Buried roof and podium deck waterproofing

The recent trend in basement extensions for residential properties has created a unique set of challenges for waterproofing contractors and designers.

If the basement extends past the ground floor then we will have what is known as a buried roof or a podium deck. Both of these see waterproofing failures due to poor design, incorrect product selection and inadequate workmanship.

A podium deck is in effect a roof over the basement that is exposed directly to surface water. A buried roof is, as its name suggests, an underground roof buried under soil. Both are often subject to significant quantities of water from surface water run-off as well as big variations in temperature.

Delta Membranes are best known for cavity drainage membranes such as the Delta MS system, which for the basement walls and floor are the most reliable form of waterproofing.

The best place to waterproof a podium deck or buried roof is actually on the top (known in the waterproofing industry as the positive side) using a liquid applied barrier. Delta recommends two products for this application Koster Deuxan 2c for buried roofs and Koster 21 for podium decks.

As both of these systems are liquid applied there are no seams or joints through which water can penetrate and both fully bond to the deck meaning that there is no space for water to pass between the waterproofing layer and the deck itself.

Koster Deuxan 2c is not in itself a guarantee for success, there are other design considerations. The structure of the deck itself crucial, we recommend robust, solid reinforced concrete. Surface water must be drained away from the deck before it can build up and enter at a higher point.

Delta Geodrain Quattro can be used to protect the waterproofing during the backfilling process as well as improving the drainage around the deck.

The waterproofing layer should extend around the deck to cover the junction between the deck and the retaining wall. This construction joint can be protected using the Koster Quellband.

An additional barrier waterproofing system such as Koster NB1 Grey should be applied to the bottom of the deck (known by waterproofers as the negative side) in all buried roof situations.