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Basement Waterproofing

Is your basement protected from the risk of flooding?

All below ground structures require a level of protection to eliminate any risks of flooding from the ingress of ground and surface water. Make the most of your damp basement and convert it into a dry room so it can be transformed into something more, such as storage, car parks, accommodation, gyms, swimming pools etc.  This can be a cost effective and highly rewarding way of extending a home or utilising space within an existing home or commercial property.


With the huge rise in house prices across most of the country as well as the inevitable disruption of moving, more and more of us are choosing to make the most of our existing space. Additions, loft conversions and conservatories are very popular options – but don’t forget that the space under your home can be room to grow into as well. Alliance, can help you make the most of what in most cases is simply wasted space.

Basements don’t need to be damp, dark places for storing things you rarely use. Basement conversions are now very affordable and popular options for homeowners looking to increase their living, working or entertaining area. 

Underground rooms are ideal for a number of uses, especially those which benefit from a bit of privacy – from a home cinema for cosy nights in, to the master bedroom suite of your dreams. 

Unlike a loft conversion, a basement conversion can very easily have its own entrance. This fact makes the basement an ideal place for a quiet office away from the bustle of the rest of the house, and one which clients can visit without going through the rest of your home; it’s also ideal for a granny, staff or guest annex, where a private entrance is also desirable. But no matter what you choose to do with your space, basement waterproofing will add value to both your home and your lifestyle. 

Because basements are underground and often below the local water table, the most important issue when considering a conversion is of course waterproofing. Alliance are experts at turning damp, unloved basements into valuable living space. 

The first thing to do before deciding the method of waterproofing to use would be to decide ‘what the basement is going to be used for’.

What your basement is going to be used for could determine a different level of environmental performance required.  The British Standards BS 8102:2009 defines these levels as grades 1 to 3.

Grade 1 – Some seepage and damp areas tolerable. Inappropriate for dwelling.

Grade 2 – No water penetration acceptable but water vapour and damp areas are tolerable.

Grade 3 – No water penetration or water vapour acceptable. Completely dry environment.


Most basements are used for domestic accommodation which would be a Grade 3.

Garages and car parks could be classed as a Grade 2 as they may not need to be completely damp free.  

It will always be possible to upgrade from Grade 2 to 3 we would advise to construct a basement as a grade 3 as it’s more cost effective and time saving in the long run.

Upon deciding what the basement usage will be, a survey will be required in order to gather site information to determine the most suitable waterproofing design. The site survey will consider the following points:

  • New build or Existing
  • Condition of existing structure
  • Water table
  • Surface water
  • Geology
  • Soil Drainage
  • Topography
  • Grey and Foul water facilities


Structural waterproofing below ground is a highly specialised operation and must be undertaken by contractors and designers who have the requisite levels of skill, understanding and experience. Failures resulting from inadequate specifications or poor workmanship can be very costly.

Alliance are approved installers of DELTA Membrane Systems which are used in all aspects of basement waterproofing and tanking.  DELTA also provides us with full Technical Support from their fully Qualified Operatives together with site visits if required.  So you can be sure your basement will be in safe hands with us.

An existing underground structure will usually have the waterproofing applied by attaching waterproof membranes to the inside walls and floors or by using drained cavity technology.

Before basement waterproofing can begin, Alliance will first check all the drains and improve ventilation and heating. There’s usually only one solution to keeping the basement dry: tanking. This process involves the installation of a physical membrane on the inside of the basement walls, as well as channels and a sump pump. The membrane keeps the interior of the room dry, forming a barrier between your new basement space and the pressure from outside moisture; water from behind the membrane collects in the channels and sump to be pumped out of the room.


Waterproofing techniques are defined in BS8102, the British Standard for “Protection of structures against water from the ground”.

Members of the PCA must demonstrate an understanding of this standard and the Association’s code of practice for underground waterproofing. The PCA also requires that surveyors providing guidance on waterproofing must demonstrate their competence by gaining the “Certificated Surveyor in Structural Waterproofing” (CSSW) qualification.

Structural Waterproofing Systems

There are two types of waterproofing system most commonly used in existing structures. 

The first is a “Type A” waterproofing systems also known as Adhered waterproof membranes (as defined in BS8102).  These are commonly multi coat renders, cement based coatings, bituminous paints or epoxy coatings, which provides an unbroken barrier to water. They are applied to clean walls and floors and are usually protected and held in place by floor screeds, renders, plasters or other “loading coats”.

The second of which is a Cavity drainage systems or “Type C” waterproofing.  These utilise pre-formed high density drainage membranes, channels and sumps. These are installed to the walls and floors and are designed in such a way as to direct any water entering the structure back out in a controlled and managed way.  This could include directing the water to sumps or drains so it can be removed from the building in a safe manner.  

A tanking system can be installed without a sump and pump but we would not recommend it: the risk of future flooding is too high. Likewise, chemically injected damp-proof courses should not be used on outside basement walls since they will have no effect at all.

When installation is complete, your basement walls can be plastered, plaster-boarded or decorated like any others. Floors, too, can be made ready for carpet, laminate or tiles of your choice.

If you’re considering a basement conversion, contact Alliance today. Our experts will:

  • Survey your basement and determine the extent of any dampness
  • Discuss how you would like your new room to be used
  • Recommend, explain and carry out the most effective form of basement waterproofing for the site. 

Alliance will cover the following areas:-

  • Perth & Kinross
  • Dundee & Angus
  • Fife
  • Edinburgh
  • Glasgow
  • Stirling

  • 30 Year Guarantee
  • Delta membrane systems
  • Koster

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01764 663107
[email protected]alliancetimber.com
Maidenplain Ind Est, Aberuthven, Perthshire, PH3 1EL