Exterior Door Replacement Guide: What to Know First

An exterior door looks like a product decision and is mostly an installation one. The same door fitted well and fitted badly gives completely different results, and in an older house the difference is entirely about what happens to the opening.

The opening decides the job

In new construction the rough opening is plumb, square and a standard size. In a house that has been settling on piers for eighty years it is none of those. A door hung into an uncorrected opening will drift, stick, or fail to latch no matter how good the door is.

So the first thing worth knowing is whether your opening is a standard size at all. Plenty around here are not, and that changes the options: either the opening gets adjusted to take a stock door, or a unit gets made to fit. Both are normal. Discovering it on installation day is not.

Slab or prehung

A slab is the door on its own, hung into your existing frame. A prehung comes already mounted in a new frame, and the whole assembly goes into the opening.

Slab makes sense when the existing frame is sound and square, and when you want to keep an original frame that suits the house. It is cheaper in material and it takes real skill to hang well — hinges mortised accurately, the strike set to where the door actually sits.

Prehung makes sense when the frame has rot, when the opening has moved, or when the weather sealing matters. It is the more reliable outcome in an older house because the door and frame arrive already square to each other, and only the fit into the opening has to be got right.

What is usually behind the frame

Removing an exterior door frame in an older house frequently reveals things nobody planned for. The most common are rot in the framing at the base of the opening — the same water that killed the jamb reached what is behind it — and the absence of any flashing at the head.

Both matter and both are cheap to put right while the opening is open. Neither can be done later without taking the new door back out. This is why we would rather look at an opening before quoting than price a door from a photograph.

The threshold is half the job

The bottom of an exterior door is where water, air and wear all concentrate, and it is the detail most often skimped.

An adjustable threshold lets the seal be tuned as the house moves, which in these houses it will. A sill pan under the threshold routes any water that does get in back out rather than into the floor framing. And the height of the threshold matters for anyone with mobility difficulty — a lower or ramped threshold is straightforward to specify at the time and expensive to change afterwards.

Material, briefly

• Steel — cheapest, secure, dents permanently, and the finish can chalk in strong sun.
• Fiberglass — handles this climate well, does not warp or rot, holds a finish, and can be made to look like wood convincingly. It is the sensible default for most exposed doors here.
• Wood — the best-looking option and the one that needs maintenance. On a door with real shelter over it, entirely reasonable. On an exposed south-facing entrance, it is a commitment.

Whatever you choose, glazing is where the heat goes. A door with a large single-glazed light undoes a good deal of what the rest of it is doing.

What to check before you order anything

1. Measure the existing frame, not the door — height, width, and the wall thickness the frame has to suit.
2. Check which way it should swing, and whether that still makes sense for how the room is used now.
3. Press the bottom of the jamb and the sill with a screwdriver. Soft means the scope is bigger than a door.
4. Look at what is above the opening — a gutter or roof edge dumping water there will kill a new door too.
5. Decide on the threshold height before ordering, not after.

Getting it fitted properly

Hanging a door properly means shimming the frame to plumb and square within what the opening allows, checking the header has not dropped, flashing the head, and setting the strike where the door actually sits. Done right, the door stays where you leave it and closes with the same sound every time.

Door and window installation covers the work, and exterior doors goes into the specifics. If the frame turns out to be the problem rather than the door, wood repairs is the page to look at.