Welcome to SubStructural, we specialise in ground-breaking basement conversions in and around London. With extensive knowledge in the industry, and a collaborative approach, our team of highly experienced engineers, with over 25 years of experience, will offer creative ideas and solutions for your underground structure.

SubStructural leads with the latest technological innovations

We have invested heavily in design software to help support our engineers in providing the appropriate design outcomes. These technologies allow us to provide more efficient and cost-effective solutions.

We know structural engineering and construction methodology inside out, which allows us to deliver alternatives to conventional design and construction processes. This results in both cost and time savings on construction projects..

With the growing demand for more space, especially in and around London, one solution to maximise a property’s existing footprint is to utilise the ground space directly below the property.  Basement conversions are a great alternative to moving home, dramatically increasing habitable space and significantly increasing the value of your home.

Creating Luxury Basements in Central London

SubStructural has completed the design of many luxury basement conversion projects in central London, including a huge basement extension at the Shaftesbury Theatre.

We create stunning, light and airy basement conversions, from period town houses, public houses to modern executive homes.

If you would like to discuss your ideas with one of our basement conversion specialists, call SubStructural today for a no-obligation chat

What We Do


We can prepare subterranean reports that meet and satisfy Local Authority planning requirements. A Basement Impact Assessment gives due consideration of the effects of a new basement on ground water, flooding, and any existing surrounding buildings. SWe can also arrange site investigations, flood risk assessments and drainage surveys.


We use the latest modelling software to provide sophisticated designs. To help you compare costs, we can easily compare Mass or reinforced concrete walls to cavity reinforced masonry solutions. Plus, composite designs and modern methods of construction along with materials, such as StepocBlock work, Insulated Form work and steelwork can all be incorporated.


Temporary works are required on almost every project and are often an essential part of the planning and construction sequence of the basement. At SubStructural we have the resources to design, specify and supervise temporary works whether they are to support excavations, support concrete while it sets, or support tower cranes, for example.


We always ensure a safe working environment. Our designs prioritise the strength and stability of a structure during the construction process. We undertake rigorous safety audits to ensure that construction risks are minimised and controlled. We can provide comprehensive Risk Assessments, Method Statements and Site Checklists for each project.


Converting a basement or cellar has the potential of falling out with your neighbours if work becomes noisy or disruptive. SubStructural can provide suitable drawings and specifications and offer advice on construction techniques, monitoring and site surveys. If required, we can recommend surveyors who are familiar with basement projects.


We are experts in all forms of underpinning including double depth underpinning – i.e. for swimming pools – to maximise usable space. Whilst underpinning is traditionally used for construction beneath existing buildings, it can also be used for two stage new build foundation construction. This technique has proved useful for sites with poor ground and limited access, where piling may otherwise be used.


Contiguous, sheet or post piling of basements often allow rapid basement construction and to greater depths than that of more traditional underpinning techniques. Often used as part of temporary works, piling is normally a cost-effective option in new build basement construction.


If ground conditions are favourable and space on site allows, reduced dig techniques can sometimes be employed to enable reinforced concrete retaining walls to be constructed. This can be very cost effective as additional costs for either piling or an extensive temporary works scheme can be reduced.



Whether it be a large commercial project or a domestic home extension, JMS has over 25 years experience of designing basements for all applications nationwide and particularly in the London area.

As well as being able to provide robust, cost-effective design solutions, Substructural can assist from the beginning of a project, producing Basement Impact Assessments (BIA’s) to help obtain planning consent and get construction started.

The criteria set out by the planning authorities for BIA’s is often extensive and will involve a detailed examination of the ground conditions, groundwater, potential ground movement, and the impact on the surrounding area.

JMS have the knowledge and experience to address those requirements within a detailed report, ensuring that basement proposals are viable and constructed safely.