substrate for tile over wooden joists

[jake452]

Hello:

I'm going to install tile on an outside partially raised wooden joist frame (basically a deck without the decking installed). The framing is plenty strong to support the weight and greatly exceeds L360. My question is with the spacing of the joists at 12" OC, what should I install as the substrate? Plywood, backerboard, both or something completely different? I don't want to skimp on the install, but since the framing is already overkill, I don't want to do more than is necessary.

[bbcamp]

Welcome, Jake!

Go to www.schluter.com and download their Ditra handbook. Look for the detail for outside balconies over un-occupied spaces. Follow that.

Now, is this overbuilt deck well supported lateraly, i.e. tied into a more rigid building or are the piers cross braced? Do the footings extend below frost line? The big killer of outdoor tile projects (above grade) is movement of the structure. Many decks are not built to the same structural requirements of a house, and they tend to fail.

[cx]

Welcome, Jake.

What Injineer Bob said.

Outside deck also hasta slope, too. Preferably away from the house.

Your framing do that?

My opinion; worth price charged.

[jake452]

Thanks guys for the replies. One end of the "deck" ties into the foundation of the house with a ledger, therefore there is no cross bracing. I live in southeast TX (near Houston), so we don't have a frost line to extend below, just clay soil, however the footings are between 3-4' deep, down below any fill dirt into undisturbed soil. The support beams lay directly on the piers, so there will be virtually no lateral movement (i.e. swaying of posts, etc.). There will [probably] be a metal roof covering this install, however I did slope the "deck" in the event that we go with an arbor overhead. I believe the slope is 1/8" per foot. I'll read over the ditra handbook and then ask whatever questions that may come up.