How to price perimeter drains and stormwater separation (drainage)

All below-ground drainage work and any connection to the public sewer may only be carried out by an authorised drainage contractor. This follows from the authorisation rules and must be done in accordance with the Standard for drainage work (DS 432). It is not a formality you can hand to an unqualified worker, and it is part of what the customer pays for. Write the authorisation into the quote as a value, not as a given.

Before the first cut of the spade you must file a utility-register enquiry (LER) in the register of pipe and cable owners. It is legally required and free, but it takes time to process and to work into the excavation. Hit a supply cable or a gas line because you skipped the enquiry, and the liability is yours. Put the register enquiry and setting out in as a separate line item so the customer can see the groundwork is part of the price.

The earthworks usually decide whether the quote holds. You have to calculate dig depth, soil type, machine access and where the soil goes. A perimeter drain is laid below the underside of the foundation, so the dig depth often sits at 1.2 to 2.0 metres along the house wall. At depths above roughly 1.7 metres the excavation must be shored or given a safe batter, and that costs both time and equipment.

Calculate the soil volume in solid cubic metres and remember the bulking factor: excavated soil typically takes up 20 to 30 percent more than in solid ground. If the soil goes to a landfill, the price depends on analysis and contamination class, and a single load of contaminated soil can cost several thousand kroner. Break the soil item down so the customer understands why it looms so large:

• Excavation in m³ split by depth interval (shoring above 1.7 m)
• Haulage and landfill per load, with a reservation for contamination class
• Reinstatement: drainage gravel, compaction, and restoring paving or lawn
• Extra hourly rate for tight access where hand-digging is required

A correct perimeter drain is laid with a fall of at least 3 per mille, that is 3 mm per metre, wrapped in drainage gravel and enclosed in geotextile so the soil does not silt the pipe up. The drainpipe runs to a collection well with a sand trap, so sand and sludge settle before the water is led on. Without a sand trap the system clogs, and then the customer calls after a year.

For separation, rainwater and wastewater must be split into two independent lines, typically to their own connection at the boundary. Calculate the running metres of pipe for both systems, the number of wells and their depth, and the transitions at existing installations. Materials from Wavin and Uponor via a wholesaler such as Brødrene Dahl are a reasonable basis for calculation, and the price of an inspection well rises sharply with depth, so it belongs in as a variable, not a fixed unit price.

A soakaway for rainwater must be sized by the paved area it has to drain and by the soil's infiltration capacity. Clay lets almost nothing through, sand a great deal, and that decides the soakaway size entirely. Always ask for an infiltration test, or state a reservation in the quote if it is missing, because an undersized soakaway is a warranty case.

Placement is also regulated. A soakaway must typically sit at least 5 metres from a building with a basement, at least 2 metres from the boundary, and well clear of drinking-water wells. If the plot lacks room for the correct clearance, it changes the whole solution, and that must be settled before you put numbers on it. Write the concrete distances into the quote so the customer knows the placement was chosen deliberately.

After separation the lines must be CCTV-inspected and documented, and you must submit a completion notice to the municipality. It is the drainage contractor's responsibility and a fixed part of the delivery, not something the customer opts into. Price inspection, survey and documentation as a visible line item, so there is no doubt it is included. It is also your own proof that the work was done correctly, should a dispute arise later.

The full calculation should always carry the same six blocks: register enquiry and setting out, excavation and haulage, pipes and wells, connection and separation, reinstatement, plus CCTV inspection and documentation. When you enter the house perimeter and dig depth, Calco converts it into solid cubic metres of soil, running metres of pipe and the number of wells, and ties the prices to the catalogue you use yourself, for example Wavin and Uponor via Brødrene Dahl. Then the quote rests on figures and standards instead of a guess, and you can send it the same day the survey is done.

Want to see the breakdown filled in with your own prices, then try it on a real job via Calco's quoting tool for drainage contractors: /tilbud-kloakmester.