House Extension Costs | Fixed-Price Guarantee

How much does a home extension cost?

The only way to truly calculate the cost of a home extension is to combine the costs of design, building materials, demolition, construction and labour. There are a number of other factors that can influence the cost also, like the age and condition of the house, the foundations or even the soil.

This is why we recommend to anyone that the best way to find out the costs for you to extend your home is to talk to us. We are sometimes even be able to give you a guide price over the phone.

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One advantage of using Duncan Thompson Extensions to design and build your extension is that you will know how much your extension will cost, right from the beginning of the process, with no nasty surprises or extras.

Impact that various factors can have on the overall cost of an extension

High

The age of house, matching existing features, etc.
Condition of foundations and soil type
Renovation content required: e.g. repositioning of existing plumbing, etc.
Engineering content: e.g. unsupported corners on an upper storey

Medium

The size of your extension (sqm)
Your choice of materials
Fittings and finishings
Design revisions after construction has begun
Access to your block

Low

Council regulations and permits
The style of your house
The amount of windows and exterior doors
Whether you continue to live in the house during building

Free consultation

Duncan Thompson Extensions offers a free, no obligation consultation. When we meet with you we will develop a brief that will include your budget and what you expect to get for the money you spend. Because Duncan Thompson Extensions is a full-service, concept-to-completion home extension specialist, we are confident the guide price we give you will be close to the real cost to design and build your new extension.

Fixed-price guarantee

Once we have the necessary information from you and the building contact has been signed, all known costs are included in the price. If you change your mind once the build commences, we reserve the right to revisit the overall price quoted, however if this occurs you will be involved and informed of any additional costs before they happen.

Lizzy Geremia

09:20 28 Mar 18

We commissioned Duncan Thompson Extensions to renovate our 1930s single storey weatherboard. We are delighted with the result. From the design to delivery the team has an eye for quality and want to deliver the best product possible. Our house is better than we expected and we know we’ll be happy here for many years to come. Jim has a great understanding of how to interpret needs into design and Sam was patient and honest when project managing the work. We moved back in ahead of time and on budget. Happy customers

Vivienne lee

11:10 29 Aug 18

Really professional and honest site consultation and great customer service. Thank you so much for your advice Jim!

Stavros Family

07:19 14 Oct 17

After careful consideration we engaged Duncan Thompson Extensions for a second story addition - a project that they managed from start to finish with confidence. As we wanted to live in the house during the work, we found that they were not only accommodating of this, but also experienced enough to be able to cope with the added strain it brings to all.While a major renovation is daunting (for us at least), their engagement meant rare concerns and rapid progression. Jim (designer), Sam (supervisor), Dave and his team (builders), Andy (everything) and the rest of the team at Duncan Thompson Extensions were a pleasure to deal with - and handled our many queries with patience and reliability. It felt like a genuine partnership through the project and beyond - with the company standing behind its work after completion; which is something that is very important to us and an indication of their commitment to satisfaction.

Helen Nicholls

23:12 26 Sep 17

We have engaged Duncan Thompson Extensions on more than one occasion and each time have been more than happy with the result. The crew at Duncan Thompson Extensions are a professional team working efficiently with the least disruption to our household as possible and have always completed our jobs well within estimated times. They were always obliging, easy to deal with and cleaned up after themselves (a big plus). We have since recommended them to others and would do so again.

Lisa Gu

00:52 26 Jul 17

It's a great pleasure to have Duncan Thompson Extensions renovated our house. All the team members are very nice, helpful and cooperative!The Designer Tim has helped me to make full use of the space wisely. Now I have a fantastic open kitchen and a secondary kitchen for traditional Chinese cooking , a spacious living area and a big theatre for family entertainment. The renovation of our bathroom is also a smart idea from Tim. He transformed a previously not quite often used closet next to the bathroom to a shower. I just told Tim what I wanted and he magically made it all happen!Sam, our site manager, is also super helpful. Not only during the renovation, even after the renovation, he responded to my requests promptly and always helped me out in a very short time. We own you a lot of thanks, Sam!All the other members of the renovation team, they cooperated not only with themselves, but also with the kitchen guys from other company smoothly and made all this happen on schedule.It's a smart decision to choose Duncan Thompson Extensions!

