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Building a Home Extension: Step by Step Guide

If you have settled on extending your house and want to know more of the ins and outs of building an extension, this post will talk you through that process. Hopefully this will clear up any issues or questions you may have with the procedure.

How to Draw Plans

Before we get stuck into the process of building an extension, we’re going to talk about drawing plans. Most people seek the help of an architect to draw up the plans for their house and this is something we’d definitely recommend. You can share all your ideas with them but they have years of experience and a keen eye for accuracy so will be able to produce the designs needed to ensure the project is built as it should be.

You need to provide three plans for a house extension: location plan, site plan and floor plans.

Location Plan:

This should be a detailed map of the location of the site. It should identify any adjoining roads or buildings. The area of your development must be edged red. Any other land you own must be edged blue. It has to be to scale and include a north point. You can obtain location plans easily from Ordnance Survey agents.

Site Plan:

This should be like zooming in on your location plan. You must identify the direction of north and include a recognised metric scale. This plan needs to show your proposals within the site. Where the location map just identifies your build site, the site plan outlines the details. You must also show any public rights of way that abut or cross the site, the position of all trees on site and on adjacent land, any planned walls or fencing, any planned hard surfacing, all adjoining buildings, footpaths, roads and access arrangements for your build site.

Floor Plan:

This is pretty self-explanatory, you need to identify what the finished product will look like inside. Show the uses of each room including any new ones, the elevations of the building with windows and doors shown and all external dimensions. These plans only need to be provided for the floor(s) being extended. You should highlight the extended area and also note the materials you are going to be using by colour and type. Your scale for this should be a minimum of 1:100.

Project Manager

There are lots of pitfalls which can delay your application so you should look to be as accurate as possible. Check, double check and check again, you only want to have to do this once. When you’re satisfied you’ve met all their requirements, it’s worth checking their website or any informational resources they have for anything you’ve missed, it’s time to play the waiting game. Here are some additional tips when it comes to planning:

Your drawings must be to scale. Don’t assume that your local authority will let you off. It’s not a matter of them being pedantic, it is an essential requirement and one of the things they stress the most. It’s also their job, so protesting at them asking you to add detail won’t help you in any way. If they’re asking you to add detail, it means that it is required for your application to go ahead, they won’t ask out of curiosity.

Be patient with your local authority. Many people don’t realise that planning departments of local authorities often have little funding and may have small teams of people working on scores of applications a day. Planning applications also come through the door almost constantly, so they by and large know what they’re talking about. They’re much more obliged and happy to help you if you show some patience and cooperation. Arguing over small details, fine print or at their work rate doesn’t speed anything up at all.

Take your plans to your neighbours before you submit them. Showing your neighbours your plans not only is a good show of courtesy but will give them a chance to raise any issues they may have before you submit. You want to iron out any problems that arise before you submit them. Your neighbours may have legitimate concerns about the work you intend to carry out, keeping them in the loop and listening to their concerns will help you.

Hopefully, your planning applications will have been accepted and then you can move onto building. Before you start building, you need to choose a builder.

How to Choose a Builder

It’s important you take care when choosing a builder for your project, as you want to find someone who is reliable, trustworthy, understands your designs and will work according to a reasonable timescale and your budget.

Here’s how and what you should look for from your builders:

  1. Ask around. Home improvements are done all the time, one of your friends or family should be able to recommend someone that did a good job for them.
  2. Look for credentials. There are trade associations, awards and accreditations that can help you inform your decision.
  3. Avoid low prices. This might sound counter-intuitive but if you ask around for some quotes, you have to wonder why the cheapest one is that cheap. Are they going to cut corners? Do they have the best resources?
  4. Get in touch with your local authority and ask to speak to a building inspector. They will come into contact with loads of different builders and they’re literally the ones that are checking they’ve done a good job. If there are any standout builders that are generally always up to scratch, they should be happy to share that information with you as it makes their job easier if you use them!
  5. Try and organise to meet before hiring if possible. It’s good to have some personal contact so you can both sound each other out. For every cowboy builder, there’s a cowboy client. You want to know who you’re employing, and builders want to have faith that you’ll pay and that they’ll do a good job for you. If it’s a good fit, you should be able to tell.

Here are some common-sense tips about working with builders to ensure smooth sailing:

  1. Draw up a contract. Agree on a price and on the extent of work. Allow for unrealised extras. It’s easy to think that your builder is trying to swindle you with extra costs but most of the time, these are unavoidable. A good builder will be happy to explain what extra costs might be incurred and should be able to tell you how much each of them are. Don’t go by an estimate as this leaves itself open to ambiguity. Agree on a fixed price with agreed prices already laid out for extra costs should they happen. Check if VAT has been included, that they have insurance, that who’s clearing the waste materials has been agreed and a good, realistic idea of time frame has been laid out. If you have a contract, it will help settle any disputes.
  2. Honour your contract. Make your payments on time, understand the extent of the work they are doing. If you have agreed a payment schedule, stick to it. People are very quick to withhold payment because they’re not satisfied with what they’re looking at. If you have good communication with your builder, they’ll be able to tell you exactly what they’re at and how they’re meeting their end of the bargain.
  3. Don’t pay upfront. Be wary of any builder that’s asking for the entire cost upfront. You should agree a payment plan that you both feel happy with.
  4. Be wary that constant checking in on your builders and overseeing can be counterproductive. This wastes time that could be spent building and can cause friction. If you’re happy you’ve chosen a good builder, you should be happy to leave them to do their job. Obviously, you should check in now and again but know when to stop.
house builders

House Extension Building Process

House extensions normally take around 12 weeks. We’re going to look at the process at 4-week intervals and what you can expect to occur in each month.

