Replies

1. 
   calvin | Feb 23, 2011 06:22am | #1

   I wouldn't dbl the blocking-you'll find it hard not to ridge the sheets where they come together-more bearing is not necessary.

   I would thin out the subfloor (5/8's) and add an underlayment compatible with your flooring (1/4).  Stagger the seams between layers.

   2" screws would be fine with your plan (6"on the edges,8" in the field),  1-3/4 subfloor screws available for a stand up screw gun in addition to my preferred adhesive (PL Premium) would also work well-you'll end up countersinking those screws getting you into the joists at least an inch and a qtr.  Staple the underlay (2" on the edges,4-6" in the field).  Use Dependable on the seams if necessary.  If that floor covering is thicker than sheet goods, more like VCT tile-you'll not have show through and can usually skip the seam buttering.

   Gap the subfloor ply and eighth inch, and don't cramb the qtr inch tight.

1. 
   KWOLSEN | Feb 23, 2011 10:50pm | #4

   subfloor

   Calvin

   thanks for the reply, great info.  Just so I understand, when you say I should not double the blocking, do you mean that if I used T&G that with that 3 inch wide double blocking that it would be hard to get one tounge in one grove, is that what you mean by ridging the sheets ?  Is there a special screw that you use ?

   thanks,

   Kirk

1. 
   calvin | Feb 24, 2011 07:01am | #6

   dbl blocking.

   If you use two blocks, the chance that you will not get the two in a perfect plane is high.  This could cause one or both the sheets to be higher than the other, sometimes even creating an up/down situation.  Take a straighedge and lay it across the seam and it will rock.

   Even taking one flat block to center on the seam might cause the same thing.  IF you're using T&G, why would you use the blocking?  It will make it harder to get the one into the other.  Depending on the product, you'll have a time getting one into the other anyway-fighting a tight joint because of blocking would be not worth the effort.

   I block when situations arise that call for it.  Say I cut out a 2x2 pc of subfloor to gain access below or to replace a damaged pc.  Cutting back to the joist is the proper way, but what about in the other direction?  You do not have a tongue or groove now to hold the joint unless you cut the full 4 ft of the sheet.  I'll glue and screw a flat block to the underside of the subfloor, extending it out to catch the edge of the patch.  Lay the patch over the hole and secure it to the joists as well as screwing it to the flat blocking.

   I use a PAM screw gun with extension to screw down subfloor etc w/o bending over.  Various screws are offered for different applications and thicknesses.  They are on a self feed strip.  Find the length and type of screw (in this case-subfloor screw) that works.  If you plan to crawl around and use a screwgun or impact driver there's plenty of screws to choose from.  Do not use drywall screws-they'll snap and are too light.  Rust too easily also.   Stay away from phillips tips, they round out too easy.  You should be able to find a deck screw that'll work.

1. 
   KWOLSEN | Feb 24, 2011 06:52pm | #7

   dbl blocking

   ok, I understand your explanation about double blocking, makes sense.  The problem I'm facing is that I can't find 3/4 TG plywood at my local Home Depot (Monrovia, CA)  only 1 1/8.  I'm trying to be careful about the finished floor height in the new addition part of the project so that there is minimal height difference from the existing house.   I'm currently leaning towards using 3/4 " CDX plywood with  3/8 " levelling plywood (clean, near knotless stuff, whatever it's called) on top.   Your right, blocking (single or double) should not be necessary if using the TG.   Just hard to imagine that a glued TG joint that falls halfway between 2 joists is safe, but guess I will try to get over it.

1. 
   calvin | Feb 24, 2011 07:16pm | #8

   K

   T&G between joists is safe.

   Between 12" oc joists?  bulletproof.

   Remember to gap your sheets on the ends.

   And do join the tongues into the grooves.......................but don't beat the shit outta it trying to get every last stink'n bit of the tongue in there.

   Use a 2x4 laid flat on the joists and along the GROOVE edge as the sacrificial lamb while you persuade the sheet into it's corresponding mate (with a sledge, but not with gusto.

   If the addition was laid out properly, you should have no problem bringing the new to the old.  Get the subfloors right with each other and overlay the underlayment across that transition.

2. 
   KWOLSEN | Feb 26, 2011 05:41pm | #9

   Calvin-

   good advice on joining the tongues into the groves.   I will keep a 1/8 " gap on the plywood ends and split this in half  over a 1 1/2 " wide joist.  

   Question: Aren't the screws on the plywood ends (two adjoining sheets that both rest on a  1 1/2 " wide joist) going to split the plywood since there is only 3/4 " of support for each plywood end ?

