Water, Walls, and Windows
Water follows gravity and always slides through the easiest gap. The roof is meant to throw rain to the gutters, and wherever a roof meets a wall, like at a dormer or the end of a gable, that water has to be turned away from the wall so it doesn't pour behind the siding. Metal flashing is what does that work. It tucks under the shingles and up the wall so the water runoff lands on the roof or in the gutter. Behind the siding sits a second layer, often called house wrap, that catches whatever gets past the boards and sends it down and out.Now here's the issue: windows punch holes through that protective wall and wrap. Any time you've got a hole, you've got potential for leaks, so around each window the opening needs its own wrap of flashing, with the bottom piece sloped so water runs out onto the face of the house rather than into the wood. If the roof flashing, the wrap, and the window flashing don't overlap, water will find the cut and get into your walls.
How Heat Harms
The same joints that can leak water are also your weak point for leaking air. Warm air leaving the house in winter and hot air coming in during the summer travel through the attic, through unsealed wall cavities, and around old window frames. A tight roof with a vented, insulated attic is great: but it doesn't really do much if the walls below it are drafty. New siding put over rotten wrap and leaky windows still leaves you with cold spots at every opening.Meanwhile, putting new windows into walls that have no continuous wrap still gives a great path for air intrusion. That's why the roof, the siding, and the windows all have to be dealt with as a unit.
What a Coordinated Exterior Remodeling Refresh Does
On paper, it can look cheaper to deal with just one piece at a time. In reality, that can end up costing you more. New siding that's cut around old window frames will only perform until the caulk dries and splits. A new roof dropped onto walls that will be stripped later means the roof-to-wall flashing will be disturbed again. New windows set into tired siding leaves the wrap incomplete.A whole-home refresh allows you to put the wrap on as one sheet, with the window flashing taped into that sheet and the roof flashing tucked into it, before the siding covers the upright legs. The house then sheds water the way it was meant to: roof to flashing to wrap to the outside face.