What does basement waterproofing cost?

Firstly, the cost will be influenced by whatever the requirement is. Waterproofing could be required in a number of scenarios and for a number of reasons:

1. Converting a basement to a finished habitable space.
2. New-build basement waterproofing.
3. Dealing with a flooded cellar.
4. Addressing problems in a leaky finished basement.

Basement Waterproofing Conversion Costs

Our basement conversion costs are based upon prices (rates) that we charge for individual materials employed to form different waterproofing details, for example a square metre of wall/floor membrane, a lineal metre of channel, butyl tape (m), preparation of a substrate (m2), 250w pumps, 400w pumps, 750w pumps, battery back-up, how many batteries, what size of batteries, what type of high level alarm, cutting chases, making good chases, sealing service penetrations (multiple details for this).

With a basement conversion there are materials beyond the waterproofing, insulation, plasterboard & skim, and other factors such as the extent of plumbing & electrical installation. Any structural alterations, doors, windows (means of escape), joinery.

So what we do is to identify a design for the waterproofing, plus other factors, and then we measure and draw out the space, calculating the areas of the walls/floors and different details/materials, which when calculated against the rates, provides a project cost.

Therefore, an example of what can influence cost particularly, is the extent of the areas. Not just in that a bigger space will result in a greater cost, but a basement made up of lots of smaller rooms (as an example), will have a greater total wall area (lots of internal walls), and this influences cost, whereas a larger more open basement space equals lesser areas, lesser work and lower cost. A broad range would be £1000/m2, to £1750/m2 of floor area.

While waterproofing design for existing basements in a residential setting can often (but not always) share a lot of similarities, every space is different and the differences can influence cost.

So, the slightly 'cop out' answer regarding the cost of basement conversion in 2022, is that 'it depends'. Disclaimers aside, we would advise that it is not a low cost undertaking and projects are generally in the tens of thousands of pounds range, from circa £20k for a small project, to £100k+ if essentially adding an extra storey to your home.

To find out more, please visit our basement conversion page here.

Newbuild Basement Waterproofing Costs

If there is a lot to consider with newbuild basement conversion, new-build waterproofing turns it up to 11. This is in part because of the variation in forms of structure employed in building basements, and the different ways in which these structures are treated to achieve the required end result (combinations of tanking, waterproof concrete and cavity drainage), and the nature of the site itself (how wet, any contamination/ground gas requirements?) and then the end result itself (standard of environment required?), can vary depending upon what the space is being used for.

In some cases it may be possible to provide effective protection with quite a light touch - house into a hillside, suspended beam and block floors, this can reduce costs. At the other end of the scale we've designed for basements sitting in water table, which extend out beyond the house above, with car lifts (take your car from driveway to basement), or connecting new basements below gardens to existing basements beneath houses.

Size, is again a factor, because again, we work out the areas and rates times areas = cost.

Cost range? £10k to £100k plus and beyond.

Costs for Dealing with a Flooded Cellar

An example could be a basic cellar space suffering from issues of flooding. In it's most basic form, waterproofing for such a space could include some perimeter drainage channel and a basic sump pump system. Such a specification can be effective, simply at preventing standing water (flooding). £3k plus.

Cost of Fixing Leaking Basements

A difficulty with many new-build basements is that they are designed to be perfect barrier to water, but when constructed are not. In a finished habitable basement, the structure is typically concealed in its entirety, making it difficult to see if and where it is leaking, and this implies a process of investigation to identify what the issue is, and what the solution is. We advise clients of costs associated with the investigation, and then seek to understand what's required. Cost range? Could be £350 if not a waterproofing issue, < £5k if localised repairs are viable (it depends). If investigation results in requirement for extensive remedial waterproofing measures, the cost of strip out + waterproofing + cost of reinstatement.. Cost range is likely in the multiple tens of thousands to £100k plus depending upon the space and extent of fit out. Find further guidance here.

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What's involved with basement waterproofing?

Exterior Waterproofing involves taking measures to keep water out of the foundation. Foundation Sealing includes applying waterproof coatings or membranes on the exterior foundation walls to stop water from getting in. Another method is using French Drains, which are drainage systems installed around the foundation to redirect water away from the basement.

For Interior Waterproofing, efforts are made to prevent moisture from coming in from the inside. This can be done through Interior Sealants, where waterproof sealants or coatings are applied on the interior walls. Additionally, Interior Drainage Systems, such as sump pumps and French drains, are installed to collect and pump out any water that may accumulate inside the basement.

Crack Repair focuses on identifying and sealing cracks or gaps in the foundation walls or floor to prevent water seepage. Proper Grading ensures that the soil around the foundation slopes away from the building, guiding surface water away from the basement.

Window Well Covers are installed on basement windows to prevent water accumulation and potential leaks. Gutter Maintenance is vital, involving the use of Downspout Extensions to direct water away from the foundation and regular cleaning to keep gutters free of debris, allowing proper water flow.

For more information, read our expertise on basements on our waterproofing design specialist page.

Basement waterproofing costs summary

We hope this helps answer your questions. If you would like further guidance, the ideal is to provide us with information so that we can review and potentially provide budget costs. Info such as: photographs of the space/area in question, a description and any drawings including dimensions.  For new-build waterproofing, please include a copy of the site investigation report if available.

Our contact page can be found here.