FAQs

Service risers are vertical shafts or openings that run through the floors of multi-story buildings. Their primary purpose and function is to house mechanical, electrical, and plumbing (MEP) services to enable utilities to be distributed to each floor level throughout the structure.

Clearance: Ensure the structural opening allows enough space for both the services and the support frame.

Coordination: Services positioning should ideally follow Comtec’s Design Guidelines and coordinated within the BIM model to avoid clashing with the GRP joists.

Safety: Design the floor to meet specific load requirements (e.g., 2.5kN/m² or 5kN/m²) based on expected foot traffic.

Services exit from shaft: Consider the best method for services distribution to exit the shaft at each level

Riser floors should be considered during the Pre-Construction/RIBA Stage 3 design phase. Early integration allows for better BIM coordination and ensures the “cast-in” shutters are ready for the concrete pour. It also allows early identification for the potential to use the WallBeam product which provide a much more effective alternative to secondary steel beams for supporting partition walls.

The biggest challenges include managing potential clashes between structural supports and MEP services, ensuring fire-stopping compliance, and maintaining a safe working environment during the construction of the shaft.

Coordination is typically achieved through 3D BIM modelling. MEP engineers place their pipes and ducts in line with Comtec’s Riser Design Guidelines then our design team will finalise positions of GRP joists and support beams around those services to ensure no overlaps or clashes.

By designing the riser floor before services are installed, joists can be positioned specifically to leave clear paths for large ducts and pipes, preventing the need for costly on-site modifications.

In traditional systems, this causes delays and rework. In the AlphaRiser system, the adjustable channel allows joists to be moved or repositioned manually to accommodate the clash without structural compromise.

Space is maximized by using high-strength GRP profiles that require a smaller footprint than traditional steel, and by utilizing the AlphaRiser cast-in channel which ensure zero protrusion into the riser void, or the slimline FreeBeam which, at 32mm deep does not clash with typical MEP bracketry. Furthermore, the GRP grating has equal structural strength in both directions laterally meaning that cantilevered overhangs of up to 300mm can be achieved.

Future-proofing is achieved by using the AlphaRiser system. The patent-pending AlphaRiser channel enables support joists to be relocated by releasing the bolts and sliding the joists within the channel as required, without the need to drill new holes in the concrete core wall or floor slab. Grating can be easily cut or replaced in the future if new services need to be added, and the non-corrosive nature of the material ensures a long lifespan.

Yes. Systems like AlphaRiser FR are designed with a “drop-floor” mechanism that allows the floor surface to be lowered after service penetrations are complete. This provides a 100mm deep “tray” which can be effectively fire stopped and then filled with a fire-stopping compound (like Quelfire QF2) directly around the services, creating a horizontal fire seal. This system is tested to BS 1366:3 and provides in excess of 4 hours fire resistance for both integrity and insulation.

A slim steel mesh is fixed over the GRP grating, followed by proprietary fire batts e.g. Rockwool approved product or similar in accordance with manufacturer’s instructions. Appropriate sealing must be applied around all interfaces to ensure compliant smoke and fire seal is achieved. Careful management of this area will be required during construction to ensure integrity and insulation are maintained. GRP/steel mesh combination.

Specialist fire-protection contractors provide these services. They often use products from manufacturers like Quelfire, Hilti, or Rockwool that are specifically tested for use with GRP riser floor systems.

Where a fire-rated partition passes through a riser, the floor system must be broken using the WallBeam or steel beam clad in layers of fire rated board.

Falls from height (during construction).

Falling objects hitting workers below.

Manual handling injuries (heavy steel vs. light GRP).

Fire spread through unsealed shafts.

Structural failure due to inadequate joist supports.

They eliminate the “leading edge” risk by providing a permanent, load-bearing floor ahead of the floor slab being poured, or by providing a fully assembled complete unit on an existing floor void (retro-fit for existing buildings being refurbished).