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10 Expenses Homeowners Forget to Budget for When Planning an Extension

Adding an extension isn't cheap, and many homeowners forget to account for these costs when budgeting.

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Approved Construction Permit Application courtneyk/Getty Images


Adding on square footage to your house isn’t a simple task, even if you know how to build an extension. Homeowners often forget to budget the cost of permits when planning that addition. Building permits can cost $50 to $300 for small projects like plumbing and electrical, but can go into the thousands for major renovations or remodeling.

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Hiring an Engineer or Architect

Depending on the size or complexity of your project, you might need to hire an engineer or architect to draw up plans for your extension. Structural engineers charge between $100 and $200 an hour, according to Home Advisor. “For new construction or large remodels, one percent to 20 percent of the total construction price, or $1,500 to $20,000, goes to the structural engineer,” Home Advisor reports.

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Home ExtensionJames Osmond/Getty Images

Furniture or Appliances

Don’t forget to include the costs of decorating or filling out that new room.

If you’re building a second kitchen, think about an oven, refrigerator, dishwasher, etc. If you’re adding another bathroom, there’s a vanity, sink, toilet and more to account for. What another bedroom? You’ll need a bed, dresser, rugs and night stands, just to begin with. You’ll also probably want artwork or picture frames to add some personal touch to the room.

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electricalWestend61/Getty Images

Unexpected Electrical or Plumbing Issues

You never know what kind of weird issues lay behind your walls. If you’re planning to add on to your house, you might just unearth some not-up-to-code electrical or plumbing violations. Budget a buffer in case you run into any bumps in the road during your extension build.

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Dumpster rental

This might not apply to all home additions, but if you’re planning to rip out any walls or do major demolition to make way for your new addition, plan for a dumpster to haul off all the debris. The average cost of a dumpster rental nationwide is about $450, according to

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project managerDavid Sacks/Getty Images

Hiring a Project Manager

You can save a lot of money on an extension if you plan on doing it without a project manager. A project manager is largely responsible for hiring and scheduling subcontractors to complete specific portions of the project. But if you feel comfortable hiring those contractors yourself, that could save you thousands or even tens of thousands, depending on the scope of the project.

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anchor locations foundation


Foundation work will probably the most expensive portion of the extension. Keep that in consideration if an extension is right for your home.

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LandscapingAnnie Otzen/Getty Images


This might not apply to all homeowners adding an extension, but that new room of the house might require landscaping to clean up around the house. Dirt, plants, stones and more can add up quickly, so plan accordingly if this applies to you.

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Replace Dated Light Fixtures in kitchen with modern pendant lightsalexandre zveiger/shutterstock

Fixtures and finishes

Think carefully about all the fixtures and finishes you’ll need for your home addition. Maybe faucets, lights, flooring, paint, shelves, moulding, knobs and handles. Project managers might upcharge you on items they purchase, so you can save a lot of money by buying the fixtures and finishes you like that are on sale or secondhand.

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shutterstock_169825319 roofing singlesTFoxFoto/Shutterstock

Roofing costs

Second to foundation work, roofing might be the most expensive portion of your extension. That’s especially true if the room you’re building is an odd shape or doesn’t seamlessly transition from the current home layout.

Alex Shoemaker
Alex is an avid DIYer but had little experience before purchasing his first home in 2019. A Family Handyman subscription was one of his first purchases after becoming a homeowner, and he's been hooked ever since. When he’s not working, he can be found fixing up his 1940s Florida home or relaxing on the beach with his family.