Wood Blocking in Metal Studs: How to Install It (and Why Pre-Cut Dado Backing Is Faster)

Wood blocking in metal studs is plywood or lumber fastened between steel studs so there’s something solid to screw into behind the drywall: cabinets, grab bars, handrails, TV mounts and anything else that gets hung on the wall. Steel studs can’t hold those loads with a drywall screw, so the backing does the work. This guide is for drywall subs and GCs on commercial steel stud jobs. It covers how the blocking goes in, what goes wrong when it’s cut on site, and how to skip the cutting.

I’m Lewis Murton. I handle EZI BACKR™ at High Crest in Surrey, BC. We cut plywood backing to spec for steel stud jobs, mostly towers and commercial buildings. A lot of what’s below comes from our shop team and from a teammate who used to work on site cutting and installing this stuff himself.

In this guide:

• Metal stud blocking: dado cut vs strips

• How to install wood blocking in metal studs, step by step

• Fastening plywood backing to steel studs

• What goes wrong with blocking cut on site

• How long it takes to cut blocking on site

• What if the studs aren’t 16” on centre?

• The mistake I see over and over

• Plywood vs steel backing for metal studs

• FAQ

Metal stud blocking: dado cut vs strips

There are two shapes of plywood backing for steel stud walls, and they do different jobs.

• Dado-cut pieces go between the studs wherever something is drilled into, hung or installed. A groove (the dado) is cut along one edge so the piece hooks onto the stud. About 80 to 85% of what we sell for steel stud walls is dado cut.

• Strips are long, straight pieces used mainly for window and door liners: the framing you screw the doors and windows into.

If you’re blocking for cabinets, grab bars or fixtures, you want dado-cut pieces. Ours are 15 13/16” wide, sized to fit between 16” on-centre steel studs, in heights from 6” to 96”. Strips are 96” long in widths from 3” to 10”.

How to install wood blocking in metal studs, step by step

A steel stud is C-shaped when you look at it from above: one side is open with a small return lip, and the back is flat and closed. The dado is what lets a piece of plywood lock onto that lip.

1. Mark the height. Snap or draw a line across the studs at the height where the cabinet, rail or fixture will hang. Check the drawings, not memory.

2. Seat the dado on the open side. Slide the piece in between the studs and wedge the dado groove onto the lip of the stud’s open side. The groove holds the piece in line with the face of the stud.

3. Butt the other edge to the next stud. The far edge of the piece sits against the closed, flat back of the next stud. There’s no lip to hook onto there.

4. Screw it off. Fasten through the stud into the backing on both sides. On the closed side, you screw from inside the stud into the edge of the plywood.

5. Check it before the board goes on. Make sure every piece is at the right height and solid. Once the drywall is up, nobody sees the backing until something pulls off the wall.

That’s it. The install is simple. As I tell people, the installing is the easy part. Producing the pieces on site is the hard part.

Fastening plywood backing to steel studs

Use the screws your crew would normally use on site for steel stud work. There’s nothing special about fastening EZI BACKR compared with backing you cut yourself.

Two practical notes from the field:

• Screwing into the edge of the plywood from the closed side can occasionally split it. The screw is small, so it’s rarely a big problem. Back it out and move it a little higher or lower until you have two or three screws holding.

• For anything structural, such as the load a grab bar or heavy cabinet must carry, or what the code requires, talk to your framer or the engineer of record.

What goes wrong with blocking cut on site

When I ask crews what goes wrong, the answers are pretty consistent:

• Wrong size. Someone mismeasures, the piece doesn’t fit, and it gets recut. That’s the most common one and it’s pure wasted time.

• Studs that aren’t where they should be. If the studs aren’t the proper width apart, pieces need trimming to fit.

• Cleanup. This is the one I underestimated. Cutting and dadoing a stack of plywood makes a huge mess. Ten storeys up, that sawdust has to be vacuumed and bagged and carried out. My teammate who did this on site says it gets everywhere, including in your eyes even with eye protection on.

How long it takes to cut blocking on site

I’ve asked a lot of people this question, and I got a lot of different answers. The number our shop team and I settled on is this: cutting a sheet of plywood into backing on site takes about 20 to 30 minutes. You get about 24 pieces out of a sheet.

