Sliding Doors – The Good, the Bad and the Jaw Dropping
Sliding windows and doors are extremely popular in South-East Asia. They allow for very large, minimally-obstructed glazing areas that brighten up the living space. Sliding panels can be wonderful design pieces that make the most of a stunning view or enable indoor / outdoor living.
They are also a practical choice for openings that are wider than they are tall or in areas with living spaces close to the window, such as the kitchen. Though the appeal is clear, it is also crucial to carefully evaluate which solution will best fulfil the requirements of a specific project. For example, low thresholds, heavy, large movable sashes and minimalist profile design might come at a cost the owner is not aware of. Flooding of the living room in heavy rain, a large sliding panel that is too heavy for the occupants to operate regularly or being able to hear every word the neighbours speak in your own bedroom are very common problems with low quality sliding systems. Conventional Inline Sliding panels are sadly often the worst performing windows and doors in the house when it comes to water and air tightness, sound insulation, and energy efficiency.
Unquestionably we want to avoid ending up with a leaking and whistling sliding door such as this one in a hotel in Vietnam during a storm:
The challenge lies in the basic structure of sliding sashes, which do not allow for tight sealing. The traditional Inline Sliding sash sits on top of the track and is insulated by brush seals:
Therefore, no compression (which is necessary to enable tightness) can be achieved. Not only that, but these seals need to be flexible to enable the smooth opening and closing of the panel. After some time, the continuous opening and closing of the sash often results into the seals being slightly dislocated, resulting in additional reduction of tightness. Furthermore, sliding doors are designed with weep holes in the track to allow for water drainage, which brings another negative effect on the performance. This reduction of tightness compared to other opening types, like casement windows, means that sliding windows are generally less energy efficient and don’t block sound out very well.
These two Singaporean standard windows (the first in a DBSS, the second in a 4-year old condominium) demonstrate clearly the typical problem – once the brush seals wear out you have a direct air gap from the outside into your room:
Sliding panels are generally seen as low maintenance, however dust and debris can accumulate in the track and that can lead to the sash being very difficult to operate or cause damage to the rollers or track if not cleared out regularly. It is also easy to get carried away with the sizes of the panels; to ensure easy operation for panels over 200 kg, specialised systems are advisable.
To be able to fully utilize the advantages that sliding doors offer and to minimize their disadvantages, we compiled a list of intelligent systems beyond simple Inline Sliding, each designed to solve a specific problem –
If it needs to be tight:
For projects where wind and weather tightness or sound insulation are at the forefront, there is no better solution than the new Roto Patio Inowa. Reasonably priced, it is a high performance inline sliding door for excellent tightness. Perfect for high-rise residential projects, the patented Inowa system allows for an all-round seal with rubber gaskets, achieving compression through locking points on all 4 sides of the sash. Extra safety is included as additional bonus and there will be no clattering in the wind of these panels as it is even typhoon tested!
It is an ingenious system where the sash does not sit on the sliding track but gets moved 8mm out at the turn of the handle. The operation is basically the same as for Inline Sliding and therefore very user-friendly. It is energy efficient and received very good sound insulation ratings; tests in Singapore showed an STC of 37, which was 2 points better than the glass – excellent for a sliding door. We also like that the threshold is 20mm, that is pretty low for such tightness. It is a product more for standard-sized balcony doors, as its recommended size is 2.7 m high and 1.5 m wide to a total weight of 200 kg per sash. Perfect for two sashed balcony doors, although scheme “D” is also available, it can run inside or outside. Design and hardware come from Roto in Germany and the doors are locally manufactured.
Available in aluminium (manufactured in Singapore); uPVC and timber options are also available imported from overseas).
On this topic we also have to mention the Tilt & Slide or Parallel Slide Systems when talking about tightness for sliding doors.
If you want to slide, then there are probably prettier and more user-friendly solutions out there. However, it can be a good option if a manufacturer needs to use existing profiles as these doors can be built using European standard door profiles or if really high-performance ratings need to be achieved. The profile has a middle gasket and allows for all-round locking, which will make the door incredibly tight. To slide, the sash moves 100 mm forward from the frame and then runs on a front-mounted track with tandem bogies.
Suitable for sound blocking and energy efficiency, these rebated systems allow for proper compression and with the high threshold they also perform very well with regards to water tightness. But there we have it – the ugly high threshold. We are all for using a small threshold to increase tightness performance but here we speak about a full door profile section you have to step over. Not only that, but plus all of that visible hardware. Our main concern though is that it is not easy or intuitive to operate for the average customer. For hotels or rental apartments where the end user cannot be individually trained this is certainly not the best choice.
Tilt & Slide panels are available in aluminium and uPVC in Singapore (in timber as import), this video shows an example of the VEKA uPVC system:
If the panels are heavy:
Moving a 200kg Inline Sliding door is not something you want to do 3 times a day – not to speak about larger sashes. Special systems that assist with the movement of large panels are necessary.
Such an option is the ‘Lift & Slide System’ and these doors are stunning. 3m x 3m movable openings are possible and up to a weight limit of 400 kg – although you’ll want to automate them above 300 kg. While a standard Inline Sliding door sits on rollers and is pulled along the track on the handle, a Lift & Slide door is literally lifted from the track.
In closed position the doors sit directly on the track; the handle then has to be turned 180° to ‘lift’ the door up on to its rollers so that the sash can be moved without friction. This allows even very large panels to slide easily. When locked, the sash drops down a few millimetres and allows for compression on the weather seals.
Our pick is the German GU Lift & Slide System. GU invented the concept in 1958 and we still think they are leading in this technology, especially when it comes to automation.
