How To Replace A Wooden Window Sill

A window sill is not just a decorative element of a window, but actually serves a few essential functions that aid in the operation and durability of the window itself. Firstly, the window sill acts as a stop for the glass plane that slides up and down for windows that open. It is important that the window itself has a solid place to rest on for the window to open and close properly. More importantly, the window sill also acts as a seal for the window, keeping water out and away from the window itself. 

How Window Sills Get Wood Rot

A Window Sill most often gets damaged over a period of time by a slow or consistent water leak. Although physical damage can also occur, most often it is water damage that contributes to the creation of wood rot. Wood rot can eat away the window Sill over time, and if gone unchecked, can cause the window to leak more severely. Wood rot can even cause the structural integrity of the window to deteriorate, and could pose a safety risk for those operating it.

How To Replace A Window Sill In 7 Steps

A way to ensure that your window remains well sealed and operates properly is to replace the entire window sill. This can be a very involved process requiring significant time and money. Here are the steps so you can replace a window sill yourself.

1. Remove Current Window Sill

The first step is to remove the wood window sill rot. You can start by using a utility knife to cut through any sealant, caulking, or paint that binds the window sill to the wall. Remove any screws that may hold the old sill in place. Then carefully use a crowbar or other tool to pull the entire window sill off of the window. You may need to also remove other parts of the window like the side molding to get the window sill detached. Remove them carefully and remember to put them back on later.

2. Clean The Framing

Use a utility knife and a rag to clean away any excess debris, glue, or caulking on the window where the window sill used to be. You can use sandpaper or solvents to remove stubborn areas. Be sure to get all of the screws and nails out as well.

3. Measure The Space

Use a tape measure to get the dimensions of your window sill.  You can measure your old window sill, if it’s even still intact. Just keep in mind that measuring the old window sill is sometimes not a good idea because it can warp and change shape over time. The most accurate measurement will come by measuring the actual space the window sill will sit. You can then use new 2×4 or 2×6 pressure treated lumber and mark the dimensions on the board for your new sill.

4. Cut New Window Sill

Once you have measured out the new window sill on a piece of wood, you can use a table saw to cut the wood to shape. A jigsaw can be used for smaller and angled cuts. Accuracy of your cuts is key but if you are newer to DIY projects, make sure to cut longer versus shorter. You can always trim down your wood, but you can’t add on! It can be a good idea to get extra wood just in case a cut doesn’t work out.

5. Attach New Window Sill To Frame

Place your new window sill where it needs to go, and make sure it is lined up and level. If your old sill was sloped, be sure to match the slope on your new window sill. This may require the use of shims. Then nail or screw your new window sill into place. It’s a good idea to reuse existing screw holes when installing your new window sill.

6. Apply Caulking

Use a caulking gun to apply caulking around the edges of the window sill to seal it in and protect it against water and other elements. It’s important to choose an outdoor, waterproof caulk to ensure that the window sill is properly sealed. If you need to add back any old elements like trim, be sure to wait 24 hours for the caulk to dry before doing so.

7. Sand & Paint Wood

The final step is to make the new wood look just like the rest of the window. It can be difficult to perfectly match the existing stain as new wood will always look different than old wood. However, you should still sand down the window sill and apply paint or a stain to help it blend in with the rest of the window, and give it a nice finish.

Time Expectation & Cost To Replace A Wooden Window Sill

Replacing a window sill can be a job that ranges anywhere from a few hours to a few days depending on the extent of the damage and the experience of the person doing the replacement. Buying and cutting a new window sill that perfectly fits and matches the old one can be a trial and error process. Meanwhile, the cost to replace a window sill will also vary depending on the local costs of material and labor. Typically, homeowners might expect to spend anywhere from a few hundred to a couple of thousand dollars per window for a professional window sill replacement, depending on the damage.

Is Replacing A Window Sill Better Than Restoring It?

Choosing to repair a wooden window sill rather than replacing it can be a more cost-effective decision. It can also be more environmentally friendly, and save you time in the end. Not only does repairing a window sill allow you to cut out the cost of new materials, but it also allows you to keep the original look of your wood. Unless the damage is extremely severe, most of the time it is a better choice to repair a window sill than it is to replace the entire thing.

