Understanding Bifolding Door Threshold Options

One of the key features of bifolding doors, when compared to patio doors or French doors, is the threshold.  On most swing entrance doors or French Doors you will find a “step over” type of threshold although a low threshold option is available with most quality door products.

It is this threshold feature that makes bifolding doors popular.  It is a  key feature of bifolding doors- to bring the outside in and create that seamless link between the inside of your house and your garden.

bifolding doors showing exposed threshold
The low and flush threshold is a feature of bifolding doors over patio sliding or French doors.  Origin doors by Cheam Windows.

Bifolding door threshold choices:

Most common door thresholds on all types of doors have a rebate.  This is an upstand that is designed to create a physical barrier against any water entering the inside.  It also plays an important role in keeping the doors sealed.  This rebate can also be seen around the rest of your door frame and it is what the door shuts against.  Typically you may see some kind of rubber, nylon or brush seal there as well to further aid air and water ingress.

There are two types of bifolding door thresholds available.

The standard threshold is a rebated type that provides a bifolding door with its weather rating.  One great feature of even the rebated threshold is that it can still be sunk below floor level to create as flush a threshold as possible.

If you are building a new aperture for your bifolding doors, this is something that can be established with your builder.  The surveyor representing the window company you are purchasing your doors from that will visit you to take the manufacturing sizes.  These sizes will also take into account as flush a threshold as possible.

If you are replacing old patio or french doors for new bifolding doors, it may be necessary to remove a course of bricks to achieve a flush threshold compared to what you had before.  Again your surveyor will be able to advise you accordingly.

The flush or low threshold.

A flush threshold has no rebate and is designed to be a low “ramp type” threshold.  You should be aware that these doors offer no weather rating.  This is not to say that the doors will leak, however every manufacturer of most products (not just doors) must put procedures in place to minimise risk as they cannot accommodate every circumstance.

If new doors with a low threshold are fitted in a sheltered location with little driving wind and rain, or with a canopy above then these doors are less likely to suffer from water ingress.

Furthermore, the weather testing to British Standards that reputable manufacturers adhere to is always carried out with a rebated threshold. This is because rebated thresholds have the seals and design in place to prevent water ingress to required standards.  Low thresholds do not.

Where can you use doors with a low threshold?

Bifolding doors with low thresholds normally have no recognised weather rating and are intended for internal applications such as room dividers.  Air bifolding doors are one example of a high end bifolding door that offers a low threshold with a weather rating where other bifolding doors do not or recommend a low threshold for internal use only.

Some people choose to install bifolding doors to garden rooms and obviously bifolding doors are installed in swimming pool enclosures.  If you are not worried about water ingress or the possibility of water ingress a low threshold can be used at your own risk. But bear in mind your doors will not be covered by any warranty should any water find its way inside.

As we say, there are bifolding door systems avaialble that do offer low thresholds with a weather rating so contact us and we can help you further and provide you details of suitable products.

What is the cill

The cill is a separate aluminium extrusion similar to a window cill you see externally.  The bottom of the door sits on top of the cill that is designed to project water away from the brickwork underneath the frame.

Thresholds enable transition from inside to outside.

You must take into consideration the location and use of your bifolding doors.  The rebated threshold is the best type and as this can be set lower with only a marginal up stand of 12mm this is the most appropriate option.  A 12mm up stand is hardly noticeable in normal use and will give you the peace of mind that your doors remain air, wind and water resistant.

Our gallery below shows the various threshold options available on market leading Origin Bifolding Doors and how they interact with the internal and external floor levels.



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