29
Jan
Basement Conversion & Extension Guide
What do you do if you want to extend your home, but your garden is too small to allow it, or your loft is unsuitable for conversion? You may think the only way to get extra space is to move house. However, there is another possibility. Consider a basement conversion, or basement extension, excavating below ground to gain space from a basement.
“Basements are slowly becoming more popular in the UK as people look for more space and don’t have the ability to extend wider, longer or higher.
Sometimes, the only way to get more room without moving house is to go down into a basement.
To understand the issues, benefits and cost related to basement conversions please scroll below for brief description of what is required or alternatively just get in contact with us and we will be glad to assist.
Why is a basement conversion or extension a good value for money?
11 Ways to a Better Basement
Basement Typologies
Basement Conversion or Extension Suitability
Outline your Aims
Basement Extensions:Statutory Approval
Party Wall Award for Basements
Why is a basement conversion or extension a good value for money?
As always the building trend of basement related work started in London due to the limitation of space and high cost of moving to larger property. Converting or extending the basement or cellar into habitable space became feasible and became the obvious choice to create that extra room or the secret wow factor within the house of which started the phenomenon to grow across the country.
The clear benefits outweight the extra cost for the basement conversion or extension, these are;
-
The extra space will add value to the house.
-
The space is more adaptable and can offer variety of use: bedroom, study room, store room, bathroom, cinema etc.
-
Due to the popularity of having basements it has led to technology and products which have made it easier to build and manage the internal environment easier.
-
There are more options to attractive spacious design of basements and is viewed as desired option rather than moving to bigger house.
-
It is easier to obtain Planning permission for basement conversion or extensions than building extending your building on single or double storey extension as it is out of sight and can be approved as it sits within permitted development area.
On the flip side, the major disadvantage of going down into a basement can be the cost. However, in areas where building land is scarce and property values are high, basements can work financially. If the property has an existing basement in your property, even if it is in a bad state of repair or with a low ceiling, it will still be cheaper than a traditional new build extension.
Another disadvantage is that the construction process of a basement conversion or basement extension can be complex. Like any building work it will be disruptive, noisy and messy especially if underpinning is required. Even though excavation is usually accessed externally the breakthrough isn’t until it’s time to install a connecting staircase and the neighbours won’t like it.
So, yes a basement extension is a good idea! Don’t be put off. You just need to come at it from the right angle. And that’s where a good architect comes in. Give us a call if you have a basement in mind.
11 Ways to a Better Basement
One of the main reasons people renovate their basements is because they’re looking for more usable space. Whether you’re interested in adding a new game room, wine cellar or bar, a newly renovated basement can offer you ample space for many of your needs. But before you tackle such a project, bear in mind the basic functional requirements in any design is providing the air, access and escape route that would satisfy Building Control Requirements. Nevertheless, the challenges inherent in basement renovations are many and listed are few items to which need to be consider before you go underground.
How to Finish Your Basement the Right Way
11 Rooms with no light
Rooms that work well without light are wine cellars, cinema and entertainment rooms, utility rooms, storage rooms and perhaps bathrooms and WC. However, if there are certain places that you simply can’t get natural light, the artificial light product, the “Coelux-Generation-2” has just been launched. Watch the video to see this great artificial skylight product.
Basement Typologies
-
Basement refurbishment or conversion of an existing cellar. This is the most straightforward option that uses old cellar spaces which often have bare brick walls and lack waterproofing. They tend to exist beneath Victorian and Edwardian houses. If there is enough headroom such a basement conversion would involve damp proofing, improving the staircase and access, and finishing works. If there isn’t enough headroom the build gets more complex as the basement conversion will need the floor to be lowered and the ceiling to be raised.
-
A retrofit basement is when a basement is added to an existing home. Adding a new basement to an existing building requires extensive and pricey excavations and possibly underpinning to party walls. However, such basement conversions are still viable in high value properties and neighbourhoods or when there is no other way to achieve more required space. Such basement extensions can be underneath your property or extend further out.
-
Building a new basement from scratch. This is when basements are constructed as part of a new build. This is a straight forward option and can be fully or semi underground. Including a basement in a new build design can be a great way to get more space from your land.
BASEMENT CONVERSION OR BASEMENT EXTENSION SUITABILITY
Property Buildability and Contractor Access
One of the first things to consider is how constrained the site is? What level of access would builders have for such things as the removal of spoil, and delivery and storage of materials? How close are the neighbours and what effect will any works have on them?
Property Reparability
What is the structural state of the existing property? How much extra will it cost just to bring the property up to par and is it possible to do so?
Surrounding Geology
What are the local ground conditions and soil types in the immediate area? A good place to start is to talk to your local building control officer and pick his knowledge of his patch. Obviously, carrying out a couple of trial holes will also establish this information quickly. These tend to be carried out during a site investigation, soil survey or geology survey. They should be carried out before construction begins as the results should inform the design and build of the basement and property.
Water Table
Establishing the drainage characteristics of the local soil and water table level is important because it has a direct effect on the choice of structure and waterproofing of the property. If there is an existing basement, consider if it has a history of flooding, or, is it currently damp? Can anything be done to control this? It is important to seek expert advice to ensure costs do not spiral out of control if the issues are not dealt with early enough.
Topography
Are there level differences that can be exploited for the provision of external access, light and ventilation?
