Hey there,

I've been trolling around here for quite a while but I've never actually found the answer to a couple (specific) questions I need answered. There are several threads asking what I'm about to, but every single one has been derailed into another question based on what the floor cover will eventually be or a "glue or not" debate... so here goes! lol

I have an older house (1950's) with the old 3/4" thick plank subfloors (not diagonal). I'm putting down 5/8" BCX plywood to strengthen them up before installing 2 rooms of hardwood and a hallway with carpet. I newly screwed the planks down to the joists. Now I'm going to screw the plywood to the planks (not the joists) and I'm not going to glue it down.

When looking up what type of screws to use, it seems I should be using 1 1/4" deck screws to secure the 5/8" plywood to the planks. The problem is, 1 1/4" deck screws for this application are nearly impossible to find, and the ones I CAN find do not have the thread-less area near the head that is recommended to help secure the plywood down without it being suspended above the planks in spots. ( I forget what that's called).

Secondly, I can find no collated subfloor screw strips -at all- less than 1 3/4". So I'm left with 2 options: Either get 1 3/4" screws for the screw gun (which would significantly go thru the bottom of the planks when sunk), or use a regular drill and take forever doing the 1 1/4" screws (without the threadless area people suggested). Plus I've read conflicting advice about whether or not to pre-drill holes for the screws... and am not even sure how that would work if you planned on using a screw gun... and it would double or triple the work time!

So here are my questions:

1. What exact type of readily available screw should I use to attach 5/8" plywood to 3/4" plank subfloor?

2. Is it ok if the screws go completely through the planks into the space below (the 2 rooms in question are above a garage and a den)?

3. Should the screws have the threadless space near the head or is that not a big deal? (also some of the subfloor screws I see have a gap between the bigger threads and some tiny threads near the head?)

4. Where can I get collated screw strips for subfloor that are less than 1-3/4"? Do they exist?

5. Should I pre-drill holes for every screw or is that as ridiculous as I think it sounds? (we're talking two 16x16 rooms and a hallway between them)

6. Are the usual 6" edges and 12" in the field screw-down techniques correct for what I'm doing? Or is that overkill since it's technically the 2nd layer of subfloor?

Thanks in advance, i really appreciate it!

Brian

 

I know that Menards in your area has either 1 1/4" gold construction (deck) screws and also 1 1/4" torx screws in either gold or exterior coated. You probably won't find anything short that is collated for a decking screw gun. Pretty sure Lowes and Home Depot have the same selection.

Not if the bottom of the floor is exposed where someone could get hurt on them. If the ceiling is covered in drywall I wouldn't worry about it. You "could" use the 1 3/4" - *if* you can determine what the gap is, and that it's not going to screw you...

The space is so that the subfloor will pull down. But if the space is larger than 5/8" you are losing precious thread that should be going into the planks.

Doubt it. There are 1 1/4" collated screws for steel and for drywall but I don't think you will find them for decking. And I'm sure you know that you don't use drywall screws. Since the point of the screw is worthless as far as holding power goes, you will really only have about 1/2" of thread in the planks if you go with a 1 1/4" screw... you might find that some of them will spin. Menards also sells boxes of 1 5/8" gold construction deck screws and that's probably what I would use if I was doing it... and screw it by hand with a drywall gun.

Last subfloor I did (for my parents house) I did predrill and countersink the holes, but it's mainly because you often won't have enough meat to countersink the head. if you don't. But you can see how it goes. Plus if you are using all-thread screws, the pilot hole will help to suck the top layer down tight. Drilling by hand is not all that bad. Certainly not as fast as collated.

That's what I would do.

 

Why BCX, Advantec is stronger, not going to flex at the joints because it's T X G and may even cost less.
I lay a layer of tarpaper and only use 8D ring shanked nails when doing this job, far faster, 1/3 the cost, not going to leave raised areas where the screw compresses the wood.
Never once had a call back for squeaks.

 

Get some SPAX construction screws. Put them in with an impact driver. The don't require predrilling and will pull tight. HD carries them. GRK screws are good too.

 

Simpson makes both 1 1/4 and 1 5/8 collated decking screws:

DSV Collated Wood Screw by Simpson Strong-Tie - DecksDirect.com

I'd use the 1 5/8 if the bottom surface isn't exposed; they will hold a lot better.

As X said, the unthreaded portion of wood screws would help pull the ply down tight, but I think they are also more likely to squeak later. I use full thread and put my (considerable ) weight right over the driver to hold the ply tight to the planks while driving the screws.

I second Joe's recommendation for advantec.

 

@XSleeper Great answers, thanks man. I think I may just get the right stuff and do it by hand. And here I was hoping for a shortcut! lol

 

@joecaption

Because I already cut and fitted the plywood... lol

Not worried about the cost. Skeptical of nails being better than screws for "raised areas". I'll check out advantec for my living room though! (it's next).

@JIMMIEM I'll check em out... why impact driver? Won't it shoot a lot of screws thru the ply?

@CarbideTipped - Wow those are expensive! Are they compatible with Senco/Ridgid (box store) screw guns? I'll keep the (considerable) weight technique in mind as well.. I'm about 230 myself hehe

 

Actually a couple more questions if you guys dont mind...

Is T&G like Advantec made to go over old plank subfloors? Or should it be stand-alone? (or does it not matter at all)

And I did find some 8 x 1 1/2" collated subfloor screws from GripRite on their website (SKU is SF112C).. but they carry them nowhere, and I even called GripRite and was basically told to buzz off.... pretty lame since it's on their website as a stocked item

It'd be great if I could find some EMPTY (new) plastic screw strips to buy that were senco compatible. I could load them myself with the screws I actually need. Would still save a lot of time. Google didn't help with that unfortunately lol