Window Flashing in Massachusetts
If you ever see water staining on the inside of a wall under a window, the cause is almost always failed flashing.
Here is what proper window flashing looks like in a Massachusetts home.
The Layered Approach
A correctly flashed window has THREE layers of water management:
1. Pan flashing at the sill. A self-adhered membrane (Grace Vycor Plus or equivalent) tucked behind the WRB (weather-resistant barrier) and lapping into the sill. Catches any water that gets behind the cladding.
2. Jamb flashing. Membrane up both sides of the window opening, lapping over the pan flashing.
3. Head flashing. Membrane across the top, lapping over the jamb flashing AND over the top of the window flange. The WRB on the wall above must lap OVER the head flashing — never under.
This shingle-style layering ensures water always flows outward and down.
Common Mistakes We See
❌ Window installed against bare sheathing — no pan flashing ❌ Caulk used instead of mechanical flashing ❌ WRB lapped under the head flashing instead of over ❌ Window flange not sealed to flashing ❌ Tyvek tape used in place of self-adhered membrane (Tyvek tape fails in MA winters)
Any one of these creates a path for water to get behind the cladding and into the wall cavity.
Why MA Is Especially Tough on Windows
- Driving rain from nor'easters
A window flashing detail that works in Atlanta will fail in Massachusetts.
What We Do
When we install siding or windows, every opening gets:
✅ Full self-adhered pan flashing ✅ Jamb membranes lapping over the pan ✅ Head flashing lapping over the jambs and window flange ✅ Cap bead of high-quality sealant on the exterior ✅ Backer rod and sealant on the interior
If we are replacing siding only and find inadequate flashing, we recommend re-flashing every window during the re-side.
📞 (774) 512-3176 — Free siding + window inspection 📧 info@rs-developmentgroup.com
In the trade since 2008. Latino-owned.
