Combination ring-beam & traditional build

This new basement was constructed using a combination ring-beam & traditional build approach. The neighbouring property was very close on one side. This meant the full traditional build of a basement was not an option, instead a combination of a ring-beam and traditional build was required.

The neighbouring property was supported first with a ring beam. The second stage was to create the rest of the basement with a traditional open excavation build.

This ensured the structural integrity of the neighbouring property and a cost effective build for the clients.

The combination ring-beam & traditional build basement started by supporting the neighbouring properties. This was carried out in two stages:

Creating the top section of the ring beam

Stage one was to support the neighbouring house by creating a ring beam. This beam is a reinforced concrete wall that prevents the ground collapsing and destabilising the foundations.

Once excavated, the foundations were supported with timber and struts. The first 1.2m of the wall was constructed with reinforcing steel, shuttered and cast with concrete.

Underpinning the top section of the ring beam

Once the first 1.2m had been supported, it was then underpinned in sections, to lower the support to 2.4m. This would eventually form part of the walls of the basement.

Once dug, the excavation was cleared out and a base concrete slab laid. This slab was linked to the wall via reinforcing steel. This steel would then link to the top section of the ring beam by more reinforcing steel. Eventually, when fully cast the basement walls had been formed and the neighbouring building and foundations had been supported.

Stage 2 – Traditional build

With the neighbouring properties supported, the rest of the build could take place.

Excavation & slab construction

The whole basement space was excavated to formation depth of around 3m. The formation base was blinded and compacted to give a strong base to work from.

Shuttering was used to form the outline of the slab and included a kicker upstand.  Click here for details of standard build construction

Reinforcing steel was installed and the ring-beam base steel linked into to the traditional build. Levelling rails we installed and set, and finally the concrete slab was cast.

Wall construction

When the slab was cured the walls were constructed in two halves to prevent cracking.

Shuttering was installed externally and then steel linked to the slab and kicker. With all steel installed, internal shutters were built, supported and finally the walls cast in concrete.

Once the first half was cast and concrete cured, it was stripped of shuttering and the second half constructed in the same manner.

Finally all shuttering was removed, tie bar holes filled and waterproofed and the basement backfilled ready for the next stage.

Primary System (Combined Type A & Type B)

Type A – Cementitious slurry Barrier Protection

The ring beam, underpinned walls and floor were all coated with a two coat crystallising waterproofing slurry. This provides this section of the basement waterproofing protection.

Type B – Waterproof concrete integral protection

The traditional build concrete walls were created by erecting temporary shuttering and steel work and then cast with concrete including a waterproof additive. The steel reinforcing within this structure was designed to reduce the cracking to less than 0.3mm, also providing integral protection.

Secondary System

Type C – Drained cavity protection

With the primary waterproof concrete system providing most of the protection, the secondary system was installed. All walls and the floor were lined with a cavity drainage membrane (CDM). These membranes were linked to sump chambers via the a preformed perimeter channel. Within the sump is two pumps and a high-level alarm. This system is designed to catch any water that is not stopped by the primary system and discharge it automatically. Flushing and maintenance points were installed to allow future servicing of the system. The front and rear lower sections are linked with a underground pipe.

Both basement waterproofing systems were designed by Structural Surveyors in Structural Waterproofing (CSSW) in accordance with BS8102:2009

All waterproofing materials were supplied by Triton Systems Ltd