Tile over tray or screed for hobless shower on timber joists?

threemore

Hi all,

I’m planning a bathroom renovation in my 1983 home and I’m hoping to achieve a fully hobless shower and a flush transition from the hallway into the bathroom. I’ll be doing most of the work myself and bringing in a licensed electrician, plumber and tiler where required.

The bathroom has already been stripped back to studs and joists. My plan is to install 19 mm Secura flooring, a tile‑over shower base (still deciding which one), and a Hotwire under‑tile heating system. The shower will be 900 × 1200 mm, fully enclosed, with the shower rose and door on the 900 mm sides.

I have 36 mm available from the top of the joists to finish level with the hallway floor.

Proposed floor build-up

• Secura floor – 19 mm
• Waterproof membrane – ~2 mm
• Hotwire heating + self levelling encapsulation – ~4 mm
• Tile adhesive – ~5 mm
• Tiles – ~9 mm

This totals roughly 39 mm, so I may need to plane the joists by about 3 mm to achieve a flush finish. Joists are 95mm x 45mm hardwood.

Questions

1. Are there any major issues with removing around 3 mm from the joists? I’ll need to plane them slightly anyway to level the subfloor.
2. What tile‑over shower base would you recommend for this type of installation?
3. If a tile‑over base isn’t recommended, what would be the best way to achieve a hobless shower on a timber floor?

Thanks in advance for any advice.

MitchellMc

Welcome to the Bunnings Workshop community @threemore. It's terrific to have you join us and many thanks for you question on bathroom renovations.

It sounds like you've put a lot of thought into the build-up and are approaching the project the right way by planning everything out before you start.

In regard to the joists, removing around 3mm is typically not an issue, particularly if you're already planning to plane them to achieve a level subfloor. Given your joists are 95 x 45mm hardwood, taking a small amount off the top to fine-tune the floor height shouldn't cause any concerns.

For the shower area, I'd strongly recommend using a purpose-made tile-over tray rather than trying to form the falls solely with screed on a timber-framed floor. A couple of good options are the https://www.bunnings.com.au/wet-area-solutions-900-x-1200mm-rear-channel-patterned-tile-over-tray-system_p0177610 or the https://www.bunnings.com.au/wet-area-solutions-900-x-1200mm-rear-channel-tile-in-tile-over-tray-system_p0177607 .

The main advantage of a tray is that it removes a lot of the guesswork from creating the correct falls. With a hobless shower, achieving adequate fall to the drain is absolutely important. Any flat spots or insufficient fall can lead to water escaping the shower area or pooling on the floor. A pre-formed tray provides consistent falls from the outset and helps ensure compliance with waterproofing requirements.

You should also be aware that the joists beneath the shower area will likely need to be recessed further to accommodate the tray and maintain your desired flush floor level. The exact amount will depend on the tray you select and your final floor build-up, but it's common practice in timber-framed installations to create a recessed shower zone to achieve a truly hobless result. You might need to add additional timbers here to accomodate.

The other benefit of using a tray is that it works very well with your planned floor heating system. The remainder of the bathroom floor can be levelled and heated as normal, while the shower tray provides the required falls independently.

Overall, I think your proposed approach is sound. I'd lean towards the tile-over tray system rather than a screeded shower base on timber joists, as it will make achieving a reliable, fully hobless installation much more straightforward.

Let me tag @Nailbag, @PoodlesRule, @anthonyu and @handyman1010, to see if they have any thoughts.

Please keep us updated as the project progresses, and don't hesitate to ask if you'd like help refining the floor build-up once you've settled on a specific tray system.

Mitchell