Shower Tray Installation: Low-Profile Trays, Waste Positions & Floor Reinforcement

Quick Answer: Most UK shower trays are 900×900mm or 1200×800mm acrylic or stone resin, installed on adjustable legs with 100mm minimum working space below for the waste connection. The shower waste outlet must connect to a P-trap with a minimum 38mm water seal. Low-profile trays (under 40mm rim height) require a recessed floor void or a riser kit. Always test the waste before enclosing the tray.

Summary

Shower tray installation seems straightforward but has several failure points that produce expensive callbacks. Most common: a waste connection that leaks slowly into the subfloor unnoticed for months; a tray installed without adequate support that flexes and cracks the silicone seal; and tiling completed over a tray that was never properly level. Each of these problems has a simple fix at installation stage — they become major works to remedy afterwards.

The UK shower tray market has split into two distinct segments: standard-height acrylic trays (typically 70–120mm rim height) that sit on adjustable feet and are easy to install and plumb, and ultra-low-profile stone resin trays (25–40mm high) that require a floor recess or riser panel system and more careful planning. The latter are increasingly popular for accessible and contemporary bathrooms but are unforgiving of inadequate floor preparation.

Key Facts

Quick Reference Table

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Tray Type Height Substrate Required Special Notes
Standard acrylic 70–120mm Any sound floor Adjustable legs; easy waste access
Stone resin (standard height) 80–100mm Solid floor preferred Heavy — 20–40kg; reinforced legs
Low-profile stone resin 25–40mm Recessed floor void Requires riser panels or floor recess
Wetroom former/tray 15–25mm Solid concrete or ply Built-in falls; tanking essential
Quadrant 700–900mm radius Any sound floor Curved front; matching quadrant enclosure
Waste Position Standard Term Notes
Centre Centre waste Most flexible for trap connection
Corner Off-centre Limited trap types; check clearance
Offset/off-centre Brand-specific Match to enclosure position
Linear/channel Edge waste Requires linear shower waste (40mm min)

Detailed Guidance

Subfloor Preparation

Concrete: Check is level (within 3mm). Fill depressions with floor levelling compound. Scrape off any high points. A flat floor is critical — a standard acrylic tray will flex to an uneven floor, but stone resin will not, and gaps will form under the tray edges that allow water ingress.

Suspended timber: The shower tray (particularly stone resin, 20–40kg) and the weight of an adult in it creates a point load that typical floor joist spans cannot support without deflection. Add noggins between joists directly below the tray perimeter, and install 18mm exterior-grade plywood as a deck, screwed at 150mm centres. Check for any signs of rot or woodworm in the joists before proceeding.

Tile backer board: For wet areas, lay a tile backer board (Hardiebacker, Wedi, Jackoboard) as the substrate for wall tiling around the tray. This is waterproof and dimensionally stable — unlike plasterboard, which rots.

Waste and Trap Selection

Before purchasing the tray, establish where the waste pipe will connect. The waste pipe must drop through the floor (to an underground drain or to a soil stack in a multi-storey building) or run along the floor void if there is one.

Low-profile tray challenge: A 40mm tray rim plus a P-trap (typically 50–75mm deep) gives less than 100mm working height below the tray — enough only if the waste pipe can connect immediately below. In many UK houses, the existing waste run is at a height that doesn't fit under a low-profile tray. Options: raise the floor using a waterproof riser platform; use a flat shower waste (no trap — anti-siphon device in the trap tube instead); or resite the waste outlet.

Trap types:

Waste connection: Connection to 40mm waste pipe using solvent-weld or push-fit fittings. Waste pipe run to soil stack or via a standpipe. Minimum fall 18mm per metre, maximum 90mm per metre (excessive fall creates negative pressure pulling water seal from trap).

Setting Out the Tray

  1. Establish the finished floor level at the tray position
  2. Offer up the tray and measure the height of the waste outlet above the floor — this determines the trap type and waste pipe routing
  3. Mark the wall faces for tray position. Allow clearance for the tray rim to sit tight to the wall (or overlap the wall if tiling the walls first)
  4. Assemble the adjustable feet and the waste assembly before positioning the tray in the room

Two Approaches: Tile Then Tray, or Tray Then Tile

Tile first: Tile the walls down to the floor, then install the tray against the tiles. The tray rim sits against the tiles. A silicone seal is applied at the tray-to-tile junction. This approach is used in high-quality refurbishments where the tray is changed frequently.

Tray first: Install the tray first, tile the walls down to the tray rim, and then silicone the junction. This approach is common in new-build. The tray rim must be perfectly level and the tiling must be accurate to the tray edge.

For a watertight installation either way, the key is: tanking membrane applied to the lower 200mm of wall before tiling, lapping onto the tray rim by 50mm. Then tile over the tanking. Then silicone at the tray-to-tile junction.

Installing the Tray

  1. Position the assembled tray (feet attached, waste connected) on the subfloor
  2. Check level in both directions — adjust feet individually. Most adjustable feet have a locking nut to prevent movement once set
  3. Allow at least 10mm clearance below the frame assembly for waste connection access. Do not place tray directly on concrete without feet
  4. Connect the waste pipe to the trap outlet. Test with 5 litres of water before tiling — watch for 5 minutes for any drips
  5. Once tested and passed, silicone the perimeter frame to the floor (stops splashback water from getting under the tray)
  6. Build up any bath panel or side cladding

Silicone Sealing

Apply neutral-cure silicone (not acetoxy/acid-cure — this attacks some tray finishes and some adhesives). Clean the joint thoroughly and apply silicone in a single smooth pass using a silicone gun. Smooth with a wet finger or silicone finishing tool. Do not apply silicone over existing silicone — remove all old silicone first.

Silicone at the tray-to-wall junction is a maintenance joint. Advise customers to check it annually and replace at the first sign of cracking or discolouration.

Frequently Asked Questions

Can I install a low-profile tray in an upstairs bathroom?

Yes, but it requires careful planning. The standard 40mm low-profile tray, combined with a 60mm flat trap, needs only about 100mm below the waste outlet — but that space must be there. In a first-floor bathroom, you typically have a 200mm-plus floor zone available. The challenge is getting the waste pipe to fall to the soil stack at the correct gradient without dropping so far that it runs out of the floor zone before reaching the stack. Draw a section through the floor before specifying the tray.

Do I need to tile before or after fitting the tray?

Either is acceptable if done correctly. Tiling first gives a better result aesthetically (no visible tray rim meeting unfinished wall), but means the tiling must be precisely positioned to the tray opening. Tiling second is easier to sequence but requires that the tray is installed perfectly level and the tray-to-tile junction is carefully sealed.

What causes shower trays to crack?

Stone resin trays crack when inadequately supported — typically when the tray spans an uneven or unsupported floor with just the perimeter feet taking the load. Cracks form across the base from stress concentration. Prevention: ensure the floor is level, add additional support under the centre of large trays, and never install without adequate subfloor preparation.

Regulations & Standards