Frequently asked questions – Basement waterproofing

Delta Membrane Systems Limited has a dedicated team of Waterproofing Design Specialists.  Our trusted Technical Team offer knowledge and experience and are able to provide expertise in Structrual Waterproofing.  As a Waterproofing Specialist Manufacturer, we work with architects, surveyors, contractors and engineers alike to provide a design service which complied with BS8102:2009 and offers the highest level of technical expertise and assurance.

Our staff are able to provide assistance on projects of all sizes, whether you require some general advice about damp or waterproofing or support with technical drawings and specifications.

Are all Delta and Koster products stock items and how long does it take for delivery?

Almost all of the Delta and Koster range is available on a next working day delivery (Mon-Fri) if you order before 2:30pm (early deliveries available at an additional cost).

As a pump station is an essential part of a cavity drainage system designed to prevent ground water from damaging a Basement, what emergency provisions are recommended?

The sump must be provided with duplicate pumps together with UPS (uninterruptible power supply), usually consisting of an automatically trickle charged battery system. A high water level alarm is also essential, and if the property is frequently left unattended for long periods, then it would be wise to include a Telemax SMS messaging system for remote warning.

Please note that remote warning should also be considered for rainwater and surface water applications.

Can pump stations be used for rainwater applications?

Small sheltered catchment areas up to 12m² (such as Lightwells or Stairwells) can normally be served by the same pump station that serves the cavity drainage system. For larger or more exposed catchment areas separate pump stations are advisable, and it is also important to ensure that adequate provision has been included to prevent internal flooding of the building in the event of a 24hr disruption, e.g. power failure. We will be pleased to provide further guidance if required.

Can we make a sump chamber ourselves out of concrete rings?

The answer is yes but this is a risky strategy as you will be de-watering below the top of slab level as water enters into the chamber through the ring interfaces. Call us on 01992523523 and ask for our pump department for further advise.

Can you mix Groundwater/Surface Water with Foul and Grey Water Sump Pump Systems?

No, we advise to keep these systems separate for the following reasons:

Blockages – if the Foul Sump blocks due to liquid fats and/or foreign bodies (wet wipes, nappies etc.) you can stop using the basement toilet and kitchen facilities and there is no immediate emergency and there should be no damage caused. The Groundwater/Surface water sump needs to be operational at all times otherwise if the mixed system blocks the build up of water behind the membrane system can back up into your basement causing significant damage which could be very expensive to rectify.

Foul smells – if a mixed system the smells from the foul system can travel back behind the membrane which can enter the residential parts of the basement.

Larger chamber – Deeper excavations especially in basements where there are water table problems can be more problematic and costly. It is often more economical to install two smaller separate chambers as opposed to one large chamber.

Do I Need Ventilation?

Heating and Ventilation: The environment in basements should be controlled by having balanced heating and ventilation to combat the small risk of condensation. All habitable rooms, kitchens, utility rooms, sanitary accommodation and bathrooms located within the basement, should follow the ventilation provisions of the Building Regulations 2000 part F1.

If it’s feasible for a basement or lower ground floor area to discharge by gravity drain to the sewer, is this acceptable?

If the floor level is below street level and contains habitable rooms then it is usually considered sensible to incorporate a sump station. The pumped main should be arranged to form a back flow loop so that it is higher than the flood level. If the flood level is unknown, we normally recommend the invert of the loop is at least 300mm above the surface of the adjacent road. This will provide the best flood protection in the event that the sewer becomes surcharged (full and pressurised).

Please note that anti-flooding valves should only be used for flood protection when the rooms are of minimal importance and the occupants have access to other sanitary appliances above street level that do not discharge via the anti-flooding valve.

My Architect has recommended your system, how do I get the system installed?

Delta have a nationwide network of registered installers. Please call 01992523523 or complete our contact us page and we will be happy to give you information on local contractors.

Should we consider external waterproofing in addition to the Internal?

Where possible this is always recommended as the building is the first line of resistance and every attempt should be made thus reducing the work the internal sump is required to do.

What are the acceptable levels allowed for ponding when using your Delta MS 20 system on a concrete floor?

See section 15.2 of our BBA certificates;
The concrete base must have a surface regularity with a maximum permissible departure of 5 mm from the underside of a 2 m straight edge, resting in contact with the floor, in accordance with BS 8204-1: 2003.

After carrying out a flood test to determine any depressions, and falls, they should be made good in accordance with Clause 15.4.  In any event ponding should be avoided.

What are the sump chambers made from?

Virgin HDPE tested to ISO 14/15 so they are pressure resistant and spun bonded so there are no joins on the chambers.

What is the difference between structural waterproofing and damp proofing?

Structural waterproofing deals with a range of  below ground problems for example basements/cellars, underground vaults, tunnels, car park decks etc. Any structure that has retaining walls (walls that have soil behind them).

Damp proofing deals with problems at ground level and above.

What is the difference between the MS 500 and Delta PT?

The Delta PT has a thermicaly bonded mesh which provides a key for either directly applied plaster or a dot and dab thermal or plasterboard. The MS 500 is designed to have dry lining in front of it, either independent or timber battens screwed into the Delta plugs.

What are Delta MS 500 and MS 20 made from?

Virgin High density Polyethylene, it is not recycled but recyclable. Beware some similar looking products imported by other as these are often made from Polypropylene and can get brittle and crack below 5 degrees.

What is the power supply required for a sump?

13 amp non switchable spur, ideally not off the basement ring main.

What is the stud depth of the MS 500 and MS 20?

8 and 20mm

What product can i use to waterproof a lightwell?

You can use our Delta PT-Lath meshed membrane to waterproof a lightwell

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