Can floor sheathing be glued to cold-formed steel floor joists?

[cliff234]

We are designing a multi-family residential structure using floor sheathing over cold-formed steel joists. The sheathing will be screwed to the joists. When we use wood joists, we require the sheathing to be glued and nailed to the joists. Can floor sheathing be glued to cold-formed steel joists? If so, what kind of glue should we specify?

 

[XR250]

Polyurethane subfloor adhesive sticks to everything.
Liquid nails used to make a wood to steel product - not sure if it still exists.

 

[atrizzy]

Are you using the floor as a diaphragm? If so, I'd be weary of such an attachment.

 

[XR250]

Please elaborate

 

[cliff234]

XR250 and atrizzy: We are using the floor for a diaphragm, however for structural purposes we are only relying on the screws for strength. As I understand it, the glue helps quiet squeaking of the floor. We always require sheathing to be glued and nailed to wood joists - and I was wondering if you could glue sheathing to CFS joists (to help quiet the floor).

 

[dhengr]

Cliff234:
There are adhesives that are claimed to be able to do that, and they do seem to work initially. But, you better get some assurances from the adhesive’s manuf’er. as to its various strengths, durability and resistance to environmental degradation. You should also clear this with the AHJ because there is some doubt/concern within the construction industry about the long term strength of various adhesives.

 

[oldestguy]

I'd bolt on 2 x's on the metal with carriage bolts and nail or screw, etc. onto that wood.

 

[cliff234]

I'll call some adhesive manufacturers and discuss. We can't bolt 2x's on the joists because that would be prohibitively expensive. The joists are spaced at 16" o.c. We're doing this to attempt to eliminate squeaky floors, so it's not a life safety issue. Likewise if we bolt 2x's to the joists we'll still run the risk of the squeaking between the 2x and the joist. I framed a similar floor several years ago without specifying glue between the sheathing and CFS joists and have not heard of any problems. I was just wondering if gluing floor sheathing to CFS framing was a common practice that everyone (but me) knew about.

 

[txeng91]

http://www.huberwood.com/assets/user/library/AdvanTech_SubFloor_Adhesive_-_Submittal_Form-v12.pdf

Might take a look into this, it says "metal" in the list of compatibles substrates but doesn't really say anything about cold formed steel joists. You might give them a call and see if it's commonly used.

 

[MikeHalloran]

<tangent>
My father bought a newly built house in 1950. He had the opportunity to inspect it during construction. He was pissed that the guy installing the tongue and groove hardwood floors (over shiplap) was only nailing every third course, but of course the guy refused to take orders from Dad, who did not own the house at that time.

Sure enough, the floor started squeaking not long after we moved in, and kept doing it.

More than ten years later, when the floor was still driving Dad nuts, and I was in engineering school, I proposed sistering the joists.

Dad threw a fit about the stupidity of placing an entirely new joist next to each and every one, and the impracticality of somehow inserting them through the rim joists, or ripping up the floors, or whatever; he couldn't see a way to do it.

So I told him he only had to sister the middle half.

He was resistant to that idea, until I reminded him that one of the school buildings under his supervision had had an extra flexible roof fixed by an engineer (for whom I had worked in high school), who had doublers welded to the bottom flanges of the roof beams, and pointed out that the doublers only covered the middle half of the beam bottom flanges.

So, he glued and screwed 3/4" plywood to both faces of the joists under the high traffic areas.
... and the squeak disappeared. ... and is still absent, fifty years later.

</tangent>

It occurs to me that bonding the joists to the sheathing would not have prevented the squeak that my Dad fixed by stiffening the joists.

If you were using wood joists, you could glue and nail half-length sisters to them before placing them, with relatively little cost or time penalty.

With steel joists, you could add a bit of depth to reduce deflection, but there's probably a tight height budget.

Or you could join half-length formed channel steel sisters, again before placement, by spot welding, or glue and self-drilling screws, or maybe with RoLoc punches if you're doing a bunch.

