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Basement Conversions, 5 Key Considerations

Mar 14, 2022


In today’s property surveying blog, we are going to be looking at Basements Conversions and Developments and what needs to be taken into account before proceeding with these complex structural works!

Residential basement extensions are often of major concern to owners and occupiers of neighbouring properties, particularly in respect to noise and disruption that will be caused for a considerable amount of time during the construction.

Furthermore, the potential for structural and percussive damage to their property is an ever growing concern and consideration.

These concerns are substantiated, there are a number of high-profile cases where the basement works have caused substantial and even catastrophic damage to adjoining properties so it’s more than understandable.

Basement Extensions, Brief History

Historically, residential basements were constructed and utilised only as storage for coal, wine, and foods, as it was found to be a reliable means of providing a reliably cool and ventilated environment for these items.

As time went on, by the early 1700’s, residential properties had become more stylish and grander. The desire for basement, or “lower ground floors” became more of a luxury. Large basements of lower ground floors were created as part of newly built properties to provide storage and working spaces – usually kitchens or sculleries, and for domestic staff accommodation.

Fast forward to the 19th and beginning of the 20th century, domestic staff were no longer widely employed. The arrival of canned foods and refrigerators for food storage, meant that large storage and preparation areas were no longer required. As a result, most properties built since the 1960’s had no cellar or basement.

When it comes to creating new space directly beneath your property, with endeavours to expand your liveable area, here at Stokemont, we think there are 5 key things to consider before proceeding in order to make sure you have all your bases covered.

Statutory Consents

One of the first considerations would be to make sure you notify your neighbours both informally and formally, as generally speaking it’s a good gesture given that the works are naturally going to be a nuisance, likewise, making sure the formal protections in light of any damages are in place will put everyone at ease.

The following below requirements should be addressed in this regard:

Building Regulation Compliant

Building regulations are the bare minimum standards for design, construction, and alterations to virtually every building.

The regulations are developed by the UK government and approved by Parliament.

Once this is approved, generally speaking it would mean that the proposed works and conventional and has all the main requirements in place which would make the construction liveable and sound.

The Party Wall etc Act 1996

The Party Wall Act will guide you in the right direction to make sure you follow the legal procedures in relation to carrying out any excavations and party wall structure works. Which may affect your adjoining owners.

The Act will act as a framework to prevent any disputes in this regard, Party Wall surveyors will be appointed to professionally deal with the matter via a legal document referred to as both a Party Wall Agreement and Party Wall Award.

Planning Permission

Planning Permission, is where you are provided legal permission to procced with works by the local authority after the proposal has been assessed in relation to the area and building itself.

Permission can either be granted or granted, subject to certain conditions, or refused. It is your responsibility for seeking, or not seeking, planning permission.

Lease / Contractual Obligations

The Covenants within your lease for conveyance documents should be thoroughly assessed.

Restrictive covenants within a lease set out the actions which are not obligated to the land or premises.

Works carried out which are not in line with these covenants can be enforced via courts, resulting in highly costly fines or a judgement for the property to be put back to its original form as per the lease.


Adequately waterproofing your basement is essential, as being beneath the ground the area is prone to moisture ingress.

If waterproofing isn’t done to great standard it will lead to disastrous outcomes such as leaks, damp penetration, or structural damage. It should be noted that all the potential outcomes mentioned can happen to your property as well as to neighbouring properties, which should be of major concern as the potential liabilities associated with the latter could easily lead to paths that wasn’t once imagined or budgeted for.

There are two common kinds of waterproofing involved in basement design. One well known method of waterproofing is referred to as ‘basement tanking’.

Basement Tanking is essentially the method of applying either a render, membrane, or coating to the inside or the outside of the structure. This would act as barrier to water ingress, stopping water entering the habitable space of the property thus making the basement watertight.

Within the waterproofing industry this is defined as ‘Type A’ waterproofing.

Alternatively, to the waterproof the basement, a method known as Cavity Drain or a Cavity Drain System can be utilised. This approach is much more complex and costly, however it’s the method which would provide the most certainty as a barrier.

The method enlists  waterproof membranes, drainage, pumping, and control systems. These systems will manage water entering the property and safely remove it.

Careful Selection of a Team of Specialists

Choosing a team based off merit, reputation and experience would be the best advice in relation to complex jobs such as Basement excavations.

It wouldn’t be advisable to select a team solely based on the competitve cost in this regard, significant damage or unfavourable outcomes or damage being caused to an adjoining property is almost always the result of poor design or engineering, or poor construction techniques and/or a failure to follow the temporary works design.

Appoint a team of consultants that have substantial experience of in all the aspects of the procedure, such as the design and undertaking basement extensions itself , and in particular the temporary works.

Temporary works are vital in construction as they provide the correct structural support when the rest of the building is compromised in one way or another.

At a minimum, your team will need to include a proficient structural engineer as he or she will be more less be the star player in the team.

Structural engineers through a means of calculation and other detail, ensure structures can withstand the stresses and pressures proposed and confirm whether or not the proposal is safe and sound how to be best approached.

In many cases an experienced geotechnical engineer will also be required, particularly where there are difficult soil conditions. You’ll need to assess the soil and ground condition thoroughly to make sure the ground is suitable. Existing services, unsuitable bedrock, structures are water table are things to consider.

Warranties and Guarantees

It’s important to have all your Warranties and Guarantees in place in case something doesn’t go to plan, thus leaving you vastly out of pocket and possibly in a poor health and safety scenario. 

Make sure your selected contractors and companies associated with the basement works offer some sort of warranty and guarantee. This could be for the following below:

  • Company backed structural guarantee
  • Insurance backed guarantee
  • Manufacturer guarantees on waterproofing systems.

Furthermore, product and installation warranties are normally required

It is all worth it, the cost, the hassle?

Although Basement extensions have become somewhat the norm in London, the cost to undertake the development is still very much a costly endeavour and can be a lot higher than originally budgeted for if things take a wrong turn.

Be sure to ask yourself whether it makes sense proceeding with the task if you can’t get exactly what you imagine.

Whether it be a gym, cinema room, bowling alley or some cases, known as “Mega basements ”, an additional further two to three levels.

It really all falls back to our previous advice of selecting a good team, getting professional advice is the best way to manage your budget.

A proficient architect will work with you to make sure you are spending your budget in the right way and advise where costs would be unnecessary or could be minimised. For larger or more complex extensions, you may benefit from using a quantity surveyor too.

If you are planning on carrying out any basement works, here at Stokemont, we would advise getting Party Wall Notices served as soon as you possibly can, as ultimately that will reduce the likelihood of total delay to the works and ensure that the party wall procedures and Party Wall Award have been agreed and served well in advance of the proposed construction works commencing.

Party wall procedures, while simple on the surface, can quickly lead to complication and complexity.

If you would like to discuss party wall surveying procedures with our team of party wall surveyors here at Stokemont, give us a call today and we will be more than happy to assist you.

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