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Old 03-15-2012, 11:28 AM   #16
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Is this enough subflooring support?


Under the kitchen flooring , the joists are split by a sistered beam at 4' from the outside wall that carries the majority of cabinets and plumbing
The joist continue for another 6 feet where they are then supported by another sistered beam

Still can not find a place to measur the subfloor. Does being 1/2" thick make that much difference when compared to 3/4" thickness?

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Old 03-15-2012, 11:44 AM   #17
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Is this enough subflooring support?


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Originally Posted by TinaB View Post
Under the kitchen flooring , the joists are split by a sistered beam at 4' from the outside wall that carries the majority of cabinets and plumbing
The joist continue for another 6 feet where they are then supported by another sistered beam

Still can not find a place to measur the subfloor. Does being 1/2" thick make that much difference when compared to 3/4" thickness?
Yes, it makes a very big difference.

What is the length of your joists from vertical support to vertical support? What I understand to be a "sistered beam" is a piece of wood attached along side of another piece to add structural strength due to weakness of the original. That is not the same as a vertical support - a wall, a metal pole, etc.

For example, in my basement, I have 12x2 joists, 16 inches on center, that are 15 feet from outside wall to support wall in the middle of the basement. In one area, there is a 4x4 that is perpendicular to the joists with a metal pole under it to strengthen the joists in that area. In another area, some moron cut the center out of the joist and just left it hanging there without any support. In that place, I need to jack up the joists and attach sister beams on both sides so that the sagging won't get worse. So - the 4x4 creates a shorter span in that section of the basement - 10 feet instead of the 15 elsewhere. But when I sister in the beams around the joist that was cut, it will still be a 15 foot span. Does that make sense?

You may be calling a sistered beam something other than what I call a sistered beam, so that's the place to start, so we're all talking apples and apples. A photo may help as well.

The horizontal length of your joists between supports from the floor to the ceiling is necessary information to figure out the load your floor can support without flex.

As for the subfloor, look for a place where pipes run through the floor. Drain, water, gas, whatever. Shine your flashlight into the space around the pipe and you should be able to see the thickness of the subfloor.
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Old 03-15-2012, 11:57 AM   #18
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Is this enough subflooring support?


Quote:
Originally Posted by TinaB
Under the kitchen flooring , the joists are split by a sistered beam at 4' from the outside wall that carries the majority of cabinets and plumbing
The joist continue for another 6 feet where they are then supported by another sistered beam.
If you can upload a wide angle photo this will solve some questions about how it's sistered.


Quote:
Originally Posted by TinaB
Still can not find a place to measur the subfloor. Does being 1/2" thick make that much difference when compared to 3/4" thickness?
Yes it does make a big difference, need to make shore what size it is look for gaps along the walls
See if you can get a measurement in there.
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Old 03-15-2012, 12:44 PM   #19
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Is this enough subflooring support?


The same morons that visited your house were here as well. They used carpenter's glue to 'seal' all the places where PVC and wiring go up from the crawl space.
But i did find a bent corner in one of the floor vents and dropped a small tape measure thru and it caught on the bottom of the subfloor opening. Looks like I have 3/4" thick subflooring.
Sistering joists have the flat side of joist planks glued and screwed together

This is a two story structure with our kitchen on the lower level with crawl space of about 4' underneath, more shallow as you go to the center of the house. The ceilings are 9'.
When i tiled the Laundry Room with ceramic tile, my husband went underneath and added planks between the joists and that was like 10 years ago and it was a 12 x 12 ceramic tile.
Could something like this work with 3/8" granite? Largest area this would cover at a single run would be 8' by 10'.
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Old 03-15-2012, 01:06 PM   #20
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Is this enough subflooring support?


Ok, then sistered joists have nothing to do with the span of the joists. Do the joists run the 10 foot direction of the room or the 9 foot? And what is the support at the ends of that distance?

The joists are the key thing right now, not just the sub floor, since they are what carry the ultimate load.

According to the deflectolator and the dimensions you gave earlier - if the joists are ten feet:
Quote:
Thank you for using the John Bridge Forums Deflect-O-Lator :-)

For joists that are SYP or Douglas Fir, in good condition, 7 inches tall, 1.5 inches wide, 16 inches on center, and 10 feet long between supports, the deflection calculated is 0.273 inches.

This translates to a deflection of L / 440.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile, Congratulations!
If the joists are eight feet:
Quote:
For joists that are SYP or Douglas Fir, in good condition, 7 inches tall, 1.5 inches wide, 16 inches on center, and 8 feet long between supports, the deflection calculated is 0.127 inches.

This translates to a deflection of L / 754.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile or Natural stone, Congratulations!
The key here is also "in good condition" and no one here can gauge the condition of the joists without pictures at least, but even then, being there is very different than looking at pictures. The other question is WHY were the beams sistered? Rot? Damage? Cutting chunks out to run wires or pipes?

No matter what though, that hardwood needs to come out. Then you add plywood over the existing subfloor (if it's plank) or if it's 3/4 inch plywood already, you can put the cement board down to that and then the tiles on top of it. All dependent on the joists of course.

