A good estimate for your extension cost is to multiply the square meter area of the proposed extension by £1500. Therefore, if you have an extension which is 5x4m – 20 square meters your extension would roughly cost £30,000. You should also factor in any potential VAT which would add a further 20% to the costs. This estimate doesn’t include the internal works if you were fitting a new kitchen, say. Depending on your specification, it could be £2000 per square meter if you are having a high-quality specification and finish. On average you should have roughly £40-50,000 for a typical single storey rear extension.

You may have read that you don’t need planning permission for your extension. This can be true in some cases as you can use your permitted development rights to extend under certain parameters. For example if you have a semi detached house, you are within your rights to extend 3m from the existing rear wall of your property without planning permission.

We would suggest that you check with us whether your extension will need planning permission or not. Use this link to head to the planning portal which also has further information.

Yes. You can extend to the boundary line. If you are going up to another extension, you may want to employ a party wall surveyour, who will document the process and ensure you are covered if any damages arise from the works. This is unlikely to happen if your builder is competent.

Yes. You can apply for a domestic build over application to Severn Trent. This process is similar to that of a planning application. They will charge a small application submission fee and will require details of the proposed manhole. This should be completed as early as possible to ensure the building works can be signed off.

They can, but it wont make a difference. It is your right to extend your property under the permitted development rules. Just as your neighbour has the same right to extend under permitted development. As long as you extend under permitted development rules (which you can find here PDF) it wont effect your extension.

They can extend to the boundary in most cases. However, they should appoint a party wall surveyor or serve you a 14 day notice. Excavating within 3m of an adjoining owners property you should appoint a party wall surveyour. This is under the Party Wall Act 1996. In most cases, party wall agreements can resolve any disputes. Just speaking and coming to an agreement with your neighbour is always the best solution before any works begin. You can use many sites online where you can create your own Party Wall Notice. We use https://www.rocketlawyer.com/gb/en/sem/party-wall-notice.

That will depend on the space you have to the side of your property and what new rooms you require with your extension. Should you have over 3m of space at the side of your current house to the boundary, it could be worth it. A key aspect to consider is if you need any side access for bins, rear access and egress, which would be important for a semi detached property, say. In addition your new cavity wall would take up 300mm. So if you needed a side access of 800mm plus your cavity wall of 300mm this would then remove 1.1m of space and your left with 1.9m width of floor plan space. Therefore, you would only be left small room options such as a pantry, storage, utility, WC, office and so on. Its key to understand the rooms you will need first and if you can save cost by including these spaces in the original house with a re-configuration. Just note that a side return extension would require a planning application.

In almost all cases you will need a structural engineer for your extension loadings calculations. This will be for things such as foundations, rafters, floor joists, lintels and RSJ steel beams. Steel beams installed to open up the floor plan – usually removing the rear or side wall of a property – are very common place for extensions.

Both will achieve the same goal and sign off of your extension with a building control notice. Private will mean you get a more personal service and are sometimes easier to deal with than councils – in terms of response time but can be more expensive. Councils can be cheaper and your sign off will be via the council authority rather than a private company. We usually would advise to go privately.

Yes. We work closely with lots of different contractors for our extensions. We can recommend trusted builders to help you with your project should you need them.

Drawings for your extension are detailed references for either the planning department, your builder(s) and ultimately, yourself. Therefore, its important you obtain drawings from an architectural designer or technician. If you require a planning application for your extension (which does not fall under permitted development) then you will require the following drawings for your planning submission;

• Existing Location Plan 1:1250
• Existing Block Plan 1:500 
• Existing Floor Plans, Sections & Elevations 1:50 or 1:100
• Proposed Block Plan 1:500 (with measurements to boundary) 
• Proposed Floor Plans, Sections, Elevations 1:50 or 1:100 (with measurements of building heights, eaves, extension depth/width) 

This list is not exhaustive, but will be required as a minimum for a planning submission for a extension. Should you use your permitted development right to extend, drawings are still very useful as you will be able to plan out the following elements for your building regulation stage;

• Demolition 
• Full detailed dimensions 
• Drainage runs/connections 
• Manholes
• Electrical (Sockets, Switches, Lights, Fuse Spurs, Electric Meter) 
• Mechanical (Radiators, Boilers, Water Heater, Extract Fans) 
• Fire Safety (Smoke Alarms, Heat Detectors, Fire Doors)
• Window & Door Specification Schedules
• Skylights Specification Schedules
• Structural (Joist & Steel Specifications) 

In summary, we would advise that you obtain drawings for your rear extension and hire an architectural designer.

A typical timeframe from engaging your architectural designer to competition for your rear extension is 9 months – 1 year.

• Architectural Planning & Design Drawings (2-4 weeks) 
• Planning Submission & Permission (8-10 weeks) 
• Architectural Building Regulation Drawings (2-4 weeks) 
• Builder Invite to Tender/Cost (2-4 weeks) 
• Construction (3-6 months) 

Builders can draw up your rear extension for you. But be careful. You will need to check the planning rules for your rear extension and what you are permitted to do with and without planning permission. Use our helpful PDF guide for your permitted development rights. For example, if you wanted a wraparound extension, this would require planning permission and your builder would need to draw out plans to scale to submit to your local authority. Therefore, we recommend that you employ a professional to do your drawings. 

Typically, architects will charge between 5%-10% of the overall cost of the project. Say your extension costs £50,000 to build, they would charge £3,750 at 7.5%. Of course, this price will vary and will likely include both the planning design and building regulation drawings. If your extension is simple, then the figure would be around the 5% mark. However, you usually pay for what you get. The cheaper architects will do very basic plans and won’t show design detail, interiors, exteriors and want nothing to do with the build aspect or communication throughout the project at planning and the building stage. It’s worth asking for examples of the architects work if you have been given a cheap quote and decide for yourself if it is what you want.

It can be common that neighbours will object to your extension. Its simple, people don’t like change and if they don’t have it then neither can you. That being said, unless your extension is completely out of proportion, massively overbearing and blocks all of their light you wont have a problem with obtaining your planning permission. Planning officers will take into consideration your proposal under its own merits and could potentially get objections from both nieghbours and still approve it. This is where a good architectural profession will really help as they should have referenced or looked at the councils local plans and supplementary design guides. These go into detail all of the design requirements the council would like to see for certain types of development. For example, side extensions (especially double) often have 300mm set back from the front of the original house to show that it has been extended and subservient. Another example is to have obscure glazed windows on side elevations to stop any overlooking issues onto your neighbours property. If these guides are checked and complied with, it will be extremely difficult for a council to refuse your extension, even with objections.