Start Designing 

An initial appraisal of the site needs to be carried out to assess where your extension can be located and how large it can realistically be. Points to consider:

Orientation

The orientation of your extension may not be something you have much control over, but wherever possible it is worth considering where the sun rises / sets and how the natural light can be used, passive heat harnessed in winter and overheating controlled in summer. This is a fine balancing act and needs to be considered in conjunction with the technical design and specification - something your Architect would usually advise on.  At this early stage though, you can think about general strategies.

Planning Constraints

In most cases the position of your extension will be quite obvious - dictated by the available space, your brief and the other factors listed here. Another key aspect is the planning regulations and in particular permitted development. Wherever possible, extensions and alterations are carried out using a property’s ‘permitted development rights’ which allow you to add a certain amount to your home without the need for planning permission. 

To find out what you can do, please use this link to the Planning Portal

Neighbouring buildings / boundaries

How will your proposals sit in relation to these - is there the potential for a negative impact upon them?  Things to avoid would be:

• Blocking of light to existing windows.

• How your building meets the boundary - avoid overhanging eaves, ensure you know where the boundary is and agree with your neighbour where you will build.

• If you have roof windows - will they be able to see straight into these?

• Will there also be the potential for loss of amenity from noise? (yours or theirs)

Existing Trees

Are there any mature or particularly attractive trees which would be in the way and should be preserved? If you are planning to retain and build around these you will need to consider the root system and special foundations may be required.

In some cases these may be protected (by a Tree Preservation Order) and permission should be sought so this needs to be dealt with early in the process as it could be a barrier to development. For more information please refer to the 'TPO' link. If in doubt you should try to speak tot he Tree Officer at the local authority or liaise with an Arboricultural Consultant.  

Find out more about TPOs

Below Ground Drainage

Are there any manholes visible in the vicinity of your extension? If so, you need to ascertan where the waste runs to/from and this may require further investigation by the following methods:

• lifting manholes and trying to work out the direction of flow

• Getting an 'asset plan' from your local authority which shows main sewers (but not generally smaller branch runs in gardens)

• Commissioning a CCTV survey from a drain specialist who can then map the routes.

If your proposed extension is near or over a shared sewer (i.e serving your property and at least one other) then a build over agreement may be needed. This can require special foundation designs or re-routing of pipes so is worth checking at an early stage. Enquiries should be made to your local sewage authority but for general guidance you can refer to the link below.

The Thames Water 'Build Over Guide'

Access for works and future maintenance

• How will the builders gain access the site? Will they have to go through the house and if so how will this be managed?

• Can the work all be carried out from within your boundary or will the builders need access from the neighbouring gardens? (Refer to the Party Wall section)

• Once the work is complete how will you get access for cleaning and maintenance? For instance, a very deep extension may impeded access to upper floor windows for cleaning - how will this be managed?

The existing building needs to be measured and 'as existing' drawings prepared - these will form the basis of all drawings and designs.

The survey should be relevant to the proposal 

You need to have sufficient measured information to enable the design of your proposed extension and to successfully submit the relevant applications. So if you are considering a rear ground floor extension for example, you will not really need the front elevation or  roof space to measured and drawn in great detail. Likewise, if you are proposing a loft conversion you will not need to measure the details of the garden.

In most cases though, it is advisable to get the whole building surveyed at the same time in order to get as complete a picture as possible. This also means if plans evolve or expand you will have the information to hand that you require.

1. • A typical set of ‘existing’ drawings would include: 

   • Floor plans (including the site up to the boundaries)

   • 1 or 2 sections (cut through the areas where where you are looking to extend or alter)

   • Elevations 

Ensure you have all the information needed

It is important that the surveyor picks up all details such as:

1. • Level changes & rooms heights plus beams & down-stands

   • Soil pipes, meters, inkling services, boilers

   • Existing radiators or other possible obstructions

   • Landscaping features & materials

   • Boundary treatments including heights

   • Manholes, gulleys & drains

   • Any other external features or obstructions which may effect the proposal.

