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The Homeowners Guide To House Extensions

Building a house extension is one of the biggest projects you can do so to make sure your project is a complete success we have come up with a homeowners guide to building a great house extension.


Building a house extension is one of the biggest projects you can do so to make sure your project is a complete success we have come up with a homeowners guide to building a great house extension.


Our easy to follow guide has 31 steps and is packed with with lots of essential tips and guidance to ensure your build runs smoothly and creates desirable living space that all the family can enjoy.


1: Work Out What You Want To Achieve

This is the time where you have a good hard look at your home and make determinations as to what your needs are. For example if you are building a single storey extension you may like the idea of a:

  • downstairs wc

  • downstairs shower or bathroom

  • a utility / laundry room

  • a larder

All of these elements are very popular with our clients but in most cases there isn't enough space for all of them so you do in effect have to work out priorities and what is most important to you. Your designer will be able to help you work out what is possible for your particular property.


2: Find an Architectural Designer To Create Your Design Plans

Working with a professional designer will get you the best possible outcome for your project. In most cases there will be various options to consider and a skilled designer will be able to explain the pro's and cons of each option and help you to reach a conclusion on what is the best layout for your property. A creative designer will also be able to show you how to reduce costs, add the most value two your property and guide you through the woes of planning.


3: Create a Mood Board

Mood boards are an essential part of the design process. Before you start looking at styling and designing your own home, it’s important to define your own style. Do you know what you do and don’t like? You might be able to think of a few things that you do and don’t like, but can you picture them collectively and visualise the common thread that runs through them?


A moodboard definition is a visual tool that communicates our concepts and visual ideas. It is a well thought out and planned arrangement of images, materials, pieces of text, etc. that is intended to evoke or project a particular style or concept.


You will use the mood board as part of the design brief to your designer to visually express the vision you have in mind for the project.


4: Establish a Budget For Your Project

Now would be a good time to establish a budget for the project. Your designer will give you a rough costs but all the decisions arr yours with regard to the quality of the build and how much you are prepared to spend on fitting out. The kitchen will be a big ticket item as the average spend will be £13k / £20k but a good architectural designer can show you how to cut that cost by half and still give you quartz worktops and high-end appliances. If you need to reduce costs the designer will be the best person to show you how to get more value for your money.


5: Submit The Planning Application

The planning application is not just about completing a few forms and pressing the submit button. At Draw Plans we process about 50 planning applications each month and if we didn't monitor or liaise with the apointed planning officer most of those application would fail.


In most cases we have to negotiate, amend plans or deal with complaints from neighbours so unless you really know what you are doing I strongly recommend that you leave the planning application to your architectural designer.


6: Deal With Party Wall Issues

A party wall is a dividing wall between two adjoining buildings that is shared by the occupants of each residence or business. Typically, the builder lays the wall along a property line dividing two terraced houses, so that one half of the wall's thickness lies on each side. This type of wall is usually structural.


Under the party wall legislation if you want to carry out alterations to a party wall or wish to excavate for new foundations within 3 metres of an existing party wall then you will need a party wall agreement with your neighbour.



7: Building Regulations Plans For Building Control

Building plans for your extension will be required by the builders and building control. They detail how you are going to build and let the builder know the technical specification for elements such as foundations, walls, floors, roof, doors, windows, and drainage. They will also provide all the information to ensure that the build is done under the current building regulations.


8: Structural Design & Calculations

All house extension require structural design plans along with loading calculations for foundations, roof, door and window openings along with any structural alterations to the existing property.



9: Decide Your Build Route

When it comes to getting you extension built there are two main build routes. Option 1 is to give the whole job to one builder which means you only have to deal with one company. Option 2 is where you break down the job and hire different contractors and service providers for diffeent parts of the job and the scheduling will be down to you. Option 2 usually takes twice the amount of time than option one but you can save up 20/30% on the build cost.


10 Time To Get Quotes

This is where the project get exciting as you start to find out the reality of how difficult the

tendering process is. Get at least 3 quotes for everything and keep in mind that the quotes can vary by as much as 100%.


11: Choose your Builder or Service Provider

Now comes the hard part, you know what you're doing, you know how much it costs so you need to instruct your builder or service providers. The key point here is called due dilligence. In other words, once you have decide who to instruct make sure you do some research research online about the person and the business. Check social media accounts and also check out the adddress to see what comes back. Look for negative reviews on the business and make sure you read through existing reviews before you instruct.


When you are ready to instruct complete a service contract which will deal with issues such as start and finish dates, deposits, invoicing and payments, warranty. Having that all signed up at the start will help to ensure you get a better job because everybody knows where they stand right from the start.


12: Groundworks / Stripping Out + Excavations

The day you have been waiting for has finally arrived. Hopefully you got in plenty of tea bags and biscuits and cleared away any items out of harms way. Groundworks is where a lot of progress is made in a very short time. Most of the stripping out works get done, removal of the patio and any out buildings and the excavations for the foundations gets under way. Once the excavations are complete, building control will need to visit and approve before moving to the next stage.


13 Foundations

Once Building Control have approved the digging out you are ready to pour the concrete foundations. This work is done by mixing up the concrete on site and pouring or using a ready mix concrete service where the concrete is either pumped or wheel barrowed into the trench. The ready mix concrete option saves a lot of time and if the concrete is pumped you should have your foundations in as little as two hours.


