Weeping Tile near you

Most failures are silt. A drain laid without a geotextile filter, or with the filter torn during backfill, or with crusher dust instead of washed aggregate, will slowly fill with fines until the pipe is a solid tube of mud. It keeps working for a season or two, which is why the damp comes back years after the work was done and nobody connects the two events. Roots do the same job more aggressively, since a subsoil drain is a reliable water source in a dry country and trees find it.

The second common failure is a discharge point that does not work. A drain graded correctly but discharging into a silt pit that is itself full, or into a stormwater line that surcharges in heavy rain, will simply hold water. The Housing Provisions set the relationship explicitly, requiring the level of discharge from the silt pit or sump into an impervious drainage line to be not less than 50 millimetres below the invert level of the inlet, and requiring provision for cleaning and maintenance. Both halves matter.

The third is specific to Australia and is the reason this work needs an engineer's eye rather than a landscaper's. The Housing Provisions explanatory guidance warns that in clay soil, subsoil drains can alter the long-term moisture content in the soil, adversely affecting the building foundation by removing or, in some cases, introducing water, and that in such conditions subsoil drains should only be used where there are no other options for dealing with subsoil water. On a reactive clay site, drying one side of a slab is itself a cause of movement. A drain installed to fix damp can become the cause of cracking.

Subsoil drainage sits in an awkward middle ground. In Victoria, drainage is defined in the plumbing regulations to include below-ground stormwater drainage to the point of discharge, and drainage is a separate class of licensed plumbing work there. Queensland issues drainage licences separately from plumbing licences, with a drainer's licence covering above and below ground wastewater, stormwater and sanitary drainage systems. New South Wales requires the right licence or certificate before any plumbing, draining or gasfitting work regardless of its cost. Where the subsoil drain connects to a stormwater system or discharges to a legal point of discharge, you are in licensed territory.

Excavation near a footing is separately constrained. The Housing Provisions require that excavation for drains adjacent to existing footings be within the area described as safe for excavation, which is a real limit when someone proposes digging a trench along a slab edge or beside a strip footing. That is a reason to have the trench line set out before a machine arrives rather than after.

On a reactive site, get the design question answered by someone qualified to answer it. Foundations must be classified in accordance with AS 2870, and the classes range from Class A, most sand and rock sites with little or no ground movement from moisture changes, through Class S slightly reactive, Class M moderately reactive, Class H highly reactive and Class E extremely reactive clay sites, to Class P for problem sites. The Housing Provisions state that where a site is classified H, E or P, reference must be made to AS 2870 for design and construction information. Knowing your site classification before you install drainage is the single most useful thing you can do.

This is buried work, so the record is the asset. Ask for photographs of the open trench showing the geotextile, the pipe and the aggregate before backfill, a sketch of the line and the discharge point with dimensions off a fixed feature, and the invoice describing materials by type rather than as drainage works. Add any engineer's advice or site classification report. A future owner, a future plumber and any insurer will all want that file, and none of them can dig for it.

Under the Australian Consumer Law, services must be supplied with an acceptable level of care and skill, be fit for any purpose you made known, and be supplied within a reasonable time where none was agreed. Stating the purpose in writing is particularly worthwhile here: if you engaged someone to stop a subfloor staying wet, say so in the correspondence, because that makes it the purpose the work has to be fit for rather than merely installing pipe. Where a problem is major you may cancel and seek a refund, or keep the work and pay a reduced price.

LokalMatch handles the introduction only. You describe the drainage problem once, with your postcode and details such as whether the water is seeping from a cut face, sitting under the floor or showing behind a retaining wall, and drainage businesses covering your area contact you. Those businesses pay LokalMatch for the requests they receive. LokalMatch does no drainage work, provides no quotes and does not vet, rank or recommend any business, so checking licences and asking for the site classification are still your steps.