Commercial to Residential Basement Conversion

09 March 2021


Basement type: Retrofit Building type: Residential
Type of waterproofing: Type C

Member: Delta Membrane Systems


It may be last orders for some of our great British pubs but this is creating exciting opportunities for transforming commercial structures into luxury residential dwellings. The growing trend of converting old inns into residential properties is providing new homes with a unique history, packed with character and features.

Delta Registered Installers were engaged to assist on a troublesome vaulted basement to a property in central London, which had already been converted into high-end living accommodation.   

Just off the basement area were two large vaults around 12m long.  Made from brick barrel construction, this below ground space had previously been used for storing kegs of ale!
One of these vaults had previously been converted into a spa area with jacuzzi and steam room, the other was used as a storage area.  The owners had had the storeroom tanked with a Type A render system, however this approach repeatedly failed, allowing for substantial water ingress which was causing damage to items stored in the area.

With structural waterproofing, one of the major contributors to project failure lies with the design. When hiring contractors, ensuring the design, procurement of materials and installation is undertaken by one specialist will naturally reduce these known and associated risks.  A specialist contractor will always be able to offer quality assurances.


Consideration to the grading of the structure (habitable requirements in this instance) is key to specifying an appropriate waterproofing system. 

For Grade 3 Habitable environments, two systems of waterproofing may be required.

For Grade 2, Habitable environments, only one form of waterproofing may be required, but caution should be applied because different stored items may require different environments.

Prior to any product specifications, the waterproofing contractor undertook thorough site investigations. This initial investigation allows for important ‘cross-checks’ to ensure any proposals meet not only customer requirements but also conform to BS 8102:2009, the British Standard for waterproofing.

On surveying the site, which was directly below a road, it was evident that vibration from traffic was causing the existing render system to crack, which was resulting in frequent water ingress.

The waterproofing contractor proposed installing the Delta Type C Cavity Drainage System along with mechanical ventilation.  The Delta Type C Cavity Drainage System allows for slight movement and vibration without altering the dynamic properties of a structure.

A cavity drainage dystem allows for moisture or running water to travel behind the membrane in a controlled way, whilst requiring minimal preparation and disturbance to an existing substrate.

Delta MS 500 was installed to walls and barrelled ceilings, with Delta MS20 loose laid to the floor with a protective screed subsequently poured on top.  Below the floor membrane, perimeter drainage channels were located within rebates allowing for any future water ingress to be diverted to suitable discharge points.

The waterproofing contractor also considered the operation of building, ensuring the Type C System was serviceable and that future and ongoing maintenance was possible.

After the Type C System was installed, walls and soffits were battened and boarded with moisture resistant plasterboard and plastered over.  Once complete the walls were painted with an anti-mould paint, with insulation and timber oak flooring then being laid.

A moisture sensitive, humidistat-controlled fan was fitted as well as new lighting to give the client a new dry storage space.



The clients were delighted with the approach adopted by the Delta Registered Installers. An initial site investigation identified key considerations for the installation, allowing for a suitable solution to be developed and the waterproofing contractor was able to sequence the works in just 3 weeks.

Download the case study PDF.