That covers ripping and dadoing only. It doesn’t include vacuuming, and it doesn’t include carrying material to the saw and pieces to the crew, which adds a few more minutes per sheet. The dado itself is the quick part. The saw is set to depth and you run the piece over it. The ripping and handling are what eat the time.

One of our guys cut a full pallet with a table saw and dado saw. It took him about 12 hours, in a shop with no one in the way. On a busy jobsite, with everything else going on, I’d call it closer to 16 hours a pallet.

Worked example (illustrative, not a real job):

• A tower needs 400 sheets of plywood turned into backing.

• 400 sheets × 25 minutes = 10,000 minutes, or about 167 crew hours just ripping and dadoing.

• Add 3 minutes a sheet for handling and moving material: 400 × 3 = 1,200 minutes, or 20 more hours.

• That’s roughly 187 hours before cleanup, recuts or setting up a cutting station on each floor.

On real jobs, the published results tell the same story. On Brentwood Towers 5 and 6 in Burnaby, we supplied 23,000 pieces of 3/4” backing and the job saved an estimated 1,400 hours. On Scotia Place in Calgary, 9,216 pieces saved 550 hours.

What if the studs aren’t 16” on centre?

Most steel stud walls are framed at 16” on centre, and that’s what our standard dado-cut piece is sized for. But it isn’t always 16”. Some walls are 12”. Studs get shifted to go around pipes, which leaves an odd space. Occasionally you’ll see 24” in a spot where nothing heavy gets hung, like a drywall wall braced to a concrete wall.

What we tell customers: we can cut to any width. Tell us the spacing and the quantities, and that’s what shows up.

The other question I get is, “What if it doesn’t match the stud spacing on site?” Framers aren’t perfect. Sometimes a stud is off and a piece needs half an inch or an inch shaved off. That’s a minor adjustment, and it’s still a lot better than cutting every piece of backing on site.

The mistake I see over and over

The biggest mistake is only counting the cut. Crews think about the minute it takes to rip a piece and forget everything around it: moving sheets, setting up the saw, recutting, vacuuming, carrying pieces to the floor. On a tower with 300 to 600 sheets of plywood going into backing, those small movements add up over the whole project. Sixteen hours a pallet, times dozens of pallets.

There’s a related shortcut I’ve heard about. Some crews skip the dado entirely and just screw flat plywood in between the studs, which bends the stud out a little. It saves a few minutes per piece, and the drywall covers it right away. If what you really want is to save time, get the dado done before the plywood shows up.

Underneath both is the idea that cutting on site is the only way, because “we’ve been doing it this way forever.” People used to cut their own bread too. You might have a favourite knife and your own way of doing it, but it’s still easier to buy the loaf pre-sliced. I think pre-cut backing will be the standard eventually. Most crews just haven’t tried it yet.

Plywood vs steel backing for metal studs

You’ll also see steel backing (flat strap or channel) sold for metal stud walls. That’s a separate decision with its own trade-offs, and we’ve covered it in Flat Stock vs. Plywood. This guide assumes you’re using plywood.

FAQ

How do you install wood blocking in metal studs?

Mark the height, slide a dado-cut plywood piece between the studs, hook the dado onto the lip of the stud’s open side, butt the other edge to the next stud, and screw through the studs into the backing on both sides.

Do you need a dado cut for blocking in steel studs?

The dado is what lets the piece lock onto the stud lip and sit flush. Some crews skip it and screw flat plywood in, but that can bend the stud out. Pre-cut dado pieces give you the proper fit without the extra cutting.

What size is blocking for 16” on-centre metal studs?

EZI BACKR’s dado-cut pieces are 15 13/16” wide for 16” on-centre steel studs, in heights from 6” to 96”. For other spacings, we cut to the width you need.

What screws do you use for plywood backing in steel studs?

The same screws your crew normally uses for steel stud work. For load requirements on grab bars or heavy fixtures, check with the framer or engineer of record.

How long does it take to cut plywood backing on site?

About 20 to 30 minutes per sheet for ripping and dadoing, at roughly 24 pieces a sheet. Cleanup and handling come on top of that.

Can I get fire-rated blocking for steel studs?

Yes. EZI BACKR cuts standard, fire-resistant and pressure-treated plywood. More in my guide to fire rated plywood.

Ready to stop paying your crew to cut plywood?

Tell us the stud spacing, sizes and quantities and get a price in the quote calculator in about a minute. You’ll also see what cutting it on site would cost you.