How do I make an access panel to get at the plumbing under a bath or shower?
Where an access hatch belongs, how to cut one into tiled or boarded boxing without wrecking it, and the removable fixings that keep it usable.
- Difficulty
- intermediate
- Time
- 1 hr 30 min
- Read
- 4 min
- Safety
- caution
Short answer
Put the hatch at the tap end, because that is where the tap tails, the isolating valves, the trap and the overflow all are. Find the pipes first, cut a rectangle between the studs or battens, line the opening with battens, and fix a panel over it with magnetic catches or domed screws — never silicone it in.
Do this first
A boxed-in bath with no access panel is a plumbing job waiting to become a demolition job. Every fitting under there — the tap backnuts, the isolating valves, the waste, the overflow hose, the trap — will need reaching at some point, and the whole of that cluster sits within about half a metre of the tap end. The drawing shows what is behind the panel and why the tap end is where the hatch belongs.
Safety
Before cutting into any boxing, find out what is behind it. Bath and shower boxing routinely contains hot and cold supply pipes, a waste, and sometimes a cable to a shaver socket or a fan. Use a detector and cut shallow with a hand tool first — a multi-tool blade at full depth through a supply pipe turns a small job into a flood.
What you'll need
- A pipe and cable detector
- A multi-tool or a padsaw
- Timber batten, roughly 38 x 38mm, for lining the opening
- A hatch panel or a ready-made access panel
- Magnetic catches, or domed-head screws and cup washers
- A tile bit and a diamond blade if the boxing is tiled
- Sanitary silicone for the top edge only
Step by step
- Decide where it goes before you decide how big.Stand at the bath and work out where the taps are, then look at the boxing directly below and in front of them. That is the zone. On a shower it is wherever the waste and trap sit, which is not always the obvious end — run the shower and listen, or look at the pipe run in the room below if you can.
- Find what is behind the boxing.Run a detector across the whole area in both directions. Mark the pipes, the cables and the framing timbers. If the detector is ambiguous, drill a single small exploratory hole with a hand drill and look through it with a torch and a mirror or a phone camera.
- Size the opening to the frame, not to your convenience.Cut between the vertical battens or studs rather than through them. A hatch of roughly 300mm square gets an arm and a torch in; 400mm gets both arms and a wrench. Cutting through a frame member means adding a new one, which is a longer job.
- Mark the opening squarely and cut carefully.On plain boarding, plunge-cut with a multi-tool set to a shallow depth for the first pass, then increase. On tiled boxing, drill the four corners through the tile with a tile bit first, then cut tile-to-tile along the grout lines with a diamond blade so the visible edge lands on a grout joint. Never cut the first pass at full depth.
- Line the opening with battens.Screw battens inside the opening, set back from the face by the thickness of your hatch panel, so the panel sits flush and has something to screw into on all four sides. Without a lining the panel edges have nothing to bear on and the whole thing rattles.
- Make the panel from the piece you cut out where possible.If the boxing is tiled and you cut on the grout lines, the removed piece drops back in and the joint reads as a grout line. Ease the edges slightly with a file so it goes in and out without catching.
- Fix it so it comes off again.Magnetic catches are the neatest and are invisible. Domed mirror screws in cup washers are the most secure and look deliberate. Turn-buttons work on plain boxing. What you must not use is adhesive, silicone all round, or a screw into an unlined edge that will strip after two openings.
- Seal only the top edge, if anything.If the hatch is low on the boxing and never gets wet, seal nothing. If it can catch splash, run a bead of sanitary silicone along the top edge only, so water is shed but the panel still lifts out. A hatch sealed on four sides is a hatch you have to cut out again.
- Ventilate the void.The space under a bath gets damp. Leave a gap at the bottom of the boxing or fit a discreet vent, so the void can dry. A sealed damp void grows mould and rots the framing.
- Label what is behind it, out of sight.Write on the back of the panel what is in there — 'bath trap, hot and cold isolators, overflow'. In five years you will not remember which hatch is which.
Tips
- Ready-made plastic access panels with a snap-in frame are cheap and fine on plain boarding in a cupboard or a low-visibility position. In a tiled bathroom they look exactly like what they are.
- If you are having a bathroom fitted, ask for access hatches in writing at the quoting stage. Retrofitting one costs far more than including it.
- A removable bath panel already is an access panel. If your bath has one, do not box the bath in — refit the panel properly instead.
Common mistakes
- Cutting first and detecting afterwards — Supply pipes and the waste run exactly where the hatch wants to be. A cut pipe behind sealed boxing is the worst possible place to have one.
- Making the hatch too small — A hand-sized hatch lets you see the problem and not reach it. Size it for a forearm and a tool, not for tidiness.
- Siliconing the panel in place — It is then not an access panel, and the next person cuts a new hole somewhere worse.
- Cutting through a stud or batten to get a neat rectangle — The boxing loses its support and the surrounding tiles start cracking at the grout lines within months.