Weeks 1-4

The first week will be dedicated to getting the building site prepared. All the building materials will need to be acquired and transported to the site. Any hoarding will be put up, with site accessways laid out. If you have children, ensure the site is safe.

The second week should see the beginning of groundworks. Foundations will be dug out, with drainage and pipework also carried out if needed within. This is where you can potentially encounter extra costs. Your foundations may need extra fortification depending on the soil type. The foundations will then be levelled with concrete. Building Control will have to come and approve the foundations and footing.

The next couple weeks should see the construction of your superstructure. Any preparation for pipework and drainage will be carried out. This might involve digging trenches or fitting drains. Brick-laying will start but only up to the damp-proof level. Building Control will need to visit again.

Weeks 5-8

Your external walls will start to go up at this point. Any apertures for window or door frames will be considered as the walls are built. You should see any cavity walls being insulated and your new walls will be fitted to your existing ones with wall ties.

The internal walls will then be able to take shape around roughly the sixth week. Ensure that any tiles, doors, windows that you plan on installing have been sent off for. They won’t be installed at this point, but they often have a few weeks’ wait time.

The seventh week is normally when work on the roof structure begins and goes into the eighth. If you have included roof-lights or dormer windows in your plans then these will be fitted at this point. The structure will be built itself and then put into place the following week along with roof tiles etc. Internally, your builders will be laying down the floor screed.

Weeks 9-12

Your construction will be about to enter its third month. The ninth and tenth week will be spent installing the windows and doors. This is really where it all comes together externally. You’ll have a roof, windows, doors, gutters, drainpipes, plumbing, electric and any external rendering will be carried out.

Next up, breaking through to your new extension. This is where you’ll want to completely clear the room that’s being broken through and maybe get out of the house while the drills are out. The existing walls will be knocked down to join the extension to the rest of the house.

The walls will get plastered in the eleventh week with further insulation carried out. The plastering must be left for a week before it is decorated.

In the final week, what’s known as the ‘second-fix’ will be carried out. This is basically just putting on the finishing touches. Lights and light switches will be installed, plug sockets will be made live. The flooring will be laid down, any kitchen units will be installed and any plumbing work left to be done will be carried out.

You’re not entirely out of the woods yet but should everything go to plan your extension has been built. There will be something called ‘snagging’ done. This is where you can report any immediate issues with the build and they’ll be corrected. This can include sticking windows, leaks etc. Hopefully, there won’t be anything to report and anything that does go wrong should get fixed within a week.

That is a skeleton layout. The time it will take and exact order of work will differ on what you’re getting done. To the untrained eye, things may look like they’re going slowly and naturally you’ll want to be reassured that everything is going okay.

People often wonder how often they should ask for updates. Builders appreciate it when they’re left to do their job without disruption however it’s a big investment on your part and you want to make sure it’s being done well, that’s totally fine. We recommend arranging a weekly catch-up session. Sit down, have a brew and talk about the work. Voice any concerns but don’t jump to any conclusions. Some companies also have project managers who oversee the building work and ensure the project is going ahead as should. These will be your go to contact should you have any questions throughout the process, and this leaves the builders time to continue working on your home.

How much Disruption will the Building Process Cause?

Living in your home during an extension is definitely doable. It depends on the extent of the work being carried out. In some cases, a lot of the house will be affected by the building works and will result in all the stuff in that area having to be put somewhere.

If you’re getting a lot of work done, some people have found that they basically have to live out of their bedrooms. There’s other things to consider too, there’s a lot of dust so bear that in mind if it will aggravate any medical conditions you or any family members may have.

Putting things in storage is recommended if you can do so. There are also certain periods during the build where your house will be much more habitable and some where it will be quite tough. Some people stay somewhere else during the roofing stage.

It’s a matter of personal preference and there’s different levels of disruption depending on the work you’re carrying out. Talk to your builders in detail about when you can expect the most disruption during the build. If the plumbing and heating are turned off, when and for how long? You can make your build as painless as possible with good communication.

This should have cleared up any questions you had about the process of building an extension and offered some sound advice. Our main points to take away: be patient and cooperative with your local authority and builders. Your local authority stands between you and your extension, so you want them ‘on side’, same with your builders. Be picky when selecting your builders, it’s a big investment so make sure that you get on well with them and that they’re up to scratch.

If you’re about to undertake an extension, we hope this guide has been helpful. Check out our other posts about extensions or conversions and don’t hesitate to get in touch if you have any questions.