MEP Design Sections: Water, Drainage, Heating, Electrical

MEP design places a building's hidden systems in advance. What water supply, drainage, heating and ventilation, and electrical sections cover, and how they are coordinated.

In the first months of construction everyone looks at the foundations, frame and façade. Pipes, cables and ducts are left aside with the thought that the tradesman will sort them out on site. The result is drilling holes through beams for drainage after the walls are built, tearing down a finished ceiling, or running air-conditioning pipes openly across the façade. Mechanical, electrical and plumbing (MEP) design exists to position these systems at the same time as the structure and architecture, without them getting in each other's way.

Water supply: from source to tap

The water supply section shows where water enters the building, the location of the meter and filters, and the routes of hot and cold water pipes. In villas it often also includes a storage tank, a pump set and water treatment equipment.

The design shows pipe diameters to each fitting, the location of manifolds and isolation valves. The type and position of the water heater are chosen. In a long villa plan where hot water takes a long time to reach a bathroom far from the source, a recirculation line is provided. This is one of the decisions that are hard to add later.

Drainage: falls and venting

Drainage works by gravity, not pressure. The key issue in this section is therefore fall: horizontal runs must be laid at a gradient, and stacks should line up floor by floor wherever possible. Moving a bathroom far from the stack on an upper floor requires depth in the floor, which means either a step or a raised floor.

Stack venting, the position of access points and the level at which waste leaves the building are resolved here too. Where there is no public sewer, the location of an on-site treatment unit and service access to it are considered together with the site plan. Rainwater is a separate system: roof drainage, yard gullies and discharge off the plot are shown separately in the design.

Heating, cooling and ventilation

This section is based on calculations of the building's heat loss in winter and heat gain in summer. The figures depend on insulation of walls, roof and windows, room orientation and the size of glazed areas. The heat source, whether a boiler, heat pump or another system, is then selected, along with emitters for each room: radiators, underfloor heating or fan coils.

For cooling, the positions of indoor units, a place to group outdoor units out of sight, and routes for refrigerant and condensate lines are determined in advance. Ventilation is often forgotten. Modern airtight windows and well-insulated walls reduce natural air exchange; extract ventilation is considered for kitchens, bathrooms and dressing rooms, and in larger houses a mechanical system with heat recovery. Because ducts are large, their routes directly affect ceiling heights.

Electrical and low-voltage systems

The electrical section starts with the incoming supply, the meter and the main distribution board. A load calculation is carried out, circuits are grouped and protective devices chosen for each. Kitchen appliances, heaters and air conditioners get dedicated circuits. Earthing and additional protection in wet rooms are included as well.

The socket and switch layout is developed together with the interior: switches on both sides of the bed, sockets for a desk, garden lighting, gate automation. Low-voltage systems such as internet, television, intercom, CCTV and alarms need their own cable routes, and running them alongside power cables is not recommended.

Coordination: when systems clash

The hardest part of MEP design is not preparing each section separately but bringing them together. Typical clashes include:

• a ventilation duct and a beam passing through the same point;
• a drainage stack landing in the middle of a wide glazed opening on the floor above;
• no wall recess provided for the underfloor heating manifold;
• the electrical board placed in a damp plant room beneath water pipes;
• a concealed light profile and an air-conditioning unit competing for the same space in a suspended ceiling.

These clashes are found on paper, when all sections are overlaid on the same plan. Before concrete is poured, the positions of openings through slabs and beams must be agreed with the structural engineer.

A quick check for clients

When approving the design, ask: where is the plant room, and is there access to replace equipment; are all stack positions shown on the plan; where will outdoor units sit on the façade; and have spare cable routes been left for systems that might be added in future?

Alongside its construction service, Zaferoğlu İnşaat also works in the energy and electrical fields. You are welcome to discuss questions about planning the building services for your house with us.