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Question DetailsAsked on 8/20/2016

I have a 7' x 12' outer patio, , I want to add 3" to the top so i can have a floor toh same height as the slab flol

The patio has ceramic tile on it. I've enclosed the patio, so I want to have both floors the same height to re-tile or carpet as one big room

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Assuming the enclosure is totally waterproof (fully enclosed as a room) and adequately above surrounding ground level and maximum runoff water elevation (say 4-6 inches minimum), if a raised patio or porch I would put down a wood grid (treated wood preferqably, especially if any chance of moisture), make sure the joist space is open to the house joist space with vent holes, insulate that joist space with unfaced batt insulation, put 3/4" subfloor over it to put new flooring on. In that environment, unless the porch is real hefty built, I would not count on a new tile not potentially cracking a fair amount - so carpet or floating vinyl laminate flooring would be my recommendation.

You need to be careful about vapor transmission issues - I would use unfaced fiberglass insulation because the underlying tile (unless you remove it) will act as a vapor barrier to some extent - which is why you need to be sure you have ventilation communication with the house joist space to dissipate moisture coming through from the "room". A small air gap under the subfloor might be a good idea too - say 1/2" - to allow for moisutre dissipation from that space. And put good rim joist insulation inside the perimeter 2x material on the new elevated subfloor.

You will have to figure the new joist thickness needed to match up with the existing "indoor" flooring - if 3" is what it will take to match up to existing flooring then taking away 3/4" for the subfloor and maybe 1/8-1/4" for the padding under the joists, that means the new "joists" would be about 2" thick if you =leave the existing tile (and assuming that surface is flat and level enough for you) - not really thick enough to make the new subfloor heavy enough to not bounce, so I would drill through the tile with a carbide bit and put in deck screws to hold it tight down to the existing subfloor under the tile.

To avoid drumming, in addition to the insulation I would personally put padding under (and only under) the new subfloor joists - foam carpet padding works well, just make sure it is not real thick so you don't get a lot of settlement as it compresses. Sticky backed foam or nail-on felt strips also works to keep the joists from bouncing and thumping on the tile.

One other thought - depending on how you enclosed the porch, if there is any chance it will get wet (iffy roofing, not 100" water tight siding, etc) I would make sure the tile surface does not slope towards the house, and personally I would put a very slight slope (probably 1/2-1" drop over its run front to back) just in case, so any wetness does not run into the interior room.


Variation possibility - when you say "patio", if you mean a concrete slab-on-grade with tile on it, not dramatically raised above the ground level, then that is a "damp" environment - so I would not recommend putting a wood structure on top of it, especially if ever prone to flooding. In that case, I would chip off the tile and put on a concrete overlay - though bringing it all the way up to the interior room height would NOT be recommended because of the risk of exterior water coming into the interior room - normally one would leave a drainage and expansion gap between the existing foundation and the patio, and normally a 1/2-1" step-down to the patio, with appropriate sill or transition strip.

If you are positive the "patio" will never get wet, then if it is currently tile on slab-on-grade, you would want to put a 6-8 mil vapor barrier over the new elevated concrete layer (3" topping course) before putting down floating or carpeted flooring on it, unless tiling it. 3" is OK but on the minimal side for a topping lift on tile - so at a minimum it should have anchors put into the tile to bond it, or the tile removed before the topping lift is put on (the most professional solution) - though that will add maybe $100-300 to the job - not a major percentage.

One other thought - because this "patio room" is not part of the original house foundation system (presumably), you can expect it to eventually settle a bit, almost always away from the house - so runnning the flooring directly across from interior room to patio room is almost certainly going to have a problem in the future at the interface. I would treat it as two rooms even if continuous open space - put a transition strip at the interface to accomodate any future change of slope or minor dropping of the patio room.

Also, if the patio room is not on a permanent foundation like the house, you do not want to tie these together in any way (other than by a transition strip) because you CAN expect differential movement - plus against code in almost all areas. The best bet is to keep them separate to the maximum extent possible, with just a transition strip between them which can tilt a bit to accomodate some settlement, and thereby also avoid any structural damage when the patio moves.

One last thought - if you enclosedthis without a building permit, I would guess you are in for a rude surprise come house sale time - if that is the case, I would talk to the building department (or an Architect is you want a pro to do that for you) about getting an after-the-fact building permit and inspection approvals. Generally required for any closing-in that makes it a "room", especially if any utiilities like electricity were run into it. Commonly screened-in enclosures are exempted as long as structural members are not involved.

Answered 3 years ago by LCD

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