Initial Design Considerations

The design of your cellar conversion will normally be dictated by the size of the existing cellar although it is possible to extend the current area or fit a completely new cellar.

It is important to be sure that you have looked at the options open to you and gathered as much information as possible before you proceed with a specific design. It will cost time and money to change your mind later on and, when all the work is completed, you should be satisfied that you have the best solution for your needs.

We would strongly recommend that you use an experienced architectural designer to carry out your initial scheme design as they will be familiar with the limitations that are imposed by planning permission and building regulations and they will know how to make the most of the space available.

myhome mygarden can provide you with a comprehensive Feasibility Study for any cellar conversion proposal that you are considering which is an excellent way of finding out what the possibilities are at your own home.

The main considerations you will need to think about at this stage are listed below.

A. Your Requirements

Often know as the 'Client Brief', your first task is to define what you actually require from the conversion.

These rooms are often multifunctional rooms and can be used as a place to relax and watch TV or perhaps as a guest bedroom using a sofa bed. Cellar conversions are versatile and are also commonly used for gyms, home offices, kitchens, home cinemas and games rooms.

They are generally very well soundproofed and free from dramatic temperature changes.

Most designers like to have a clear Client Brief from you so that they can help you to create the space you need and give you an idea of furniture layouts. If necessary, create a list of priorities, dividing it into essential works and desired, but not essential works.

B. Size

There are essentially three options when determining the size of your cellar conversion.

1. Existing Footprint – the first option is to convert an existing cellar and the size will be governed by the existing walls.

Be aware of how the existing walls align with the ground floor walls above as you may find the cellar is internal and new windows can not be provided. For this type of cellar, it is often a good idea to combine the space with a room above as this will overcome the building regulations light and ventilation requirements (see item C below).

2. Extended Footprint – the second option is to enlarge an existing cellar.

This may be a necessary option in order to enable light and ventilation to be provided or just to increase the available space.  This is potentially a costly exercise as it could involve underpinning the foundations of the existing house.

If you are considering this option, it may be worth looking at extending the cellar into the garden area as this will be easier to access for excavating and will have less impact on the existing foundations.

3. New Footprint – the third option is to provide a complete new cellar.

This is the most costly and disruptive method and could involve extensive underpinning and ground works. For an existing property, you may be better considering other methods of providing additional space as this type of cellar is better suited to new build homes.

 

C. Glazing and Ventilation

It is essential in any cellar conversion that you introduce sufficient daylight and ventilation, not only for your own benefit but also to satisfy building regulation requirements.

You may already have an existing window or external door which could be used to provide light and ventilation or you could enlarge this by additional excavation works.

Under the building regulations, the cellar should have it’s own natural light and ventilation if it is a separate room.  The window area should be a minimum of 10% of the floor area and ventilation should be provided by openable windows and doors of no less than 5% of the floor area.

Also be aware that if you are creating an ‘inner room’ (i.e. it is accessed from an existing ground floor room such as a living room or dining room and not the hall), the window should also provide a means of escape and be a minimum size of 500mm wide x 850mm high.

If you are unable to provide the required amounts of light and ventilation in the cellar, you can treat it as part of a ground floor room (i.e. a split level room) and use the light and ventilation from the room above. The cellar will have to be open plan and have no separating door.

If you are forming a kitchen, utility room or bathroom, you will need to provide an extractor fan which should be ducted to the outside air.

D. Access and Levels

It is quite likely that you will need a new staircase for access into your converted cellar either because it is in poor condition or if you intend to change the floor level.

The stairs should exit to a hallway or lobby unless you are creating an inner room with a means of escape or a split level room combined with the space above.

The stairs will have to conform with building regulations requirements including ensuring there is a minimum of 2m headroom over them and the maximum pitch (angle) is 42 degrees.

There are a vast array of styles and materials available from simple timber, to glass and polished metals so make sure you have a good look around before you make your final choice.

Most cellar conversions will require a new floor to be provided. If you have an existing cellar, it is quite likely that the floor is not protected against damp and may need to be lowered.

If you are lowering the floor, be careful that you do not excavate below the house foundations – dig trial holes close to the external walls to establish the depth.

Any new floor will have to include proper damp proofing and, if possible, insulation. There are many proprietary products available and this subject is covered in more detail below.

E. Waterproofing

One of the most critical design aspects of any cellar conversion is ensuring that it is waterproof. We have summarized this under floors and walls below but clearly there is a need to ensure the floor and wall membranes are continuous in order to avoid damp penetration at the joint.

Floors

Your choice of damp proofing the cellar floor will depend upon the amount of damp penetration.

In most situations, a standard modern membrane such as Delta FM or Newton System 500 will be the best choice.

These membranes are specifically designed for floor applications, to combat dampness, and contamination and the membranes are studded with a low stud profile (usually 3mm).  These membranes can be used in new build, remedial or refurbishment projects.