Consider the context

For some proposals, most notably those that require planning permission or listed building consent, you may want the surveyor to measure adjoining buildings and site sections in order for street scenes to be prepared. This is particularly useful where the heights relative to existing buildings is important, or certain architectural fetaures and relationships need to be respected or replicated. 

Consider how much you want / are able to spend and ensure you have the funds arranged before starting work. Make sure you consider all the possible costs:

Build Costs

1. • This is of course the primary cost and will probably account for 85 - 90% of all costs. Therefore if you have £100,000 to spend, you should be thinking in terms of an £85,000 build-cost so you have money set aside for all the other fees (see below). 

   • You must also consider VAT. Many builders will quote figures net of VAT so make sure you are clear if this is included or not. Some builders may not charge VAT, and some may offer cash deals but beware, not only is this in danger of being considered tax avoidance, it also puts you in a weak position if you subsequently get into dispute with your builder. Without a clear contract, proper paperwork and a clear paper trail for the money you may not be able to make an effective claim for damages if you need to do so.

Consultants Fees

Whilst you should be able to deal with a certain amount of the management opf your project using this guide, there will still be professional fees to pay. The scope of these will of course depend upon the complexity of your project but may include:

• Survey / existing drawings

• Architectural Design fees

• Structural Engineer’s fees

• Other Consultants fees where required

As you confirm these you can add the figures into your cost plan (in the project plan) to start building a complete picture of all costs.

Planning Application fees

The fees will vary depending upon the type of application you need to make - the most common are:

• Prior Approval (for 'larger extensions') =

• Lawful Development Certificate (Proposed Use) =

• Householder Planning Application =

• Listed Building Application =

Building Regulations Application fees

The building regulations application fee is usually confirmed at the end of Stage 3 when you have full design proposals established. The applicatio can be submitted to a private 'Approved Inspector' or the local authority. The former usually quote on a job by job basis but the latter often have fee schedules on their website so these figures can be referred to at the initial project planning stage to help establish your budget.

Other possible costs

Further costs can arise for a number of things and these will need to be monitored and added to the budget as they are confirmed. This may include:

• Party Wall costs (see party wall section)

• Build Over Application costs (if building near of over a sewer)

• Asbestos survey (if you suspect or are unsure about the presence of asbestos)

Consider the amount of time needed for the design process and when you can realistically start building work

Use the pre-filled programme in the Project Plan as a template

This gives a typical timeframes that we would anticipate for a normal house extension. There are a number of variables though, depending upon the type of project, its complexity and the planning route you are going to take so this is just an ‘average’ guide that needs to be adjusted to suit your specific project.

Establish the planning timescales

Through your initial site appraisal, you should have established the type of extension you are proposing and therefore the type of application. This will in turn dictate timescales:

• Householder planning or listed building applications = 8 weeks + 3-4 weeks for the optional pre-app For more details refer to the section 'Prepare & Submit Pre App'

• Larger extension application = 6 weeks determination period (if there no objections) - extending to 8 weeks or more if prior approval required.

• Certificate of Lawfulness Application = 8 weeks

All these timeframes are targets and recent experience has been that Local Authorities are not hitting these targets and will often request an extension of time in order to consider the application. This is frustrating but in most cases you are probably best advised to go with it. You can appeal for ‘non determination’ if an application is not decided within it’s timeframe and you have not agreed an extension- but this process in itself will take several weeks and adds more work.

The discharge of planning conditions are a complete unknown at the outset and these would only apply to householder or listed building applications. The extent will be known once you receive a Conditional Approval and the work can then be planned. 

How to 'fast-track' the programme

If you want to ‘fast track’ your project you can continue with the Stage 4 work ‘at risk’ whilst the planning is being considered. This would mean that all approvals should line up at the same time enabling you to start work almost as soon as the planning permission is received. 

