What choice of material is best for a bi fold door?
Choose from timber (engineered or laminated frames being less likely to warp), uPVC or aluminium bi fold door frames – or a combination of aluminium and wood.
The most affordable option for folding sliding doors tends to be uPVC – but it is always a good idea to get quotes from several suppliers and compare what is offered. A material that does not require much maintenance, uPVC can cope well with any environment. The standard colour is white, but uPVC doors are also available in other colourways, including some very convincing woodgrain effects. As with any material, it is very important to choose a good quality supplier as a poorer quality uPVC bi fold door can suffer if the frames twist or warp and it can be difficult to repair.
Considered contemporary in concept, FSDs also suit a traditional home. Timber frames, in particular, work well in both modern and period properties. As well as perimeter framing, timber is ideal for adding features such as decorative base panels and glazing bars.
With its impressive eco credentials and high thermal efficiency, timber is available in hardwood and softwood, off-the-peg or bespoke designs. While solid hardwood has been traditionally considered the most durable, it is worth asking about chemically improved softwood, known as accoya, which has been introduced recently.
New engineered or laminated timbers can provide extra strength for greater expanses of glass, as the bonded sections help minimise warping and twisting, improving structural stability while increasing thermal efficiency. Warping can cause the weather seals on a door system to fail, as well as affecting the operation. Look for the Forest Stewardship Council (FSC; fsc.org) logo to check timber comes from a sustainable source.
A timber bi fold door needs ongoing maintenance to ensure that it lasts over time. They may be painted or stained and varnished, or clad externally in aluminium and then powder-coated. Oak stain is a popular option, as are painted sets in neutral and classic colours, or you could opt for ready-primed frames.
Darryl Jeffree, timber and joinery buyer at Wickes, says: ‘Timber doors are the best option if you want an environmentally-friendly option, but consider thermal efficiency and ensure the wood is FSC-certified. An important decision is whether to choose pre-finished doors, which won’t need to be decorated once installed – saving time and ensuring the product is sealed and finished correctly – or unfinished doors. These let you stamp your individuality on your home.’
‘Although folding-sliding doors are available in timber and uPVC, the preferred material is aluminium as it won’t twist or warp with age and exposure to the elements,’ says Brendan Day, head designer at Apropos. ‘If the seal on a double-glazed unit fails, and the cavity starts to mist up, it’s usually due to movement in the door frame rather than a failure of the glazed unit itself. An expanding frame around the glass can create fractures of the seal and lead to the failure of the double-glazed unit.’
Aluminium is lightweight, strong and dimensionally stable – meaning it does not twist or warp in response to changes in humidity or temperature – making it ideal for door frames and surrounds. Its strength allows the frames to be very narrow, maximising the glazed area, so it is well-suited to contemporary folding sliding door styles where a minimal look and maximum light are required.
Check that the bi fold door you choose conforms to the current regulations for thermal efficiency, which require frames to be thermally broken to avoid cold bridging (where energy is transferred through the frame, causing heat loss from inside to out).
Aluminium doors are low-maintenance and can be powder-coated in any colour or even a realistic woodgrain effect. In a marine environment (within 5,000 metres of a marine or saltwater site), they can be upgraded to withstand the highly corrosive nature of saltwater.
With growing demand for ever larger expanses of glass and designer-style minimalist framing, the latest FSDs are the perfect complement to the modern home.
Durable, maintenance-free aluminium is an ideal choice, as its innate strength allows for a thin frame profile that can support vast areas of glass. Such lightweight doors require less stacking space plus there is a wide range of anodised finishes – with an electrically charged oxide layer to protect against corrosion – and powdercoated colours. New energy-efficient frames feature a thermal break to help prevent heat loss and condensation. Alternatively, you may prefer alu-clad or composite frames that combine a timber interior with a hardwearing aluminium exterior. Although less expensive, uPVC won’t be as strong or offer such slim sightlines (frame profile).
Matt Higgs, director of Kloeber, says: ‘A major advantage of aluminium FSDs is a low-maintenance powdercoated finish, plus a slimmer, more contemporary profile. However, thermal efficiency is also paramount, as typically a metal product will not insulate as well as timber. A thermal break in the frame is therefore essential. This usually takes the form of a polyamide insulating strip placed directly through the centre of the frame, splitting the aluminium into two and stopping the conduction of heat.’