If an external window sill is rotten or damaged in some way, it can immediately compromise the overall aesthetic of your home. Even if you have a great front door and a lovely garden, any visitor will find their eye drawn to the damaged sill. Additionally, a damaged sill can allow damp and adverse weather to impact your home’s comfort.
A damaged sill or anything that compromises the seal on your windows and doors will introduce an air leak in your home. This means that your heated or cooled air can escape from your living area. Essentially, you’ll be paying more on your heating and cooling bills while not enjoying the desired atmosphere.
Damaged sills can also allow damp to seep into the window, which means that you could end up needing premature windows replacement. Fortunately, it is possible to replace an old sill with some basic DIY skills. In this article, we’ll guide you through the process step by step to help you confidently complete the repair.
Common Signs You Need to Replace an Exterior Window Sill
Before you start to consider exterior window sill replacement, you need to examine your window sills for signs of whether you need to complete this work as part of your exterior home improvement plans. If you suspect you have a rotten window sill, you will need to check the extent of the damage to plan your approach.
Some common signs to look for include:
- Spongy or soft areas in the wood, pay close attention to the joints of the sill
- Dark spots or discoloration
- Cracks in the surface or peeling paint
- Visible mildew or mold growth.
Once you have checked for damage, you can determine whether you will need to replace the entire exterior window sill or if you can simply address a part of the sill. If the damage is not significant, it may be possible to repair small areas of damage using wood filler, but with extensive damage, you’ll need to replace the window sill exterior fully.
Types of Materials for Exterior Window Sills
Now you’ve determined the need for an exterior window sill replacement; you need to think about the choice of durable window sill materials. There are several options on the market:
Wood:
Wood is a traditional option for an outdoor window sill installation, offering a combination of versatility and appeal. Wood offers a classic look that can be stained or painted to complement your home aesthetic.
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PVC:
PVC or vinyl windows have become increasingly popular in recent years. This synthetic material is highly durable and requires little maintenance. PVC can also be a good option if you have concerns about preventing water damage on window sills as the material is impervious to water.
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Aluminum:
Aluminum is a modern material for constructing windows and window sills, but it can provide a contemporary aesthetic and unrivalled durability. This can be a great option if you have a modern architectural home.
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Concrete:
Concrete or stone is an excellent option to replace window sill exterior projects, as it is highly durable and offers a virtually maintenance-free finish.
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Can You Replace a Window Sill Without Removing the Window?
Now you know you need to attempt some DIY, you may be wondering, “Can you replace a window sill without removing the window? There is no simple answer to this question, as it will depend on your windows and window sills.
If you have old wood sills, you may be able to wiggle them out of place and then install a new sill, securing it to the framing. If the sill is a little tight, you may need to cut a section out of the old sill to loosen the attached pieces by using a screwdriver to lever the sill away from the staples holding it in place.
Just be aware that it is often a good idea to fully inspect the window as the rot may have spread from the damaged window sill to the underneath of the window frame, which would also need some attention.
Step-by-Step Guide: How to Replace an Exterior Window Sill
Now we’ve reached the part of this window sill repair guide where we’ll cover how to install an exterior window sill with step-by-step instructions.
Gather Your Tools:
One of the most important aspects of how to install an exterior window sill is preparation. You don’t want to start the job only to find you don’t have a tool or material on hand. For this type of project, you’ll need:
- Saw
- Caulk gun
- Hammer
- Pry bar
- Level
- Chisel
- Drill with drill bits
- Screwdriver
- Utility knife
- Sander
- Paint and brushes
- Waterproof sealant
- Primer (if you’re using a wood external window sill)
It is also a good idea to have work gloves, safety goggles and a dust mask.
Remove the Old Sill:
Use a reciprocating or circular saw to carefully remove the damaged section of the sill. For a complete sill replacement, make cuts at either end where the sill meets the frame.
Use your pry bar to remove any fixings holding the old sill; just be careful not to damage the siding or window frame.
After you remove the old sill, clear any old caulk, rotten wood or other debris from the space.
Prepare the Area:
Once the old sill is out, you can inspect the area for indications of rot or water damage. You’ll need to fix any issues before you install your new sill. If there are any small gaps, you can use exterior grade wood filler, but make sure it is completely dry before you continue.
Use your level to ensure that the sill space is even and if necessary create a level surface using shims.
Install the New Sill:
If your sill is not precut, you’ll need to cut it to size using your measurements to ensure the correct sizing. Just be sure to account for any slope or overhang. Place the new sill to ensure a snug fit, you can secure it using exterior grade nails or wood screws, depending on the sill material.
Apply exterior grade caulk to create a watertight seal around the edges. For a neat finish, smooth the caulk with a tool or your finger.
Sealing and Finishing:
If you’re using a wood sill, sand it to ensure a smooth surface. Apply a coat of primer and then use paint or stain to finish the sill. If you’re using another material, you’ll need to follow the manufacturer’s finishing recommendations. Apply a final bead of your caulk where the sill meets the frame to ensure proper weatherproofing.