It comes with a secure ventilation feature and multipoint locking on the handle side. An optional sash-speed limiter is available that we believe to be an essential accessory; you don’t want to have your hand in a 300 kg door slamming shut! You can choose from manual or automated operation. The visible hardware is minimal and while special profile systems are needed, the one-handed operation is intuitive and easy. Different threshold options balance the need of tightness and barrier-free living and can be chosen according to project needs. Best used in openings up to 6 metres wide as the panels cannot be stacked, Lift & Slide is a great option for patio doors. Especially if they are covered as the weather tightness is better than for simple Inline Sliding but is not comparable to Inowa.
Lift & Slide doors are available in aluminium, timber or uPVC.
If the panels are super-sized:
If you want to go very wide it would be possible to go with a series of multiple ‘Lift & Slide’ doors. However, with these doors you will always have a fixed sash – so if your glass area is 6 metres, only 3 metres of that can be opened while showing a lot of bulky profile sections.
If you want to open it all, a great option is a Bi-fold Door. You fold the glass panels away to the side like an accordion and then have the entire space unobstructed. The technology for folding doors has greatly progressed in the last few years and is a far cry away from the draughty, leaky wooden folding doors of yesteryear. While requirements in weathertightness and the desire for super-low thresholds have to be frankly discussed when choosing a model, modern Bi-folds can be manufactured to quite high weather resistance standards and the hardware available enables many years of smooth operation.
It is also a really fantastic option for restaurants or showrooms when you want to be flexible as to using the space as outdoor or indoor area.
Our favourite version of the Bi-fold is the Solarlux folding system, marketed as “Nanawall” in the US. The system looks great, has minimal visible hardware, is sealing tightly and is tested to run smoothly for 20,000 cycles — the equivalent to opening twice a day, every day for 27 years! It is super space saving, a 5 metre folding wall will just take up 50 cm once folded up, so you’ve got 4.5 metres of unobstructed opening! With folding doors you will want to make sure that the system (especially hinges, track and bogies), are of great quality and are adjustable, otherwise after a year the folding panels can become a fixed glazing area. Solarlux products are Made in Germany and their components are of the highest quality. Excellent craftmanship in the manufacturing process and perfect installation are necessary to ensure a long, happy life of a folding door.
Many different versions are available, from totally flush thresholds to thermally high performing systems and they come in aluminium, wood-aluminium, wood only and a stunning externally glazed “all glass look”. The panels can fold out or in, fold left and / or right and can be top hung or bottom running. Maximum size depends largely on the max weight of 100 kg per sash but is in the realm of 3 metres high and 1 metre wide.
We recommend thinking about practicalities and how often the entire door will be opened when choosing an opening schema. We advise to incorporate a swing door for easy access, so you don’t have to fold up the entire thing when you just want to quickly access the patio. That’s what it means when you see the description 431 – it is 4 panels in total, 3 of which can be folded away to one side and 1 swing door to the other side that can be operated independently.
The Solarlux Bi-fold range is available in Singapore.
Folding doors look amazing when they are open, however they do have the disadvantage that you see a lot of profile sections when the door is closed.
Engineered for extra-large openings with minimally obstructed views through small profiles, the relatively new “Minimalist Sliding Systems” are amazing design pieces. We are stepping up in the price category speaking about these systems, but they are just so beautiful and the technology behind them is amazing.
Our choice is another Solarlux product, CERO. The profiles are so ultra-thin it creates a near-frameless look.
We think CERO it is one of the best slim-profile sliding systems available and is unparalleled in performance, quality and style. 34mm profiles allow for 98 % glass usage in huge panels up to 15m² or 1000kg each. That is seriously large! The heavy panels can be moved either manually or may be motorized. This piece of German quality engineering is ultra-strong and comes with heavy-duty fittings and runners and still performs well with regards to tightness despite its slimline design. We like that the unique stainless-steel runners are integrated in the sash profile and are protected from dirt by cleaning brushes. This reduces the need for maintenance and makes them run smoothly long-term. We also find it very practical that the rollers can be replaced without removing the sash; a real plus when dealing with panels of this size!
Different profile versions for different climatic conditions are available up to triple glazing. CERO offers a lot of design possibilities since the panels can be stacked, and open, movable corners solutions are possible.
Available in aluminium in Singapore, CERO is an excellent choice for light flooded spaces. https://www.cero.de/en/cero.cfm
As a bonus because we love this option so much: why slide when you can descend?
If budget is of lesser concern but you want to use the most impressive window out there, there is nothing like the HIRT descending window.
With virtually no size restriction (their “small” HIRT SF 90 model can cover a surface area of 18 m2!) all you need is a small technical room below your panel that the window can descend into. No need to decide how big the patio and how big the living room should be – make it one single area! At the press of a button it is either weather-protected or part of the outdoors. A window or swing door can be integrated in the panel for ventilation and passing through.
A total design game-changer! HIRT has been quietly installing their amazing panels all around the world from their manufacturing plant in Zurich, Switzerland, where they pay meticulous attention to every detail. They make it possible no matter how tight, how big, or out of what material you need it – it does not have to be glass, you could descend an entire wall. Each and every panel is custom-made according to the project specifications.
HIRT descending windows are finally available in Singapore. A solution like this needs to be taken into consideration early in the design process to allow for the necessary space and technology, contact us and we will be happy to walk you through what is needed.
Sliding doors can be a huge asset to the design of a project, we hope this compilation helps to highlight the key challenges of sliding systems and shed some light on ways to overcome them.
If you are not sure which system is best suited to your project’s needs or where to source them, drop us a line at firstname.lastname@example.org and we will gladly help you choose.