The system works on a ‘floating floor’ principle with either a screed or a flooring grade chipboard laid over the membrane.

In situations where the cellar is very damp or even prone to flooding, you may also have to provide drainage channels around the perimeter of the room that drain to a sump. This will hold a submersible pump and drain the water away from the building.

Walls

It is generally accepted that the best solution for cellar walls is to not worry about the walls themselves being damp but to prevent the damp entering the interior space.

Again, the choice of membrane will depend on the amount of damp but the most popular solution is a dimpled membrane that allow the water to pass behind and drain naturally into the ground.

The wall membrane will need to be sealed with the floor membrane to ensure a complete barrier. You may also need to waterproof internal walls if they are connected to the external ones.

It is also possible to seal the walls with a variety of bitumen products including self adhesive sheets or a paint type product applied with a roller.

However these products generally rely on the wall being dry in order for them to adhere so they tend to be more suitable for new build applications or very dry cellars.

In some situations, the exterior surface of the walls are waterproofed but this can be an expensive option due the excavation works required.

It is always best to get specialist advice for the most suitable product for your own home.

F. Services

At the design stage, you will need to consider how you intend to heat and light your new space.

Underfloor heating can be  a good option for cellars as it avoid the need to use up valuable wall space and provide fixings into the wall.

Recessed lights save headroom and are commonly used in cellar conversions

There are often a number of service pipes and often the consumer unit (fuse box) in the cellar so ensure that you know how you intend dealing with these and be specific about what is included in any builder’s quotation.  

G. Budget/Value Considerations

There is sometimes a reluctance to talk about budgets at an early stage, but this can often be the single most important factor that determines your final design.

Whilst you will be building the space for yourselves, we would always recommend that you consider the resale value that your conversion will add. It will need to blend in well with the existing and it may be worth asking a local estate agent about the potential increase in resale value.

You may wish to consider designing the room in a flexible way so that it could easily be converted back to a garage by a future purchaser.

Our section on Cellar Conversion Costs provides lots of information on cost influences that you will need to consider.

We would always recommend that you allow a contingency (we would suggest 10-20%) for the unknown when working out your costs at the feasibility stage

H. Planning and Building Regulations

Once you have decided to proceed with the design of a project, you will need to finalise the design details and to obtain any formal approvals required.

Your designer should be able to advise you on this matter and, if planning permission is required, make sure you are aware of any local planning policies that may restrict what you can build.

Planning Permission

Under planning laws, most properties have Permitted Development rights which allows a certain amount of development work to be carried out without the need for planning permission. Further information on this subject is available in our factsheet on Permitted Development

In most cases, planning permission is not required to convert your cellar providing that you are not adding a new entrance or windows at the front of the property or digging an entirely new cellar.

Also, if you live in a listed building, you will require planning permission as the fetures in a listed building are protected for historical reasons.

We would always recommend that you or your designer checks with your local planning authority if planning is required. For added peace of mind, you could obtain a Certificate of Lawfulness which is a formal confirmation from the planners that you do not need planning permission.

If planning permission is required, it is a good idea to have an informal discussion with your local planning office prior to making any submission as they will normally be pleased to give you guidance that could save you time and hassle in the long run.

Your designer will usually deal with the application for you, acting as your agent and will ensure that the plans are to the correct scale and include additional information required for the planning submission such as a location plan, block plan and a design or access statement.

For  more information on this subject, please refer to our factsheet on Making a Planning Application

Building Regulations and Working Drawings

Cellar conversions will normally require building regulations approval as you will be creating a habitable area.
The work is likely to involve upgrading the floor and walls to ensure they are damp proof and insulated and making sure there is adequate ventilation and natural light to the new space. You will usually be adding a staircase and all of these areas are covered by the building regulations.

If you are providing a new bathroom, you may need to include new drainage which will also need to be approved by the building inspector.

Your designer will normally prepare building regulation drawings and submit these for approval to the council or to an approved inspector.

The drawings that are completed for building regulations approval are commonly known as the working drawings and these will contain all the information needed to ensure your proposal meets with the current regulations. They also need to be clear and have sufficient detail for your builder to be able to use to accurately to carry out the building work.

Other Approvals

You may need to obtain other approvals for your proposal and your designer will usually help you deal with these. You may need to involve your solicitor to check if there are any restrictive covenants and a party wall surveyor if your proposal is close to another property. We have provided factsheets on these issues below.
The Party Wall Act
Restrictive Covenants

Specification for Works

Once the working drawings are complete, we would also recommend that a written specification is also prepared for your project as this will minimize misunderstanding between you and your chosen builder/supplier.

There are many aspects of your project that will not necessarily be shown on your drawings (e.g. type of ironmongery, floor tiles, etc) but these need to be defined so that a builder can properly quote for the works. The specification will also usually form part of your agreement with the builder when works commence.