Pascale Mercader

00:57 27 Jun 17

We would like to express our thanks and gratitude to the whole team at Duncan Thompson Extensions for the wonderful work done to transform our home. Tim designed our perfect home; he listened to our dream, our ideas and our vision and came up with a design that not only complimented the existing home (something that we were adamant about) but that brought it gently into the 21 century. The new kitchen, dining and living room layout functions brilliantly for our family; it is open, airy, spacious and flooded with natural light. The new ensuite, walk-in robe, laundry and alfresco area exceeded all of our expectations. Our ‘new’ home will bring us much joy for many years to come. Matt and his apprentice managed to get the place built in rapid time and nothing was ever too much for these guys; every request, concern, or small mix up was rectified to ensure we were happy with the result. Matt was an absolute champion; always happy to explain what he was doing and keeping us in the loop as the building progressed. He also was extremely accommodating of our 2 yr. old who was determined to get in on the action whenever there were power tools, nails, hammers or the like being used. Our project manager coordinated the whole project seamlessly, fielded our endless calls, texts, questions and concerns to make the entire process as stress-free as possible. When friends and family ask us about our renovation and whether we had issues we honestly only have good things to report. The whole experience for us was extremely positive and we put this down to the professionalism of the Duncan Thompson Extensions team. We would not hesitate to recommend their services to anyone looking to renovate their home.

Terence McAleenan

09:58 15 Oct 18

We initially engaged Duncan Thompson Extensions due to their reputation and experience. Bryn was personable, a good listener and made sure he understood our needs. He and owner Chris were flexible in negotiations, ensuring a win win outcome. Site manager Sam, foreman Robbie and team, were highly professional, excellent communicators and made sure the work was completed on schedule and to budget. We now have an attractive and spacious family home which we have no intention of leaving! My wife and I would not hesitate to recommend Duncan Thompson Extensions.

David Button

02:45 12 Feb 19

We engaged Duncan Thompson to manage and build a second storey on our existing home. We initially interviewed three companies and although Duncan Thompson didn't provide a 'free design', we thought it was worth the money due to Jim's architectural experience. We weren't disappointed as Jim came to us with a very different design to the others, even incorporating an existing fireplace and chimney - which the other two companies told us to convert to gas - Jim thought outside the box. The three quotes we received were very close to each other. We decided to engage Duncan Thompson due to their local experience and after knocking on a few doors of previous clients (who were all very happy). The build was seamless, even though we decided to live in the house during the build. James (supervisor) and his team were impeccable and nothing was too much trouble. Rob (builder) and his crew were very clean and courteous at all times. We would not hesitate to use Duncan Thompson again and have recommended them to our friends.

Michael Carter

09:03 17 Feb 19

We are very pleased with the attentive service we received from the team at Duncan Thompson. It all began with the initial consultation & design process which showed us an innovative plan to relocate our kitchen (including a pantry which is a first for us) to the west side of the house while keeping the integrity of the 1940’s character of the dining room & retaining a serviceable laundry. The carpenters & building supervisors were a punctual, efficient & considerate bunch - sensitive to our needs to keep living in the house during construction. The completed result looked very close to the concept sketches created at the start & we are very happy with our new space, expanded family room & wonderful kitchen & pantry.I would highly recommend Bryn, James & the tradies on the team for any extension work.Michael & Wendy

