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  • Writer's pictureDraw Plans


Updated: Nov 22, 2022

Building an extension is one of the biggest home improvement projects you are likely to complete in your lifetime. It is expensive, it takes months to complete and its disruptive simply because the whole house gets turned upside down during the second phase of the build.

Why do I know this? I’ve built hundreds of extensions for clients all over London and the south east. When I say built, I don’t mean I dug the foundations or laid the bricks, I built as a project manager responsible for delivering a completed project on time on budget. Well, that’s the theory anyway but even for a veteran like me I still had loads of overruns and I’ve sacked more builders and tradesmen than I can count.

When it comes to building an extension there is a process, that if followed, dramatically increases the odds of a successful build. The problem is that few homeowners are aware of the process and the reason I say this is because we get about one hundred calls a week at Draw Plans from homeowners asking advice on how to build an extension. In fact, because we get so many calls about extensions we decided to do a really decent article that laid bare the steps you need to take to build you own extension without your hair falling out or without getting robbed blind.

The one bit of advice I will give you now is to take the time to read this article because it will save you more than money if you follow the 6 key steps for how to build an extension.


You have no idea how many people looking to build an extension start off by calling the builders. Its not just a rookie mistake, it is easily the worst mistake you can make if you are unlucky enough to find one that is happy enough to get cracking without any plans. Even worse if he says he can sort out the plans for you.

Lets just wind things back for a minute. A house is the most expensive thing we are likely to buy in our lifetime; an extension is probably the biggest home improvement project we are ever likely to carry out and you are happy to let a builder who possibly doesn’t know his arse from his elbow do your plans?

Okay, so you get my point, use the builder for building an extension and find a designer to create your extension plans so that you can start your project with a reasonable chance of a successful build.

If you’re unsure of how to find a designer or architectural technician with talent that won’t break the bank then I suggest you talk to one of our team at Draw Plans who will give you expert advice and a free quote.

You should also be aware that the demand for architectural technicians has grown considerably over the past decade. The reason for this is mainly because homeowners have come to understand that if they hire a technician to create the drawings, they will save a bit of money as the technician will cost considerably less than an architect.

You should also know that nearly all architectural practises use technicians to do the donkey work. What I mean by that is that if you hire any design expert to create the plans for your extension the job will probably end up in the hands of a technician. Of course there will be input from the architect but unless you are looking for something out of this world as an extension for your home then why not cut out the middle man and go straight for the architectural technician to create the plans, after all he has probably done more of them than the architect and certainly knows how to create them.


Every day we advise homeowners on how to build an extension and explain that when you extend your home you have to reconsider the layout of the entire house. For example, if you add a single storey extension to the rear of your property you usually end up with several options. For example, would you like a:

  • · Utility Room?

  • · Downstairs W/c?

  • · Laundry Room (not the same as a utility room)

  • · A Larder? (Very fashionable)

Personally, I would want all of them because they will give back endless pleasure for the duration of your stay at the property. However, I realise that because of space and budget we have to be realistic. My point of course is that a professional designer such as an technician will generally be able to provide you with a few more options that you may not have considered. Budget plays a big part as does the type of property, the amount of space and most important where your priorities are.

Most homeowners building an extension these days tend to have the kitchen in the centre of the house and more living space towards the rear next to the garden. It makes perfect sense, looks fantastic and adds the most value.

On the subject of value, it is also a consideration because if you add a box to the back of your house rather than skilfully extending your property then you may end missing out on a huge opportunity to add significant value to your property as well as getting the space you want.

In fact, if you do it right and have a good designer (Draw Plans) then it’s a win win situation because whatever amount of money you spend on your extension you will get it back and probably double through the added value to your home.

So now you should be able to see why step 2 is extremely important because if you create design plans that really work for your home and create really good living space then you are adding real value whereas if you don’t then you may end up building an extension that adds little in the way of value to your home/


Have you ever tried submitting a planning application for building an extension? If you have then I am confident you did not achieve success at the first attempt. Before you can start the application you have to find the forms and most of use start off by looking for application forms relating to extensions and conversions when we should be looking for a householder application which is what is used to submit a planning aplication for a house extension or a loft conversion.

It’s about this point where you begin to get an inkling that perhaps you should have asked your technician to do the submission. This is confirmed when you are asked to submit an ordinance survey map showing a site plan or block plan which you don’t seem to have.

