building valuations


Basement Conversions


Do They Add Value?



If you have run out of space but do not really want to move then a basement conversion may be the answer. Here is some information that we hope will help you decide whether a basement conversion is for you.

Our surveyors pride themselves on a high standard of work. We can offer a Building Survey (also known as a Structural Survey). We also carry out Specific Defects Reports, sometimes called Engineers Reports or Damp Report, and we can also carry out Independent Valuations (Note: these are not for bank lending but are to advise you how much we feel the property is really worth).

Free phone us on 0800 298 5424 to speak to a surveyor.

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Can I Carry Out A Basement Conversion?

Some considerations when carrying out a basement conversion are: Is the existing basement damp? Does it have suitable head height? Whilst alterations and movements can be made, for example, to give you enough head height by lowering the ground level, as you can imagine it is painstaking, labour intensive and therefore often an expensive job.

Does It Require Planning Permission For A Basement Conversion?

Typically, no permissions are required from the Local Authority. However, do check if the property is Listed or in a Conservation Area or whether structural work, such as moving walls, is required, as this will then require either Planning Permission and/or Building Regulations (we would always recommend that you check with the Local Authority just to see if there are any improvements needed and you also may get some very useful information from them with regards to the local area and the water table level).

What Does A Basement Conversion Involve?

Normally the usual options are either to tank the cellar, which is the traditional method, or to dry line the walls. For either option you really require builders that are used to this type of work, or to be very experienced at D.I.Y.

What Do The Builders Do?

There are commonly two systems in use; one known as tanking and the other known as the dry lined drainage system.


This is where the basement is lined to stop water getting in. Ideally it should be lined on the inside but this is difficult where it is an existing basement and often it is lined on the inside. It should include the floor area. This can unfortunately lead to a build up of pressures and cause damage and deterioration if not carried out properly.

Dry Lined Drainage System

This is where the basement is drained of any dampness within it behind false walls into a sump pump, which is a pump located at a lower level within the floor of the cellar.

A Basement Conversion Your Design Choices

There are few choices with a basement conversion, such as:

Light - do you wish to add windows to give natural light into the basement?

Ventilation do you wish to add a mechanical ventilation system, or even a real air conditioning system (this is one where the heating, the cooling and the relative humidity is controlled by air ventilation, but these are expensive. The term air conditioning is used when air handling is occurring).

Sump pumps there is a range of sump pumps available, including those with alarms in case the sump pump doesn't cope or fails for some reason and also there are those with back up sump pumps.

Brief Specification of the Works Carried Out for a Basement Conversion by the Builders

Tanking System :-


Removal of all items within the basement.

Preparation of basement

Adding a sump pump (if so required)

Possibly replacing the floor if it is not considered suitable.

Applying first coat to the wall

Applying second and third coats to the wall

Tanking the floor area

Adding appropriate falls onto any water that does get into the basement towards the sump pump.


Dry Lining Drainage System :-

Clearing of cellar

Checking of floor timbers and protecting as required

Preparation of walls

Adding a drainage channel

Adding sump pump

Applying fixing plugs

Applying plastic sheeting to walls

Adding dry lining

Adding a fall to the floor to stop any water.

Getting On With Your Builder

It is very important to build a good relationship with the builder carrying out the basement conversion. We feel fundamental to this is a detailed agreed quotation for the work, together with discussions on any possible extra items that may come to light. Agreement on when payments will be made, for example within two weeks of the work being completed, possibly an official contract, although some smaller builders tend to be put off by this. Set and agree the site rules, i.e. what time work can begin and whether you are happy for the builder to work at the weekend and provide lots of cups of tea and bacon sandwiches, assuming your builder is not a vegetarian!

We would add that the role of project managing the building work is often under estimated and certainly there is a builder inside of you that is trying to get out! Where there are many trades it does require much co-ordination and cajoling from the builder to co-ordinate everyone. It is also important that if things are going wrong you deal with them in a logical and rational manner and if things go extremely wrong and you get into a dispute situation where the builder, for example, walks off site.

We would be more than happy to help; please contact 0800 298 5434 for help and advice with regard to basement conversions.


See our other articles on adding value to your home:

Loft Conversions - do they add value?

What is my Home Worth?

Adding Value to Your Property


Independent Surveyors

If you truly do want an independent expert opinion from a surveyor with regard to valuations, mortgages, mortgage companies, surveys, building surveys, structural reports, engineers reports, specific defects report, structural surveys, home buyers reports or any other property matters please contact 0800 298 5424 for a surveyor to give you a call back.


Commercial Property

If you have a commercial property, whether it is freehold or leasehold then sooner or later you may get involved with dilapidation claims. You may wish to look at our Dilapidations Website at and for Disputes go to our Disputes Help site

We hope you found the article of use and if you have any experiences that you feel should be added to this article that would benefit others, or you feel that some of the information that we have put is wrong then please do not hesitate to contact us (we are only human).

The contents of the web site are for general information only and are not intended to be relied upon for specific or general decisions. Appropriate independent professional advice should be paid for before making such a decision.

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