Or you could add some 'I' to the cold formed joists by folding an extra layer onto the flanges, i.e., subbing a hemmed edge for the sheared edge top and bottom.




Mike Halloran
Pembroke Pines, FL, USA

 

[dik]

"As I understand it, the glue helps quiet squeaking of the floor. We always require sheathing to be glued and nailed to wood joists - and I was wondering if you could glue sheathing to CFS joists (to help quiet the floor)."

Glue does more than keep the floors from squeaking... I've disassembled glued flooring from 20 years back and also steel straps glued to the U/S of the joists after 20 or 30 years and it's still remained attached... a real 'son-of-a-gun' to remove. Adhesive actually has higher strength than screwed fasteners. After several decades, the failure is through the wood product.

Problem is in obtaining certified test data attesting to the strength, and over time.

Dik

 

[Ron]

Yes, as others have noted, you can glue sheathing to cold formed steel. I agree with mechanically fastening as well.

If the fasteners are taking all the load, you don't really need the adhesion, just the "gasketing". You can use a strip of butyl tape on the top of the joist as a gasket. It will remain pliable for many, many years.

If you want adhesion as well, consider structural silicone adhesive such as that used for structural glazing. A double bead along the top of the CFS would provide both adhesion and gasketing as this material has some flexibility as well.

Heed MikeHalloran's advice....the smaller the deflection, the less squeaking you'll get! Squeaking comes from differential shear at the interface of different materials. If there is no deflection, there is essentially no shear "flow".

 

[dik]

Squeaking also occurs when the sheathing (no ply) shrinks and leaves a bit of a gap between the member and the sheathing and the squeak is sometimes caused the the sheathing 'riding up and down' on the nail shank.

Glue always keeps the member and the sheathing in contact... adhesive strength is generally in excess of 1000 psi or more.

Dik

 

[Jerehmy]

i've only ever seen squeaky floors when theyre nailed. I've never seen them squeak when the sheathing is screwed.

Has anyone experienced squeaky floors when the sheathing is screwed to the joists?

 

[dik]

Not that I'm aware of... I think Ron and I have explained the reason for the squeak, and not involving screwed fasteners.

Dik

 

[Jerehmy]

I was looking for anecdotal evidence of screwed fasteners not experiencing squeak for curiousity sake i fixed my squeaky floors by screwing every piece of hardwood to the joists. In regards to differential shear, there shouldnt be a difference between the nails or the screws. So if that was the cause the squeak would remain.

The screws ensure the sheathing is in constant contact with the joists. So is it the gap that causes the squeaking? Also, I'm curious if squeaky sheathing is more from the nails rubbing against wood or the wood rubbing against wood. I also wonder if wood sheathing rubbing against the metal joists would cause much squeaking. Just looking for what others have noticed in regards to screwed sheathing. Maybe the force from the screws squeazing the sheathing to the joist provides enough frictional resistance that everyday walking isn't enough to have differential movment.

Itd just be nice if adding a few screws per joist per [pre][/pre]4x8 sheet can eliminate most squeaking

 

[Backcheckrage]

We did an auditorium floor out of CFS joists. I'm pretty sure the contractor did not lay down glue on top of the joists... not a squeak! These particular floor joists were designed to be very very stiff. There is plywood screwed to the top, and then timber flooring/wearing surface laid over.

Although I swear i could hear some steel grinding against eachother? But that's a nuance of this particular system and not due to plywood movement relative to the floor structure. If it were my project, i would feel comfortable omitting glue.

Check out CFSEI oh guidance. they have heaps of Technical Notes!

 

[KootK]

Stumbled upon this while boning up my CFM chops. From one of the CFSEI tech notes and in the context of pneumatic pins rather than screws.

I'll call some adhesive manufacturers and discuss.

Anything to report on that front?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dik]

KootK... in this case, the squeaking would be caused by the movement on the shank of the pin... Dik

 

[KootK]

Well...yeah. Isn't that pretty much always the case with sheathed floor squeaks? Hence the whole gluing and screwing business?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.