Derek Nicholas

05:00 12 Apr 19

It was a pleasure dealing with Duncan Thompson. From the first appointment with Jim our designer it was a case of doing everything they promised when they said it would be done, unlike the other builders we spoke to while trying to organize our renovation and extension. This continued once the actual construction commenced and the entire project was completed ON TIME AND ON BUDGET. Our initial discussions with Jim our designer, were very helpful and he was able to formalise our wants and ideas into a concrete proposal. At all times he was open to discussion and willing to explain why an idea was or wasn’t possible, or the consequences of an idea eg. an increased cost for little gain. The various trades people who worked on our job were a credit to themselves and the company. They were polite and helpful and as we were living on site throughout the renovations they tidied up at the end of each day to leave the site as clean as possible. Our young carpenters worked diligently together and as a team. Our project included an extension with extra deep foundations, all dug by hand, as well as internal renovations to a bathroom and various other rooms. The whole project ran smoothly and continuously from start to finish. We would have no hesitation recommending Duncan Thompson to our friends or anybody else needing renovations or an extension.Derek and Pauline Nicholas

Adem Majtara

01:51 29 Oct 19

Fuss free phone ordering and delivery

Philip Peitsch

09:54 14 Feb 20

Duncan Thompson executed a great an extension on our 1960's brick veneer house in 2019.The team at Duncan Thompson made the experience straightforward and as painless as a major renovation can be.Of special mention was the site manager, who's frequent visits kept us well informed of progress and hiccups. He was always responsive to queries, and gave us plenty of useful advice and tips along the way. After dealing with previous renovation companies, it was refreshing to have a single point of contact with in-depth knowledge of the job and enough authority to solve issues and address mistakes.The other special mention goes to the very dedicated builders we had. We lived in the house during the renovation, and were continually impressed by their friendliness, professionalism and site cleanliness. Seriously... I did not know a construction site could look so neat. Thanks guys!As example of this attention to detail and customer focus, we had a new baby arrive during the renovations in the middle of winter. The DT team went so far as to put up insulation on the temporary wall erected between the existing house and extension to ensure enough heat could be kept in.I would happily recommend Duncan Thompson for future renovations.

Craig Sayers

06:21 04 May 20

We engaged Duncan Thompson to renovate and extend our 1930’s California Bungalow chiefly adding a second storey. From the outset they were excellent to deal with. Jim, the architect, come up with a great design for our family, listening to what we needed, and blending the design in with our existing home. James, the site manager, and all the tradesmen were very professional and delivered a high quality build. I would highly recommend them to friends and family. Their after completion follow up and maintenance shows why they have such a successful business. At the end of the day, their business is built on their customers happiness.

Marilyn Small

03:06 26 Mar 20

When we told friends we were going to extend, they said 'be prepared for all sorts of hidden costs, the time will blow out etc etc'. Not only did that not happen, the team at Duncan Thompson kept us in the loop from beginning to end, not surprising us at any time throughout the build.From the time I rang the company to enquire about extending and spoke to Bryn Richards, the Design Consultant, (who was great), to meeting the boss Chris, and our wonderful site supervisor Sam, to the very final day of the build, Duncan Thompson did the most professional, job leaving us with a gorgeous second storey. The quality of the work is outstanding, thanks to Robbie, Travis, Woody and the all the other tradies. We couldn't be happier with their work. I would recommend them in an instant to anyone who is contemplating extending their home.

Camilla Fiorini

08:21 04 Jun 20

I originally reached out to Duncan Thompson through a recommendation after my original builder pulled out three weeks prior to commencing our renovation (in the end, what a blessing!!). Chris, the owner, made the time to meet me with his team and from the get-go they were professional, helpful and did quality work. My Project Supervisor, Sam, was a delight; forever flexible, helpful and patient. The tradespeople - special shout-out to Nick - were polite and respectful and would always try and deliver any random requests.As a bonus, they are one of few building companies that will extend up without you having to move out. They even made living in the middle of a renovation easier than I thought it would be.The final result exceeded my expectations. Absolutely love my 'new' place. I would highly recommend Duncan Thompson without reservation.

