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The Complete Guide to Extending Your Home

Renovating your home can reap huge rewards. When done correctly, it helps you bring your home up to date and add value to it. Whether you plan to renovate a bathroom or extend your home within permitted development rights, you should approach your project with laser eye focus to stay on budget and complete it on time.


Why is it important to prepare for your home extension project


This helpful guide will allow you to plan your house extension expertly and to avoid the common mistakes that can eat into your budget before you even start. It will answer common questions that become obvious only once you start making mistakes! I learned the hard way during our recent single storey extension. So read on, to give yourself the best chance at a smooth house renovation.


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1. Find out if you need planning permission


About 3 years after I achieved planning permission for our rear single storey extension, and another 2 months after receiving a Non material Amendment to my initial permission, I found out that I didn't need planning permission to begin with. This is because the size of my extension was within permitted development rights.


Under new permitted development rules, homeowners in terraced and semi-detached homes are able to put single story extensions of up to 6 metres at the rear of their properties without needing to obtain planning permission. Those in detached homes are able to extend by up to 8 metres.


To qualify for permitted development, the following need to apply:

  • your home has not previously been extended

  • your home is not listed

  • your home is not in a conservation area and there is nothing prohibitive in your deeds.

Tip: Do not assume that your home has been extended previously, even if you see a past planning approval. Check the original plans of the home versus what was approved to confirm whether any works had ever been executed. If you need confirmation, your local building control office will be able to confirm this.

2. How Close to a Boundary Wall Can I Build an Extension?


You can build right up to a boundary wall but know that if building your extension involves digging or building foundations within 3m of the boundary, party wall or party wall structure, or digging foundations within 6m of a boundary, the work will require you to comply with the Party Wall Act.


3. Do I need an Architect involved?


Assuming you have identified that you need planning approval, you will need to discuss your project with an architect who will provide the relevant plans and elevations to support your planning permission.


Do not expect the architect's drawings to include the detail of where things start and end. Everything seems to be drawn on approximation which can lead to frustration and will not help your builder down the line.


Here is an early iteration from my architect. The drawing looks cool. It incorporates a rooflight as well. But while drawn beautifully, this design is technically impossible to build. Why?

Because our architect already knew that our internal ceilings throughout our home have the very standard 240cm height. That would live just 10cm allowance for a roof. Well I can tell you, you cannot build a flat roof that is 10cm thin.


Tip: Instead of taking the measurements at face value, ask your architect for proof of concept. Ask them to split the height into the various sections. Ask them to further split the height they allocated for a roof to its various elements too.

If your architects numbers are not correct, you will lose more time trying to correct them once your plans have been approved and the build has started, and that is an absolute nightmarish situation. It may take a minimum of a month for the planning officer to review and approve non material amendments.


An alternative that has become popular is to hire an architectural rendering company. It's said that their numbers are more accurate and you'll also be able to view a life-like rendering of your project.



4. What to Consider Before Drawing up Plans


Although your architect should be able to advise on this, by visiting your property, some aspects can restrict what you can and cannot do in your design including:

  • soil type on the site (might require different type of foundations like beam and block)

  • services access (you cannot build over manholes)

  • surrounding trees (your foundations might need to be deeper)

  • any history of flooding

  • site access

  • rights of way.

5. Who submits the planning application to Council?


If you have an architect assigned, ask if they will submit the planning application on your behalf, acting as your agent. Having said that, if you have the drawings it is easy to submit the application yourself, there are no technical questions.


If you plan to save some money and submit for planning permission yourself, try to look up planning permission applications submitted recently by others in your area - these will be available on your local Planning Authority's portal, just look up by address to find recent applications.


The cost of applying yourself is less than £50. Your architect may charge around £400 to submit your application.



6. How long does it take for a planning permission to be issued?


If you require planning permission before you start your works, you will need to submit plans, showing the current and future design of your home. To do this, your architect will need to survey your home to get accurate measurements. Plans submitted must be to scale!


You should allow up to two weeks for the survey to take place (depending how busy the architect's surveyor is).


Once the survey is done, the measurements will be shared with the architect who will work on a couple of concepts to discuss with you. This stage can take as long as you need to decide on the final look and feel of your extension.


Once submitted to your local planning Authority, expect anything up to 12 weeks for your approval to come back. The local council will need to allow enough time for neighbours or the local Parish to raise any concerns before they make a decision on your case. This timeframe is relevant only where the council approves your plans without conditions.


7. Do I need Building Regulations plans?


Once you have your planning permission you can move to the next stage: Building Regulations plans: these are your builder's guide to building your home to exact specifications according to your architect and structural engineer.


These plans will show you where to fireproof walls, what insulation materials to use, ventilation requirements, drainage etc. They can also show in more detail specific parts of the build in line with the structural engineer's requests.