14: Walls To Roof Level

Now that the foundations are in the bricklayers can get ahead with the walls. You will have already decided if you are going with a brick face for the walls or a block cavity wall which gets rendered. Block walls go up quicker and work out cheaper than bricks but if you do prefer a brick finish then only use brick for the extension walls that you are going to see when it is built.


15: Structural Alterations

The structural alterations are the most dangerous part of the work because the house has to be supported when opening up loadbearing walls to create and open plan look or to insert doors or windows. Steel beams and supports will be installed as per the structural design and all this work has to be approved by building control before it is covered up.


16: Drainage

This is another tough part of the job because it usually means lots of careful digging to find pipe runs to connect into. In some cases it means that manholes have to be moved and new rainwater gullys and inspection chambers installed. In most casea rainwater from a new extension now have to be directed to a new soakaway further down the garden rather than directed into the main sewer.


17: Roof To Completion

New extension roofs tend to be flat mainly because a pitched roof is unsuitable for larger extensions because the roof pitch angle would be to low. Another popular option is the pitched gable roof.


For straight forward flat roofs we generally recommend EPDM rubber because it is easy and quick to install and will last for 25/35 years. Because it is one large sheet of rubber it is virtually immune from leaks.


18: Fascia Boards & Soffits

Often overlooked. the fasciaboards and soffits make a huge contribution to the exterior design of the extension. A modern contemporary style extension with large Aluminium or uPVC Facia boards look best for a flat roof extension.


If the doors to the new extension are finished in anthracite grey we generally recommend the same colour for the facia boards and soffits.


19: Doors & Windows

Almost all the extensions we create plans for inlude a large opening to the patio with aluminium sliding or bifold doors. We generally advise our clients to source the exterior doors and windows themselves rather than including the work within the builders schedule.


Full height floor to ceiling doors generally look best but if you have tall celings consider adding a fanlight above the doors.


20: Plumbing & Heating

When it comes to the plumbing and heating now is the time to determine what upgrades you need. If you're adding and extra bathroom or shower consider the extra demands on the boiler. The same for heating as you boiler will now have a bit more work to do. In many cases when we create plans for an extension the boiler get updated or moved to accomodate new layouts.


If you are creating an extension with a modern openplan layout then consider creating a wet underfloor heating zone. It costs a bit more than a few extra radiators but if you like the look then go for it.


21: Electrical & Lighting

Electrical and lighting is another area that tends to be overlooked by homeowners. Its obvious a few more sockets and lights will be required for the extension but as designers we can't pass up the opportunity to let people know about home automation technology such as Ring and Nest. we also remind our client about installing an Electric Car Charging point, and specialist lighting which can have a huge impact on the interior design of the property.


22: The Kitchen

The kitchen is one of the most talked about elements within any extension project. Most homeowners blindly accept that they will pay £15/£20k for their new kitchen until we show them how to cut the cost by half and get a better overall kitchen at the end of the day.


Our advice is to focus on the worktops and appliances because that is all your visitors will ever see. However, if you have a big budget just forget you read the paragraph above and we will send you to Germany for the weekend to choose your new kitchen.



23: Plastering Drylining + Rendering

Plastering out the property after weeks of ripping it apart will have a huge impact because now you really will be able to visualise your new home. New walls are generaly done with dot and dab plaster board and we generaly recommend that you have all the ceilings and walls to the affected rooms skimmed out so that everything looks new.


On the outside, any blockwork will need to be rendered to finish off the walls.


24: Joinery & Carpentry

When it comes to finishing off the joinery the carpenters won't have to much to do at this point. Once the door linings, doors, locks, architrave and skirting is fitted he/she will be done.


25: Painting & Decorating

We always put in a provisional amount in the budget to cover the cost of painting and decorating but we also use this item as contingency for other additional expences on route and the reason for that is if the budget runs out then the painting and decorating can always be left to do at a later date when more funds become available. We also get clients that decide to do the painting themselves which means the painting budget can go to something else.


Dont forget that there will be a bit of painting to the new rendering on the outside of the extension and if there are existing painted areas they will need to get painted also.


26 Finished Flooring

Flooring is amother big ticket item depending on the size of your extension. In many cases the back half of the house will also require new flooring and possibly the entrance hall to give a sense of continuity.


The most popular choice of finished floor choosen by our clients over the last few years is engineered flooring. Draw Plans have trade accounts with the largest flooring companies in the UK and we get discounts of up to 65% on the most popular engineered floors.


27 Patio and Landscaping

When it comes to the patio we always look to create a new patio at the same height as the existing interior floor. That way when the doors are opened up the patio area will make the space look even bigger.


Its also a good idea to set a little budget aside to for returfing, repairing or replacing fences and to generally give the garden a decent makeover.


28 You Made it

You made it to the end so hopefully you are now motivated to get you extension underway as soon as possible. Its not rocket science but it can be a daunting and challenging experience to build an extension so the more prepared you are the easier it will be to manage your project.


It is my sincere wish that you find our guide helpful and that you use it to navigate your way to creating a stress-free extension that all the family can enjoy for many years.

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