The Essential Guide to Threshold Drainage

What is Threshold Drainage?

Threshold drainage is a surface water management system installed at the boundary between two surfaces. This could be between a pavement and a wall or a doorway from an outdoor area to an indoor area, for example.

Unlike general surface drains that cover a wider drainage area, threshold drainage serves a more specific purpose. They are designed to create a barrier against water ingress at entry points or where pooling water could damage a building’s foundations.

In short, threshold drains act as a last line of drainage defence during heavy rainfall, channelling excess surface water away to safeguard your property from potential damage.

A Brief History of Threshold Water Management

The need to control water around entry points is as old as buildings themselves. Historically, solutions were often simple, using mild slopes, raised thresholds, or basic channels carved into stone or earth. Early efforts focused more on redirecting flow than fully managing it, often leading to less effective results during heavy rain.

Today’s modern threshold drainage options represent a notable advancement over earlier efforts. They deliver more efficient water collection, use more sustainable materials, and feature designs influenced by evolving building standards.

Why is Effective Threshold Drainage Important?

Ignoring the importance of proper threshold drainage solutions is never advisable. Poor drainage can lead to surface water pooling at entryways or flowing unimpeded into a building.

The consequences of allowing this to occur can vary from minor inconveniences to significant issues. However, they are almost always expensive to fix. These may include:

Water Damage to Buildings

Persistent moisture can weaken foundations, cause timber frames to rot, damage flooring (both internal and external), and harm interior finishes like plaster and paint.

Safety Hazards

Safety Hazards - Standing water can often leave a slimy film on surfaces due to the growth of microorganisms. This can create dangerous slip-and-fall risks for residents and visitors.

Pest Control Problems

Poor drainage creates ideal breeding grounds for insects, and moisture can also attract rodents, leading to further issues inside your property.

Increased Maintenance Costs

Ongoing issues with water damage, mould growth, and material deterioration caused by dampness will inevitably result in increased maintenance costs and more frequent repairs.

Reduced Property Value

A property showing visible signs of water damage or a history of drainage problems can discourage potential buyers and substantially lower its market appeal and overall value.

Investing in a robust and efficient threshold drainage system is not just about convenience. It is a vital step in safeguarding your investment by improving safety and preserving the long-term integrity and value of your property.

Threshold Drainage Solutions

The advancement in construction materials and design principles has transformed threshold drainage from simple run-off solutions into sophisticated, integral parts of modern building design. Today's systems not only manage water efficiently but also significantly enhance the visual appeal and overall functionality of a property.

Common Types of Threshold Drainage Systems

While various drainage solutions are available for thresholds, certain types have become industry leaders due to their effectiveness and suitability for this vital surface water management role.

Linear Channel Drains

These are the most common and effective modern threshold drainage solutions available. Linear channel drains feature a long, narrow channel, usually with a removable grate, that can be installed along the edge of a doorway, patio, or pathway, etc.

Recent innovations in channel drainage have resulted in specialised threshold channel drains designed with lower profiles and enhanced flow characteristics that seamlessly integrate with modern door systems, such as bi-fold and sliding doors.

Point Drains/Gullies

Typically, point drains or gullies consist of a square or circular grid or grate in the ground, beneath which is a drainage gully or trap that connects directly to an underground drainage system.

While effective for localised pooling, they lack the continuous intercepting capacity of linear systems, making them less suitable as primary threshold drainage for larger or more exposed entryways.

As arguably the most effective and cost-efficient form of threshold drainage, let’s take a closer look at the channel drain solution.

Key Features of Modern Threshold Channel Drains

Modern channel drainage systems designed for thresholds are characterised by several key features that improve their performance, appearance, and user experience. These include:

• Low Profile and Minimalist Design - modern threshold channel drains sit flush with or just below the surrounding surface. This low profile ensures a trip-hazard-free transition and maintains clean, uninterrupted sightlines, which are crucial for contemporary architectural aesthetics.
• High Flow Rates - Despite their slim appearance, these systems are designed for high hydraulic efficiency, capable of quickly draining large volumes of water during heavy rainfall, thereby preventing dangerous pooling.
• Aesthetic Grates - Beyond mere functionality, the visible grates that sit on top of the channels can be incorporated as a design feature. Available in a wide range of materials and grid patterns, it is possible to select a channel drain grating that complements the surrounding paving or building façade.
• Easy Cleaning - To maintain optimal performance, modern threshold drains often feature easily removable grates to simplify the removal of debris, such as leaves and sediment. This design makes routine maintenance straightforward, ensuring the system stays unblocked and fully effective.
• Durability and Longevity - Made from strong, corrosion-resistant materials, these systems are designed to endure the elements and frequent foot/vehicular traffic, ensuring many years of dependable performance with minimal wear.
• Versatile Connectivity - Modern linear threshold drainage systems provide flexible connection points to standard underground drainage pipework, including end outlets, bottom outlets, and corner units, enabling adaptable layouts to meet various project needs.