What finishes most homeowners off is the dreaded “Design and Access Statement” or the “Flood Plan” or the “Biodiversity Report”. These are just a few examples of the types of additional documents that can be required as part of a planning application.

What about the fee? This is another high fence because most homeowners don’t know the correct fee to pay. What if you are exempt and don’t have to pay a planning application fee? Will you know? Of course, you won’t know and why should you.

Maybe you’re a really determined individual and after a whole evening and a bit of swearing you get rewarded with sight of the “Submit Your Application” button. Well, good for you if you make it this far on the first attempt but you still have a long way to go even after you press the submit button.

Once you do manage to put together all the necessary and submit your application you will feel great for getting over all the hurdles. That’s is until about a week later when you get an email to tell you that your application failed the validation checks and that you need to provide another list of bits and pieces to get the application validated.

Getting through validation can take weeks or months depending on how eager you are to satisfy the planning department with more paperwork but with a lot of patience and resolve you will get there at some point.

So, what happens after the application is validated? Do you find out who the planning officer is? Do you make contact and introduce yourself? Of course, you don’t. You’re so exhausted after the application and getting it through validation you no longer wish to rock the boat and take the path of least resistance.

Many planning applications don’t get monitored simply because the client doesn’t know how, and the designer’s job is done so he puts his or her time to better use. What this means is that if there are any hiccups you won’t really find out about it until your application fails.

At Draw Plans we monitor all the planning applications we submit and establish direct contact with the case officer dealing with each application. This is a highly successful strategy because by establishing contact we can resolve issues or tweak the plans a bit to ensure the application gets recommended by the planning officer and in almost all cases this will lead to approval.

So hopefully by now you understand why having your designer submit you planning application for building and extension makes super sense and will improve the likelihood of getting approval for your project.


The need for another set of plans to do the actual work comes as a big surprise to many homeowners who think they have all the plans they require to complete their project. In simple terms they don’t know the difference between Design Plans which create the new layouts and the Building Regulations Drawings which are used for the building process.

In many cases the client doesn’t bother to read the small print and in other cases the designer is less than transparent with costs and the other services that a client may need to complete the project. This is a useful oversight when it comes to winning projects as everything looks great at the outset, but it usually leads to resentment and arguments further down the line.

Our advice is that even if you are a starving designer, be transparent with fees and costs from the beginning. You may lose a few potential clients, but it is better to lose a few clients early than to have to operate sharp practice and end up with unhappy ones further down the line.

At Draw Plans we are always transparent with fees and advise potential clients about the likely costs relating to Building Regs Plans, Structural Calculations and Party Wall Agreements which are almost standard for most extension and conversion projects.

Okay, so getting back to building regs plans. What are they and why do we need them?

Building regs plans, also called building regulations plans and building plans are needed to show how we intend to build. They will tell us the size of the foundations, what the walls and roof are made of and if the work gets a little tricky then the designer will provide detailed sections to show us in detail how to do the work.

Of course, if you are a builder and you have built a few extensions then you have a reasonable idea of how to build already which is great if you are building a standard extension. But what if you’re not building a standard extension? What if you are building a glass extension with structural glass supports? What if you’re installing a 3mt x 4mt roof lanterns or full height floor to ceiling doors or glazed panels?

My point of course is that how we build is changing and extensions and conversions are no different. This is where the building plans are an essential tool for the builder because they specify exactly what the client wants. How else will he know which type of windows, what the exact size of the windows are or where they are to be positioned. A builder may know how to build but without building regs plans he can’t build anything.

One other point which is worth a mention is that all building work needs to meet the current building regulations and when the designer or technician specifies the work required they have to ensure it meets with the actual building regulations.

When it comes to structural work the plans will also have to show all the details including steel sizes, padstone measurements and of course nothing can get done without structural calculations.

What about electrical work? Positioning of lights, sockets, switches? All of these details have to be incorporated into the drawings.

Same for heating and ventilation which will show the position of radiators, underfloor heating, thermostats and boiler location.

If you’re installing a security system, the installer will need to know the position for all the elements and without an electrical plan there can be no installation.

Bathroom layouts and kitchen layouts are also essential and can be incorporated into the building plans.

Plumbing and drainage also feature in the plans. How else do we tell the builder where the new drains go, the position of the rainwater gullies or where the water from the kitchen sink discharges.

