Drainage

Before any new design is drawn, find out what drainage already serves the site: is there an existing connection, and does it work; where do existing pipe runs cross the plot, and are there any easements or rights allowing a neighbour's drainage to cross the land, or this site's drainage to cross someone else's; and what condition are any existing inspection chambers, septic tanks or soakaways in.

Existing drainage that appears unused is not necessarily disused — it may still be live, and building over or near it without checking is a common and costly mistake.

Where a mains sewer connection is available, the practical questions are where the connection point is, how deep it runs, who owns and maintains the section between the site and the main, and whether any adoption agreement is needed for new drainage that will eventually be adopted.

Where mains drainage is not available — common on rural Cumbrian plots — the site needs an off-mains solution: typically a septic tank or package sewage treatment plant discharging to a soakaway or, in some cases, a watercourse. What is acceptable depends on the site, the receiving ground or watercourse, and current environmental regulation — a package treatment plant discharging to a watercourse, for example, generally needs to meet specific quality and permitting requirements.

Roof and hardstanding water has to go somewhere, and the options are broadly: a soakaway, a watercourse, a surface water sewer, or attenuation with a controlled discharge rate. Which is available and acceptable depends on the ground, the site's flood risk and any discharge restrictions imposed by the planning authority or drainage authority.

Discharging to, or working near, a watercourse can bring its own consent requirements from the relevant environmental regulator, separate from planning permission. Levels across a site also matter more than they first appear — drainage runs by gravity, and getting falls wrong, or discovering the invert level needed is deeper than assumed, changes excavation depths and cost.

Where drainage needs to cross a neighbouring property, or a neighbour's drainage crosses this site, a formal easement — or the absence of one — is worth establishing before design rather than after a dispute arises.

Building over or near an existing sewer, even a private one, is generally controlled and may need agreement from the sewer's owner or the water company, particularly if it could later be adopted. Beyond the build itself, inspection chambers need to remain accessible for maintenance for the life of the building — burying a chamber under a patio or driveway creates a maintenance problem that outlasts the original contractor by decades.

Surface water disposal in Cumbria usually comes down to a small set of options, and the right one depends on ground, site levels and any restrictions imposed by the planning or drainage authority.

Septic tanks discharge to a drainage field or soakaway and rely on the surrounding ground to treat the effluent further, which means they need the same percolation testing as a surface water soakaway, and generally more land around them than a compact package treatment plant. Package treatment plants actively treat the effluent before discharge, which allows discharge to a soakaway or, where permitted, a watercourse, but they need a power supply and periodic servicing that a septic tank does not.

Both need adequate separation from the building, from any water supply (particularly a private well or borehole), and from site boundaries — the exact distances depend on the system and the receiving ground, and should be confirmed with the system manufacturer's guidance and the environmental regulator rather than assumed from a neighbouring property's installation.

Drainage runs by gravity from the highest point that needs draining to the lowest point of discharge, which means the invert level required at the connection or discharge point can set the excavation depth for the whole run, sometimes deeper than groundworks would otherwise need to go. On a sloping site, this interacts directly with cut-and-fill decisions — the final building platform level affects whether drainage can fall to the outfall at a sensible depth, or whether a pumped solution becomes necessary.

Getting a topographic survey done before the drainage strategy is fixed avoids discovering, mid-excavation, that the discharge point is higher than the pipe run needs it to be.

Farm and rural sites often bring extra drainage complexity: yard water that may be contaminated with slurry or fuel and cannot simply join clean roof water, land drains that were installed decades ago and are poorly recorded, and watercourses used for stock or irrigation that any new discharge needs to respect. Separating clean and dirty water at source is usually cheaper and more robust than trying to treat combined water later, and is often expected by the environmental regulator in any case.

SHS is the contractor, not the planning authority. What SHS can do is look at the drainage strategy from a build point of view — access, ground conditions, levels, drainage, foundations and buildability — and tell you plainly what the construction side is likely to involve.

If drawings already exist, send them. If they do not, a site visit and a conversation usually establishes what information you need to gather next and who you need it from.