Repairing rotted sills, loose glass and failed glazing putty
Water is the enemy of an old wood window. Where it sits, wood softens and putty cracks, but small areas of damage can be repaired without replacing a window.
Where water gets into a rowhouse window
The usual places are the sill, where rain runs off the glass and sits, the bottom rail of the lower sash, and the joint between the frame and brick. Gutters on rowhouses are often shared or hard to reach, and a leaking downspout or a failed brick joint above a window can send water into the frame for years before anyone sees it.
How to tell repairable rot from rot that needs more
| Sign | Usually repairable | Usually needs a new part |
|---|---|---|
| Soft spot with a screwdriver | Small area, solid wood around it | Spreads across the full rail |
| Paint peeling at the sill | Surface only, wood is hard | Wood crumbles or has holes |
| Glass rattles in the sash | Putty dried out, wood sound | Muntins or rails loose at the joints |
| Water stains inside | Single window, cause found and fixed | Several windows, brick or flashing problem above |
Common repairs
- Consolidate and patchSoft but intact wood is hardened with a wood consolidant, then filled with epoxy and shaped to match.
- Splice in new woodA rotted sill end or rail bottom is cut out and replaced with a new piece joined to the sound wood.
- Re-glazeOld putty is removed, the rabbet is primed, and new glazing compound is applied and painted to seal the glass.
- Replace a paneA cracked pane is removed and cut glass is set with new glazing points and putty.
Philadelphia specifics
- Masonry joints matter
- Brick rowhouses need sound mortar joints and flashing around openings; otherwise a repaired sill gets wet again. A good installer looks above the window as well as at it.
- Lead paint rules apply to rot work too
- Cutting out rotted wood and removing putty disturbs old paint. In pre-1978 houses, that is work for lead-safe certified firms.
- Historical Commission review
- On a property on the Philadelphia Register of Historic Places, a repaired window that keeps its original profile is generally easier to approve than a replacement that changes the appearance.
Keep reading on this site
Sticking and painted-shut sash
Freeing sash, replacing sash cords and balances, and ending the rattle.
Storm windows and weatherstripping
Comfort upgrades that leave the original sash in place.
Window repair in Society Hill and Old City
Historic townhouse sash, Commission review and lead-safe repair.
Window repair in South Philadelphia
Block-long brick rows, shared walls and old sash.
Questions people ask
Can a rotted sill be repaired without removing the window?
Often yes. Rot limited to the sill can be cut out and spliced from the inside and outside while the frame stays in the wall.
Is glazing putty safe to remove in an old house?
Old putty may sit on lead paint, so removal in a house built before 1978 should follow lead-safe practices.
Should I replace single-pane glass with double-pane?
That is a replacement decision, not a repair one. If your goal is comfort, storm windows and weatherstripping on the existing sash are a common middle path.