Such valuation issues also could help in convincing the IRS that the cost, or at least a part of it, for a swimming pool is deductible.

"That's the most common home improvement tax deduction question," says Fisher. "And there are times when a pool could be deductible. If it's prescribed as physical therapy, an ongoing treatment and not just for a few weeks. You also need to prove it was for medical purposes and are using it as prescribed. Special equipment bolsters the argument, for example, a bar to hold onto or special chairs, special jets beyond a typical pool."

Documentation demands
In such cases, the extent that the pool cost exceeds the improvement value is deductible. But in order to successfully claim the deduction, you'll need documentation.

The best audit ammunition is a doctor's letter or statement detailing why a home improvement is recommended therapy for treatment of a chronic condition. "If there are alternatives, the IRS might say no, so be ready to show that the alternatives were too burdensome or didn't address your condition,'' says LeValley. In the case of a pool, for example, showing that not every nearby gym has a pool or not every pool is open year round could help convince the IRS of the medical claim's validity.

"You're getting into situations that are very fact-specific and you should pretty clearly have it documented that any improvement is a medical necessity," agrees Luscombe.

Filing details
Finally, when claiming medical deductions, both the medically necessary home improvements as well as the more run-of-the-mill health care costs must be itemized on Schedule A. And only the amount that exceeds 7.5 percent of your adjusted gross income is deductible.

If you have to make major residential renovations, that threshold might not be a problem. But if it looks like you might fall just short of the required amount, coordinated health care and tax planning could help.

Consider bunching your expenses, including home improvements, when possible. "You probably don't want to wait on serious medical conditions," says Luscombe, "but if it's possible to push improvements into one tax year so that you get over the 7.5 percent, do that."

And don't forget about the alternative minimum tax (AMT). If you end up facing this parallel tax, the threshold to deduct medical expenses goes from 7.5 percent to 10 percent. Talk with your tax adviser or use the IRS's AMT online calculator to see if the tax might pose problems with any medically-based home improvements you plan to make.