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To convert part (about 3x8 meters) of the unused attic to a storage area, I want to tile the concrete subfloor with ceramic tiles.

The problem is that there are several corrugated flexible hose pipes laid on the bare concrete. Those conduits go either to my neighbours (20mm for TV cables) or are part of my electrical installation (25mm). Yes, those pipes are up to code in my location. It isn't up to code to lay the TV conduits through my attic, but those things are kind of grandfathered and I don't need a fight right now.

I now am searching for a way to lay those tiles without re-locating those conduits.

Update

I see that burying the conduits under some kind of flooring is way to go.

Goals:

  • Make it light. Ceramic tiles should be ok. Just not two tons of screed and the need of approval from an engineer...
  • Minimize height. Ideally 25mm, plus the height of the tiles.

The desired tiles are ceramic tiles.

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    Probably be best to use a raised floor system and cover the conduits. Lay 2x4, or 2x3s on floor and screw plywood on top to lay tiles. Notch 2x4s where they lay over conduits.
    – crip659
    Aug 12 at 9:49
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    pssstt... @crip659 - That's a good 'un, but answers down there...
    – FreeMan
    Aug 12 at 11:39
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    Without extra information, the OP might just want a simple floor covering that does not include building a higher floor. Budget and low ceiling might not work with a raised floor.
    – crip659
    Aug 12 at 12:28
  • @crip659 I like the idea of burying the conduits under something. Minimizing height is important for me. Also making it light, as I don't want to involve an structural engineer. What additional information do you need? Perhaps can you suggest a good, cheap material? Aug 12 at 12:38
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    Type of tiles is important. Stick on vinyl is big difference to ceramic compared to base they need. With the conduits you need space above them so screws/nails don't hit/enter them, laying 2x4 on side probably will not give enough for safety.
    – crip659
    Aug 12 at 12:51
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Your goals with your situation are almost impossible.

Ceramic tiles like to be on very solid floor, cement floor is good, a wood floor needs a minimum of 3/4 to 1 and 1/2 inch of wood(plywood) on 2x4s.

Code probably requires 1 1/2 spacing from edge of 2x4 or a metal plate for conduits.

Would either change type of tiles or think about moving conduits out of the way. For storage use, would lay tiles on cement floor and then use 2x4s to raise storage items above conduits. Imagine you can raise conduits enough to lay tiles underneath them.

Maybe someone else will be able to give a better answer.

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  • Would it be viable to lay two layers of green drywall on the floor, around the conduits and bury the conduits under cement? Aug 12 at 14:06
  • Not if stepping or putting any weight on it. Any drywall not solid enough for any flooring, even on cement. Think there is a 'cement board' that might work.
    – crip659
    Aug 12 at 14:30
  • Thank you. I am going to abbandon the ceramic tiles. I must admit it often takes an surprising amount of arguments to make me change plans. That sounds like a good idea. Aug 13 at 11:43
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You have a concrete floor in your attic? I'd guess that the whole house is built of concrete then. Even if it is, adding the not insubstantial amount of weight for a subfloor and tile could push you near the design load limit for your attic floor. Adding storage on top of that could push you over the limit. It might not, but why take the chance when there's a cheaper and lighter way of doing it.

Instead of tiling why not just create a raised subfloor of 2x4 (as suggested in another answer) in order to clear the conduit, then lay down tongue and groove (T&G) plywood flooring. Once this is screwed or nailed in place (with glue if you'd prefer to eliminate the possibility of squeaking), use the plywood itself as your storage surface.

You would, realistically, need to have at least one layer of this as a base for your tiles, possibly two, so why invest all that extra in a 2nd layer (plus the tiles, mastic & grout) for a fancy attic storage space, when a simple plywood floor will do the trick. If you want to spruce it up a bit, you could put down some inexpensive vinyl flooring, maybe even the self-stick vinyl floor tiles. The vinyl has the added bonus of making it easier to slide boxes around, too. TBH, though, I've got some simple plywood (OSB, actually) storage in my garage attic and sliding boxes on that isn't an issue at all.

If there are fireproofing requirements in your local building codes, I'm sure you can get some sort of subfloor material that's treated with a fireproof material that will meet your local code. Optionally, you could probably get some sort of fireproofing coating to paint/roll/spread on the plywood that would meet local code.

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  • Thank you. Unfortunately I can only accept one answer as correct. Aug 13 at 11:43
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Thinset/modified mortar plus concrete board plus thinset/mortar plus concrete board until you hit height. Cut around the wires/conduit. Fill in the conduit with thinset/mortar and tile on top.

Caveats...

  1. I am assuming conduits and wires there can be buried in concrete.
  2. I am assuming that your attic is load rated take all of that weight plus people standing up there.
  3. I am assuming you want no access to electrical running in your attic and you are OK with destroying parts of this floor to run new wires or troubleshoot.
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    Thank you. Unfortunately I can only accept one answer as correct. Aug 13 at 11:44

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