more. This metal’s primary attribute is its self-protecting patina, which shields it from corrosion and the adverse effects of weathering.

PVCu
Modern manufacturing techniques mean PVCu is an option for Annexes, as it comes in an array of finishes and hues. It doesn’t warp, twist, shrink or rot, so proves an appealing low-maintenance alternative to timber.

PVCu’s durability has improved in recent years, but it’s more vulnerable than some materials to the damaging effects of UV light. Overall, you can expect a life span of around 20-30 years.