The Complete 20 Step Guide To Extend Your House
If you are planning to extend your house but you’re not sure where to start, or if you just want to know what you should do and when, then this post is for you.
Just follow this simple 20 step plan and it will take you from the very first step through to a complete extension. This is The Complete Step-By-Step Guide on How To Extend Your House.
1. Write A Simple Brief
Nothing complicated. Just have a think about what you want to get out of the project, and write it down in a few lines. It could be as simple as how big you want the space to be, or what you will use the extension for. Try to include a first stab at what your budget might be as well. You can use our Cost Calculator if it helps.
If you can jot all this down in a simple email it will become a useful document for you to send out to architects in the next step.
2. Find An Architect
Contact two or three architects and share your brief with them. Ask what they think about the brief and your ideas to extend your house, and get a fee proposal for their services. Use our guide to Architects Fees to help make sure you get the best value for money.
Have a look at their portfolio of similar extensions, and have a chat with them either on the phone or in person before deciding on the architect you want to appoint.
3. Get Concept Design Drawings
Now that you have your architect you can start to look at Concept Design options with them. Make sure you say what you like, and what you don’t. And talk to them about any design ideas they’ve had or details you hadn’t thought of. This will help you check that your brief covers everything you want, and get the best out of your project.
It’s more and more common for architects to be able to give you 3D images and files at this stage. This can be a great tool that can really help you visualise the design, so if you think this could be useful to you then make sure your architect can do this.
4. Get Planning Permission (Or Permitted Development Approval)
Once you’re happy with the design, your architect can develop the drawings and complete all the paperwork to make an application for Planning Permission (or Permitted Development Approval) for the project. You can expect the Council to take about 8 weeks to give you a decision. If you think that your project might be Permitted Development then you can check our Guide To PD here.
Decide with your architect if you will pause while you wait for the planning decision (good idea if there’s a risk of refusal), or to press on if the planning risk is low, as this could save you time and get to completion more quickly.
5. Appoint A Structural Engineer
Once you’ve got Planning Approval it’s a good time to find a structural engineer to do the design and calculations of any structural parts of the work. This usually includes things like steel beams, structural timber, concrete and any special foundations.
Your architect will probably have a few structural engineers that they can recommend and have worked with before, and this can be quite a good idea but should not stop you from using someone else if you have an engineer in mind. Ask your architect to look at any quotes to make sure they include everything you need.
6. Get Detailed Technical Drawings
Your architect will lead the technical design process, and coordinate any input needed from the structural engineer. Detailed architectural plans will show how the extension will be constructed and the materials that will be used. Your architect will also add any construction details that are needed to show how the building will be put together.
You will need to rely on your architect during this step, as they will be responsible for producing a well designed and detailed set of drawings for your extension. But don’t be afraid to ask questions as a good architect will always be happy to explain what is involved.
7. Get Building Regulations Approval To Extend Your House
Choose Council Building Control or a Private Approved Inspector to approve the technical drawings and issue a Building Regulations Plans Check Certificate. This will show that the planned work complies with the latest Building Regulations. Private Inspectors tend to be a bit quicker than the Council, so can save you a few weeks but might cost a little bit more.
Remember that all building work in the UK is required to meet Building Regulations even if Planning Permission is not required, so you should never skip this step.
8. Sort Out Any Party Wall Agreements
If you are building on (or near) the boundary you will probably need a Party Wall Agreement with your neighbour before you can start work. Discuss this with your architect and if necessary get a Party Wall Surveyor to serve the correct notices and get agreement for you.
It is a good idea to speak to your neighbour in person, with your plans to show them that the work has all been professionally designed. This can help avoid any dispute and make sure that the agreement is simple. You might like to read our Guide To Party Walls For House Extensions for more information.
9. Check Any Other Consents You Need To Extend Your House
This is a good time to check any other consents you need. These could include Build Over Agreements with the Water Board or sewerage company if you are building near any shared drains; and Freeholder consent if you own a Leasehold or a share of Freehold.
Most consents are really simple to sort out once you have identified what is needed. But it is a good idea to get them all resolved at this stage, as you do not want any surprises to come up after the building work has started.
10. Make As Many Detailed Design Choices As You Can
Now is the time to work with your architect to make detailed choices about as many of the materials and fittings of the extension as you can. This can then all be included in the architects drawings and specifications. Choices such as floor and wall finishes, materials and colours can all be included; as well as more detailed choices such as the exact tiles, light fittings, switches, and kitchen and bathroom furniture that you want.
Your architect will be able to give you suggestions for any, or all, of these. But you might have your own preferences that you want included as well. And if there’s anything you don’t want to choose at this stage then it can be included as a provisional sum, for your architect to instruct on later.
