Not sure if there is a cap, I found the following when I pulled a search:
Home Improvement Deductions
Save receipts and records for all improvements you make to your home, such as landscaping, storm windows, and fencing. You can’t deduct these expenses now, but when you sell your home, the cost of the improvements are added to the purchase price of your home to determine the “cost basis” in your home. This serves to reduce any potential taxable gain that you may have from the sale of your home. For more information, see How Home Improvements Affect Your Taxes.