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Need help deciding on best way to lay subfloor over 20 oc joists.

Need help deciding on best way to lay subfloor over 20 oc joists.

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  #1  
Old 11-03-10, 10:34 AM
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Need help deciding on best way to lay subfloor over 20 oc joists.

I have a rather large open area on the main floor of my house. I will be putting porcelain tiles in this entire area. What I have done so far is ripped up the old tile and the old oak hard wood floor that the tile was laid over top of. (go figure the grout popped within a year of it being laid by previous owner). This house was built in the 60's and they put 2x10 20" oc joists my longest run is 11 feet. Over top of the joists they layed a subfloor of 1x4s spaced about a quarter inch apart. The sub floor is in good shape and it runs perpendicular to the joists.

My plans is to lay 3/4" t&g over this sub floor then ditra and then tile.

So my question is how to go about laying the subfloor? because it is 20 inch on centre the 4x8 sheets are not going to join up on top of a joist like they would with 16" oc joists. If i start cutting the t&g to 40 inch sheets then I lose the advantage of t&g. So do I start on a joist and from there just join em where they end up even though they will join in between joists?
 
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  #2  
Old 11-03-10, 02:23 PM
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For this layer, you don't want the screws going into the joists anyway, so you just lay it as you would normally, just disregard the joist spacing.
 
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Old 11-03-10, 08:56 PM
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The spacing should be 19.2" not 20". The subfloor is the 1x4's not the plywood you're installing, that is the underlayment.

As Chandler mentioned you should fasten the new ply to the 1x4's only, so no prob. Use 1 1/2" flooring screws NOT cheapo drywall screws. Be sure to leave the recommended gap between sheets. You didn't have to buy T&G for this installation.

By you asking about cutting the sheets to 40", you were thinking of installing the sheets in the wrong direction. The sheets are installed with the face grain running across the joists not parallel to them.

Jaz
 
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Old 11-04-10, 04:32 AM
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Jaz, I think the OP was thinking of cutting the sheets to 40" so they would hit over the joisting/truss tops.
 
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Old 11-04-10, 08:10 AM
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Yes I understand the OP was thinking just that. If he was going to make them 40"x96", that would be wrong cuz they would be oriented parallel with the joists. Cutting the sheets to 48"x80" would work, if the were 20" apart....But they are not, they are 19.2" apart. PLUS you do not want the ends fastened to the joists as already mentioned in this case.

Why 19.2"? So it works out even over 5 joists. 19.2 x 5 = 96"

Jaz
 
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Old 11-04-10, 09:12 AM
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Do you know what the recommended gap is?
 
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Old 11-04-10, 09:30 AM
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ok to summarize here's what I am doing.

laying the 4x8 sheets perpendicular to the joists so the long edge 96" span runs perpendicular to the joists.

I'm using 1.5" flooring screws.
I am not screwing into the joists but into the 1x4 planks below the plywood, above the joists.

I am going to leave a 1/8 inch gap between the sheets. I already have the T&G plywood so I am going to use that. but still leaving a gap of 1/8" with the tongue in the grove.

I am going to stagger the seams.

If I got anything wrong with that let me know.


I am also going to use PL400 glue to glue the sub-floor to the 1x4 planks below and to glue in the tongue and groves.
 
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Old 11-04-10, 12:37 PM
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Spacing underlayment 1/8" is normal procedure. However you are using "t&g sub flooring" as the underlayment so the procedure may be different. Most t&g systems are designed to be butted (inserted) tight and the design of the t&g allows for expansion. You should follow the instructions of the manufacturer. What brand is it?

Glue in the groove is probably correct, but you should NOT apply beads of glue under the panels. Use fasteners only. The beads of glue create voids and therefore more bounce.

Jaz
 
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Old 11-04-10, 01:10 PM
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I am also going to use PL400 glue to glue the sub-floor to the 1x4 planks below and to glue in the tongue and groves.
Skip the pl400, it'll do more harm than good. Just use screws every 6" in the field and 4" around the edges. Make sure the planks are fastened properly and solid before you add the plywood. Add screws to secure the planks as needed.
 
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Old 11-04-10, 01:45 PM
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Originally Posted by HeresJohnny View Post
Skip the pl400, it'll do more harm than good. Just use screws every 6" in the field and 4" around the edges. Make sure the planks are fastened properly and solid before you add the plywood. Add screws to secure the planks as needed.
I'm getting conflicting reports on the glue some say use it others say don't. I really want to avoid any squeaks and moans and i'm not worried about the additional costs or additional labour. So I guess what is the harm that will be caused from gluing? I know Jaxman mentioned below that additional spaces could be created however that can be easily remedied by spreading the glue evenly and srewing it while while the glue is wet.

Or would you only glue if I was putting the sub floor over plywood as opposed to planks.

Without or without glue I will be screwing the plywood down using the spacing you described.
 

Last edited by ethermal; 11-04-10 at 02:21 PM.
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Old 11-04-10, 02:19 PM
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Originally Posted by JazMan View Post
Spacing underlayment 1/8" is normal procedure. However you are using "t&g sub flooring" as the underlayment so the procedure may be different. Most t&g systems are designed to be butted (inserted) tight and the design of the t&g allows for expansion. You should follow the instructions of the manufacturer. What brand is it?

Glue in the groove is probably correct, but you should NOT apply beads of glue under the panels. Use fasteners only. The beads of glue create voids and therefore more bounce.

Jaz
Not sure of the manufacturer I bought the plywood at Lowes in Canada. I guess I could talk to them or I could cut the tongue off and use it as normal plywood.
 
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Old 11-04-10, 03:18 PM
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Every sheet should be stamped with all kindza good info like who made it, where, when and much more.

As far as glueing with something out of a tube, do not do it, it'll create voids cuz it's thick. There's no doubt in my mind that you are getting conflicting advice on that. Do not listen to anyone except Johnny and Me.

You can not work fast enough to spread that gooo to get a full spread. The only way to do that is to have two people ready and work fast with fine notch trowel, but with liquid wood glue, not that thick stuff.

That would be a "lamination" and although not necessary, it would indeed add stiffness between the joists. Of course you'd need many gallons of the stuff since most of it would go thru the cracks to the room or ceiling below.

You never glue ply to ply. The only time you glue ply is when it's the subfloor on the joists.

Jaz
 
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