How to Repair Wood Window Frames: A 3-Step Guide

Wooden window frames are always one of the first places to show signs of rot in a property. Being so exposed to the elements, even indoors, moisture, condensation, and humidity can cause wood around a window to become damp and damaged over time.

The best way to prevent wooden window frames from rotting is to seal the wood with a waterproof sealant and routinely replenish the protective layer. Doing this every six months to a year, or more frequently if your home is particularly humid, can reduce the risk of unattractive decay and keep your window frames looking nice year-round.

Keep reading to learn how to repair wood window frames, and how to replace rotted wood around windows, in this step-by-step guide.

Can You Fix Wood On Windows?

Rotted wood on windows can easily be fixed, provided you’ve caught the rot early enough and it hasn’t been affected by dry rot. Most window frames are affected by wet rot vs dry rot, which is significantly easier to fix. You’ll know if your window has dry rot if the surrounding wood has fungal, mushroom-like spores, white fluffy strands, or a grey-white skin.

Dry rot is serious and needs to be treated immediately after spotting. Otherwise, it can quickly spread across brickwork, masonry, timber, floorboards, and plywood subfloors in your home. Once spread, dry rot can cause significant structural damage that’s costly to fix. You’ll usually need to enlist help from a professional if you suspect dry rot in your property.

Rotting window frames and window sills are typically caused by damp, humidity, poor ventilation, or moisture seeping into the wood. This can happen because the wood hasn’t been sealed properly, or the sealant has worn away over time. It can also be caused by the frames simply being old and losing their structural integrity. Generally, wooden window frames only last between 10-20 years before needing replacement.

Can Rotted Wood Windows Be Repaired?

Yes, rotted wood windows can easily be repaired. You have several choices when fixing wood on windows. You can either repair the rotten section or replace the entire frame using exterior plywood. Before repairing rotted windows, it’s important to inspect the area and locate the source of damp. This will need to be treated before repair work can take place.

Oftentimes, damp is simply caused by rainwater, but it could be coming from something else, like a leaky pipe or masonry damp. If you suspect dry rot may be the issue, it’s best to seek professional help. They can identify the source of the issue and accurately determine how far it’s spread, before fixing it properly.

How Do You Fix Rotted Wood Without Replacing It?

Before you attempt to fix rotted wooden windows, you’ll need to treat the issue causing the damp. Wooden window frames are always going to experience rotting at some stage, particularly if they haven’t been sealed properly or if they aren’t routinely protected. Investing in vinyl or plastic windows is a much more effective way to ensure your window frames always look nice.

1. Inspect the damage

First, inspect the damage to determine its extent. When inspecting the rotted wood, look for signs of flaking paint, sunken corners, or crumbly patches. If the entire frame is damp, sunken, and crumbly, you may need to replace it all. If only a corner or area of trim (like the windowsill) is rotted, you can repair it without replacing the whole window frame.

2. Cut away the rotted areas

Prepare the surrounding area, laying a dustsheet or plastic covering to catch the rotted wood. Using a hammer and construction chisel, chip away the rotted areas of wood. Continue scraping the wood until you reach the healthy wood that isn’t rotting or crumbly. Once reached, brush away any residue. If the entire strip of wood is rotted, keep chiseling or use a handsaw to remove the whole piece of trim.

3. Splice repair or fill in the trim

You have two options depending on how badly your window frame has rotted. If the whole section is unsalvageable, you’ll need to splice repair the trim. To do this, you’ll need to:

• Use a handsaw to neatly cut the existing trim – it’s best to cut wood diagonally rather than horizontally
• Apply a dry rot treatment to the existing windowsill or frame
• Trim new timber or exterior plywood to fit the replacement area
• Glue your splice repair using an exterior wood adhesive or resin
• Once dry, sand the splice to neatly fit in place with the existing trim
• If you spot gaps in the new splice, fill these with exterior wood filler
• Apply a mildew-resistant exterior primer
• Once dry, apply at least two coats of latex paint in your chosen color
• Finish the wood by applying a waterproof sealer
• If preferred, use exterior caulk to seal gaps in your window frame

After splice repairing a wooden window frame, monitor the wood routinely, especially during periods of wet weather. Regular cleaning will help prolong the life of your waterproof sealant. Keep your frame clean of leaves and dirt using a brush. Use an exterior wood cleaner to prevent mold from building up on your wooden frame. Every six months to two years, reseal your wooden window frames to prevent severe rotting.

Provided there is only minimal rotting on your window frame and a healthy amount of wood exists beneath the rot, you can chisel it off and fill it in, rather than adding a splice. To fill an exterior window frame, you can:

• Once you’ve scraped away the rot, clean the area with a brush
• Drill holes into the frame using a quarter-inch drillbit, spacing the holes at least one inch apart
• Brush any dust or wood chips from the area
• Apply epoxy wood consolidant to the holes
• Apply exterior wood filler to restore the shape of the frame
• When dry, sand the surface to ensure a smooth finish
• Apply a mildew-resistant primer, at least two coats of paint, and a waterproof sealer to finish the repair

How Much Does It Cost To Repair Wood Rot Around Windows?

Repairing wood rot around windows can be relatively cheap, depending on whether you plan on DIY-ing the repairs yourself or seeking help from a professional. Treatments for rotted window frames can vary in price, but often costs between $50-$400 per window. Naturally, doing the repair work yourself will be significantly cheaper than hiring a contractor.

It’s less expensive to splice repair rotted areas using exterior plywood or wood putty, rather than replacing the entire trims. The most expensive fix for rotted frames will be if you have dry rot (that requires specialist attention) or if you want to replace your windows with vinyl or plastic frames, which are much more durable and long-lasting than wood.

Here’s a guide to the cost of repairing wood window rot:

Fix	Pros	Cons	Average US cost
Splice-replace a rotted corner of a window frame	Offers the cheapest solution to fixing rotten window frames	Can appear slightly different to the rest of the frameRequires routine treatment to ensure it doesn’t rot	$50-250, depending on the size of the splice repair
Replace entire window frame with new timber or plywood	Offers a clean finishLasts longer than splice-replacing the rotted area	Needs to be routinely treated and resealed to prolong life and prevent future rotting	$200-400 per window
Replace windows with vinyl or plastic	Offers a long-term fix	Is the most expensive repair option	$350-800 per window

Summary: Things to Remember

• Always check for signs of dry rot before attempting any repair work
• Consider how much maintenance you want to do long-term before deciding whether to fix the rot or invest in new windows
• Splice repairs are significantly cheaper than replacing the entire window, but they require more maintenance long-term
• Doing the work yourself can save money, but only if it’s completed properly and the wood is suitably sealed