The focus on these advanced features ensures that today's threshold channel drainage solutions deliver an unmatched combination of efficiency, durability, safety, and aesthetic appeal.

Factors to Consider Before You Buy Threshold Drainage

Before making a purchase, evaluate the unique requirements of your project. This initial assessment will help you identify the most effective and long-lasting drainage solution. Be sure to consider the following carefully:

Expected Water Volume and Runoff

One of the most important factors is the amount of water your threshold drainage system will have to handle. To determine this, you’ll need to consider the size of the catchment area, assess the permeability of surrounding surfaces, and assess local rainfall patterns.

Traffic Type

The type and frequency of traffic that the drainage system must endure directly influence the required load-bearing capacity of its grates and channel body. You need to assess if your system will be subjected to pedestrian, light Vehicle, or heavy vehicle traffic.

Aesthetic Considerations

Modern threshold drainage is no longer just functional; it also contributes significantly to your property's visual appeal. Think about how the drainage system will blend with the surrounding architecture, paving materials, and landscape design.

Available Space

The depth and width of the available installation space, especially for door thresholds, are crucial factors to consider. Ensure the dimensions of the chosen system align with the structural constraints and finished floor levels.

Budget

While it might be tempting to choose the cheapest solution, remember that a threshold drainage system is a long-term investment in your property's protection. It’s always best to try to balance the initial cost with long-term value and peace of mind.

Threshold Drainage Material Choices

The materials used for both the channel body and the grating of your threshold drainage system play a crucial role in its durability, maintenance, and visual integration with your property.

Different materials provide unique benefits tailored to various uses and aesthetic tastes. Here's a brief overview of some of the available options:

Channel Body Materials

• Plastic (uPVC) - Light, affordable, easy to install, and resistant to many chemicals. Perfect for light-duty applications and where cost-effectiveness matters.
• Steel (Galvanised or Stainless) - Provides exceptional strength and durability. Galvanised steel is strong and economical, while stainless steel offers excellent corrosion resistance and a high-quality appearance, ideal for high-end applications and harsh environments.
• Concrete - Very strong and durable, commonly used for heavy-duty applications where substantial load-bearing capacity is necessary.

Channel Grating Materials

• Plastic - Cost-effective and lightweight, commonly used with plastic channel bodies for light to medium duty load areas.
• Steel (Galvanised or Stainless) - Galvanised steel grates are strong and commonly used for various traffic loads. Stainless steel grates provide a sleek, contemporary appearance with excellent corrosion resistance, making them a popular choice for architectural finishes.
• Aluminium - Lightweight, strong, and highly resistant to corrosion, offering a clean, modern look.
• Iron (Cast Iron) - Extremely robust and durable, typically used for heavy-duty applications (e.g., D400 load ratings) where maximum strength is required, often providing a traditional or industrial aesthetic.

If you would like a more detailed explanation of the options available, take a look at our “Channel drain material and grating options explained” article.

Understanding Load Ratings for Threshold Drainage

When choosing a threshold drainage grate and channel, understanding load ratings is essential for safety and durability.

These ratings indicate how much weight a drainage system can safely withstand, as outlined by standards like BS EN 1433 (see Standards and Regulations section for more details). For threshold drainage, the most relevant ratings will be:

Always ensure that the load rating of your selected channel and grating matches the maximum expected traffic load of the installation area. This will help to maintain safety, avoid damage, and guarantee the long-term performance of your surface water drainage solution.

For more detailed information about loading classes, please see our “Choosing the right loading class” article.

British Standards for Threshold Drainage

BS EN 1433: Drainage Channels for Vehicular and Pedestrian Areas is the most significant standard for linear channel drains. It specifies the requirements for the design, materials, testing, and marking of pre-cast drainage channels used for the collection and conveyance of surface water.

Threshold Drainage Building Regulations

In the UK, all building work, including the installation of threshold drainage, must comply with the Building Regulations 2010. Approved Document H: Drainage and Waste Disposal - Requirement H3: Rainwater Drainage is especially relevant, as it specifies that your drainage system must be capable of effectively collecting and safely discharging all rainwater falling onto its catchment area, preventing damage to the building fabric, poor conditions, or adverse effects on the health and safety of individuals.