Repairing rotted trim around windows is a very common malady for homes built prior to the introduction of composite and synthetic window components. Your average residential window unit is built with the same components on the exterior. The perimeter trim is usually brick moulding, the trim that your siding terminates into around the window. This is probably the most common part on the exterior of a window unit to rot. The biggest reason for this is that the wood brick moulding was never properly primed when the home was built. Often referred to as “dry rot”, the reason it rots is because it gets wet and the moisture causes a fungus to grow into the wood fibers which eventually decays or rots it. If the wood trim was never primed properly the water will work it’s way under the paint and that’s when the trouble starts.
The next most common part of a window to rot is the sill or bottom horizontal part of the window. Most residential window sills are comprised of two parts; the sub-sill and the sill connector. The sub-sill is the larger of the two and is where the window comes down and hits when closed. The sill connector is the very outer part of the sill and in most cases is attached by finger joint and is removable. Occasionally you will run into a window where the sub-sill and connector are one piece. These are much tougher to repair. If left alone long enough a rotted sub-sill will rot thru and allow water to enter into the framing of the wall below. These repairs can be expensive and messy depending on how much water has been getting in and for how long.
The good news is that now there are synthetic materials that can replace the old wood parts that rotted. All exterior window components are now made in PVC, which is a rot-proof substitute for the old wood components. Caulking these new parts with a urethanized flexible caulk is important because PVC contracts and expands with the weather. You can help prevent your windows from rotting by keeping an eye on the caulking and paint. Also if the surface of the wood appears wavy or uneven there is a real good chance it is rotted under the paint. A little preventive maintenance goes a long way and can save you a lot of money !! Whether doing repairs or remodeling these are important facts to consider.