Draw the rainwater route from the new roof to its final discharge or collection point. Review changes to existing pipes, the terrace and garden at the same time. A new downpipe without an assessed downstream connection is not a complete drainage proposal.
How does the existing drainage work?
Identify where rainwater currently leaves the house and any outbuildings. Mark visible downpipes, gullies and other connection points. Describe locations where water collects or reappears without assuming the cause. Old drawings may help, but they do not necessarily confirm underground routes.
Establish which connections require investigation. Identify pipes or chambers that will end up beneath new floors or paving. Components that become difficult to reach deserve attention before work starts, particularly where their current location would conflict with the extension’s foundation or intended internal layout.
How do the roof and garden routes connect?
The roof has its own drainage pattern, but the water must then travel elsewhere. An outlet position can conflict with a garden door, access route or existing foundation. Show roof drainage on the same site plan as the external layout.
Coordinate paving falls and levels with the threshold. Concealing water behind a finish does not resolve the question of where it goes. Ask how the extension affects existing outlets and which will be relocated or altered so no part of the route depends on an unexplained assumption.
How will drainage remain accessible for maintenance?
The system needs to remain accessible, not merely connected on a drawing. Discuss inspection points before fixed cabinetry, floors or terraces cover the area. Ask which parts require periodic attention for the selected arrangement.
Keep planting and storage away from components that must remain reachable. Record the installed route with photographs and an updated plan. This helps during later changes when the original installer is unavailable or visible components have moved, and reduces reliance on informal recollection of what was installed beneath finished surfaces.
Which solution fits the particular site?
Discharge, collection or another treatment of rainwater requires consideration of local conditions and relevant arrangements. Do not assume an existing pipe is suitable for the altered layout without assessment. Ask which information supports the proposed approach and whether municipal coordination is needed.
The quotation should identify included connections, excavation and paving reinstatement. This avoids treating the roof as complete while the downstream route remains unresolved. Record the responsibility at any boundary between the roofer, groundworker and other contractors contributing to the same system.