Frequently Asked Questions

For most domestic properties, a half-round or ogee system with 112mm guttering is sufficient. Larger roofs, commercial buildings, or areas with high rainfall may require our deep-flow or high-capacity systems. The key calculation is effective roof area combined with local rainfall intensity. Our technical team can help you calculate the correct system—just contact us with your roof dimensions.

Our rainwater systems are available in White, Black, Brown, Grey (RAL 7016 Anthracite Grey), and Caramel. Foiled woodgrain finishes including Rosewood, Oak, and Anthracite Woodgrain are available in our KlassicoGee premium range. All colours are manufactured through the material, not painted, so they won't peel or flake.

Our PVC-U rainwater systems are designed to last 30+ years with zero maintenance. The material won't rot, rust, or corrode. Colour stability is ensured through UV-resistant formulations. When registered, our guarantee covers rainwater products for up to 15 years.

While some dimensions may appear similar, we always recommend using a complete Kalsi system for guaranteed compatibility, joint integrity, and warranty coverage. Mixing brands can lead to leaking joints due to slight dimensional differences between manufacturers.

SN4 and SN8 refer to ring stiffness classifications. SN4 (4 kN/m²) is suitable for most domestic applications with standard cover depths. SN8 (8 kN/m²) is designed for deeper installations, areas with heavier traffic loading, or poor ground conditions. For typical garden/driveway drainage, SN4 is usually sufficient. Always check building regulations for your specific application.

Our 110mm underground drainage can be installed at depths from 300mm to 10m depending on the pipe class and bedding conditions. For standard domestic installations under garden or patio, minimum 300mm cover is recommended. Under driveways, minimum 600mm cover with SN8 pipe is standard practice. Always refer to Building Regulations Part H.

Inspection chambers (up to 1m deep) are used at junctions, bends, and changes of direction in domestic drainage runs. They provide access for maintenance and clearing blockages. For depths exceeding 1m, a manhole is typically required. Building regulations require access points at certain intervals—consult Part H or your building inspector.

Push-fit systems are faster to install and allow for thermal movement, making them ideal for most domestic applications. Solvent weld provides a permanent, rigid joint that's preferred in commercial applications or where movement must be restricted. For internal soil stacks in residential properties, push-fit is the most popular choice among installers.

Basins, baths, and showers typically use 32mm or 40mm waste pipe. Toilets (WCs) always connect to 110mm soil pipe. Kitchen sinks generally use 40mm waste. A washing machine or dishwasher typically connects via 40mm waste pipe. These sizes are specified in Building Regulations Part H and BS EN 12056.

An air admittance valve (AAV) allows air into the drainage system to prevent trap siphonage, without the need for a traditional open vent pipe through the roof. They're commonly used as an alternative to a vent pipe in loft conversions, extensions, or where running a vent pipe to roof level isn't practical. They must be accessible for maintenance and positioned correctly per building regulations.

It depends on the condition of the existing timber. If the boards are solid and level, capping boards (9mm) can be fitted directly over existing timber. However, if the timber is rotten, warped, or damaged, it should be removed and replaced with full replacement boards (18mm). We always recommend a proper inspection before deciding—rotten timber behind capping boards will only get worse.

Building regulations require adequate roof ventilation to prevent condensation in the roof space. As a general rule, continuous ventilated soffit (or solid soffit with separate vents) should provide 25mm continuous opening or equivalent. For rooms-in-roof construction, different ventilation requirements may apply. Always check with your building inspector or refer to Approved Document C.

Our PVC-U roofline products are manufactured with UV-resistant formulations designed to maintain colour integrity for decades. White products remain white, and our foiled woodgrain finishes (Rosewood, Oak, Anthracite) are laminated with high-quality exterior-grade films. Some very slight weathering is normal over 20+ years but dramatic fading should not occur.

Yes, our PVC wall panels are 100% waterproof and impervious to moisture—making them ideal for bathrooms, shower rooms, wet rooms, and kitchens. Unlike tiles, there are no grout lines for water to penetrate. The tongue-and-groove joints create a virtually watertight surface when properly installed.

Yes, panels can be fitted over existing tiles provided they are securely fixed to the wall and the surface is flat. Use a suitable PVC adhesive (we recommend a grab adhesive) applied to the back of each panel. This saves the time, mess, and cost of removing old tiles. Ensure the wall surface is clean and dry before fitting.

We primarily supply through our network of stockists and builders' merchants across the UK. For trade customers, this provides local availability, credit facilities, and convenience. To find your nearest stockist, visit our stockist finder page or call our sales team on 0121 693 0373.

Standard guarantees vary by product range, from 10 years for rainwater systems to 25 years for underground drainage. By registering your products within 30 days of purchase, you can extend the guarantee period significantly—for example, rainwater systems extend to 15 years and roofline products to 20 years. Register at our guarantee registration page.

Stock availability and delivery timescales depend on your chosen stockist. As a UK manufacturer, we maintain comprehensive stock levels at our Birmingham warehouse and supply merchants daily. Most standard products are available from stock. For larger project quantities or non-stock items, please contact our sales team to confirm availability.

Yes, we can provide product samples for colour matching and specification purposes. Contact our sales team at sales@kalsiplastics.co.uk or call 0121 693 0373 with your requirements. Sample packs are available for roofline, cladding, and wall panelling ranges.

Key product ranges including our rainwater systems, underground drainage, and soil & waste systems carry BSI Kitemark certification. This means products are independently tested to British Standards, our factory is regularly audited, and ongoing surveillance testing takes place. See our Quality & Certifications page for full details.