How much will it cost?

The Royal Institute of Chartered Surveyors (RICS) gives a guide cost of from £1,275 m2 for a basic design to £2,500 m2 for a high end extension. So they estimate that the shell of a 20-square metre, single-storey extension might range from £25,500 to £50,000 – that’s for base, walls to plaster finish, tiled roof, one radiator, one ceiling light and 2 double sockets. You then need to put down flooring and add extra costs for, say, roof lights, bi-fold doors or installed kitchen. Remember also to allow a further 15-20% for professional fees (architect, planning application, building regs, structural engineer) + VAT.

How about a double storey extension with the same footprint?

As a rule of thumb you can add 50% extra to the build cost of a single storey extension. So, £25,500 + 50% = £38,250. Add on 15-20% for professional fees (architect, planning application, building regs and structural engineer) + VAT suggests a Double Storey Extension = £55,080.

A typical loft or garage conversion should cost from £1,500 per square metre, but this can easily rise to £700 a cubic metre depending on the design.

How long will it take?

The Project Schedule will be agreed with you in advance by your Builder but may look something like this:

Time Description
Week 1-2
Setting out, footings dug, and foundations poured.
Week 3-4
Building up to damp-proof course (DPC), drains installed, DPC installed and concrete floor structure put in.
Week 5
Building of external walls.
Week 6
Internal walls built.
Week 6-7
Roof structure built.
Week 7
Roof coverings.
Week 8
Install windows and doors.
Week 9
First fix electrics and plumbing; carpentry.
Week 10
Break through from existing house, steels put in place, joins made good.
Week 11
Plastering, followed by a period of drying out.
Week 12
Second fix, electrics, plumbing, flooring fitted, and kitchen units installed.
Week 13

Ensuring Project Success

Be realistic with Your Schedule as some projects can take longer than anticipated. Being aware of this from the very beginning can help to avoid stress.

Budget wisely

Get fixed price quotes where you can and try to have a contingency fund (around 10 percent). There is nothing like a half-finished project, ground to a halt by an empty bank account, to get you down.

Be decisive

We all change our minds and it can sometimes be the case that once a project is underway, part of the design no longer seems the good idea it initially did. However, sticking to the original plan as much as possible will avoid delays and overspending.

Choose a reputable builder

Don’t let your project turn into a series of arguments and let-downs. Choose tradesmen based on their previous work and trusted recommendations — not on the cheapest quote.

Consider bathrooms

If you are adding bedrooms, you may well need to add a bathroom, or at least a shower room. If you are having more than three bedrooms, you will need more than one bathroom — otherwise future buyers could be put off the house.

You also need to remember the following:

  • Your tradesmen will require access to water and electrics.
  • Make sure you have a Builder that believes in regular communication.
How do I know I can trust you to do a good job?

Begin by asking every person you have ever known; family, friends, colleagues, if they have had building work done in their houses and, if so, who they used and how did they get on. Was the relationship difficult? Was the timekeeping good? Was the quality of work good? Was the supervision of employees good? Did they show respect? Did they feel intimidated in any way? Was any guarantee given on the work?


It is so much better to use a builder who is known to you, even via a third party, than to grab someone out of a local paper or off the Internet. Then contact your local Trading Standards Office to ask if the builder has ever been investigated by them.


A trawl of the internet can bring up all kinds of information. Use it wisely to carry out your own ‘due diligence’ on your chosen Builder BEFORE you sign the contract.


A contract is a MUST! Make sure you are offered a contract that is clean, clear and concise and protects you, your home, family and money from potential mistreatment.


Be aware that –


Reputable builders do not knock on peoples doors touting for work. However, they DO make contact with you if they are working in your street and want to encourage you to speak directly with them if you have any queries at that time.


The best builders are always busy. If a builder says he can start tomorrow, the chances are he has no other work to do.


Professional builders have a professional set-up. They may work from home but they will not be frightened to give you their landline number and personal home address.


Well-established builders will prefer payment directly by bank transfer. Always insist on a written receipt or statement for each payment made and on the Builder’s headed paper.

Respectful, decent, truthfulness and honest communication should be your Builder’s hallmark. Make sure your builder speaks to you and treats you appropriately, explaining everything to you in advance, in clear terms that you fully understand.

How can I finance my building project?

You can either fund your home improvement project:


  • with cash
  • by increasing your mortgage to release funds, or
  • by taking out a home improvement loan.

Re-mortgaging will usually offer the cheapest rates, but shop around for the best deal. Switching mortgages at this time can present you with the opportunity save you money and help reduce the impact of the extended or bigger mortgage.


