House Extensions Adelaide - Custom Extensions & Additions

Single-storey and second-storey extensions built to last, from a licensed builder with 25+ years across South Australia.

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Licensed Builder

Fully Insured

25+ Years Experience

10-Year Guarantee

25 +

years building across SA

10 +

years guarantee on all our work

2023

MBA National Excellence Award

AllenCo Construction

Adelaide's Custom House Extension Builders

AllenCo Construction is a custom house extension builder working across Adelaide and South Australia. We design and build single-storey and second-storey extensions for homeowners who need more space without leaving the home they love.

As a family-owned business operating since 1998, we treat every extension like it’s being added to our own house, because our reputation is on the line for every job we take on.

0429 999 478

About Us

Our Services

Our Extension Services

Single-Storey Extensions

Ground-floor extensions that add living space, bedrooms, or open up your existing home, designed to flow naturally from the original house.

Second-Storey Additions

Adding a second storey gives you the space of a much larger home without losing your block. We've delivered two-storey additions across Adelaide that change the way a family lives.

Home Additions

Targeted additions for a specific need, from an extra bedroom or bathroom to a new family room or studio space at the back of the house.

AllenCo Construction

Built to Match the Home You Already Have

A good extension doesn’t look like an extension. The brickwork lines up, the roof flows, the new rooms feel like they belong, and the original character of the house is respected.

AllenCo Construction specialises in custom extensions that match the home they’re added to. We work across heritage and character homes, older brick homes, and modern builds, designing each extension so the finished result looks like it was always meant to be there. We use rustic, salvaged and recycled materials where they suit the existing home, alongside new products that match what’s already in place.

We’re not a volume builder, and we don’t repeat the same extension over and over. Every job is designed around your home, your block, and how you want to live.

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0429 999 478

Why Choose Us

Why Choose AllenCo Construction

Custom Builder

We design every extension around your home, not a template. The finish matches the original house and the layout works for how you actually live.

Award-Winning Builder

Winner of the 2023 Master Builders Australia National Business Excellence Award for small residential builders.

Fully Insured Licensed Builder

All extension work carried out under our builder's licence with $10M public liability cover, and backed by our 10-year guarantee.

Family-Owned Since 1998

A South Australian family business with over 25 years of additions and extensions behind us. The people who quote your job are the people who do the work.

What Our Customers Say

    
 
 
       Posted on Google  
   
   Tim Leeuwenburg 
 
 
 
 Trustindex verifies that the original source of the review is Google. The team at AllenCo have helped us out with underpinning on a couple of places and have been excellent and knowledgeable
  
 
      Posted on Google  
   
   Romeo Vella 
 
 
 
 Trustindex verifies that the original source of the review is Google. AllenCO have just completed an underpinning job at my property and I have been impressed from start to finish with their attitude, workmanship and professionalism. I would highly recommend them to anyone faced with undertaking this work.
  
 
      Posted on Google  
   
   Angus Hards 
 
 
 
 Trustindex verifies that the original source of the review is Google. I had a fantastic experience with Allenco. I own St Canice Catholic Church in Snowtown, which I purchased two years ago, and unfortunately the building required significant underpinning due to major cracks opening up in the brickwork.
From start to finish, the team at Allenco were professional, knowledgeable, and extremely thorough. Underpinning a historic building is no small task, but they approached the job with care, precision, and clear communication throughout the entire process. Their workmanship and attention to detail gave me real confidence that the structure is now secure for the long term.
I truly appreciate the quality of their work and would highly recommend Allenco to anyone needing structural or underpinning services. A very professional outfit and well deserving of 5 stars.
  
 
      Posted on Google  
   
   Jo Lush 
 
 
 
 Trustindex verifies that the original source of the review is Google. Cody was very thorough and careful to explain everything during his initial visit to quote for underpinning at our house. When his workmen arrived to begin on the first day I was impressed that they all took time to introduce themselves to me and answer any questions. The team varied across the time of the works, but they always kept us updated on what was happening. They were neat and tidy and made sure everything was tidy and safe at the end of the day. They consulted with us and took care with our gardens and lawns. Cam, Liam, Kyle, Mark, Jersey, Leo and the others were a delight to have doing the work and I would highly recommend them.
  
 
      Posted on Google  
   
   Sue Watson 
 
 
 
 Trustindex verifies that the original source of the review is Google. Cody gave us valuable, honest advice. He went over and above to help. Would highly recommend.
  
 
      Posted on Google  
   
   Farron Studt 
 
 
 
 Trustindex verifies that the original source of the review is Google. Appreciate all the work from Cody and the guys, very easy to deal with, kept things tidy and got the job done with no fuss.

Our Process

How It Works

Every house extension we take on follows the same 4 steps, so you know exactly what to expect from start to finish.

0429 999 478

Contact Us

1. Free Consultation

We visit your home, talk through what you want to add, look at the space we're working with, and get a clear picture of what's possible.

2. Design & Quote

We develop the extension design with you, work through council requirements, and provide a clear, fixed quote so there are no surprises.

3. The Build

Our licensed team carries out the build, manages the connection to the existing home, and keeps you updated at every stage.

4. Handover

We walk through the finished extension with you and don't call it done until you're completely happy with the result.

AllenCo Construction

Featured Project: Glenelg North Two-Storey Addition

The Glenelg North project saw AllenCo Construction add a full second storey to an existing single-storey home, transforming the way the family lives without forcing them to leave the suburb they love. Hear from the client directly about working with AllenCo from design through to handover.

Contact Us

0429 999 478

Let Us Restore It

Get Your Extension Started

Join South Australian homeowners who’ve added space, value and quality to their homes with AllenCo Construction.
Free quote. Licensed builder. Custom workmanship.

Start Your Project

0429 999 478

Get a Free Extension Quote

*Thinking about extending your home? Let’s talk through what you want to add. We come to you, walk through your home and your block, discuss your ideas and budget, and give you a clear, accurate quote.