   Question: Are the tongue and grove sides, when joined,  designed to give you some expansion gap already ?   I just join them together with that PL premium adhesive and not worry about the gapping, right ?  

   I got these 2 1/2 " GRK subfloor screws that look substantial, if not overkill.  With 3/4" GP Pytatium this gives screw embedment depth of 1 3/4", my arch plans call for min 1 5/8 embedment, so should be ok.  Now if could just stop the rain (but do have massive tarp to keep subfloor all dry until walls and roof go up).  

3. 
   calvin | Feb 26, 2011 05:48pm | #10

   Answer............

   Question: Aren't the screws on the plywood ends (two adjoining sheets that both rest on a  1 1/2 " wide joist) going to split the plywood since there is only 3/4 " of support for each plywood end ?

   Well, you might have that problem.  But it will be minimum if the screws are oversized and you angle them from almost an inch in from the ply edge and run them down into the joist.

   Question: Are the tongue and grove sides, when joined,  designed to give you some expansion gap already ?   I just join them together with that PL premium adhesive and not worry about the gapping, right ?  

   You can I suppose glue that groove..........................but no one does.

   I don't think you need to worry about that stuff moving around once joined.   Best practice calls for glue on the joists only............and that would be the top edge of the joist, not slopped all down the side.  Stagger the sheet ends at least two or three joists.

   I got these 2 1/2 " GRK subfloor screws that look substantial, if not overkill.  With 3/4" GP Pytatium this gives screw embedment depth of 1 3/4", my arch plans call for min 1 5/8 embedment, so should be ok.  Now if could just stop the rain (but do have massive tarp to keep subfloor all dry until walls and roof go up).  

   You will be fine-remember, that it'll countersink unless you fuck up.  And, what are you going to use to drive them?

   Screw guns do work, but not as good as an impact driver.  If you don't have one-get one-you'll love it and use it often.

   Best of luck.

4. 
   DanH | Feb 26, 2011 06:51pm | #11

   IMO, the 2.5" screws are

   IMO, the 2.5" screws are overkill -- you'd do just as well with 2".  But the longer screws won't hurt in this situation, and it's not worth arguing.  The GRKs are certainly up to the job -- IIRC, they have a self-countersinking head, so your real worry is driving them to China, not leaving them proud.

5. 
   DoRight | Feb 28, 2011 12:04pm | #12

   Do you really need T&G?

   Sure seems like I have been in countless houses with just plain CDX 3/4 inch, 16 OC, without any additional underlayment with no noticible problems.  When did T&G become all the rage and why?

6. 
   calvin | Feb 28, 2011 08:27pm | #13

   When, why?

   Well, in the 70's when we framed, we sheeted the floors with 5 ply half inch.  It was common practice to come back over that with ....................ugh, particle board.  Masonite products were common as underlay for vinly/lino from the 50's, through the late 70's.

   Prior, maybe 50's/60's, you'd find T&G 1x6 or ship lapped laid diagonally across the joists. This subfloor seemed to become popular in the 30's.  B/4 that, square edged individual boards were what we'd find here.

   I'm thinking as the 70's ended, 5/8's or 3/4 T&G was the norm-at least here in NW Oh.

   T&G holds the long edge in plane with each other.  Not a bad idea.  Even carpet could show a ridge if it wasn't in the same plane-things like vinly over a thin underlay might appear spongy as the underlay slowly became loosened with movement.

   Another why?   sustainable construction practices-smaller non old growth used for plywood and now harvesting quick grow small stock for OSB.  Too bad they didn't save more of the old growth.

   Some close minded people think just use it up-don't worry about it..................man has little impact on the earth.  It'll be here forever.

   Boy are they misinformed.

2. 
   DaveRicheson | Feb 23, 2011 06:23am | #2

   Subfloor material.

   Go to a lumber yard and get 3/4" Advantec subflooring. It is T&G and flat and a heck of a lot better than any OSB or plywood product you will get at a big box store. you won't need ant blocking on the 8' edge.

   Any vinyl or tile flooring going over the subfloor needs to be installed over the appropriate underlayment. Not directly on the subfloor.

1. 
   KWOLSEN | Feb 23, 2011 10:55pm | #5

   subfloor material

   Dave

   thanks for the reply.  I will look into that Advantec 3/4 " that you mention plus I need to find out from Amtico vinyl mfg what thickness underlayment they recommend. 

   thanks,

   Kirk

3. 
   DanH | Feb 23, 2011 07:13am | #3

   Yeah, you'll need an underlayment (as speced by the vinyl mfgr) in addition to the subfloor.  The underlayment is generally stapled with a narrow staple.