You will need to prove you can afford the bigger mortgage and will need sufficient spare equity in the property to raise capital. It’s important to factor in any switching costs as well but many deals will offer a free valuation and free legal work for remortgages, which helps to cut set up fees.


Speak to your lender about your options. But also speak to a mortgage broker who can scan the whole market and find the best deal for you. If you already have a really good rate that you don’t want to lose or are tied into a deal with early repayment charges, you could consider additional borrowing from your existing mortgage provider. The rates may not be quite as keen and there could still be fees but it could work out to be the cheapest overall package.


Lenders will ask the reason for raising capital but should allow equity to be released for the purpose of home improvements.

Mortgage rates vary depending on the percentage of the property your mortgage represents, known as Loan to Value or LTV. Lenders will limit the LTV to which they will allow capital to be raised for home improvements, typically to 85% or 90% of the property value. That will be based on the current property value and not a predicted value after completion of the work.

Bear in mind that the higher the LTV, the higher the interest rate will be. Of course, you can review the rate once any deal has come to an end. If the improvements have added value then there may also be an improvement in the LTV which should, in turn, improve the mortgage options.


Another option could be a secured loan¸ unsecured personal loan or even a credit card, depending on the sums required, from another provider. However, these will usually carry higher interest rates.

Do I need to leave my home?

This depends entirely on the nature of your building project and whether it encroaches upon your day-to-day living space. However, it is not always necessary to move out for house extensions, garage and loft conversion.

Your building contract should state that it is your responsibility to keep all children and animals safely away from the building works.


A good builder will ensure that the site is left clean and tidy every evening but you must remember that this is a place of work and there is likely to be mud, dust, dirt, machinery, holes in the ground, electrical wires and dangerous equipment on site. Life will feel quite a bit different until the job is finished, so you need to prepare yourself for at least a little disturbance.


Most homeowners can find a way to live alongside the building work, that is until the bathroom or kitchen is being replaced. Then is probably a good time to take a holiday or, perhaps, stay with friends or family for a few days until the toilet and water supply are reconnected.

Can planning permission be granted retrospectively?

Legally, your local Council is obliged to consider retrospective planning applications, even when it appears unlikely that planning permission would be granted. If this approach is unsuccessful, or if a retrospective application is refused, this involves serving an enforcement notice requiring the unauthorised work to be removed, or the activity to cease, within a specific timeframe.

It is an offence not to comply with an enforcement notice. If the offender is found guilty in a Magistrate’s Court, there is currently a maximum fine of £20,000. At a Crown Court, there is no limit to the fine that could be imposed.


It’s true that not all development or change of use requires planning permission, but, if you have already completed your building project without asking the question, how do you know where you stand with the local Authorities?


Let’s look at the kind of things that DO NOT require planning permission in this area.


  • Internal works to a non-listed building (but you might need Building Regulations approval).
  • Operating a business from home where the residential use remains the primary use and there is no adverse impact on residential amenity.
  • Insertion of some windows in houses – once a building has been occupied, windows may be inserted into existing walls, provided there is not a planning condition to prevent this.

A breach of planning control can include all sorts of issues, including:


  • building work or a change of use without planning permission
  • work that is not in accordance with approved plans and conditions
  • work to a Listed Building without consent
  • untidy land or buildings that affect local amenity

You may not feel that your particular build falls into any of the above-mentioned categories, and there is a chance that no one will ever question what you have done. That is, not until someone complains to the local Authority or you try to sell the property.


Still not sure if you need to worry? How about some good news!


For a period of six years, between 30 May 2013 and 30 May 2019, under something called Householder Permitted Development, householders will be able to build larger single-storey rear extensions under permitted development.


The size limits will double from 4 metres to 8 metres for detached houses, and from 3 metres to 6 metres for all other houses.

However, these new, larger extensions (i.e. if they extend between 4 and 8 metres, or between 3 and 6 metres) must still go through a process.


There is no fee in connection with this process but the homeowner must notify the local planning authority and a copy of this notice must also be sent to the developer.


Getting Something in Writing


Maybe you are looking for peace of mind or are ready to sell your property and want something in writing that confirms whether or not planning permission is required.


You will need to make a Certificate of Lawfulness application.


You will need to complete a form and pay a fee, which is worked out as half of the amount you would pay if you were applying for planning permission.


Clearly, this only covers part of the current rules and regulations and refers to the Stafford Borough Council area.  For more information, go to your own local council website and search for their Planning Portal.