Exterior aluminum cladding pulled away from a wood window, revealing the wood frame beneath. In this case, water leaked behind the cladding and caused the wood to rot, loosening the cladding. If you notice cladding detaching or wood discoloration, it’s a red flag for rot.  

Wood rot is the bane of any wood window or wood-clad window. Because Indianapolis gets its share of rain, humidity, and even ice, the wooden parts of your windows are at risk if not properly protected. Rot is literally a fungal decay of the wood, requiring moisture and often time to take hold . Here’s how to spot and deal with wood rot in windows: 

Common Areas & Signs: Rot loves to start in window sills, bottom frames, or any horizontal surfaces where water can collect. The exterior cladding (whether aluminum or vinyl) is supposed to protect the wood, but if there are gaps or the cladding doesn’t fully cover the wood, water can sneak in . One common sign is discoloration or staining on the interior wood trim or sash – often brown or blackish areas that persist even after cleaning. This can indicate moisture has penetrated from the outside and the wood is rotting internally . On the exterior, paint peeling or bubbling on woodwork is a classic symptom . If paint is flaking off and the wood underneath looks fibrous or crumbly, rot is present. Also, if you see any aluminum or vinyl cladding lifting or separating from the wood, that’s often because the wood behind has rotted and can’t hold nails or staples – as shown in the image above and corroborated by real-world cases where water leaking behind cladding rotted the wood . Another sign is the cladding itself falling off or easily pulled off, as rot can destroy the wood that anchors it.  

Soft or Spongy Wood: Not all rot is visible on the surface. Do a poke test – take a screwdriver and gently press suspected areas (especially window sills and lower corners). Healthy wood will resist, but rotting wood will feel soft or spongy and you may press right into it . If a chunk of wood flakes away or you can sink the tip in easily, you’ve got rot. Interiors can be tested too: if the inside lower sash or frame feels soft or you can flake bits off with a fingernail, that’s advanced decay.  

Windows Stuck or Misaligned: As rot progresses, it weakens the structural integrity of the window. The frame might start to sag. You could notice the window doesn’t sit squarely, or it becomes difficult to open/close (because the frame is literally deforming) . In older wood windows, sometimes the sash falls apart at the joints because rot ate away the wood around the joinery. If a window has unusual play or movement, or the muntins/bar in a true divided light window rot, the glass may even crack or fall out. These are severe cases, of course, but we have seen century-old windows in historic homes with such extreme rot that they’re falling apart. Usually, long before that, you’ll see the other signs and address it. 

Repairing vs. Replacing Rot: Minor rot can often be repaired by a professional carpenter or window restoration specialist. This usually involves removing all the decayed wood (digging/grinding it out until only solid wood remains) and then either patching with epoxy or splicing in new wood. Epoxy wood consolidants and fillers can work wonders on small spots – they essentially harden and replace the rotted material. This can extend the life of a window if the rot was caught early and is in a non-critical area (like a small patch on a sill). However, if rot is extensive – say an entire sill is punky, or the frame around the glass is rotted – a full frame replacement is often more economical and prudent . As one source notes, the most reliable long-term fix for significant rot is a full replacement, because all the damaged wood is then removed and replaced with new, sound material . Simply put, if over 10-15% of the window wood is rotted, replacement is likely the best route.  

Preventing Future Rot: If you replace your windows, you might consider rot-resistant materials (like Fibrex or fiberglass) so you never have to worry about rot again. If you keep your wood windows, ensure they are well-painted or sealed regularly. Pay special attention to caulking and flashing around the window – gaps allow water to seep to wood. For wood-clad windows, make sure all cladding is intact; if you ever notice a section of cladding loose, get it resealed ASAP to keep water out. Modern Day Window & Door offers composite and aluminum-clad wood windows that have warranties against rot – Andersen, for instance, treats and clads their wood such that rot is highly unlikely. We can also perform rot repairs on-site if feasible, or do full replacements with materials that won’t rot. 

One specific note: Our Andersen product lines include wood windows with vinyl exteriors (Andersen’s Perma-Shield®) that fully encapsulate the wood, virtually eliminating exterior rot issues. We’ll discuss this more in the materials section, but it’s good to know there are wood-based options that are very rot resistant.