How To Repair A Wooden Window Sill In 6 Steps

Although repairing a wood window sill is faster than replacing, it still requires a bit of expertise to properly accomplish. It is essential that you do a comprehensive and correct repair to ensure that the wood window will not be prone to further damage. It may be better to call a professional in most situations. Below we have listed out how to repair a wooden window sill so that you can give it a try yourself!

1. Identify All Areas Of Wood Rot

The first step is to identify the areas of the window sill that have succumbed to wood rot. It is a good idea to mark the areas with a pencil or erasable marker as well.

2. Remove All Wood Rot

Use a chisel or screwdriver to remove all of the window rotted wood. It’s important that you do not leave any rotten wood, as even just a little bit left over will allow the wood rot to continue to spread . When you’ve removed all of the window wood rot, clean the healthy wood off and remove any leftover debris.

3. Apply Wood Hardener

Next to repair a wooden window sill, drill a few holes in the healthy wood. This will allow for some extra surface area for the wood hardener to attach to, increasing support strength. Fill in the holes, and cover the exposed wood with a generous amount of wood hardener. Be sure to get a comprehensive and even coat. Allow the hardener to dry completely before applying any additional coats. 

4. Apply Wood Epoxy

Now comes the most important step! Carefully use a knife to spread a wood epoxy or wood filler into the cavities. Be sure to firmly press the filler in so that it takes up the entire space, and forms well to the original contour of the window sill. You can let the filler expand past the shape of the window sill a bit, as you can always sand it down later. Allow it to dry according to the instructions.

5. Sand And Smooth Area

After allowing the epoxy to fully dry, you can now begin sanding down the filled areas.Start with a lower grit to get the epoxy and wood level. Then work up in grit until everything is smooth.

6. Paint The Restored Window Sill

The last step is to paint the repaired areas to match the rest of the window sill. Luckily, since you aren’t replacing the entire window sill, it might be easier to blend in small repairs, especially if the window has a historic look.

Time Expectation & Cost To Repair A Wooden Window Sill

To repair a wooden window sill is a much quicker process than replacing it with a new one. The tedious steps of measuring and cutting to the perfect size are eliminated. Since you typically only work on small areas, the window repairs will go by much quicker! In addition, the reduced material and labor costs will make a wood window sill repair cost anywhere from one hundred to a couple of hundred dollars, a fraction of the cost of replacement!

Who Is Preservan

Preservan is a wood rot repair service that is dedicated to providing you with a cheaper alternative to replacing rotted wood. Since 2016, Preservan has used cutting edge resin technology and a high quality of service to provide customers with quick, easy, and affordable repairs to wooden doors, windows, and more! Preservan is proud to help reduce the environmental impacts of bigger construction projects by instead focusing on small and eco-friendly repairs. Their methods are approved by the National Parks service, and allow projects to be generally completed in less than 36 hours, saving the homeowner up to 90%! If you need wood window sill repairs or other wood rot repair services, Preservan is the company for you.

Choose Preservan To Repair A Wooden Window Sill

Need wood window sill repair? Not sure if you need wood window sill repairs? If you have a wooden window sill that is showing signs of wood rot, you should do something about it soon so the issue doesn’t worsen. It might seem like a daunting task to try and replace or repair a window sill yourself, which is why the experts at Preservan are here to help. We provide top notch wood rot repair services on windows, doors and other wood in your home or business.

Our highly experienced and friendly technicians ensure that every repair is low cost and quickly executed, leaving you with wood that looks good as new! If you are interested in learning more about what we can do for your wood rot, visit our website. You can also book an appointment, or give us a call with any questions you may have about wood window repair. If your wood window sill has wood rot or dry rot, contact Preservan Wood Rot Repair. Our wood rot repair experts are ready to save your building from the dangers of wood rot. Our epoxy treatment can repair wood window sills without costly replacement and is eco-friendly too. Check out our website for more details and to schedule an appointment to have wood window sill repairs or to repair wooden windows at your home. 

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