Basements are used for a number of different purposes with the most common types as follows:
- Car parks
- Car parks with storage units
- Plant rooms
- Habitable room spaces
Depending on the basement usage there is a different demand on the waterproofing. The different requirements for the four types are discussed below.
Cars bring water into the basement when it is raining and drop much of their surface water onto the ﬂoor of the basement. This can be observed in shopping centre carparks where water is carried often hundreds of meters into the carpark as vehicles enter. With these types of basements it is important that there is a waterproof seal at the wall-ﬂoor junction otherwise water can pool on the ﬂoor of the carpark, as shown in Figure 1, which makes the basement unserviceable in the ﬂooded area.
If there are many cars using the basement then it is important that the ﬂoor is sloped to a drainage system so excessive water does not build up on the ﬂoor of the carpark. Calciﬁcation on the wall of the carpark as shown in Figure 1 does not make the carpark unserviceable but is an acetic issue. If, however the carpark in built under an external exposed deck the area of the deck needs to be considered. If the deck has lengths in excess of 4 metres then there is the possibility of the deck cracking causing leakage into the concrete deck roof. This can result in water leaks into the roof of the car park with damage to the paint work of the vehicles that continually park in the same spot under the drip. Dripping from the roof of carpark with this type of cracking in a deck roof is shown in Figure 2.
With metal decking supporting the concrete roof it is very difﬁcult to trace the source of the surface leak as the water ﬂows along the metal deck surface before it shows up on the under surface. In the event of such a leak occurring it is often easier to install a channel drain under the leak which will prevent dripping onto vehicles parked below.
- Carparks with storage units
Often basement carparks associated with units have storage cages. These are usually located in front of the carpark space and can have a spoon drain running along the wall-ﬂoor junction which makes the storage cage serviceability questionable as shown in Figure 3. In this case the user has lifted the valuables by placing them on a timber pallet. If a waterproof seal had been made at the wall-floor junction the water flow in this case would have most likely not occurred.
- Plant rooms
These usually have a ﬂoor sloped to a ﬂoor drain to cater for a plumbing leak that can occur as these rooms are usually only visited for maintenance. Calciﬁcation and slight water leakage with this type of basement is only an acetic issue as the drainage to the ﬂoor waste will handle any slight leakage into the basement through its structure. Waterprooﬁng is not as critical for this type of usage.
- Habitable room spaces
These are becoming more frequent with the use of below ground theatre rooms to restrict noise pollution. They require a much greater detail into the waterprooﬁng especially if they are a single skin wall construction. Also the ﬂoor requires complete waterprooﬁng usually with two layers so a waterprooﬁng membrane can be installed between the two layers along with a water vapour barrier. The waterprooﬁng of the walls needs to have a lower water vapour transmission than the internal wall ﬁnish otherwise the vapour will end up trapped behind the internal ﬁnish and can condense. Once vapour condenses it can pick up salts from the wall resulting in ﬂacking of the internal ﬁnish as shown in Figure 4.
These habitable rooms built below ground level will have remain to serviceable for the life of the building. With single skin walls this means the waterprooﬁng usually will need to remain serviceable for the life of the building also, as often there is limited or no access to the external walls below ground level to replace any failing waterprooﬁng. In some habitable room basements where the waterprooﬁng has failed where access to the external wall was not possible the problem has been solved by installing a drainage system and a vented cavity by placing battens supporting a plasterboard wall lining away from the structural wall. Figure 5 shows the wall situation before the plasterboard wall was installed.
In the design of a waterprooﬁng system for basements the major factor that must be considered is the use of the basement as different uses require different performance requirement for the waterprooﬁng system.