Sliding Glass Doors

Key Questions to Ask When Specifying a Slim Sliding Door

Slim sliding doors are a popular and effective architectural glazing solution that brings in light and minimises the division between the inside and out. However, as with all products, not all slim sliding door systems are made equal. Some systems are cheaper for a reason. Below are some key questions to ask your architectural glazier to ensure you are getting a high-quality and fully weather-tight system.

How many sides of the sliding pane are bonded?

When you have a very slim sliding door the insulated glass units are structurally bonded into the frame. This means that there is no need for glazing beads to fix the glass into the frame and makes the system as slim as possible.

The structural bonding of glass into framing is a key element of the system’s ability to withstand rain and wind. It must be done properly and should be done on all four sides of the sliding pane.

We have found that some slim sliding systems only structurally bond the glass on two sides of the glass unit (normally the vertical profiles) and just slot the glass into the frame on the other two edges.

This is not a recommended solution for slim framed sliding doors as it will expose the system to water ingress and create unsealed edges on two sides of each sliding panel. If you have a very large elevation of sliding glass this is a large area of unsealed glass.

We always bond on all four sides of each minimal windows® sliding pane. This makes the system extremely robust for a long-life expectancy and ensures a weather tight glass elevation.


What silicone is being used to structurally bond the system?

Another question about structural bonding. That is because it is an important element of the system. You need to ensure that your glazier is using high-quality structural silicone that is designed for metal to glass connections.

We have discovered that some slim sliding door systems use structural silicone that is designed for glass to glass connection to bond the glass units into the frame. This is problematic as this silicone type is not designed or tested for this purpose.

The silicone used to bond the insulated glass units into the metal frame should be tested and designed for metal to glass connections.


What drainage solutions are integrated?

We get a lot of rainfall in the UK. That means that it is very important to ensure that your sliding door system has a high volume and integrated water drainage system as standard (not an expensive optional extra).

The issue that you will get is that many drainage solutions are designed for evaporation drainage. That type of drainage solution does not work for the UK climate as we do not get breaks in weather to allow the collected water to drain away.

You should ensure that your sliding door system includes a proper drainage solution that takes water away from the flush threshold (and stops water building up in the sliding channel).


You can see below a diagram of the minimal windows drainage solution. The neoprene drainage block is an included part of every installation of minimal windows. The drainage channel or system on the outside may differ from project to project depending on the requirements. This gives architects flexibility on the neoprene block height and external drainage solution used.

Two Part Drainage Block

Drainage Block

What paint/powder coated finish is going to be used?

Aluminium is a very versatile framing material as it can be powder coated in any RAL colour and can also have specialist metal finishes applied (such as textured powder coats or anodisation). But not all powder coated finishes are the same.

We powder coat the minimal windows profiles to 60 microns thick as standard. This is classed as a marine grade finish, but we find this higher specification of finish is more robust and offers a longer life expectancy to the framing.

In our opinion, you should not be using powder coated finishes that are thinner than this (nor should you use finishes that are much thicker as this leads to other issues).


If we are installing in a true marine environment, we then take additional steps to protect the aluminium frame from the harsher environment (such as pre-anodising and marine grade powder coating on top of that).

How do users slide the doors?

How are you sliding each pane if there are more then 2 panes? Are these handles on each sliding panel?

These are important considerations, especially for private residential projects where the clients will be using these doors on a daily basis. You need to make sure they are ergonomic, easy to live with an easy to operate.

Some of the things that can make slim sliding doors difficult to operate can be:

  • The location and operation of the lock activators (see below for more on this).
  • Having a handle on each sliding pane. This takes away from the minimal design.
  • Having no handles on each sliding pane. This means that you have to drag all sliding panes via the leading doors. If there are lots of doors that are large this can be a very heavy movement of glass for users (i.e a minimal windows® or minimal windows® 4+ installation can be up to 500kg per pane before automation is recommended. If you had 3 sliding panes at 450kg each dragging all 3 in 1 movement would mean sliding 1350kg of glass!)

The minimal windows® system has no 'handles'. Instead, the vertical coupling (where the sliding panes meet) is ergonomically sculpted to allow that to be used to slide the sliding panes individually if needed. This solution is very useful on large elevations of minimal windows® or where very heavy sliding units have been used.


How does the locking system work?

As above, how the user has to operate the doors is a key component of the overall success of architectural glass installations. How the locks are activated is very important to the system's usability.

On some systems, you have to activate a lock at the base of the sliding panel and at the top. If the doors are very tall this could cause an issue, also locking at the base is not ideal.

Having a lock on each panel is also an awkward solution. If you have a four-pane sliding door you don’t want to have to lock and unlock every sliding pane to open the elevation.

What you want is one lock at the leading edge of the sliding door that when unlocked allows the whole elevation to slide.


The minimal windows® system has one locking location at the leading edge of a sliding run. So, if you have a three-pane installation (with one fixed and two panes sliding in the same direction) you have one locking point.

The locking activation point of the minimal windows® system is in one location. Whether the system has a two-point or four-point locking system you operate this from one location via one handle/key.

This handle or key can also be installed at any height on the vertical profile required. As standard, we would set this at 1.1m from the finished floor level but this could be higher or lower depending on the project requirements.

What Next?

If you are interested in specifying a slim framed sliding door on your project visit our Contact Us page to see the different ways you can get in touch with us. We are happy to answer any questions you have, no matter how technical. We would also encourage you and your clients to visit the IQ Glass showroom in Amersham to investigate the functionality of different sliding door systems for yourself.