A key feature of bifolding doors is the threshold. Many French or swing entrance doors include a “step over” kind of threshold, while bifolding doors normally have a lower threshold – making them a popular choice.
What are thresholds?
Manufactured from metal or wood, a threshold is the sloping cross-piece that extends across the bottom of the door area. Slightly raised to stop water from coming in, it’s often fitted with a weatherproof strip to provide insulation.
The threshold shouldn’t be confused with the sill, as this is the part of the door frame that runs across the bottom, sitting directly on the floor. The sill, a cross-piece that completes a pre-installed door frame, sits underneath the threshold.
What are the differences between the available thresholds?
The two main types of bifolding door thresholds are a low or flush threshold and a standard threshold. There are also various fitting options available:
- Low threshold without a sill
- Low threshold with a sill
- Standard rebated threshold set on a sill
- Standard threshold without a sill
A rebate is an up-stand that keeps the doors sealed and creates a physical barrier that stops water entering the property. A standard rebated threshold provides the bifolding doors with their weather rating. The rebated type can still be sunk below ground level to create as low a threshold as possible.
How does the threshold affect the weather rating?
A flush threshold doesn’t have a rebate and as such doesn’t have a weather rating. This doesn’t mean the doors will leak, however. Although low thresholds are usually used internally, they can also be suitable for external use in a sheltered location.
The bottom of the door sits on top of the sill to project water away from the brickwork under the frame. The best threshold aesthetically is one that’s as low as possible, thus creating a smooth transition.
Schuco & Raynaers bifolding doors
Two popular bifolding door manufacturers, Schuco and Raynaers, are both renowned for manufacturing high-quality products.
Schuco aluminium bifolding doors have two threshold options: low and standard. The low threshold is suitable for internal use or sheltered locations. Often used on bifolding doors between two interior rooms, with a rise above the floor of only 3.5mm, most of the threshold is positioned beneath the finished floor level.
The Schuco low threshold can be used to connect the interior and exterior parts of the home. A low threshold without a sill can be an effective way of creating a smooth transition. However, a low threshold isn’t recommended for areas that are exposed to a lot of wind and rain.
The standard threshold has an up-stand on one side of 60mm and provides a complete weather shield. When combined with a sill at 25mm, this means it retains maximum protection from the wind and rain, while still being relatively low.
A popular design, the Schuco ASS-70FD aluminium bifolding door comes with standard or flush threshold options – the standard being weather rated.
Reynaers’ alumiunium bifold doors are manufactured with standard or flush threshold options. The popular CF 68 bifolding door is highly versatile, providing four different threshold options that range from wheelchair-friendly flush thresholds to the standard threshold.
The flush threshold is only 0mm to 15mm above the ground, with a wheelchair ramp option; the low is 9mm to 30mm; the double weatherseal option is 23mm to 44mm; and the high performance is 23mm to 74mm. Each has a different performance level in terms of water/air-tightness and wind-resistance.
Why would you choose one threshold over another?
If you’re looking for weather rated bifolding doors for exterior use, the standard threshold bifolding doors would be preferable. If you’re looking for a smoother transition between two areas, a flush threshold door will achieve this – although it is better suited to interior applications or in sheltered exterior areas.