Check whether your site is protected in some way which may limit the type and extent of development you can carry out.

Introduction

If your property is listed, you will be required to make a listed building application for any changes. Additionally, Permitted Development Rights will be affected if your property is on 'Designated land’ (Article 2(3)) which includes National Parks and the Broads, Areas of Outstanding Natural Beauty, Conservation Areas and World Heritage Sites. 

Do a Planning Search

Go to the 'planning application search' tool and look for your property address - again this should bring up details of past applications and particular restrictions applicable to your site.

Search the Policies Map

Go to the 'planning policy' section and search for your property on the 'policies map'. This should show relevant policies, restrictions and also historic applications both for your site and those nearby (useful for judging what is possible). Not all local authorities will have this search facility.

Search the Conservation Section 

Go the the 'Conservation' or 'Heritage' section and do a search of the Local Authority lists / maps for Conservation Areas and Listed Buildings. This is also useful for finding maps and 'Conservation Area Appraisals' which give more details about the each individual Conservation Area. These appraisals will vary between authorities but some can be very thorough, with clear advice about alterations and detailed analysis of the area - sometimes on a street-by-street basis.

Use your initial research to create a detailed brief - for your own benefit and to help when briefing others.

Introduction

This process of formalising your brief will help at the next stage where you are looking to create concept designs. Whether you are trying to sketch out something yourself, or instruct others to do this on your behalf, a clear brief will help in this process, making sure you make informed decisions, taking all factors into account.

Creating the brief is really a case of pulling together all the factors from the preceding stages to help inform the extension design. 

Size & Location of the Extension

Where is it to be located, how wide, deep and tall?

Proposed Use of the Spaces

What is the room to be used for and are there related alterations - such as moving existing functions into the new extension or making other internal layout changes.

Style, Look & Feel

Record any  preferences you may have for style, look, feel and aesthetics - you can find source images for reference. If there any specific materials or specifications to be used please note these but if you are trying to use permitted development rights the materials should normally be 'similar in appearance' to the existing.

Other Specific Requirements

Do you have any other requirements such as views, links to the garden and sustainability strategies (e.g solar panels, heat pumps, insulation standards etc)

Landscape / External Features

For ground level extensions, the link to the outside can be very important and a well-considered landscaping design can really transform you scheme. Consider access to the outside, hard landscaping features (such as walls, paths, terraces), materials, planting, and specific features (such as ponds, fire pits, BBQs, lighting, audio installations, gazebos or outbuildings.

Using your existing survey drawings and the brief, you can now prepare concept designs for your proposed alterations.

Establish the footprint

Using your initial analysis you can set-out the footprint for your proposed extension (or loft conversion). This will often be based on the permitted development rules and site constraints. Where you are applying for planning permission, there will be more flexibility but you should consult the design guidance on your local authorities website. 

Consider the internal arrangements

Having set-out the footprint of your space you can now consider how you want this to be arranged. Things to consider are:

• Use of the space and those adjoining it

• How you want the new space to link to the rest of the house and the outside

• Views in/out,  natural light and ventilation

• The detailed arrangement of how the spaces will be laid-out, where furniture will go and how this relates to windows and doors.

• Location of supply and waste pipes where you are installing bathrooms or kitchens.

Think about the form of your proposed extension

The internal layouts will help to generate the external form, with the placement of windows, doors and rooflights to suit the spaces. The height / form of the extension may also be dictated by permitted development rules and the constraints of the existing building.

Consider the external appearance

Having established the general form of your extension you can now think about how you want it to look. Things to consider:

• For permitted development the materials should be 'similar in appearance to the existing'

• If you are making a planning application you can generally be more creative but the planners will assess the quality of your design (which is of course subjective) amongst other criteria.

• Listed buildings and those in Conservation Areas need careful handling and whilst modern designs are not out of the question, they will need to respect and enhance the heritage assets or context. 

