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Unread 03-18-2004, 02:20 PM   #1
I2NdHelp
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Question Porcilan w/ Morter bed over RFH tubes

Long time listener, first time caller . . .
Please check the integrity of my plans!
I’m preparing to lay 18” x 18” porcelain tile over 1” mortar bed with ½” Radiant Floor Heating (RFH) tubes embedded. The joists span is 15’ long, 1-1/2” x 9 (2x10’s ??). The subfloor is composed of 1 x 6 boards diagonally spaced, then ½” plywood. Am I on track for a successful job?
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Gregg
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Unread 03-18-2004, 06:39 PM   #2
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The TCA states 3/4" min over top of tubes.
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Unread 03-18-2004, 06:44 PM   #3
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Is there any way you can cut that 15' span down some?? your numbers for deflection are somewhere between L/240 and L/320
depending on type and condition of joists.Putting a beam across an area to bring that span down to say 11 pr 12 feet would be a good move.Cutting it in half would be even better
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Unread 03-19-2004, 01:34 PM   #4
I2NdHelp
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Thank you both for the info . . .

Todd,
I do have basement access to add a beam; however, I'm concerned about lost head room. What size beam would make a difference under the run of my 23' span?

In addition, are there any resources to help me 'map-out' zones for my RFH tubes?

Gregg
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Unread 03-20-2004, 06:37 AM   #5
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Gregg,

I have radiant in the house my wife and I are building. You might want to check this site out Radiant Panel Accociations

Hope this helps

-Peter D
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Unread 03-20-2004, 08:09 AM   #6
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Welcome, Gregg.

Sounds like you're a perfect candidate for one of our closet-near-the-basement-wall floor stiffening fixes. By building a full wall (with openings, of course) you get some extra storage space, reduce the span of the floor joists above by a couple feet, and don't have a beam to duck under in the basement.

The beam across the center give you the most effect, as Todd points out, but you will have at least a couple 2x10s running across there to duck under that way, and posts spaced about 6 feet apart (we'll let Injineer Bob tell you exactly what you need there).

I think we're all assuming your joists are spaced at 16 inch centers, here. Tell us if that's not the case.

Then we can get your mud bed up to snuff, as Eric has suggested.
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Unread 03-20-2004, 08:34 AM   #7
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I am still a bit concerned about that large format tile with a closet shortening the span.center run is still the best option. that large format tile really needs to have a floor near specs for stone and thats twice as stiff as for tile.If you havent purchased the Tile yet 12 x 12's may be a better option given your situation.and even then you will need to cut that span down.
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Unread 03-20-2004, 08:36 PM   #8
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Hi Gregg,

I don't think you're planning enough mud, either. A one-inch bed will leave you with about 3/8 in. over the tops of the tubes. Not much mass there. Where is the lath going to go? Under the tubes or over?

I'm not real proud of your floor structure either. Let CX or Todd help you shorten it up.
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Unread 03-21-2004, 01:10 PM   #9
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Thank you Peter, CX, Todd and John,

Here’s the Facts:
1. My joists are 16” OC.
2. The total ‘accessible’ area under the run in the basement is 26’ at half the 15’ joist span.
3. I’m going to “beef-up” the mud to 1-1/4” over the tubes, (or use 3/8” tubes with 1” mud).
4. The lath will be under the tubes.
5. We have purchased the 18”x18” tiles already.

So, my next questions are directed at the new beam. I would like to minimize the beams used; therefore, I would like to spread the distance between posts to 13’. Can I place four 2x10’s spaced the entire 26’ run over three posts for enough support? (See attached new beam diagram file) Or should I nail three 2x10’s together per beam span? Help me out Injineer Bob!!
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Unread 03-21-2004, 04:31 PM   #10
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I'll bump you up, Greg. I don't have any span tables here, but CX does if Bob doesn't come back around.
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Unread 03-25-2004, 12:36 PM   #11
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Hello,
While I'm waiting for an engineering analysis, has anyone had experience with “Ultra-Fin”? It is PEX radiant floor heat tubes placed throughout the under floor joist spaces, where heat from the tubing is conducted to attached aluminum fins. The fins transfer the heat by convection through the joist spaces.
I’m considering it instead of embedding the tubes in a mortar bed. Four reasons: First, Ultra-Fin advertises their boiler water temperature can be set lower due to convection; hence, you need less BTUs to generate comfortable heat. Second, because water temperature in the tubes is lower, you’re less likely to get cracked tiles from close contact to hot tubes. Third, less PEX tubing is used, because the tubes are inserted lengthwise perpendicularly through the joists with 30” loop spacing (16 OC joists). By the way, that appears to be the only downside to this method . . . drilling ½” holes through the joists every 30” under heated floor space. Fourth, this method allows you to heat under any floor surface. So, like in my case, I can heat an entire floor level with both tile and hardwood flooring mixed throughout.

Please respond if you either have knowledge on this subject or you have used this method under tiles. I’ve got to make my decision in the next few days.

Thank you in advance . . .
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Unread 03-26-2004, 08:35 AM   #12
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Gregg,

Check out this thread regarding ultra fin over on the Radiant Panel website:

http://www.rpa-info.com/forums/Forum24/HTML/000638.html

Another thing to consider is a product called warmboard (www.warmboard.com). Kind of pricy, but it might eliminate the need for the mudbed. It is basically thick plywood with grooves in it that is stamped with sheet aluminum. The tubing snaps into the grooves, then you would put CBU over the assemblage for your tile.

If you want to spend less but do more work, you could build a sandwich on you subfloor. Use plywood sleepers, into which you would place extruded aluminum plates, into which the tubing snaps. Like warmboard, CBU & tile complete the job.
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Unread 03-26-2004, 09:31 AM   #13
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Gregg,

When I looked at warmboard I couldn't beleive the price, $160 for a 4'x8' sheet. It would have cost close to $11,000 dollars. Instead I caclulated that the extra sill plate, floor joist bump up, and gypcrete probabliy cost somewhere in the $6000-$7000 range.

Another problem with the warmboard install is you are pretty much locked into the predesigned tube layout.

I contracted for the gypcrete install myself so I did not have to pay for the HVAC contractors markup.

-Peter
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Unread 03-26-2004, 01:14 PM   #14
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Sorry I'm late for the party!

If you want 13 feet between the posts, your beams will need to have 5 2x10s spiked together, or 3 2x12s.

If you could live with 10 feet between posts, then 2 2x10s with a 3/4" thick by 9.25" wide strip of plywood sandwiched in between would work.

Bob
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Unread 03-26-2004, 01:50 PM   #15
I2NdHelp
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Wow . . . just 5 little beams . . . Thank you Bob (I think?)
CX’s ‘closet in the basement’ fix is starting to look good all-of-a-sudden!!!!!
I’m sorry Bob . . . Now, if I go with the conventional 6 feet between posts, what beam would I need?
Thanks again!
Gregg

PS:
Thank you Brewbeer, that was a good link.
I still would like to hear first-hand experience with any ‘Ultra-Fin’ users??
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