Your Builder will need to see these plans before providing their detailed quote. Knowing what I know now, I would suggest that you go through them with your Builder, in detail, point out the most complex parts and have them agree that they can carry out the job.


8. How do I choose the right builder?


My best tip for finding your builder is use word of mouth. A builder that has successfully completed a project for a neighbour is a safer bet than someone you have never used and found online.


For example, if you live in a cul de sac where the homes were built by the same developer, chances are that a builder who has extended a nearby home will know what to expect during the build.


Take time in choosing a builder for major structural property refurbishments. Make sure you see evidence of your builder's insurance (check expiry dates!), and check in person their most recent project if possible. In all likelihood your builder is still working on that last project. Don't just rely on being given a phone number for references - you don't know who is answering the phone!


9. What are the stages from planning to completion of a build?


I have identified the stages between planning and completing your extension to be as follows:

  1. Identify if you will go down the route of permitted development or planning permission

  2. Find an architect to draw your plans (current and future)

  3. The home survey will take place

  4. Once you have approved the drawings, submit the plans to Council; or if you are going down the route of permitted development, you can now find a structural engineer.

  5. Once you have approval from Council ( a decision is issued), get the architectural drawings to the structural engineer. the engineer will look at things such as proximity to trees, boundaries, type of home, type of roof, removal of walls internally, rooflight requirements and provide two documents: their structural calculations and structural drawings.

  6. At this point you may also need to have a drainage survey undertaken.

  7. Give the structural drawings to your Building Regulations planner. They will produce the Building Regulations document.

  8. Give the BRegs document and the architectural drawings to a few Builders for a quote.

  9. If you are ready to accept a quote, ensure with your builder they are happy to have a contract with the full scope of works described. The contract should also mention that they will provide a builders warranty at the end of the works.

  10. Before you start any work, inform your Insurance company.

  11. Pay a deposit to secure your builder and agree a payment schedule. The schedule should explain what each payment will be for. Each payment should be relevant to a milestone reached.

  12. Agree with your builder if they will use the local Authority's Building Control team or whether you are going to a private firm. Going private may not have any perks really - your private building inspector will not necessarily be more understanding or accommodating!

  13. Book the Building Inspector - they will need to come within a couple days of the works starting. They will then need to come after the completion of certain milestones - foundations, brickwork (to check on insulation), roof completion, steelworks etc.

  14. Once the work has started, order any glazing necessary. Do not delay. Most large glazing items (sliding doors, rooflights) take around 6-7 weeks to deliver and the last thing you need is a ready roof with no rooflight to make it watertight!

  15. While the building work continues, reach out to the trades you will need at a later stage. A plumber may be needed to advice on the drainage and pipework locations for radiators and taps whereas an electrician will only need to be brought in for the 'first fix' once the roof is completely watertight.

  16. If the extension is for a kitchen, make sure you allow at least 5-6 weeks for the delivery of kitchen units. Cut off for pre-Christmas deliveries is usually early October.

  17. Before plaster-boarding the space, the Building inspector will need to attend to sign off the internal works for the roof (e.g. to check on the insulation) and steelworks.

  18. If your builder is not involved in other internal works (plaster-boarding, plastering, painting, kitchen install) then this is where they will probably leave the scene. Make sure they have made good whatever they may have damaged and leave an allowance of money against this. Give yourself time to see if anything comes up (e.g., a leaky roof) before you clear all outstanding balance with them.


10. Who will keep track of payments?


Most likely, your builder will use a software to issue you invoices at various stages of the build. even the most organised builder however will likely fall off piste and send payment requests in messages, Whatsapp or in person.


Use an excel spreadsheet with a simple formula that adds up each payment and calculates the outstanding amount.


You will also likely need to calculate separately any 'extras' that might be added along the way, e.g., if you decide to introduce a new deliverable that was not part of your original quote, or where you need additional material.


11. Can I make changes in the design during my build?


You can. Some changes may require notification to your planning Authority through a Non Material Amendment (which takes 4-8 weeks to process, especially if notification to neighbours is required once more).


Some design changes will be necessary because of unforeseen issues. But if you are making changes because you just changed your mine, know that your costs will increase - the architect and structural engineer may need to be involved to redesign aspects of your project and the builder will see this as a change request and, yes, charge more.


Best to always stick to original designs to keep the costs down.


12. Do I Need a Lawful Development Certificate?


If you chose to go down the Permitted Development route then remember to apply for a Lawful Development Certificate (LDC) from your local authority at the end. This will confirm that the work was lawful and met PD requirements and didn’t need planning permission.


If you are planning to sell your home later on, you will need this certificate where planning approval was not sought. It costs around £100, half the normal planning fee.

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