HOME EXTENSIONS

 Many homeowners choose to extend their property simply because they need more space. Whether it’s creating a larger kitchen and dining area with a rear extension, adding a side extension for a study or annex, or developing a two-storey addition to increase bedroom capacity, extending your home can significantly improve how the space works for your family. CADGUYS helps homeowners turn these ideas into well-designed and buildable projects. 

Every extension project begins with understanding how you currently use your home and what changes would improve it. At CADGUYS, we work with homeowners to explore how the household functions day to day, considering factors such as privacy, how spaces connect, and what areas of the existing property may be missing or underperforming. This helps us identify where additional space would be most beneficial, whether that means extending to the rear, the side, or developing space above the existing building.

Budget is also an important early consideration. Current construction costs typically range between £2,500 and £3,000 per square metre, so having an understanding of the likely budget helps guide the design process and ensures the proposed extension is realistic and buildable. Once we understand the space required and how it fits within the available budget, we can begin developing a design strategy and move into the planning stage.

Once we understand the type of space you are looking to create, CADGUYS will advise on the most appropriate planning strategy to achieve it. For many extension projects, there can be significant opportunities through permitted development rights, which allow certain types of extensions to be built without the need for a full planning application. In many cases, side extensions can extend up to half the width of the original house, while rear extensions are typically allowed up to three metres for semi-detached or terraced houses and four metres for detached houses. Larger rear extensions may also be possible under the larger home extension prior approval process, subject to neighbour consultation. Where permitted development rights are intact, we can prepare the necessary drawings and submit a Lawful Development Certificate application to the local authority to confirm that the proposal complies with permitted development rules. This process usually takes around six to eight weeks and provides formal confirmation from the council that the extension can be built without full planning permission. Where permitted development does not apply, we will instead develop the proposal as part of a standard planning application to ensure the design gives the project the best chance of approval. For more detailed guidance on permitted development rights for house extensions, you can refer to the Planning Portal’s interactive guide: https://www.planningportal.co.uk/permission/common-projects/extensions. 

 Once the planning strategy has been established, CADGUYS will agree a design fee covering the preparation of the measured survey, planning drawings and planning submission. We can usually arrange a site visit within around one week of confirming the appointment, where we carry out a measured survey of the existing property and surrounding context. Using this information, we work closely with the homeowner to develop the extension layout, exploring different design options and refining the proposal through a series of iterations to achieve the space and appearance the client is looking for. Initial planning drawings are typically prepared within around three weeks of the survey, after which the client will have the opportunity to review the design and request any adjustments. Allowing roughly one additional week for amendments, the drawings can then be prepared for submission to the council.

If the proposal falls under permitted development, we would normally submit a Lawful Development Certificate application, which typically takes six to eight weeks for a decision. Where a full planning application is required, decisions are usually made within ten to twelve weeks, although some projects may require additional supporting surveys depending on the site and local authority requirements. In some cases, councils may request further information such as ecological surveys or other technical reports before granting approval.

Once the extension has received planning approval, the project moves into the technical design stage, where the focus shifts from concept to construction. At this stage CADGUYS develops a full set of construction drawings that translate the approved design into a detailed and buildable package. This process typically involves consulting with a structural engineer to develop the structural strategy for new openings, foundations and structural supports required for the extension. We also review existing drainage arrangements, ensuring that any new kitchens, bathrooms or utility spaces can connect appropriately to the existing drainage system. Where public sewers are present, it may be necessary to consult the local water authority and obtain build-over approval. The construction drawings will then be developed to demonstrate full compliance with building regulations, including insulation performance, structural design, ventilation, drainage and weatherproofing. The final package includes detailed plans, sections and construction details outlining materials, build-ups and technical requirements, allowing the project to be accurately priced and constructed with minimal ambiguity during the build stage. 

 Once the construction drawings are complete, the project moves into the tendering stage, where contractors are invited to price the works. CADGUYS works with a wide range of trusted construction professionals and can typically recommend three to five suitable contractors who may be invited to tender for the project. While clients are free to approach contractors independently, CADGUYS can also manage the tender process on your behalf, issuing the full drawing package and requesting formal quotations from each contractor. Once the prices are returned, we assist in reviewing the submissions and comparing them based on factors such as cost, programme, construction experience and suitability for the specific build type. This stage is important to ensure that the scope of work is clearly understood and that contractors are pricing the same information, reducing the risk of misunderstandings, variations or disputes during construction. 

 Once a contractor has been selected, the project moves into the construction phase. At this stage a formal building contract is usually put in place, often a JCT contract, which provides a clear framework for both the client and contractor and helps ensure the project is delivered as agreed. CADGUYS can assist with contract administration and project support, helping to organise schedules of work, monitor progress and advise on staged payments throughout the build. We can also provide project management services, including periodic site visits to ensure the construction is progressing in line with the approved drawings, agreed specification and budget. Acting as a point of coordination between the client and contractor helps minimise misunderstandings and keeps the project running as smoothly as possible. Choosing an experienced contractor with a proven track record is essential, and we always recommend reviewing previous projects and speaking with past clients before making a final decision. With the right team in place and a clear construction package, the goal is to deliver a high-quality home that performs efficiently, is built to last, and provides a comfortable living environment for years to come.