11. Shortlist 4 Potential Contractors To Extend Your House
A good way to approach this is to long list up to ten contractors, that can be a mix of any recommendations you’ve had, contractors you’ve seen working in the local area, and contractors your architect has worked with before.
Then you can review their previous work, check their financial history, and take up any references you would like, before shortlisting down to 4 for tender. The idea is that you should be happy to appoint any of the 4 if they return the best price.
12. Tender The Project To Extend Your House
It’s best to run a formal competitive tender process to get reliable costs back from contractors. Your architect can do this for you. They will need to send it out to all shortlisted contractors, and give them 4 weeks to return their prices. Contractors will need to get costs back from all of their suppliers and sub contractors in order to submit completed tenders.
All of the tenders received should be opened at the same time at the end of the process, and once they have been checked over by your architect you will be able to select the contractor you want to use.
13. Choose Your Contractor And Sign The Contract
So, we’re almost ready to start the work on site. Because you will have followed a proper tender process, this should mean that is will be pretty easy to choose the contractor that you want to do the work. The next step is for your architect to prepare the building contract so that you and your contractor can sign it. This is also a good time to finalise your plans for where you will live while the work takes place.
Once that’s done the contractor can start to mobilise, and set up the site to begin the building work to extend your house.
14. Make Sure You Comply With Health & Safety Regulations
The law was changed in 2015 and there are now more Health & Safety (CDM) Regulations on private house extension projects. The HSE can carry out spot checks and impose fines on you or your contractor, or stop the work if they find anything wrong.
The law requires that you provide written Pre-Construction Health & Safety Information with project specific risk assessments to all contractors so that they can plan their work safely. Your architect can carry this all out for you as Principal Designer to ensure that you have complied with the law. Your contractor will need to produce a Health & Safety file for the project that they keep on site at all times.
15. Make Site Visits With Your Architect
Unless your project is very small, it’s a good idea to move out while the work is taking place. But you might want to visit from time to time to see how the work is going (although some clients prefer to stay away completely until the work is done). If you do visit then make sure that you always attend with your architect – they will know how to deal with your contractor, respond to any issues that come up, and get the best out of the work.
Your architect will also probably chair a meeting with the contractor on site every few weeks to keep track of their progress.
16. Pay The Contractor Based On Your Architects Certificates
Your architect will inspect the works regularly, and every 4 weeks they will issue a certificate that shows the value of the work that the contractor has properly completed on site. You can then simply pay your contractor based on the value that your architect has certified.
This reduces risk for you, and makes sure that the contractor is only paid for the work that they have completed to the required standard. The architects certificate will also show that you should pay 95% of the value certified, so that you retain 5% until the contractor completes the project.
17. Get A Building Control Completion Certificate
Whether you chose the Council or a Private Approved Inspector they will inspect the work on taking place on site site at a few key stages. Then, when the work is complete, they will need to visit and issue a Building Control Completion Certificate.
The Building Control Certificate is an important document that you should keep with the property. It will show that the work you had carried out complies with the Building Regulations.
18. Move In After Practical Completion
As long as you are using a standard building contract such as JCT or RIBA, then your architect will be responsible for inspecting the work on site and issuing a Practical Completion certificate when it is complete. You should always wait for your architect to issue Practical Completion before you move in to your extension.
This is also important because the contract will have a penalty clause that your builder will have to pay you, per week, if they are late. But for this to be effective it’s important that you also stick to the contract terms, so just ask your architect if you are unsure.
19. Make Final Payment After A Year
At Practical Completion the amount that you will pay your contractor changes from 95% to 97.5% of the contract value. The remaining 2.5% you will keep back as retention for a year.
Your architect can still instruct the contractor to return and make good to any cracks or defects which appear; and the final 2.5% is only paid to the contractor once the full year has passed and they have made good to any issues.
20. Done – Extend Your House With Confidence
So, that’s it. 20 Steps that will take you from your first thoughts to extend your house, right through to a year after it is all complete and you have moved in.
One final tip is to always turn to an architect to get their professional advice to keep things on track. Remember that although for most people extending their house is a one time thing, your architect will have gone through the process many many times, and can help you to make sure that it all goes smoothly.
Extend Your House – Example Before And After
Before and After photos of one of our house extension project in Finchley, North London. Single storey rear and side extensions, loft conversion and full refurbishment. See the project here.
How To Extend Your House
Follow our 20 Step Plan to Extend Your House, and you will be well on your way to building a successful house extension.
And if you’ve got any questions on any of the steps; or just want to discuss something with us then Get In Touch and we’ll be more than happy to help.