Frequently Asked Questions

What is the difference between a cellar and a basement?

On this website the terms 'cellar' and 'basement' are used interchangeably to mean a room or collection of rooms that are located below (or partially below) ground level. In the UK the term 'cellar...More

How much does a basement conversion cost?

The cost of a basement conversion will depend on a number of factors including: The size of the basement Whether it is necessary to lower the floor to provide adequate headroom Whether underpi...More

How much will a basement conversion add to the value of my house?

In virtually all cases a basement conversion will add to the value of a property. However the exact increase in value will depend on a number of factors such as local property prices, the size of t...More

How much does the inclusion of a basement add to the cost of a newbuild house?

It is difficult to provide exact figures. However, the cost of including a basement as a proportion of overall project cost is lowest where land costs are high and on sites with ground conditions t...More

What can I use my basement for?

Basements can be used for virtually any purpose that above-ground rooms can be used for. Popular uses in domestic properties include playrooms, gyms, swimming pools, music rooms / studios, kitchens...More

Do I need to include a ventilation system in the basement and why?

Not necessarily, however it is important that heating and ventilation are balanced in order to prevent problems associated with condensation. Also, under Ciria 139 Levels of Dryness document, where...More

How do I install plug sockets/run cables when installing a cavity drainage membrane system in the basement?

Plug sockets can simply be surface mounted onto the plasterboard, preferably using plastic boxes. Cables, conduits and pipes can be run in the cavity between the Oldroyd Xv cavity drain membrane (h...More

Is Vandex a radon barrier as well as a tanking material suitable for application in a basement?

No. This is because Vandex ( is vapour-permeable and therefore will not act as a barrier to radon gas. A separate r...More

I have a period property. What system is best to waterproof the cellar as part of the refurbishment?

There are two approaches to waterproofing a basement internally. One method involves cementitious tanking with a waterproofing render or waterproofing slurry, such as Vandex Uni ...More

Can I do it myself? What is involved with tanking a basement?

While it may be possible to install the products yourself, we would suggest that you use a specialist contractor who has experience of the materials used,  as well as the competency to ensure ...More

What kind of finishes are available after waterproofing a basement with the Vandex system?

Cementitious tanking systems are vapour permeable. As vapour movement is usually from within the basement out towards the ground, this is an advantage. There may be occasions however when the ...More

Do I have to dig out for a channel (perimeter drain) when installing a cavity drainage membrane system in a cellar?

No, you do not, but in this case provision should be made for a high-profile drainage membrane to be installed to the floor. Also, the height of the floor within the boundaries of the channel will ...More

How do I deal with the waterproofing detailing at window and door reveals in the basement?

In below ground situations it is nearly always necessary to form a complete system. To facilitate this it is necessary to temporarily remove window frames, door frames and if present timber stairca...More

There is a high water table around the structure of the basement. What do I need to be careful of?

When deciding on your waterproofing (design), you will need to be wary of creating a perched water table and also putting the structure/waterproofing under stress. This is more of a risk if there i...More

What if the basement has under-pinning or piling?

The use of contiguous / secant piling and diaphragm wall construction techniques to construct retaining walls is common in large commercial basement projects. The nature of these construction techn...More

Do I need to include a vapour barrier with either type of basement waterproofing system?

This would depend on the intended use for the area. For example if the area is to be used for ‘habitable’ space, a Vapour Control Layer would undoubtedly be required. However if the spa...More

Why may it be better to use a high-profile cavity drainage membrane on the floor of the cellar?

If there is the risk of a higher level of water ingress into the basement, when refurbishing/waterproofing the area, it is wise to specify a high-profile membrane for the floor slab, such as Oldroy...More

Are there pipework kits available for the basement sump pump systems?

Yes, there are pipework kits available that are ordered upon request. For example, there is a pipework kit for the Sentry Twin sump and pump system which channels the two pump outlets into one disc...More

Do I need to go 'full-height' with the basement tanking?

Yes. Under the revision of BS8102:2009 (Protection of below ground structures against water from the ground), basement waterproofing designs must be to full-height in order to cover the possbility ...More

Why do I need a sump pump maintenance schedule as part of the basement waterproofing?

You can see significant benefits through: • Reduced running costs including energy and maintenance • Greater life expectancy for equipment • Reduced risk of breakdown with its res...More

Can the basement sump pump take waste from, for example, a sink in a utility room?

It is not recommended. Building regulations require two pumps, one for ground-water (uncontrollable) and one for waste (grey) water (controllable). The basement pump is designed to only take groun...More

What is the difference between Oldroyd Xp and Oldroyd Xv membrane in relation to installation in a cellar?

Generally, Oldroyd Xp membrane ( is installed in above-ground situations, for example where a new DPC has been installed and there...More

What type of insulation should I use/specify in conjunction with the waterproofing in the cellar?

The application of Oldroyd membranes ( as part of the process to provide a dry decorative surface is very broad and very often there is the tempta...More

Why is ICF with watertight concrete in not classified as a Type B basement waterproofing system?

Because it is not feasible to compact it as well as is required for water resistant concrete, plus all the ties required provide many water pathways. Further to this, does it make a difference if ...More

What does the term 'Primary Resistance' mean in relation to a Type C basement waterproofing system?

When using cavity drainage (Type C) systems the fabric of the building MUST offer "Primary Resistance". Specific guidance can be located in BS8102:2009 - Section 10.1, page 31. In some cases, local...More

What kind of systems can be considered for basement waterproofing?

There are many waterproofing solutions and products designed for basement waterproofing. Which ones to consider will depend on a number of factors, but the main question we would ask is - 'is ...More

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