Framing With Metal Studs
Wood or Metal?
When I renovated my basement, I chose to use metal studs for framing the walls. My decision was based on measuring the pros and cons of both wood and metal studs.
Strength: Wood is definitely the sturdier of the two materials. Metal tends to be flimsy, but once the drywall is screwed to it, it is strong and rigid. However, metal would not be suitable for hanging cabinets or heavy mirrors. Metal framing has no structural strength and can only be used for partition walls.
Convenience: Metal wins here, hands down. It is lighter than wood and since it is not a solid material, two metal studs only take up the space of one piece of lumber. This makes for easier transporting. Metal is cut using aviation snips, which means no sawdust. However, gloves should be worn to protect the hands and care must be taken to clean up any small pieces that end up on the floor.
Cost: At first glance, metal seems to be less expensive than wood. However, electrical boxes for metal studs cost more, and plastic grommets are required for running standard electrical wires unless shielded BX cable is used. Metal also requires screws for construction, and for attaching moldings. Even if the initial cost of lumber is more than the metal studs, the additional costs involved in using the metal evens things out.
Forgiveness: Make a mistake in measuring? Stud not vertical? Since metal studs are attached with screws removing and moving studs is simple.
Stability: Wood is prone to twisting and warping; metal is not. Wood also wicks moisture; metal does not. However, metal does rust, so a vapour barrier or sill gasket is still required between the bottom plate and the concrete floor.
Environmental Concerns: Metal framing has sometimes been promoted as an environmentally friendly alternative to wood. However, both materials have their positive and negative points. Wood comes from trees, and cutting down trees is generally seen as bad for the environment. However, wood is a renewable resource amd we are getting better at managing our forests. Wood scrap is biodegradable and smaller pieces can be composted, but it takes a while to wood to break down and most scrap ends up in the landfill anyway. Metal is recyclable, and recycling is generally seen as good for the environment. However, the recycling process does generate a certain amount of pollution. Also, the ore has to be mined and refined to produce metal, and that negatively impacts the environment. Basically, either material can be seen as better or worse for the environment than the other, depending on your point of view. Further perspectives on reducing the environmental impact of home construction and renovation can be found in this article elsewhere on this site.
Fire Concerns: Wood burns, metal does not. A wall built with metal studs is virtually fireproof.
Cold Transfer: Metal conducts cold. Metal studs on an outside wall will transfer the cold. Therefore a polystyrene or rigid foam insulation is recommended between the outside wall and the metal. I did not take this step but did not notice any major problems. With wood, cold transfer is less than with metal, but it still exists.
Having worked with both materials, I believe that one is not necessarily better than the other. It basically comes down to personal preference.
Installing Metal Studs
Metal studs come in the same dimensions as lumber. The system consists of two main components, the track and the stud.
The tracks are usually installed first fastened to the floor and the ceiling (in the case of a basement, to the concrete slab and the ceiling joists. The studs are then inserted in the tracks and twisted in place until they are square. Wafer screws or framing screws hold everything together.
Doing things the hard way:
Because the studs have to be screwed in on each side, we were presented with a problem when we did the exterior walls-- we obviously could not attach the screws from the wall side without room to get the drill in between the wall and the track. It might have been possible to attach the screw from the inside of the stud (as suggested by somebody on the DIY Forum), but we honestly did not even attempt this.
Instead, we attached the top track to the ceiling joists with a couple of screws. We placed the bottom track below it, without fastening it to the floor. We then cut our studs and attached them to the track on the one side with screws. We then removed the screws holding the top track in place and moved the entire assembly out from the wall. We temporarily attached the top track to the joists with a couple of screws. We made sure that we kept the studs at 90 degrees to the tracks and attached the other side of the studs to the tracks. Once all the studs were screwed to the tracks, we removed the screws holding the top track and moved the entire assembly back to its final position along the wall. For final installation, we attached the top track to the joists using screws and the bottom track to the floor using tap-cons.
An Easier Solution: (From the Thumb&Hammer DIY Forum)
"This is just a suggestion from several years in the construction trade. concerning metal stud framing, use a tool called a crimper, you may be able to rent it, for the back side of the studs on exterior walls of light gage framing. Screw the front, the edge nearest you,with pointed wafer screws. This eliminates pulling out the wall to reach the back and gives all the support needed for gyproc." (Aaron)
For the interior walls, it can be difficult to get the top and bottom tracks lined up perfectly. We fastened the top track permanently, but before fastening the bottom track, we installed a couple of studs first. That made it easy to check the wall for plumb using a level rather than a plumb bob. We then fastened the lower track and installed the rest of the studs according to the manufacturer's instructions.
Because the metal tends to be somewhat flimsy, we found a "third hand" to be somewhat beneficial. Small vice grips held the track and stud together while the screw was driven. This stopped the screw from pushing the stud away, and it saved our fingers.
Dog Ears
For framing around windows and constructing headers for doorways, the track material has to be dog-eared.
The track is cut about a foot longer than the space between the two studs. The sides of the track are cut so that the track can be bent and fastened to the studs as shown in the picture. For doorway headers, the track is installed so that the channel faces up. That way vertical studs can be installed for stability.
Device Boxes
As previously mentioned, metal studs require specialized device boxes. Shown at the right is one such box inside vapour barrier. This particular box has a front piece that clips onto the stud and gets screwed into place. There is also a strap that bends around the stud and gets fastened to the back.
Insulating and Attaching Vapor Barrier
Because the studs are hollow, standard insulation is too narrow. There is insulation specifically designed for metal studs (a full 16 inches wide)
Vapor barrier is attached to wood studs using staples. Staples will not work with metal studs. I cleaned off the studs and used double face carpet tape to help hold the vapor barrier. The top and bottom of of the vapor barrier were taped to the tracks with the same tape I used for sealing the seams (Tuck Tape). While I had an air-tight seal, it would have been faster and easier to use acoustic sealant which should also be used with wood studs to completely seal the vapour barrier.
Oops!
I took the extra step of installing fire and noise insulation in the interior walls. At the doorways where I had two studs close together for stability, I thought it would be easier to fill the cavity with low expansion foam.
Voice of experience here: Expansion foam is not recommended for filling narrow cavities between metal studs!