And as I mentioned before, many people will be happy to pull out a hardwood floor for you if you let them keep the wood. So the floor will be gone, and you save yourself the time and labor.
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Last edited by mnp13; 03-15-2012 at 01:11 PM.
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Old 03-15-2012, 04:05 PM   #21
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Is this enough subflooring support?


Michelle,
Will have to allow a bit of time for setting up some lighting for any pic's to take. When you have a flashlight looking at only one thing at a time, you forget how really dark it is.
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Old 03-15-2012, 08:27 PM   #22
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Is this enough subflooring support?


Mnp13--thanks for running a deflection ----I've been busy---
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Old 03-15-2012, 08:47 PM   #23
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Is this enough subflooring support?


I love that calculator thing! lol
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Old 03-16-2012, 10:04 AM   #24
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Is this enough subflooring support?


But back in the 'old' days i just worked with steel beams. Deflection is not the problem with this installer...I just want to protect the floor and add granite so it does not break or crack. Wood beams, and sistered wood beams are not a part of my background.
Michelle, a lot of my research says have a grout spacing with granite no bigger than 1/8" others say 3/8", what's the going grout size preferred?
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Old 03-16-2012, 10:43 AM   #25
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Is this enough subflooring support?


I hate grout. HATE it. With a passion that I can't describe. HATE HATE HATE. Despise it. White tile + white sanded grout + 1/4 inch grout lines = giant dirty stripes across a big open white kitchen. HATE!

Ok, now that that's out...

I do the smallest grout lines possible that will look good. And since "look good" is subjective, I use the little teeny tiny spacers. I did black grout in my bathroom. White tile + black grout = black mess everywhere. But less hate because the lines are black so don't look dirty like that horrendous white sanded grout did. But I wasted a looooong time fighting with that black grout before I called an actual expert who told me the trick for cleaning it up. Ugh.

Quote:
Deflection is not the problem with this installer...
Deflection is a problem with every install. You need to start with a sub structure strong enough for your intended use or it will fail. Maybe not immediately, but eventually it will start shifting and your tiles will start coming loose or cracking. It's not like your room is suddenly going to fall into the basement or anything so dramatic, but it will still be a major pain.

Quote:
I just want to protect the floor and add granite so it does not break or crack.
If it were me, and I'm not an expert nor do I play one on TV, I would have someone tear out the hardwood, then put in plywood over the subfloor, then level, then hardibacker, then install tile. Floor height transitions are not a big deal, and doing the floor incorrectly to minimize a height transition is just going to lead to you having to re-do the floor anyway.

In the interim, you need to make your floor rock solid, and to start that, you make sure that you have enough support under your joists to take care of the weight of the floor. Adding a support half way across your span may be an option, I don't know. Did you ever tell us how long the span is?

Frankly, I'm worried about the sistering because what was the reason for doing it? There is always a reason, and if it was rot or insect damage, I would take a very very close look at the joists next to the sistered joists to see if they were weakened by the same issue.
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Old 03-16-2012, 11:41 AM   #26
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Is this enough subflooring support?


In my opinion the hold grain deflection & span table is really for the engineers who built the homes decide what size ply to use and in what direction they should go. So now when you replace a subfloor if it's 3/4" osb you replace it with the same size but the typ of plywood they have now far exceeds the wait limit.

I can understand the hate for grout but there are requirements you need to meet when placing the tiles down usually the grout bag will tell you for what size grout lines needed to work and if it's not in that rang it won't hold.
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Old 03-16-2012, 07:04 PM   #27
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Granite is most frequently set using 1/8" grout lines----

Flat floor is needed---the reflective surfaces will make a sloppy,uneven setting job bring tears to the eyes of the owner---(that's you) no tears is good---check for flat--level and fill if needed.
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Old 03-16-2012, 08:46 PM   #28
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Is this enough subflooring support?


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I can understand the hate for grout but there are requirements you need to meet when placing the tiles down usually the grout bag will tell you for what size grout lines needed to work and if it's not in that rang it won't hold.
Why would narrow grout hold for some tiles and not others?

The first floor I did was 12 inch tiles, so I did 1/4 inch sanded grout lines - just like I was told on the bag. That was the floor from hell. My next 12 inch tile job I installed with 1/8 inch non-sanded. Much nicer, easier, better looking and didn't pick up every speck of dirt on the planet.
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Old 03-16-2012, 09:03 PM   #29
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Is this enough subflooring support?


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Why would narrow grout hold for some tiles and not others?

The first floor I did was 12 inch tiles, so I did 1/4 inch sanded grout lines - just like I was told on the bag. That was the floor from hell. My next 12 inch tile job I installed with 1/8 inch non-sanded. Much nicer, easier, better looking and didn't pick up every speck of dirt on the planet.
Yes unsanded is much nicer to work with "BUT"
You need sanded grout for any tile bigger then 4" and floors, did you know this or no?
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Old 03-16-2012, 09:17 PM   #30
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Is this enough subflooring support?


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You need sanded grout for any tile bigger then 4" and floors
Where did you learn that? The size of the tiles, nor whether floor, wall, counter or ceiling is relevant, just the width of the grout joint and sometimes the type of tile. Did you know this or no?

Also, whether sanded or unsanded is easier to work with is debatable.

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