How Much Does a House Extension Cost?

Many homeowners seek a straightforward answer to the question "How much does it cost for a house extension?" However custom builders do not have a “set price list” like you see at a restaurant, hairdresser or retail store. The answer is far more complex and a builder won’t make up a random cost for the sake of it. Making up a cost on the spot is detrimental to the builder and client should they have overestimated or underestimated the project. Remember they have only seen your house for 30 mins at an initial consultation and site inspection. 

Determining how much it costs for a house extension includes various factors, like the standard and quality of the existing house, scale of the extension, design, materials and labour, types of finishes, is a draftsman or architect required, council approvals for CDC or DA, engineering, private certifier costs. Plus business running costs such as home warranty, insurances and a builders margin. All these factors make up the cost of a renovation which is why a builder can never give a straightforward answer straight away.

A builder needs to inspect the existing home and then go away to properly review the plans, the engineering, a client's wish list and seek quotes from relevant subcontractors and suppliers. Most of the time this is all unpaid time and work a custom builder does behind the scene of a providing quote, on top of working a physical full day onsite.

Factors That Contribute to the Cost of House A Extension

Here are some key factors that contribute significantly to the overall house extension cost:

Type of House Extension

What type of extension? Are you wanting to expand the width of your existing house, a two-story extension, or add more rooms? Each option comes with its own set of requirements, structural modifications, plumbing and electrical work and architectural requirements that can impact the cost.

Materials to be Used

Documents such as the engineer report will determine if steel beams are necessary for a wall removal or timber LVLs are adequate. Something like the difference in steel or timber is a noticeable cost difference when it comes to a wall removal and providing structural support for the extension. Timber LVLs will require carpenters who would likely be onsite anyway, whereas steel may require the hire of a beam lift and welding. This poses a different set of trades, time, cost and methodology to installing different materials.

Fittings and Finishings

Fittings and finishings add the final touches to your house extension and are also factors that affect the overall cost. This all comes down to personal tastes and budget. Items such as flooring, cabinetry, countertops, lighting fixtures, tiles, kitchen appliances and bathroom fixtures all have a huge variety of options and price tags depending on their quality, brand and complexity of installation.

A great example are subway tiles and floorboards - if a client chooses to install them vertically - this is a lot quicker and easier for a tiler/carpenter to complete. Whereas to choose the herringbone pattern, takes a lot more time for installing, more cuts in the material and wastage.

Planning and Building Permits

Obtaining planning approvals and building permits such as DA and CDC are necessary steps in most house extension projects. The associated fees for these permissions vary depending on the council and factors such as the size and cost of the build.

The Scale of the Project

The scale of the project such as its size and complexity, directly impacts the cost of house extension. Larger extensions with intricate architectural features or structural modifications will naturally incur higher expenses compared to smaller, more straightforward projects. For example an extension to a home that includes a bedroom, walk in robe and an ensuite is a larger project compared to an extension for an additional lounge room.

Additional Factors to Consider in Getting the House Extension Cost

Aside from the main cost contributors, below are additional factors that also significantly affect the final cost for a house extension:

The Age of the Existing House and Matching Existing Features

The age of your house can greatly affect extension costs. Older homes often need extra work, like updating wiring or reinforcing foundations to meet modern standards. Also, blending the new extension with the existing structure may incur added expenses for a cohesive appearance in terms of style, materials and finishes.

Scope and Extent of the Extension

One factor that shouldn’t be overlooked is the scope and extent of the house extension. Excavation, foundation work, plumbing, electrical wiring, roofing and interior finishes must also be accounted for in the budgeting process. Additionally, special features such as custom-built cabinetry, high-end fixtures, or advanced technology integration can elevate the cost further. Clearly defining the project scope and a clients “must haves” from the start is crucial for accurate budgeting.

Structural Requirements

Depending on the design and layout of the existing house, structural modifications may be necessary to support the new extension safely. This could involve reinforcing foundations or redesigning load-bearing walls to accommodate the additional weight and stress. Having structural engineering consultations early in the planning phase can help identify potential challenges and devise cost-effective solutions to ensure structural integrity.

Home Extension with CastleCrew!

CastleCrew Group specialise in home renovations and extensions. We offer personal and friendly assistance to guide you through every step of the process. From initial consultation to project completion, we are dedicated to helping our clients achieve their vision within their budget.

We also provide a range of other services to meet your home improvement needs. Whether you're considering building a new home, renovation, or deck building, our comprehensive offerings ensure that every aspect of your home receives the attention it deserves. We will work closely with you to understand your goals, address any concerns and provide detailed quotes to help you make informed home improvement decisions.

Connect with our team for a personalised home extension scope of works and quote tailored to your project requirements.