I admit that I’m a life long devotee of Linn Westcott’s L-Girder benchwork. The strength, flexibility and adaptability cannot be beat. My only problem with this approach is the overall thickness of the framing. But I’ve learned to live with that.
For the St. George area, I decided to use wall mounted brackets primarily to keep the area under the benchwork as free as possible for rolling carts and other storage. The brackets are made from a 2×2 post, a pair of 1×3 brackets, a 2×2 angle brace and a plywood gusset. The posts can extend to the ceiling to support a backdrop. I didn’t bother. The wall is already painted a gray overcast sky color. If I do decide to do a backdrop, it will be mounted directly to the wall.
My posts are 54″ high. The tops will be hidden by scenery. The brackets are attached to the posts at 41-1/2″ above the floor. The L-Girders will rest on these so clearance under the girders will be 41-1/2″. This clears the roller carts I have.
The thickness of the framing is 4-1/4″ for a 1×4 L-Girder with a 1×3 flange, 2-1/2″ for 1×3 joists and 3/4″ for the plywood sub-roadbed which totals 7-1/2″. Mounted on brackets set at 41-1/2″, this gives 49″ as the nominal height of the sub-roadbed. The St. George area is relatively flat though I’ll cut out some areas of the plywood for scenery effects. Only the stream is significantly lower. This is where L-Girder benchwork shines. It’s easy to position joists to either side of the stream bed to lower the scenery. Or smaller joists can be used.
The benchwork varies from about 27″ to about 50″ in depth. Easily accomplished with L-Girder benchwork. The joists are simply cut to length as required. In fact, I’ll start with the joists a little longer than needed and trim them later. L-Girder benchwork relies on cantilevers (ala Frank Lloyd Wright) for strength so the girders will be set in from the outside edges of the joists. Ideally, about 1/5 of the joist should overhang although this is not critical. (I wouldn’t go much longer though). The front girder will be angled to keep the joist overhang in range. The rear girder will be set about 6″ from the wall.
The brackets range from 24″ to 33″ in length. For a little extra bite, beefy 1-1/4″ exterior deck screws are used to fasten the brackets to the posts. A 2×2 diagonal brace runs from the end of the brackets to the foot of the post – actually 6″ above the floor. A plywood gusset and one long deck screw are used to securely attach the brace to the post.
The posts are anchored to studs inside the wall with 3/8″ x 4″ lag bolts. I drill a 1/4″ hole through the post and into the wall stud at a 10 degree down angle. Why? By putting the lag on a down angle, the post can never come off the wall without the entire layout lifting up. In true belts and suspenders fashion, I sunk a second lag bolt 6″ below the top one. The bottom of the post has a 1/4″ – 4″ lag to stabilize it vertically.
Cantilevering applies to the girders too. Each girder is made from two 8′ long pieces. The rear girder is straight so these girders can be bound together with a splice plate at least 4 times longer than the height (say 18″) to form a 16′ girder. A 1×4 girder is strong enough to span 11′ between supports with a 2′-6″ overhang so only two posts are truly required. But the front girders need to be set at an angle to accommodate the varying depth and cannot be easily spliced. So I’ll just go with two additional brackets so that both ends of each front girder has proper support. The girders are attached to the brackets with 2×2 connectors captured within the bracket and screwed to the girder. The girders are easily brought to perfect level by adjusting these connectors.
1×3 joists cut to length plus a little, based on the plan, are screwed to the girder flanges from underneath (where they’ll always be accessible). 1×1 cleats are fastened at the top edge of the joists to secure the plywood base.
The benchwork firms up considerably as construction proceeds.