What you need to know



What you need to know about Basement Construction


Whether you own a home with an existing cellar, are in the market for a home that has one it’s essential to understand the basics of a new basement construction or an existing basement conversion. 


Before we take a look at the basics of basement construction and what you need to know about this, let’s see the primary pros and cons of basement in the UK so you know what you’re getting into.


  • Practically speaking, a basement provides more living space and/or storage and allows you to maximize the square meterage of your living area and offers additional space that’s especially welcome for large families.


  • When it comes time to put your home on the market, a basement will make your listing so much more attractive. Including a basement will almost certainly increase the value of a property. However, whether the increased value added by the basement will exceed the basement construction costs will depend on a number of factors such as the intended use of the basement, local property prices and quaility of the internal and external finishes. As you would expect, in areas with very high property prices, even relatively expensive basement dig out projects can be profitable.
  • An existing cellar conversion can often make better financial sense than moving home even when the total basement construction price is considered 
  • Other advantages include the ability to build a larger home on a smaller footprint
  • Properties with basements are up to 10% more thermally efficient than houses of the same size constructed entirely above ground. Where newbuild basements are constructed using reinforced concrete this can be used to provide thermal mass which can help to naturally regulate the internal temperature of the building


It is possible to increase the size of an existing cellar to the size of the footprint of the entire property and even to construct a brand new basement underneath an existing building. In addition, subject to basement planning approvals by your local council, it is also possible to extend cellars and basements underneath garden without actually loosing the garden area. Before making your decision on how you wish to proceed with your project, we will outline all the elements to you so you can make an informed and the best availabe decision for your needs. 


The cost of a basement conversion will very much depend on the structure in your existing basement, footprint and headroom of your existing cellar and whilst there is no simple basement conversion cost calculator for estimating the basement excavation costs, the degree and extent of the conversion will to a large degree determine how much money you will have to spend to convert the unused room into living space.

You can find more details and information at the


As you would probably expect, your newly constructed basement will require waterproofing especially if it is to be used as a habitable area. The most commonly used amongst basement waterproofing solutions is the installation of a cavity dain membrane during the construction of basement walls and floors as well as the installation of a pumped drainage system. The choice of materials and products used will depend on a number of factors such as the condition of the underlying substrates and ground water levels. 

As a Delta Membranes trained and approved waterproofing specialists, here at Kapital Basements we use the best products on the market for your and our peace of mind.   

Drainage System

The Delta cavity drainage system is a High Density Polyethylene (HDPE) membrane with superior drainage capacity and compressive strength. These types of membranes are suitable for use in all basement excavation projects, in building and civil engineering construction as a high performance water control and management system. A superior solution for waterproofing basement floors and walls.

The cavity drainage system is based around a "dimpled" plastic membrane that is applied to the walls and floors of the cellar, creating a "drainage cavity" which redirects moisture entering the basement to a sump and pump. 

In principle a cavity drain membrane system allows moisture or running water to travel behind the membrane within a controlled drainage system.  A cavity drain system requires minimal preparation and disturbance to an existing substrate and will protect your property against the damage of water ingress caused by hydrostatic pressure (groundwater pressure). Delta membranes can also be used as protection against rising damp as well as being gas proof.

The selection and application of the right products and waterproofing elements  as well as using a trained and registered installer such as KAPITAL BASEMENTS can reduce the basement waterproofing cost and your basement construction costs altogether. You will also benefit of a 30 Year product guarantee directly issued by Delta Membranes as well as installation guarantees. The guarantee covers the membrane and ancillary components, (With the exception of sump pumps), which will be covered by a separate service agreement. 

Pump Stations

A major part of the basement waterproofing will be the installation of the pump stations. Dependent of the actual size and use of the basement, number of bathrooms and drainage points the correct sized station will be advised. In summary these pump stations will be automatically managing the collection and discharge of ground and/or foul water. 

External surface water from light-wells, courtyards and terraces may be drained into the ground water sump. For each sump system, the recommendation is for two pumps in case of failure of the duty pump.  In the event of failure of the duty pump, the secondary back up pump will take over, therefore significantly reducing the risk of potential flooding. In addition we always recomment to include a high level alarm such as the Delta Alertmaxx2 and power back up system such as Delta Powermaxx in case of mains power failure, again reducing the risk of potential flooding to the basement.

We all appreciate the wateproofing of a basement is crucial and no elements on the design of the drainage system can be overlooked. For this reason, in addition of our experience accumulated over the past 10 years, we will run every project details by the Delta Technical Team.