Basement Drainage & Protection

Basement Protection

A key component of a Type C, Drained Protection System is the drainage system.  Often referred to in the industry as ‘basement drainage’.

Type C, systems are water management systems.  The Type C System manages water that penetrates the external shell of a structure by collecting it in a cavity form between the external wall and an internal lining/wall.   There is permanent reliance on this cavity to collect ground water seepage and direct it to a suitable discharge point.   For Type C, Cavity Drainage Systems to function as intended, water ingress should be removed by gravity drain or mechanical pumping.

Drainage design

Most projects require a mechanical pumping station to discharge water that has penetrated the structure.  Mechanical pumping stations in below ground application are often referred to as “Sump Pumps” or “sump and pump systems”.

Many basement drainage systems will consist of perimeter drainage channel, a sump chamber along with a primary and secondary sump pump, high level water alarm and/or control panel and battery backup.

The purpose of a sump chamber is to collect and discharge (to a suitable evacuation point) any water ingress which has collected in the cavity drain membrane system.

Basement drainage ‘pumped systems’ should be engineered to cope with worst-case scenario of water ingress.  It should always be assumed that ground water is expected to rise against any structure at some point during its service life.  Waterproofing designs should always be to the full height of the external ground level with consideration to the connection with the dpc 150mm above ground level. This may be within the cavity or dressed externally with a flashing.

Drainage channels ideally should be installed in rebates and laid level at the wall/floor junction around the perimeter of the structure to allow water to drain by hydraulic gradient and to discharge passively into sump chambers.  For larger projects, cross-floor span channels should be included in designs.

Inspection and access ports should be included in the perimeter drainage channel design.  These allow for maintenance and future cleaning of the drainage system.

The number of sump pump systems required for each project will (in part) depend on the overall basement size, perimeter and the method of drainage.  Type C membranes should be installed above drainage channels.

For each sump system, we recommend two pumps to reduce risk of mechanical failure of the duty pump.  In the event of failure of the duty pump, the secondary back up pump will take over discharging water ingress, ensuring the basement drainage is functional, significantly reducing the risk of potential flooding.

Basement drainage systems are further enhanced with additional protection with high level water alarms, control panels and battery backups as a second line of defence.  A high-level water alarm will notify a structures owner if the sump pump system has stopped working.  Battery backups will maintain power supply to sump pumps in the event of a power outage.

Multi-level systems

Multi-level systems should be detailed to allow water ingress to bypass any intermediate suspended floor slab(s) to reach drainage installed at the lowest level of the structure.   For multi-level systems we recommend the additional use of a Type A or Type B water proofer to offer a continuous waterproofing approach.

Maintenance and Servicing

Design considerations should be given to the serviceability and maintainability of the system, such as maintainable perimeter drainage and servicing of sump pumps.

With Delta’s yellow channel ‘free lime’ can easily be identified and treated in perimeter channel.  Free lime is white in appearance and can build up to a solid mass, with Delta’s yellow channel this can easily be visualised during inspection and appropriate action taken.

As with any electrical equipment, basement sump pumps will require servicing and the entire drainage system will require regular maintenance to ensure it is working effectively.

Sump pumps must be maintained.  We recommend a qualified engineer examines and services equipment every year. Pumps running more frequently due to higher water tables/water drainage, or weather conditions should be examined more frequently, we recommend every 6 months.

The Detail is in Delta!

Continuity is crucial for successful construction and waterproofing.  BS 8102:2022 places additional emphasis on good planning, correct sequencing and site management processes are in operation.

To ensure waterproofing designs are durable and fit for purpose, correct detailing and implementation of penetrations are an important discipline.  Whether pre- or post-construction these should be carefully detailed to minimize the risk of water ingress.

Delta offers a comprehensive range of Packaged Pump Stations which are suitable for the evacuation of Ground water, Surface water and Foul water. In addition, we offer bespoke chambers for larger projects.

Delta offers a full specification service for package pumps and pump stations by qualified drainage engineers specific to each project.

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