Note: This advise is relevant for a simple extension – it is advised to use an architect for ‘grand designs’.
Communicating your vision – drawing up your plans
First you need a physical drawing of what you are hoping to achieve. If you don’t already have software, there are some free online options such as ‘smartdraw’ that offer free trials or subscriptions which you can cancel once you have completed your plans and saved them to pdf.
It is helpful to begin by creating an existing plan of the property and you will also need this if applying for planning. Take the time to measure room sizes, ceiling heights, the external wall depth and window & door positions.
You can then draw up your proposed floor plan including the external elevations. It is important to consider the two together. How is the roof design going to work? Do the window and door positions look balanced?(tip: to establish the height of the building to eaves, measure the height of your brick coursing and count the courses. Each course should be approx 75 mm but this can vary with the brick type and mortar joint. To find the ridge height you need to establish the roof pitch. Measure the run from the center of the gable to the edge of the building, and count the course from the eaves to establish the rise.)
Before spending too much time on detailing your plans, consider whether you will need planning and if so, what is the likelihood of your application being successful? Planning considerations can be fairly onerous but all the information is available on the planning portal and with your local authority. You just need to sit down and spend some time going through the elements that are relevant to your design.
Check the planning portal here https://www.planningportal.co.uk/permission/common-projects/extensions/planning-permission
Once you are satisfied that your design is within the parameters of the planning regulations you can spend some time on the finer details. It is not too soon to consider all elements such as furniture placement. How do you want to live in the space? This can help you with window and door placement. Is there enough wall space for all your kitchen units or entertainment unit? etc…
Can you simplify your design to save on build costs? consider alternatives before finalizing your design. Is there access for a small excavator in order to dig the footings. A Bobcat micro-digger is a minimum 710 mm wide, and consider if it needs to turn to gain access.
If you need Planning – What comes first?
Before submitting your application for planning, you may want to get an idea of what the project will cost to establish whether you can afford to undertake the work. It can be difficult to decide what comes first, the planning application or the estimate as both items have a cost attached to them. Why pay for an estimate if you can’t achieve planning permission? why pay for a planning application if you can’t afford the build? As a ballpark, you could pay anything from £2500 per sqm2 to £3500 per sqm2 depending on the complexity of the build and the standard of specification. At this point you are not going to get an accurate cost for the work before any steels and the foundations have been designed. If needed, I would go for the planning you want, if it is granted, the permission will be valid for 3 years. If you decide to sell up, it will be beneficial and have a positive effect on the value of your home. If you do want to de-scope your plans later down the line due to affordability, you know that planning won’t be a problem as you already have permission for a larger proposal. It may also be possible to carry out the work in stages.
Design Considerations
Planning – When considering whether to grant planning permission for an extension the local authority will take account of sunlight and daylight factors, together with orientation, slope, overall height relationships, existing boundary treatment and how overbearing the proposal will be. The Planning Portal offer a very helpful interactive guide for what is and is not permissible. See link https://interactive.planningportal.co.uk/
Structural – Walls to be removed may be supporting walls. Steel beams will be calculated by your Structural Engineer. Try to ensure these can be accommodated within the floor space to allow for a nice clean ceiling line. Large spans may require a support post, it is worth bearing in mind so you don’t have any surprises once you instruct a Structural Engineer. Once your planning is granted, this will be the next step.
Drainage & Waste Positions – Consider the location of your external drainage. If you are introducing a toilet or sink on the other side of the house, you need to consider the drainage run. Locate toilets on external walls where possible, consider whether excavating for drains means digging up your nice new driveway or concrete floors.
SAP’s – You may be looking to introduce a large amount of glazing. The total amount of all external doors, windows, and roof windows, as a proportion of the internal floor area of the extension, should not be more than 25%. If this is exceeded, compensatory measures will need to be taken and calculated by an energy assessor. This may mean adding more loft insulation, or ensuring your new bi-folds achieve a better u-value which can lead to further costs.
Light & Heat – Think about the temperatures your new extension may reach and the comfort level of your new living space. If your extension is south facing, increased glazing can mean unbearable heat in the summer. Solar glass could be an option but comes with increased costs. Will you need to consider where your radiators are to be located or are you opting for underfloor heating?
Building Regulations – In some instances, Building Regulations can have an affect on your internal layout. For instance, if your proposal includes a loft conversion you will need to consider Approved Document Part B on fire safety, when considering the layout, pay attention to Section 2. Also, Approved Document Part K covers regulations on stairs (K1) including steepness and headroom.
Give yourself some time to revisit your design to ensure you are happy, if you want to make any significant changes after submitting your planning application, you will have to pay for amendments.
Submit your planning application
Now you have some carefully considered plans. It’s time to collate all the required documents and submit them for planning (if required) or apply for a permitted development certificate. Look out for my next blog where I will detail how to do this.
It may be that drawing plans and elevations and spending the time on researching the requirements is not for you. You may just want to oversee the build stage of your project. If you want this first element of the work taken care of, please contact me and I will draw up your plans and submit your planning application for you. Contact us. Depending on the size of the project I will propose a fee for the work and have your plans submitted within 2-3 weeks. (subject to any unforeseen complications that I may identify when overseeing your sketch plans).