Six Secrets to a Great Basement Build

Updated: Jun 4, 2019

With a rise in stamp duty and an increase in the cost of land, especially in London and the South East, more and more people are choosing to make the most of their existing properties to provide for the additional space they need as their families grow.

Dense neighbourhoods, combined with restrictive planning regulations, particularly in conservation areas and historic neighbourhoods, mean that it is not always possible to build upward or outward. This can leave only one choice - to go down! The result is that, after getting some bad press in the past, basements are now definitely back in fashion.

The good news is that lessons have been learned and, in the right hands, basement construction can be a straightforward process with less risk than you might think. The even better news is that with land values as high as they are, the relative cost of construction, even on a challenging site, means that as well as providing extra space, you will always add value to the property without the risk of over-capitalising.

Harris Calnan have extensive experience of basement construction and are currently working with a number of specialists on basement builds in different parts of London. Malci Construction may be a new company but their directors Agim Mesutllari and Dan Shtogu have decades of combined experience in the construction industry and have worked on basement builds of all shapes and sizes from small basements for mews houses to larger, commercial basements.

Drawing on this deep well of experience, together with Agim & Dan we have put together a list of tips for anyone contemplating a basement build to ensure that it achieves its full potential:

1. Technical Design:

Designers who understand the technical complexities of basement construction will be worth their weight in gold. Realistic expectations are crucial and having a clear picture of what is possible at the outset can save huge amounts of time and money.

The design of any basement is a multi-disciplinary task and is seldom achieved by a single designer working in isolation. The ground conditions and existing structure will form the base from which an experienced structural engineer will suggest suitable structural systems for the basement, each one of which will have different implications on the time required, the cost involved and the amount of usable space that is left over.

Drainage and services are often left as an afterthought. Consulting a services engineer and public health (drainage) consultant early on can help to avoid any subsequent delays, additional costs and loss of area or reductions in floor to ceiling heights that could result from an insufficient appreciation of the size and scale of services required. This is especially true where clients intend to make use of sustainable technologies or high levels of home automation.

Waterproofing is a key aspect to any basement design and there are a range of systems which, like the structure, all have varying implications on the ultimate cost, time and amount of space required.

Fire regulations, requirements for natural daylight and fresh air, as well as how spaces are connected and what they can reasonably be used for are all crucial to the design of any basement. By drawing together the input and advice from the rest of the design team, and then weighing the results against the needs of the client, an experienced architect should be able to present a scheme that responds best to your brief and is able to make clear the consequences for the various alternatives.

2. Planning Constraints and the Pre-App:

The level of information required by many of the London Boroughs simply to submit an application for planning consent can be substantial. In some extreme cases, it can almost be as much as that which is required for construction.

The cost of preparing this work is significant and so it is often worthwhile to obtain pre-application advice from the planning authority before launching into a full-blown application. The “pre-app” advice the planners give is not binding but it does often shed light on all the critical issues and will almost always give you a good idea as to whether your design is ticking all of the most important boxes. Most importantly, you don’t need a comprehensive set of design information for a pre-app submission and it can be done with simple sketches and a clear description of the scale and scope of work you intend to do.

Once you have the pre-app advice from the planning authorities, your design team will have a clear checklist of problems to solve or issues to respond to. It will thus significantly reduce the risks of needing to make costly re-submissions later on and the additional time required will more than pay for itself in the long run.

3. Site investigation:

For basement projects, preparation makes all the difference. A thorough soil investigation may seem like over-kill at the start of a project but it is crucial.

As well as verifying the soil’s load-bearing capabilities, checks are made for the presence of ground water, and possible contamination from historic uses, all of which can have far-reaching implications for the size and cost of your basement.

For example, if ground water is present, secant piling may be needed to counter water ingress during construction, but if not, and the soil is highly cohesive, underpinning will be sufficient – the difference between the two methods could be tens of square metres, which at current London land values, could put a significant dent in your return on investment if it comes as a surprise.

Contaminated soil is also something that needs to be checked for early in the life of a project. Aside from the more common "nasties" (lead, arsenic etc) resulting from previous industrial land use, or petrol derivatives leaching into the soil, on one occasion, Malci discovered subterranean asbestos which almost made the project economically unviable. Fortunately, they were able to use a method of segregating the soil, and safely containing the asbestos that was then left below the new basement floor level. This resulted in a very relieved client, who had already committed a six figure sum to reach the point where construction was underway.

4. Site Access:

Some sites, particularly terraced houses, have severely restricted access to the parts of the site where the basement works are going to be carried out. These restrictions can limit the options for the kind of basement structures that are possible on the site and so feedback from contractors at an early stage can help to ensure that incorrect assumptions are not made at an early stage.

Whilst the Construction Method Statements required by most local authorities will catch many issues, the amount of abortive design work that can be done leading up to this point can be prohibitively expensive.

5. Contractor selection:

If experience is important when choosing a design team, then it is even more so when contemplating a construction partner.

Engage a contractor with a proven track record of basement construction. Good workmanship and a thorough understanding of safe and proven construction methods are every bit as important as good design.

All building projects are subject to unexpected events and this is particularly true of basement projects, no matter how well prepared. However, a competent construction specialist together with a temporary works engineer can respond to these events in a way that minimises the impact on the project, reducing the potential for delays or cost increases.

6. Insurance / Warrantees:

Even the least ambitious refurbishment projects require insurance. Many home renovation projects can be done under the cover of standard home insurance policies, but basement projects often require additional insurance to be in place prior to works starting. It is not always the case that the contractor’s own insurance will cover all your potential liabilities, so it is best to check your building contract and to discuss the project with your insurers well in advance so that any additional costs or requirements can be factored into the process.

A list of collateral warranties should be prepared and issued at tender stage so that the construction specialist can ensure that all the works are covered. Some examples include:

  • Concrete waterproofing

  • Foul water pumps

  • UPS (uninterruptible power supply)

  • Basement waterproofing systems (Delta or Newton)

Basement projects don’t have to be daunting and whilst these tips are by no means comprehensive, they will help to make sure your basement project is given the best chance of success.

If you are considering a basement project then feel free to contact either Malci Construction or Harris Calnan and we will be happy to advise you on the best route forward for your project. We work with a wide array of award winning architects, engineers and design professionals who have extensive knowledge of the unique challenges posed by basement projects. Get in touch today and we can make the necessary introductions so that you can get all the guidance you need to get your project off to the best possible start.

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