Connecting with the outside

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Considering bifold or sliding doors for your self-build or renovation project? Matt Higgs from Kloeber answers some of the key questions to help ensure you choose the right glazed doors for your home

It’s not surprising that bifold and sliding doors are one of the most desired features in any self-build or renovation project. They create the wow-factor homeowners are looking for and are ideal for maximising natural light and connecting your home with the outdoors. Choosing between the two comes down to personal preference and what will work with your project, both practically and aesthetically.

WHAT ARE THE BENEFITS OF BIFOLD DOORS? 

Bifolds are ideal for welcoming the outside into your home. They are made up of multiple, hinged panels that slide and concertina together, stacking at one or at both sides. They have the ability to open up to 95% of the aperture, so are perfect for smaller openings.

Most suppliers will offer a variety of configurations, with inward or outward opening options to suit the layout of your home. And for those with children or pets, adding a single access door will be useful.

Popular material choices for bifold doors are timber or aluminium. Engineered timber is strong, durable with great insulating values and can be painted or stained while aluminium offers a contemporary, hard-wearing maintenance-free finish.

HOW DO I WORK OUT THE NUMBER OF PANELS NEEDED? 

The number of panels you will need is dependent on the width of the aperture and the width of the panels. Bifolds can start with three panels at 2090 mm total frame width or, at the other end of the scale, you can get panel widths up to 1500 mm. Speak to a reputable supplier to review your plans and work out the best options available for your project.

WHAT ARE THE BENEFITS OF SLIDING DOORS? 

If an ‘unadulterated’ view is important, then a sliding door could be the best choice. Sliding doors work well with larger apertures as they open up by sliding the panels to one or both sides with the panes fitting behind each other on two, three or four tracks. 

This means you can’t fully open up the aperture, the maximum opening will be around 70%. But when closed, the view isn’t impaired by the frame lines.

Aluminium is the popular choice for those preferring slimline frames and sleek, minimal styling but alu-clad (aluminium exterior and timber interior) is also an option for sliding doors, if a warmer internal aesthetic and higher performance is preferred. 

WHAT PANEL SIZES CAN I HAVE?  

Sliding door panel sizes start at around 500 mm and go up to a whopping 4200 mm however bear in mind that some cheaper systems may have limited panel size options, so you’ll need more panels to span a wide opening. At the higher end of the market, you will find options with ultra-slim sightlines combined with large panels on offer.

WHAT SHOULD BE CONSIDERED WHEN INSTALLING LARGE EXPANSES OF GLASS? 

The precision of the aperture is very important, the right amount of tolerance is key to installing the frame level and plumb. It’s also important to ensure there’s the right strength in your lintel above the opening. Other things to consider are how the flooring, and internal and external finishes interact with the frame. Bifold or sliding doors with large expanses of glass will lose more heat, and could let in more heat than you’d like, especially on a south facing elevation, so you need to consider the type of glass used. For example, a south facing home would benefit from solar control glass and for a north facing home, low iron glass would help increase solar gain.

HOW DO I CHOOSE THE RIGHT GLAZING FOR BIFOLD OR SLIDING DOORS? 

Try and attain the best U-values that are possible – glass will always let out more heat than a solid wall, so it’s always a good idea to consider triple glazing or a high performing double glazed unit.
Different frame materials also have different thermal properties with timber usually being a good choice. It’s important to pay consideration to how the doors fold or slide, and how they seal up between panels. Thermal and weather testing reports should be available from reputable companies who are selling high performance sliding/folding doors.

CAN YOU EXPLAIN WHAT THERMAL VALUES ARE?

A U-value measures heat loss, so the lower the U-value, the less heat lost. Doors have to achieve a U-value of 1.6 or less to comply with regulations for new builds and 1.4 on extensions and alterations. 

The G-value, is also important, which is the measure of how much solar heat and light is transferred from outside to inside. A G-value of 1, represents full transmittance of all solar radiation, while 0, represents no solar energy transmittance. Most G-values will range between 0.2 and 0.7, with solar control glazing having a G-value of less than 0.5. 

WHAT DRAINAGE AND WATERPROOFING CONSIDERATIONS SHOULD BE MADE? 

Always ask your supplier for weather testing reports. High quality doors will always have extensive weather testing and will be of a superior quality. How much your house is exposed to weather can be a real factor here in determining your choice. If you’re in a very exposed area then it’s advisable to go for a low maintenance material with good Pascal (air permeability) ratings. 

With regards to the outside it’s always best to have a small gap between the paving or decking to allow for water to drain away from the doors into a drain under the external floor. It’s also best practice to have the external floor just slightly lower than the internal, to negate any risk of water ingress. A reputable company should be able to provide details of this and show you exactly how to achieve the desired effect.

Matt Higgs is managing director of Kloeber