L Walsh

07:49 03 Jul 21

We engaged Duncan Thompson to undertake a considerable renovation to our property and we couldn't be more delighted with the outcome. As first time renovators it was important to find a reputable company who would take us through the process step by step. We first met with Jim (the DT Architect) - who drew up the concept plans and we instantly knew we had made the right decision to engage DT. Jim took care of everything including liaising with council and neighbours and ensured that the permit applications were progressing and on track. The quality of the build, team, project manager and associated trades were nothing short of spectacular. Melbourne went into lockdown after we started building and we were one of the lucky ones to continue building as our property was vacant. Our project manager James took care of everything and his dedication to our build was faultless. James kept us in the loop about everything, we received regular updates as to where things were at and if there were any 'problems' during the build, James had them sorted before we knew about them. The communication, quality of the build was exceptional and the team could not be more accommodating. The build not only came in on time but finished early . We would never hesitate to recommend Duncan Thompson - we have been in our new home for some time now and have had no issues post build .

Alex

05:51 23 Sep 23

Duncan Thompson completed our two story extension eight months ago and we are still so thrilled with the end result. The entire team were professional, friendly and accommodating at every stage of the program. Bryn’s design is gorgeous and has transformed our small, cramped bungalow into a home we never want to leave. The GM Chris took the time to check in and ensure we were happy with the works/service of the team. Our project manager, Nick, went out of his way to ensure our young family was able to live comfortably on site throughout the entire build and everything went so smoothly – even in the middle of winter. Looking back on the entire process, we were so lucky to have Nick in our corner. He managed the team through every hurdle, making the build more stress free than I ever thought possible. Everything Curtis and his team built was of such a high quality, and with an incredible attention to detail. We get so many compliments on our home, but the end result is so much more than we imagined was possible. We highly recommend the team at Duncan Thompson whenever we speak to someone considering a build.

John Tsiros

09:36 22 Jul 23

From the early dealings with Bryn, we felt very comfortable to choose Duncan Thompson for our extension. And we were so happy to have our build finished on time and on budget! Nick managed the process extremely well and Sam was always available whenever needed. Being our first extension project, we were very impressed with how the Duncan Thompson team handled everything. From the great ideas and patience given to us during the design phase, the friendliness and workmanship of all the tradespeople, right through to the excellent quality of the finished product, we highly recommend Duncan Thompson.

Natalie Cheng

03:27 22 Jul 23

When we first thought about renovating our old Californian Bungalow home, we spoke with 4-5 builders, but we are so glad we went with Duncan Thompson!  We had a wonderful experience.They were very organised from the beginning to the end of the project and delivered exactly what we wanted. Their professionalism gave us peace of mind throughout the process, and their work quality was excellent, from their wonderful Architect Jim, the engineers to the project manager Nick and suppliers they worked with.Communication with them was smooth, and they were attentive to our needs. They even came back to address any issues that arose a year later, showing their dedication to customer satisfaction. We appreciated their pride in their work and reputation, which made the whole renovation process stress-free, even during the Covid lockdown.Overall, we highly recommend Duncan Thompson for their reliable service and attention to detail. They transformed our home beautifully, and we so happy with the outcome.

Niall Keating

00:18 05 Jan 24

Simply put DT are a brilliant company to build with - from Jim's Mastery of design to the on-time, on-budget 'easy' delivery.Highly recommended

Michal Krodkiewski

04:35 21 Sep 23

We recently completed an extension to our 1920's Californian Bungalow with DTE by adding a second storey whilst living through it on the ground floor. Jim (DTE Designer) helped unlock a lot of value in maximising the upper level around structural and roofline constraints, as well as reconfiguring a problematic ground floor area to resolve functional and aesthetic issues. We tested several planning iterations in both design and cost to get the best cost-to-benefit outcome.The DTE team lifted the roof off the existing house during the wettest and windiest Spring on record in 2022, but a well planned and executed waterproofing strategy meant no water ingress or damage to the house - they also did not miss a single working day between lifting the roof and making the extension permanently weathertight.When the works moved inside DTE did everything practicable to minimise disruption and enable our family including 2 kids and a puppy to co-exisit happily! We are delighted with the outcome and the new spaces / zoning / segregation in the house has totally transformed how we use it. Contract administration was transparent and low-fuss. The extension looks great from the street and even better upon entry. On time and budget. Overall a great experience! MK