Finalise the sketch drawings

The final designs can be produced in whatever format you or your designer's prefer, such as hand drawn sketches, 2D CAD drawings, 3D renders or even physical models.  This really is the fun part so its worth spending a bit of time looking for resource images, honing your ideas and thinking about exactly how you want it to be. 

Its worth remembering that Architects are basically charging for their time, so if you pay low fees, they will not have the time for considering multiple options and creating beautiful, detailed drawings. We therefore recommend that you think about this as much as possible prior to engaging any professionals, using the internet to find inspiration and hone your ideas. Obviously a good designer should be able to suggest things that you may not have considered and elevate your ideas to a higher level, so its also worth spending time finding the right Architect to deliver your scheme.

If your extension requires planning permission you may want to seek pre-application advice to get early stage advice from the planner’s about the likelihood of your proposals being acceptable.

Submit with your sketch designs

Sketch designs can be submitted so you are not committing to so many fees before getting some feedback. Having said that, the more complete the application, the better the advice so submitting this eith very basic information may be a false economy.

Receive written feedback 

The written advice yku receive back the officer should highlight any areas of concern, hopefully giving you the opportunity to address or rethink them. You should also get details of what information will be required to accompany your planning application when you submit it. This should help you to get the application validated quickly and ensure that you don't pay for reports or drawings that aren’t required.

Build  a relationship with the planners

The pre-app process enables you to build up a rapport with the planning officer and start a process of  negotiation, this should lead to a better outcome.

Check the local requirements for pre-apps in your authority

Before submitting a pre-app you should check the costs, process and requirements with your local planning department. Although all authorities operate slightly differently, the application will usually be dealt with in 3-4 weeks and should result in you receiving a written report. In some cases you can opt for a site meeting and where applicable you may also get input from heritage officers.  Costs for pre-app advice can vary quite significantly from 'free' to several hundred pounds.

The 'designer' should identify potential heath and safety risks and try to eliminate them. Any residual risks (both in the build phase and in use) must be highlighted and solutions for their management suggested.

Introduction

The Construction (Design & Management) Regulations (2015) place certain responsibilities on the client to ensure that the project is designed, managed and constructed in a safe manner. For domestic clients these duties will normally pass to the contractor  and in practice, this should involve little more than what they normally do in managing health and safety risks.

Using a Principal Designer

If you have appointed an architect (or other designer) on a project involving more than one contractor, you can ask them to manage the project and take on your client duties instead of the principal contractor. The designer then takes on the responsibilities of 'principal designer' but must have a written agreement with you (the client) confirming they have agreed (as principal designer) to take on the client duties as well as their own responsibilities. However, if they do not have a written agreement to confirm they are taking on the client duties, those duties automatically pass to the principal contractor.

Designers Duties

Anyone undertaking a design role should consider health and saftey whilst developing their proposals and should identify the risks associated with the design. These should be designed-out wherever possible and any residual risks should be identified and made clear for the contractor and end user (i.e you). This means considering risks associated with both the building process and future maintenance and use of the premises.

Examples of things to consider

Examples of building risks would be:

• Digging trenches for foundations with associated risk of collapse

• Erecting heavy steelwork

Examples of mitigation for the above would be:

• Temporary propping

• Use of lifting machinery

Examples of 'in-use' risks would be:

• Cleaning roof windows

• Changing lightbulbs at height

Examples of mitigation of the above would be:

• Having centre pivot windows which can be cleaned from inside

• Ensuring lights are not located at such a height that they can be easily accessed from a suitable step ladder.

What to give your builder

You are advised to ask your designers for their 'Designers risk assessments' and pass these on to the contractor. They will also need the following:

• Details of any buried services or hazards that you may be aware of

• Confirmation of what welfare facilities will be available (i.e toilet) or whether they need to make alternative arrangements

• If you are carrying out major works involving large amounts of stripping out and demolition it is advisable to consider getting an asbestos survey carried out. Your builder should be able to advise on this.