How do you install pocket door split jambs?

Fasten one split jamb to each side of the pocket opening so the door slides between them with an even gap. A stepped gauge block hooked on the frame sets each jamb at the same distance, top, middle and bottom. Glue and pin the jamb tight to the block.

How much gap should a pocket door have at the split jamb?

About 1/8 in (3 mm) per side is a common starting point. Make it the same on both sides and full height, and allow a little more for thick, painted, or heavily hardware-fitted doors.

Why does my pocket door rub on the jamb?

Usually the split jamb isn't parallel to the door, or the frame or door is out of plumb. Check the gap at the top, middle and bottom. If the frame is plumb, reset the jamb to an even gap with a gauge block.

Cutting, Not HackingGuides, Gauges & TemplatesPocket door jamb gauge

How do you set pocket-door split jambs with an even gap, without shimming by eye?

The pocket door slides fine. Then you put the split jambs on, and the gap is a fat 3/16 in at the top on one side and nothing at the bottom on the other. The door kisses the jamb every time it goes in. The usual fix is shims and glue, fiddled with by eye until it sets. The Active Carpenter's caption says it plainly: that's just not for him. He uses a gauge block instead.

⚡ Rule of thumb

Glue two strips of scrap together with an offset to make a stepped gauge block. Hook the block on the pocket-door frame, push each split jamb against the step, and fasten it there at several heights. Every jamb lands the same distance from the frame, so the gap stays even top to bottom.

Starting point

Step = the gap you want each side · 1/8 in (3 mm) per side is a common pocket-door starting point

Measured

Gap between the jamb face and the door slab, each side of the pocket opening

Confidence

Creator technique

▶ Source video — Wet setting just isn't for me — The Active Carpenterwatch on Facebook ↗

Applies to

Process: Finish carpentry: pocket-door split jambs and trim
Materials: Wood split jambs over a pocket-door frame; scrap softwood for the block
Setup: Gauge block, wood glue, brad or pin nailer (or screws)
Orientation: Block registers on the frame; jamb pushed against the block's step
Assumes: The pocket-door frame itself is hung plumb

Why it matters

Split jambs have to sit the same distance from the door, top to bottom, on both sides. Get it wrong and the door rubs on one side and shows a crooked gap on the other, right at eye level in a hallway.

Shimming spot by spot means every shim is a fresh guess. Five shims per side, five slightly different gaps.

A gauge block can't guess. It's the same offset at the top, the middle and the bottom, because it's the same block.

What good looks like

An even, parallel gap between door and jamb on both sides, full height
The door slides all the way in and out without touching
The jamb face sits flush and straight to the wall edge

How to apply it

Glue two strips of scrap together, offset by the gap you want. That offset is the step.
Hook the block on the pocket-door frame where the jamb goes.
Push the jamb tight against the block's step, glue it, and pin it.
Move the block and repeat at the middle and the bottom, then do the other side.
Slide the door through and check the gap at the top, middle and bottom before you case or fill the edge to the drywall.

Test it on your setup

Gap check: slide the door to the middle of the opening and sight down both gaps top to bottom. They should look identical.
Rub check: run the door all the way into the pocket and back. Listen and feel for any contact.
Before you fasten anything, hold the block on the frame and test the step against the door itself. If the gap looks too tight or too loose, make a new block. It's scrap.

Exceptions & tradeoffs

A gauge copies the frame. If the frame's out of plumb, every jamb follows it faithfully. Check the frame before you trust the block.

If the drywall edge wanders, a gauge-set jamb can end up proud of the wall in one spot and shy in another. A scribed filler or the casing covers it.

Mind you, the right gap depends on your door and hardware. Thicker doors, painted doors and doors with pulls on the edge may want a little more room than 1/8 in (3 mm).

Common mistakes

Setting the jambs tight to the door because a tight gap looks crispKeep the gauge's clearance so the door can slide
Setting the jamb to the block at one height and eyeballing the restSet it to the block at the top, middle and bottom
Making the step by eyeMeasure the offset when you glue the block up; every jamb copies it

Frequently asked questions

How do you install pocket door split jambs?Fasten one split jamb to each side of the pocket opening so the door slides between them with an even gap. A stepped gauge block hooked on the frame sets each jamb at the same distance, top, middle and bottom. Glue and pin the jamb tight to the block.
How much gap should a pocket door have at the split jamb?About 1/8 in (3 mm) per side is a common starting point. Make it the same on both sides and full height, and allow a little more for thick, painted, or heavily hardware-fitted doors.
Why does my pocket door rub on the jamb?Usually the split jamb isn't parallel to the door, or the frame or door is out of plumb. Check the gap at the top, middle and bottom. If the frame is plumb, reset the jamb to an even gap with a gauge block.

The Active CarpenterSource & visual reference

A stepped gauge block labelled "Pocket door shimming" (0:00), held on the frame under the jamb (0:14), and the finished even gaps either side of the door (0:18) — Wet setting just isn't for me… But I prefer this method… so here it is. ↗ at 0:00–0:28.

Summarized and independently edited by Start Here from The Active Carpenter's 29-second reel, frames and caption only, no audio. The stepped block, its "Pocket door shimming" label and the finished even gaps are on screen. What the block registers against, and that it sets the jamb-to-door gap rather than the jamb-to-wall line, I read off still frames; so is my reading of "wet setting" as shims and glue adjusted while it cures. The 1/8 in gap, the plumb-frame caution and the checks are mine; he never gives a dimension.