Camilla K

03:29 04 Oct 24

We are absolutely thrilled with our home extension by Duncan Thompson Extensions and would 100% recommend them to anyone considering making the big decision to update their house.From our first meeting with designer Bryn we felt like we were in safe hands and being guided by genuine experts. The design integrated both our feedback and requirements, but Bryn’s expertise provided additional ideas and options which made the final design plans better than we could have imagined.The build process itself was completed in less than 6 months. We chose to live in our home whilst the extension was underway, which isn’t an easy feat for any family with kids but was made abundantly easier by the professionalism of the tradies working onsite. They were respectful, decent and talented professionals who somehow let us live a pretty normal existence whilst they created our amazing new extension. This professionalism extended to their communication and respect for our neighbours. Even with the best intentions and compliance, a building project is never fun when you’re living nearby. One of the best compliments was hearing multiple neighbours comment on the respect, communication and amazing work of the Duncan Thompson team.From a pricing perspective, we were impressed with the transparency and “quality for price” offered. There were no nasty surprises!It was a massive decision to extend. Both from a liveability perspective and a cost perspective. And rightly so…it’s typically the second biggest purchase next to buying a home! We are absolutely happy with the end results. The finished product is a new look home which will be functional for our family for decades to come. It has space, usability and magical wow factor. We are grateful to Chris, James, Kurt, Bryn and all the team for making it possible.

Anna B

11:23 04 Sep 24

We completed a stunning ground floor renovation and extension with Duncan Thompson which finished up in October last year. To say we are pleased with the result would be an understatement - we are still pinching ourselves every morning that this is our home. The design that Jim Despotellis came up with has not only beautified and extended our gorgeous 1900s house, but it has transformed the way we live as a family. We now share more of our lives and activities like cooking and gardening, because the indoor/outdoor open plan layout brings our family together in a comfortable way that also allows for private moments when desired. We have beautiful sweeping views over the garden that we love so much, and our extension achieved the "goldilocks" result of expanding our living area whilst maintaining the feel of a generous garden (such a privilege in this day and age with built-out blocks!) Jim listened to our brief carefully, and gave us honest feedback and guidance on what would work best for our home - and he absolutely delivered.In so far as the build process was concerned, we couldn't have been happier. Every attention was paid to our beautiful old house, to ensure that the period features were honoured and maintained in the new build. The craftsmanship (and in particular the carpentry) was superb. Our site manager James Tsivilis genuinely loved the house and it showed in the care and detail he put into the materials and quality of work the team carried out. James was an absolute delight to work with, his communication and organisation levels were fantastic. Despite the inevitable stress that comes with building, we enjoyed the journey and the strength of our relationship with James and the build team was borne out in the fantastic results they achieved.We are planning a further second story extension in a few years time and we wouldn't look to anyone other than Duncan Thompson to complete that project too. Highly, highly recommend!

Home Extension Costs

How much does a home extension cost?

One advantage of using Duncan Thompson Extensions to design and build your extension is that you will know how much your extension will cost, right from the beginning of the process, with no nasty surprises or extras.

Impact that various factors can have on the overall cost of an extension

High

Medium

Low

Free consultation

Fixed-price guarantee

Related Information

Home Extension Costs

Timeframes

Contracts

Project Management

Building Inspections

Tradespeople

Building Permits

Building Insurance

Find out how Duncan Thompson Extensions can transform your vision into your new home.