By Gene and Katie Hamilton

When an old window sill is rotten or damaged beyond repair, the best alternative is to replace it with a new one. Often the wall surface at the base of the window is damaged by moisture from condensation, or a hungry dog who used the sill as a chewing toy. Whatever the cause, installing a new sill provides protection and adds a stylish detail to the window. If there is moisture damage to the wall, make the repair and then replace the sill. And if your window was built without a sill, adding a new one will be a nice upgrade.

But now there are vinyl sills that are installed with adhesive in two styles. One has a straight cut basic style, and the other wraps around the sides of the wall, giving it a custom look. At the manufacturer's Web site, www.sill-rite.com, you can learn about the different styles, how to measure a window for a new sill and what's involved installing one.

A carpenter or window replacement contractor will charge $133 to install a 4-foot-wide sill, assuming no repair work is required on the window and wall (that will cost more). You can buy the sill for $50 and do it yourself, assuming you have some carpentry skills and tools, and save 64 percent. You'll need a tape measure, carpenter's square, saber or small circular saw, construction adhesive and weatherproof caulking and a caulk gun.

Click here to get to Home Advisor and it will open in a new tab and you’ll have to answer some basic questions about your job followed by carpenters in your area to do the job.

That sums it up. Knowing the average cost to replace a window sill lets you compare doing it yourself with what you can expect to pay a contractor. For a local cost input your ZIP Code.

Improvement and Repair Cost Updated 2019

The cost and time data is generated by averaging labor and material data from annually updated cost books used by contractors and refined by the authors' experience remodeling 13 houses. They are authors of 20 home improvement books and Do It Yourself or Not, a weekly column syndicated by Tribune Content Agency. The national cost can be adjusted by ZIP Code.