How to Replace a Shower Door Side Seal

Which vertical seal do you have?

Four different parts live on door verticals, and they do not interchange. A flap-style side seal suits an even gap under 3/16″. A bulb seal conforms to a gap that tapers — the out-of-plumb wall case. A magnetic pair latches the strike side and is always replaced as a set. An h-jamb bridges the slot between a door and an inline fixed panel. Photograph the old seal's cross-section before removal; the shape plus your glass thickness identifies the replacement.

Tools and supplies

• New seal, sized to glass thickness (1/4″–1/2″) — stock lengths of 76″, 95″ or 98″ cut down
• Tape measure; caliper if the glass class is uncertain
• Fine-tooth hacksaw or sharp shears (magnet strips want the saw)
• Plastic scraper and isopropyl alcohol for the glass edge
• Painter's tape to mark cut lines

Step by step

1. Measure the gap three times. Top, middle, bottom of the vertical opening. Even within 1/16 inch: a flap seal works. Tapering more than 1/8 inch: choose a bulb that matches the widest reading — and note the taper, because it usually means the door needs a hinge adjustment too.
2. Remove the old seal. Peel from a bottom corner, steadily. Brittle vinyl snaps — pull fragments with pliers rather than levering against the glass edge.
3. Clean the edge. Scrape residue with a plastic razor, wipe with isopropyl alcohol, and let it dry fully. Any film weakens the channel's grip.
4. Cut to height minus 1/16 inch. Measure the glass height, mark the seal with the channel facing up, and cut 1/16 inch short so the seal does not stack on the bottom sweep. Where the vertical crosses the sweep's fin, notch the last 1/8–1/4 inch instead of forcing an overlap.
5. Install dry, top to bottom. Hook the channel over the glass at the top and walk it on with your palm. No lubricant on verticals — gravity plus a slippery channel equals a seal on the curb by spring.
6. Magnetic pairs: check the click before trimming. Fit both halves, close the door, and confirm the strips meet flush along the full height and attract. If they repel, flip one half 180 degrees. Only then cut to height.
7. Test with a five-minute spray. Aim the shower at the vertical edge and watch from outside. Even compression along the full height is the pass mark; a seal tight at top and open at bottom means the door is out of plumb — fix that at the hinges, not with a fatter seal.

Mistakes to avoid

• Replacing one half of a magnetic pair — old and new strips misalign or repel.
• Cutting flush to the glass height so the vertical rides on the bottom sweep and lifts.
• Sealing the hinge side so tightly the door cannot swing; hinge-side seals must flex through the pivot arc.
• Ordering by gap alone: the channel is sized to glass thickness first, gap second.
• Running silicone caulk down a moving edge instead — see seal vs caulk for why that fails in days.

While you're there

Vertical seals rarely die alone. Check the bottom sweep with the squeeze test, confirm the door hangs square (hinge adjustment guide), and if the old vertical left tape residue, clear it properly before the new install — the residue removal guide covers razor and solvent technique that will not scratch the glass.