Threshold Channel Drainage — Bi-Fold Doors & Patio Transitions
Threshold channels provide a discreet, low-profile drainage solution at doorways and transitions between internal and external spaces. Forti Nova supplies the Pave-A-Drain polypropylene threshold system and Forti Nova threshold channels — both available with silver and black aluminium grates — with a full range of compatible accessories.
What is a Threshold Channel Drain?
A threshold channel drain is positioned at the exact transition between an interior floor and an exterior patio or step — most commonly at bi-fold or sliding door openings. It intercepts rainwater running towards the opening and diverts it to an underground drain before it can enter the property.
The key characteristic of a threshold channel is its narrow internal width — typically 36mm for the Pave-A-Drain system. This slim profile allows the drain to sit flush within a door threshold or at the edge of a paved surface with minimal visual disruption. The channel top is finished level with the external paving to eliminate any trip hazard.
Threshold channels are suitable for pedestrian use only. They are not rated for vehicle crossing. If a threshold area is also a vehicle access point — such as a garage entrance — a B125-rated driveway channel is required instead.
Threshold channel is right when:
- Bi-fold or sliding door draining onto a patio
- Water ingress at a patio door threshold
- Transition between internal tiled floor and external paving
- Narrow installation zone — no space for a standard 100mm channel
- Aluminium grate finish required for a contemporary aesthetic
Consider alternatives when:
- Vehicles will cross the drain — use B125 driveway channel
- Large patio area with high runoff — A15 channel may have better hydraulic capacity
- Heavy pedestrian traffic in a commercial or public setting
- Underground outlet pipe not close to the threshold position
Step 1 — Choose Your Channel Width
Three threshold channel widths are available — select the one that suits your installation.
Installation Overview
Threshold channel installation requires precise positioning relative to the door sill and the finished paving level. The channel top must sit flush with the external surface — any raised edge creates a trip hazard and a point of water bypass. A minimum fall toward the outlet is needed to ensure drainage, and the outlet pipe position must be confirmed before installation begins.
The Pave-A-Drain system is typically set in a concrete bed. The channel should be level across its width and at the correct fall along its length. Connectors join sections; T-junctions and L-junctions allow more complex layouts. All installation must follow the manufacturer's current installation guide for the specific product.
For product-specific installation instructions, request a datasheet from our team or read our general installation guide.
Domestic A15 Channel Drainage
For patios, garden paths and pedestrian areas requiring wider capacity.
Driveway Channel Drainage — B125
For garage thresholds and areas where vehicles will cross the channel.
How to Choose a Channel Drain
Covering application, load class, finish and hydraulic considerations.
Installation Guide
Concrete surround, fall, outlet connection and manufacturer requirements.
All Accessories
Full accessories listing for all channel families.
Technical Enquiry
Request a quote, datasheet or project advice from our team.
Frequently Asked Questions
What is a threshold channel drain and when do I need one?
A threshold channel drain is a slim-profile linear drain positioned flush at the transition between an internal floor and an external surface — most commonly at bi-fold doors, sliding doors and patio door openings. It intercepts rainwater running towards the opening and diverts it to an underground drain before it can enter the building. It is typically specified as part of a bi-fold or sliding door installation, or when an existing property has recurring water ingress at a door threshold.
What is the Pave-A-Drain system?
Pave-A-Drain is a polypropylene threshold channel system with a 36mm internal width. It is supplied in 1000mm and 2000mm section lengths and is available with silver or black aluminium grates for a contemporary finish. A full range of accessories is available including connectors, T-junctions, L-junctions, stop ends and outlets. It is suitable for pedestrian use at doorways and patio transitions.
What is the internal width of a threshold channel?
The Pave-A-Drain threshold channel has a 36mm internal width — significantly narrower than a standard channel drain (typically 100mm internal width). This slim profile is intentional: it allows the drain to sit within a door threshold or flush with a patio edge with minimal visual disruption. The narrower width limits hydraulic capacity, so threshold channels are designed for the lower flow rates typical at doorways, not for main site drainage runs.
