Case Study

Semi-Detached House - Greater London
Introduction - First Visit

DC Structural Services was contacted by the client to view their property after significant cracks started to appear inside and outside part of their property. 

 

On the initial site visit we noted extensive structural movement to an existing extension on the rear of the property. 

As you can see, the extension had moved away from the house. This particular crack started from beneath the pathway and continued right up to the roof. 

Not only was the crack mirrored internally, but there was also multiple other cracks within the extension area

During our visit we also noted various other cracks and issues resulting from the damage to the extension, most notably damp damage to adjoining rooms. 

Second Visit - Destructive Survey and Soil Investigation

Due to the extensive damage to the property and to help find the route cause of the problem, it was decided that we would come back for a second visit. This visit would enable us to carry out a soil investigation and destructive survey to the property. This would then be written into a formal Report for the client, detailing our findings, solution and costings.

We found several problems, that combined together, had resulted in the failure of the extension area;

  1. The extension foundations were at an inadequate depth to support the load of the structure.

  2. The results from the soil investigation showed that the ground was very soft and wet down to a depth of 9.6 metres.

We also found a hidden manhole underneath the french doors, this had undoubtedly contributed to some of the damage caused to the structure. 

 

We arranged for a CCTV Survey to be carried out, the findings of which showed damage to the waste pipes leading into the manhole.  

Planning & Design 

With all the information we now had to hand, we could provide the client with several different options on how to proceed forward. 

Our client decided to go forward with a total knockdown and rebuild of the extension area, whilst also rectifying the other damage caused to the adjoining rooms and moving the manhole that was discovered to a more suitable location. 

DC Structural Services Ltd managed and arranged all communications with the Local Authority and Utility Companies involved. 

With the relevant permissions granted, works began in January 2020. 

Knockdown & Discovery

The initial knockdown began in early January 2020. We started by securing the area and displaying Health & Safety signage.

Once all the Electrics, Water and Gas was turned off in the area of work, we begun the task of dismantling the Kitchen work tops and units located in the extension. These were successfully removed and stored for reuse. 

We then removed the Roof, Walls, Floor and Foundations. 

During the Floor and Foundation removal, we discovered two further defects.

The first was the drain that took all of the water from the roof and utility room. The gulley and pipe had been fed through the foundations and the 90° bend was too small. This had been leaking directly into the foundations for an unknown amount of time. 

The second was located between the Extension and Dinning Room door. The waste water pipe from the downstairs WC sink had been directed into an open gulley, these were then buried into the floor with no other form of pipework or protection. Upon further inspection, the open gulley had actually been sealed off further down the line. The water had been flowing freely underneath the concrete slab for approximately 2 years. 

Again, these two defects had undoubtedly contributed to the failure of the extension.

Foundations & Manhole

With the old extension totally demolished, it was time to remove the manhole and install the Helical Systems GroundScrews for the foundations. 

Due to the ground conditions, we piled down to a depth of 10m. Once the GroundScrews had been installed, we welded the caps into place.

With the caps welded into place, we then installed the Steel Beams and arranged for the Building Control Inspector to visit for approval. Once the visit had been completed we poured the concrete. 

We followed on by pouring the concrete oversite and began rebuilding the manhole in a new, more suitable location. 

Rebuild

With the new foundations installed and concrete poured, it was time to start the rebuild.

It was at this point in the project that the Covid-19 pandemic took hold within the UK. Whilst DC Structural Services Ltd could, and was allowed to continue working, we sadly couldn't get our materials to site, so we took the decision to cease work.

Finishing

With the lockdown eased and Builders Merchants reopening, we headed back to site to finish the project. 

We rendered and pebble dashed the exterior, relayed the floor tiles and refitted the kitchen units. 

At the clients request, we reused the floor tiles and kitchen units. There was a slight change to the layout to accommodate the new boiler.

After a deep clean, we arranged for the Building Control Inspector to come back and complete his final inspection. 

Once that had been completed, DC Structural Services Ltd finalised all the necessary Guarantees and Certificates and completed the handover to the client, thus concluding the project. 

DC Structural Services Ltd would like to once again extend its thanks to the client for allowing us to write about the project. 

DC Structural Services

LTD