The patio door is its own order

Why it is counted apart

It is a door, and doors are their own product line. Different frame, different hardware, different lead time, different price. An operator taking down "fourteen windows" and later discovering a patio door has to redo the scope.

It carries far more glass than any window in the house, so its two label numbers do more work than any single window's.

It is the opening that gets operated most. A window in a spare bedroom might be opened twice a year. A door onto a deck is used daily for half the year, and wear follows use.

What goes on a 1990s slider

The rollers. The panel rides on wheels in the bottom track. Thirty years of use flattens them, and the door starts to drag, then to need a shoulder.

The track itself. Aluminum tracks pit and deform, and once the track is out of shape new rollers do not fix the drag.

The sealed glass unit. Same failure as a window — haze between the panes that cannot be cleaned off — over a much larger area.

The weatherstripping and the interlock. The vertical seal where the panel meets the frame goes hard, and the door stops sealing even when it locks.

The lock and the keeper. A door that has to be lifted or pushed to lock has usually gone slightly out of square, which is a symptom of the track rather than the lock.

Several of those at once, on a door of this age, is the same reading as a set of windows at the end of its life.

What the replacement decision turns on

Whether the opening stays the same size. Swapping a slider for a slider in the existing opening is straightforward. Going to a hinged French door, or widening the opening, is structural work and a different permission question entirely.

Which way it should open. Sliders have a fixed panel and a moving one, and which side moves is specified at order. Worth deciding with the furniture and the deck in mind, not at the doorway on installation day.

Whether a screen is included. Often listed separately. Ask.

What the threshold looks like. The sill detail is where water gets in, and on a door opening onto a deck it matters more than on one opening to a patio at grade.

What to say on the phone

• That there is a sliding patio door as well as the windows, and how many panels it has.
• Whether it is going in the same order or on its own.
• Roughly the year of the house.
• Whether it opens onto a deck, a porch or level ground — access changes the labor, and a large door is heavy and awkward.
• Whether the opening size is staying as it is.

Common questions

Can just the glass be swapped? Sometimes, and on a door whose track and rollers are sound it can be proportionate. On a door of this age it solves the visible half of the problem.

Does a patio door need a permit? Replacing a door in its existing opening with no structural alteration is on the county's own list of work needing no permit. Changing the opening is not, and does need one.

Is a French door a straight swap for a slider? No. The opening, the framing and often the header are different, and it becomes an alteration rather than a replacement.

Does one door meet the two-window minimum on its own? A door is a door. If the reason for calling is a single patio door with nothing else, say so plainly — it saves everyone a conversation that ends the same way.