Ventilation
Is there any ventilation to any existing basement? If not how easily could it be provided?
Access from the existing property
Consider the constraints of the existing context and ground floor layout. For example, how will internal access and fire escape be provided and comply with building regulations?
Existing Foul Drainage
What are the existing foul drainage provisions? What will the impact of the basement conversion or basement extension be?
Outline your Aims
Careful planning of the basement space is crucial to its success. All too often basement rooms are lifeless areas, starved of natural light or key connection to the outside because the design hasn’t been properly considered.
“Some people might assume basements to be dark and dingy zones, but in reality, the right balance of illumination and good ceiling height (ideally at least 2.6 metres) will create bright, spacious, rooms that feel connected with the rest of the house.
The design and layout of your proposal should revolve around how you’re going to use the space. Are you creating extra room for general living areas or will the basement play a specific role, such as a cinema, gym or spa zone?
Your basement should feel like a natural continuation of your home in the same way as a good horizontal ground level extension would create a seamless flow between the stories by things like matching flooring and style. The staircase position between the basement and the rest of the building has an important role to play. Tucked away staircases can make a new storey feel like a secretive area, whilst a more visible design will add a sense of connection.
SETTING THE BRIEF FOR YOUR BASEMENT CONVERSION OR BASEMENT EXTENSION
Your basement brief is an important stage that outlines what you want your basement conversion or basement extension to achieve. Having established that your property is likely to be suitable for a basement, the next step is to define the scope of your project. What follows are some basic questions you might ask yourself:
-
How would you like to use the new basement space?
-
How big a footprint do you want from your basement? It does not need to be as big as the house above, or it could be bigger and extend under the garden to the rear.
-
For circulation, where do you want a staircase?
-
What is the desired headroom for the basement?
-
Is external access direct from the basement level required?
-
How much natural light is required?
Having clear ideas on these points will help ensure professionals like architects can help ensure your basement conversion or basement extension provides you with what you want. They can offer priceless design advice and if some aspects of your brief are not possible, they can explain why and offer alternatives.
FUNDEMENTAL DESIGN ELEMENT REQUIRED FOR ANY BASEMENT CONVERSION OR BASEMENT EXTENSION
CIRCULATION – HOW THE BASEMENT CONVERSION OR BASEMENT EXTENSION CONNECTS TO THE REST OF THE HOUSE
Along with the lack of daylight, another problem a basement designer faces is connecting the new zone to the rest of the house. Ideally, the new stairwell should link seamlessly into the hallway. A basement should always feel like it is part of the home, so it is important to give some thought to how it will connect to upper levels.
The staircase must provide a safe and direct route outside from the new lower level, otherwise, there may be problems with Building Regulations. (Note, this may not apply if you are upgrading an existing basement). The best location for the staircase is immediately below the ground-to-first-floor flight. Locating it elsewhere just eats into existing rooms, therefore reduces the project’s cost-effectiveness and use of existing space.
“Another way to seamlessly connect zones is by creating an internal balcony or a galleried landing, accessed via an internal staircase. This would not only create a dramatic double height area but would allow natural light into the basement conversion or basement extension.
How to bring ventilation into a basement conversion or basement extension
Any new habitable rooms will need to be ventilated and this can sometimes present a problem. Ventilation should be considered early in the design stage because if mechanical ventilation is required, the ductwork will need to be accommodated for.
Where the basement contains a light well, it can sometimes be adapted to include an opening window equivalent to 1/20th of the floor area of the room with a trickle vent at high level. In any bath or shower rooms and extractor fan should be fitted. If there are no opening windows in these rooms, extractor fans which are triggered by the light switch with overrun timers should be fitted. This allows the fan to remain on for a period of time after the light is turned off. Where natural ventilation through windows is not practical, a mechanical ventilation system will need to be installed. Various package systems are available on the market.
WHAT ABOUT EXTENDING OUT UNDER THE GARDEN?
The simplest way to construct a basement is to follow the line of the existing structure above. However, it is also possible to extend horizontally beyond the footprint of the house. This can be particularly effective at the rear of a house, where it is usually capped with a raised terrace or patio. This allows roof lights to be set into the ground, which floods the rooms below with natural sunlight.
Basement Extensions: Statutory Approval
Planning Authority view of basement conversion is positive and quick approval is not given to applications for converting the basement to provide separate dwelling or change of use.
Typically, permission is granted if the basement continues to be part of the original building footprint (not the front or rear garden) or if is extended but doesn’t encroaches the permitted development areas. Check out our post on Permitted Development Guidance.
Additional Information Required?
Due to increase of basement conversions many local authorities have made their policy more robust due to complaints received from neighbours and consequently this has resulted in a new policy called a ‘Basement Impact Assessment’ to ensure certain items are considered before work is carried out.
A basement impact assessment should be specific to the site and the particular development proposed. Through collation of information and detailed analysis the BIA sets out to evaluate the direct and indirect implications of a proposed development.
BIA’s normally comprise both a factual report and an interpretive report. The interpretive report is usually split into sections such as the following:
-
Site history, underlying geology and groundwater.
-
The impact of the subterranean development on drainage, sewage, surface water and ground water flows and levels.
-
Ground movement due to the proposed development (including demolition of any existing structures) and corresponding damage to neighbouring properties and infrastructure.