Flooring Tile - Drilling into backerboard...

Hi everyone,

I'm about to start putting down backerboard for my first tiling project and was wondering how concerned I should be about what runs under the subfloor (plumbing, electrical, etc...). I wasn't able to take the subfloor up to look under it because it's in a small bathroom and the sheets of wood run under the walls. This is on the third floor of our townhouse.

I'm pretty sure the 1 5/8" backerboard screws will run through the backerboard and subfloor and I'm worried that maybe there's a drainpipe, sprinkler pipe, or electrical wire under there.

Is this something that is generally a cause for concern when screwing down backerboard?

Thanks,
Bill

How thick is your subfloor?

You are going to lay the backerboard into a fresh bed of thinset AND screw it down, correct?

You always should be aware of what maybe below or in a wall cavity when you are screwing or nailing.

I think the subfloor is 1/2". It's hard to tell without taking it up which I'm not sure I can do since it runs under the walls into the adjoining rooms.

Yes, I plan to lay thinset and then screw the backerboard down into the subfloor.

I hope it's not just 1/2". Do you have any floor vents that you can remove the cover off of to see the thickness?

If you have none, I would drill a small hole and measure it that way.

Your subfloor needs to be at least 5/8" thick for a ceramic/porcelain installation. Even thicker if you want natural stone.

I'll take your suggestion and drill a small hole to measure. If it turns out that it is in fact only 1/2", what are my options? Can I lay some 1/4" material down, then mortar, then backerboard?

Good news I think; the hole drilled in the subfloor shows it to be 3/4" subfloor.

So that, coupled with 1/4" backerboard will give a 1" thick floor (plus whatever space the mortar takes up).

After looking again, the backerboard screws are 1 1/4" screws.

Should this extra 1/4" cause me to worry about not knowing exactly whats under the subfloor?

It will be fine. That extra 1/4" of screw will not puncture anything. Almost all plumbing and electrical is center within the joists for this purpose.

Great! Thanks for the advice! I'll be sure to post a picture when it's finished.