So, by now you should begin to understand why building regs plans are different from design plans and why you have to pay for them as a separate charge. You should also start to understand the importance of the building plans when building an extension and why they are an essential requirement for any build project.


Party wall agreements are now common for almost all house extensions, loft conversions or any work that involves excavations within 3 metres of a neighbouring property.

You will need a party wall agreement if the work you are going to undertake includes any or all of the following:

  • · Building a new wall

  • · Cutting into an existing party wall

  • · Making a party wall taller, shorter or deeper

  • · Removing chimneys from a party wall

  • · Knocking down and rebuilding a party wall

You should also note that your neighbours can’t stop you from making changes to your property that are within the law.

Once you serve notice to the neighbours for a party wall agreement, they must reply within 14 days giving approval in writing or refusing to give consent.

If they don’t give consent or don’t reply, then they are in breach of the party wall agreement legislation and the dispute resolution starts.

One other point is that just because the neighbour doesn’t respond doesn’t mean they agree to the works.

Don’t be fooled into thinking that because all the work is been done on your side of the fence that you don’t need the agreement because you do.

Also you should know that when you are building an extension on the perimeter you can in fact ask for a Line of Junction Notice which means that you can build the new boundary with half on the neighbours side if they agree. It’s especially a great idea if space is tight.

In the event you don’t get consent then you can still build your wall but this time all of it on your land. But remember, there is no harm is asking.

So, by now you are starting to understand that the party wall agreements are an important part of any build project and that you should start the process as early possible to avoid hold ups.

Draw Plans will be happy to get party wall agreements underway for any build project so feel free to get in touch if you need a quote, need further information or to get a copy of the party wall act booklet which will guide you through the process.


Finding a decent builder may not be as challenging as it has been in the past. These days most professionals are driven by feedback and building companies that value their reputation are likely to do a really good job.

So where do we find builders with decent feedback? Well let’s start with Google and put in a local search query such as “builders in clapham” and up comes the Google map along with local listings that contain reviews. Make sure to look at the listings carefully and only choose builders with decent reviews.

If that’s not working out then consider using a trades side such a Checkatrade, MyBuilder or Trust a Trader. The benefit of registering on one of those sites and posting a job is that you will get 3 or 4 builders responding to your job which really speeds up the process. Once someone is interested in your job make sure to review their profile, feedback reviews, website and before you select or give them a call just paste the company name into Google to see what come back.

Any company found on a site like Checkatrade will most certainly be interested in maintaining their reputation and good feedback, so the odds are in your favour of getting a decent company. You should also know that Checkatrade does a 10-point check on every company listed to ensure that they are genuine tradesmen, are identity checked well as being credit checked.

The name of the game is to find smaller companies to get the job done. If the company is too big you will generally pay more for less, so the trick is to find a good company that isn’t too big yet.

When it comes to getting the extension built there are two main routes. One is where you get a builder to do the whole job which means you only have to work with one person or company for the whole project. The main advantage is that you don’t have to find the various trades to complete the job as the builder will already have the electrician, plumbers and roofers and the builder will be the one to schedule in them as and when they are needed. This is usually the preferred option for most homeowners as it involves less work and the job is completed as quickly as possible.

The downside, it costs more.

The second build route is where you get someone to do the groundworks for you and by that I mean the groundworks company will clear the site, excavate for the foundations, clear all the debris and leave the job ready for concreting.

Next you will need to someone to organise the concrete for the foundations. This is an important job; it is usually done in a day and if you know what you are doing it will save you quite a bit of money.

So, with this build route you get quotes in from all the different trades and project manage yourself. That way you cut out the middleman and knock 20/30% of the cost of your build.

The downside, the job usually takes quite a bit longer.

On balance, if you have the funding and want to get your extension built as quick as possible then getting a builder to do the entire project is the best option. However, if you are short of budget and are not too concerned about how quickly the extension is built then option two could work out well for you.

In a nutshell, look for a builder or trades people who are concerned about their reputation and have decent reviews as these are likely to give you the best customer service overall.


So, there you have it, a six-step plan for building an extension. All the tips and recommendations offered in this article come from a lifetime working in the London property sector and project managing 100's of house extensions.

If you are currently considering building an extension then you are further advised to start your project by talking to a human at Draw Plans. 020 3921 0745

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