Building an extension costs in London

House & Kitchen Extensions Builders in London

Planning

Architect, Structural Engineer, Planning Permission and Building Control Fees

The architect is very important. If it is a complex house extension, or the property is a listed building, part of a Conservation Area in London, then it is advisable to use an experienced architect.

Drawings and Plans

The cost for an outlined drawing ( plan ) is a lot cheaper because it only shows basic details of the proposed house extension and it can be used in order to apply for Planning Application or getting estimates (quotes) from builders.

Permitted Development is where the owner of a property can build additional structures to the existing building without the need for council Planning Permission. There are clearly defined parameters for this particular feature which you should take into account.

The Government made changes to the Permitted Development policy and now it allows greater flexibility for extensions and loft conversions.

Structural Calculations

Most house extension projects require the services of a Structural Engineer if there are load bearing walls and new ( large ) openings to be made. Open space designs will involve structural works, knocking down internal walls and metal beams to support the weight of the property. This is what Structural Engineers do, they calculate the sizes of the metal beams needed for the building works. Their expertise is required by the Local Building Control and sometimes is needed for Full Planning Permission too.

Building Control

Even if your house extension, kitchen extension, loft conversion or garage conversion requires no Planning Permission (using the Permitted Development law), you still need to give notice to the Local London Council, the Building Control Department.

There is a fee to be paid, check with you local council here http://www.robuild.co.uk/councils.htm

Layout, Structure, Drains, Foundations

Side extensions or rear extensions will affect the layout of the original drains, more often than not, there is a manhole very close by. If you don뭪 want to have a manhole inside the extension, it will have to be moved outside the perimeter and it will add extra expenses. In London, most sewer pipe drains and surface water drains are controlled by Thames Water and they too require a notice (and sometimes a fee ) if a wall will be built over a pipe that belongs to them. A cheaper option is the use of a double seal manhole cover. We have had no complaints about double seal manhole covers, there is no smell but the metal frame is visible.

Foundations

Having trees very close to the ( proposed )new foundations means that the footings must be deeper than the usual requirement. The deepest domestic foundation by Robuild was 4.2 meters compared to the 1.2 meters as a standard. The cost is increased more than 3 times as deep foundations makes the job more complicated and expensive in terms of material costs, time and labour. You get extra digging, extra soil to dispose of and extra concrete. The soil also plays an important part, nice clean clay is better than sandy mixed soil as it is more stable.

Walls, bricks and blocks

Unless your house is a listed building or in a Conservation Area, the walls for the extension will be cavity walls. Cavity walls are also called double skin walls, the advantage being the insulation that is used in between the walls and it also keeps the rain water away from the internal wall.

Brick walls are generally more expensive than block walls. The reason for that is the cost of materials and labour. The drawback of using block walls is that the walls must be rendered and if the original house is a brick faced property, the new extension will not look as part of the original house, thus it will also change the visual character of the property. The best house extensions are the ones that you don뭪 notice that they are home extensions.

Roofing

Pitched roofs are the best. This type of roofing is esthetical, has a longer life span and gives better insulation by reducing the loss of heat. The construction cost can be almost double compared to a flat roof.

Flat roofs

Flat roofing is a popular choice,and when a roof is done properly it can last for over 15 years but Robuild only gives 7 years warranty because it has to be maintained after that period of time.

( keeping the guttering clean, no heavy traffic on it and so on )

A badly constructed roof leaks after a maximum of 2 years due to exposure to the heat during summer and cold during winter. We never had any complaints and we have some really old roofing jobs in London, however, we don뭪 quite follow the standard procedures. We build flat roofs the same way a swimming pool is built sometimes.

Asphalt roofs are better than felt roofing.

Lead roofing is durable( it can last hundreds of years ) and also expensive. Commonly, lead roofs are required for listed buildings.

For further information or estimates, contact us here