Can threshold channels drain large patio areas?
Threshold channels are designed for point-of-transition drainage — intercepting water at the immediate door threshold, not for draining large paved surfaces. For patios with significant rainfall catchment, a standard A15 channel drainage system is more appropriate. If you are unsure whether a threshold channel provides sufficient hydraulic capacity for your specific area, contact our team.
Can a threshold channel take vehicle loading?
The Pave-A-Drain system and Forti Nova threshold channels are rated for pedestrian use. They are not suitable for areas where vehicles will cross the channel. If a threshold area is crossed by vehicles — for example at a garage entrance — a B125-rated system is required instead. Confirm load requirements with our team before specifying.
What finish options are available for threshold drainage?
Threshold channels are available with silver aluminium grates for a bright, contemporary finish, and black aluminium grates for a darker, more discreet look. Pave-A-Drain is supplied as a complete channel with aluminium grating in 1-metre and 2-metre lengths. Corner, T-junction, L-junction and stop end accessories are available in both silver and black finishes to complete the installation.
Where should a threshold channel be positioned?
A threshold channel should be positioned flush with the door sill or just outside it — at the exact transition point where water would otherwise flow from the external surface into the building. The channel top should align with the finished external paving level so there is no trip hazard. The run must slope toward the outlet — a minimum fall of 1:200 is generally recommended, but confirm with the manufacturer's installation guide for the specific product.
Do I need planning permission for threshold drainage?
Threshold drainage is typically installed as part of bi-fold or sliding door installation or as part of a patio project. These works may require Building Regulations approval depending on the scope. In England and Wales, works affecting drainage discharge may also need to comply with surface water management guidance. Seek independent building control and planning advice for your specific project — Forti Nova does not provide planning or regulatory guidance.
What accessories do I need for a threshold channel run?
A complete Pave-A-Drain installation typically requires complete channel-and-grate sections (silver or black), connectors between channel sections, at least one stop end outlet connecting to the underground drain, and end blanks to close the run terminations. For corners or T-junctions in the run, matching aluminium accessories are available. Contact us to confirm the full component list for your specific layout and run length.
What are the Forti Nova threshold channel options?
In addition to the Pave-A-Drain polypropylene body system, Forti Nova supplies Forti Nova threshold channels with silver aluminium and black aluminium grate finishes. These are specified where the full aluminium aesthetic is required. Compatible accessories include stop end outlets, end caps, bottom outlets, joints and corner and T-junction pieces in both finishes.
Need help with threshold drainage?
Call our team in Blackburn or submit a project enquiry with door opening width, paving level and outlet position.
Compare channel systems and matching fittings
Compare the channel family, load class and grate below. Open a product for its dimensions, available pricing and compatible fittings. Load class and installation requirements must suit the project; accessories are specific to their channel family.
| Channel system | Load class | Grate | Accessories |
|---|---|---|---|
| Pave-A-Drain black — 1m completePave-A-Drain Aluminium | Confirm specification | black aluminium | View matching fittings |
| Pave-A-Drain silver — 1m completePave-A-Drain Aluminium | Confirm specification | silver aluminium | View matching fittings |
| Threshold Slot Channel — 2mPave-A-Drain | A15 | See product details | View matching fittings |
| Threshold Channel — SilverThreshold | A15 | Aluminium — silver | View matching fittings |
| Threshold Channel — BlackThreshold | A15 | Aluminium — black | View matching fittings |
| Pave-A-Drain Channel — Black Aluminium Grate — 2000mm lengthPave-A-Drain Aluminium | Confirm specification | black aluminium | View matching fittings |
| Pave-A-Drain Channel — Silver Aluminium Grate — 2000mm lengthPave-A-Drain Aluminium | Confirm specification | silver aluminium | View matching fittings |