Here are some home improvement surprises you should beef up your budget for.

Also possiblyhiding within those wallsand floors: mold, termites, and other pests or issues.

These all typically require the work of experts.

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When you dig into a wall or floor, you just dont know what youre going to find there.

There was mold hiding behind drywall, which cost another $3,000 to eliminate.

Solution:Dont open up walls or floors…just kidding.

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The best rule of thumb is to assume that somethingwillgo wrong.

A structural engineer needs to answer that question, and explain whether you might work around it.

This is one of those cases where you shouldhire a pro rather than DIY.

A metal ladder stands in front of an exposed wall with metal beams and bricks.

Solution:If you dont have room in your budget for big changes, have an alternate plan.

You might find they put pipes throughout your house willy nilly.

It might be a quick fix, or you might have to run entirely new plumbing.

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You wont know until you open it up and look.

Andvet your contractor thoroughlyto check that you wont run into similar problems.

Photos byFeng Yu(Shutterstock),danja,emmajanehw,okchomeseller,secretlondon123.

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Illustration by Tara Jacoby.

Photo of a contractor shaking hands with a client over a table spread with paper plans, tools, pens, and a calculator. Another contractor wearing a safety orange vest holds a yellow hardhat in the background.