Tips for a Successful Home Extension Project

Having done hundreds of extension projects, we thought we would share some of the tips we have leaned over the last decade.

Financial feasibility

Price per m2

• The first important step is to establish the budget for your extension by multiplying the current average construction rate per m2 by the area of new floor space created by your extension or loft conversion.

• Don’t forget to budget for kitchens, bathrooms, flooring, decorating, rewiring and removal of bearing walls etc.

• Use the Check a Trade online cost guide to research the above costs.

• Consider allocating a 10-20% contingency fund for unforeseen costs and 5-10% for professional fees and consents.

• Check you are not over-capitalising your home by spending more on buying the home and improving it than what other similar properties on your street have sold for. Rightmove is particularly useful for this as its floor plans allow you to calculate prices per m2.

Consents

Planning permission

This is the first hurdle to jump when seeking consents for your project. Its best left to an experienced architectural designer who will prepare drawings which meet your needs and those of the council, before submitting them for approval which takes up to eight weeks. You can check what has been approved in the vicinity by entering your post code on your local authority’s planning search website.

Building regulations approval

We always recommend using a private approved inspector instead of the council as the former are generally more amenable. The inspector will notify the council a week before works commence on site and will inspect various stages of the build before issuing the completion certificate. They will require structural calculations from a structural engineer in addition to your architectural designer’s drawings.

Party wall agreements

If you are doing work to the shared party wall between you and your neighbour, or digging foundations within 3m of their foundations where yours would be deeper than theirs, you will need you gain consent from them. If you are lucky, you could have them sign template letters in the party wall explanatory booklet, however they can insist you pay for one or two party wall surveyors instead!

Build over agreements

Your water utility company will require a build over agreement if you are building over or within 3m of a public sewer or within 1m of a smaller public lateral drain. Its best to check this before starting drawings as it can influence the size of the extension. This can be done by purchasing a map of sewers from the utility and checking the lateral drains by opening manholes and/or having your drains mapped.

Licence to alter

If you don’t own the freehold, then you will need to gain a licence to alter from the freeholder. Check with them if they require planning permission and building regulations approval before or after seeking their permission.

Design considerations

Impact on neighbours

This is the number one reason that planning permissions are refused for extensions, so your designer will need to ensure that your extension complies with your local authority’s loss of light/outlook policies. However, this is not a consideration if your extension is within permitted development allowances.

Aesthetics

Your local authority will normally have policies which limit the size of extensions and require matching roofs/materials etc, so your designer will need to factor this into your designs.

Trees

If there are existing trees within falling distance of your extension, then you will need to consider deeper foundations or if closer, then special foundations such as piles may be required to preserve the tree roots while ensuring your extension doesn’t move. If submitting a planning application, the officer may request a tree report from a specialist while if using your PD rights, then this is not a required document. Trees in conservation areas and those with protection orders require permission before they can be cut.

Flooding

If you are in an area of flooding on the government flood map, then you will normally be required as a condition of planning permission to use resilient construction and/or ensure the proposed floor level is no lower than the existing. If you are in a surface water flooding area on your local authority’s map, then you may be required to install water butts to slow the discharge of water from your roof.

Elements of construction

Superstructure

The main two methods of superstructure construction are brick/block and timber. The former is slightly cheaper whereas the latter is slightly faster to construct. Timber walls can be finished with brick slips or render to comply with planning constraints. Roofs are always timber construction whether they are slightly cheaper flat roofs or longer lasting tiled pitched roofs. Pitched roofs can either have regular flat ceilings or vaulted ceilings where the ceiling follows the pitch of the roof to add more internal volume. Floors are normally ground bearing slabs unless you have clay soil which moves and requires either a block and beam or timber suspended floor. All walls/floors and roofs will require insulation which complies with current building regulations.

Fenestration

Most windows are UPVC which are the cheapest option and are normally bespoke made to fit. However, if in a conservation area you will normally be required to install timber windows. Larger folding/sliding patio doors are normally metal which is stronger and can be bought in standard sizes. Roof windows allow light deep into the existing house where an extension is added and can be used as part of a loft conversion, especially on the front roof slope where dormer extensions are normally prohibited. Consider shading devices for south or west facing patio doors.

Structural elements

Structural elements such as foundations, lintels, beams, columns, floor joists and roof rafters must be designed by a structural engineer.

Drainage

Foul drainage connections from bathrooms/kitchens to vertical vent stacks, to inspection chambers, to the shared sewer or lateral drains, need consideration by your designer. New surface water drainage from your extension roof should normally be connected to a soakaway if your garden is big enough, or alternatively to the shared sewer.

Flooring

The normal choice is engineered wood flooring which give the beauty of wood while reducing material and labour costs. Bathrooms are normally tiles with porcelain being a good balance of durability with cost.

Lighting

Its important to achieve a balance of the three main types of lighting namely: task for reading/cooking/makeup etc, ambient to provide general lighting, and accent which highlight a particular element such as art in a room. This can be done with ceiling spotlights/pendants, wall lights, floor/table lamps and cupboard strip lights. Add several pools of light instead of one blanket of light in a room. If using downlights in bedrooms or reception rooms, use swivel versions sparingly to wash light onto walls. Always use warm white lights.

Kitchens

The two main types of kitchen units are standardised from a high street retailer or bespoke from a joinery company. Either supplier option will normally design your kitchen. Popular choices for standardised kitchen doors are wrapped in a range of colours or lacquered for bespoke in any colour you like. Popular worktop options range from hardwood at the budget end to natural/composite stone at the higher end. Consider two drawers instead of traditional doors, and magic corner units, for floor cabinets. Consider lining up wall cupboards 60cm above worktops and grouping tall units together for a clean look.

Bathrooms

Bathroom suppliers normally offer design services for a fee. Normally siting your bath/shower furthest from the door frees up floor space for the basin and toilet. Thermostatic mixers prevent showers going cold when others use hot water in the home. Ideally a vanity top or large basin is preferable to prevent water splashing on the floor and to accommodate toiletries. Provide lighting for your face with lit cabinets or wall lights. Small showers which are 800 x 800mm or less should be avoided. A 1.2m high shelf behind fittings can hide drainpipes and built-in toilet cisterns while allowing a surface for toiletries etc.

Heating

This can be provided by underfloor heating with pipes ideally within ground floor screed, or alternatively beneath floorboards within insulation panels. A cheaper option would be vertical column radiators which look attractive and are available in tall thin sizes (ideal for installation next to patio doors), or short wide sizes (ideal for installation under windowsills).

Hiring a builder

• Check online reviews.

• Meet some three clients at their completed projects to assess quality and reliability.

• Get competitive quotes from three builders with drawings from an architectural designer and a schedule of works from an estimator.

• Check they have the correct insurances

• Sign a contract including above documents as addendums.

• Do not pay any money upfront, only weekly for work done and buy your own finishes.

• Meet on site weekly to check progress and discuss solutions.