DIY-Prefab

My neighbor Art is retired and loves to build wooden boats and archery equipment in his spare time. His garage was getting a bit crowded for his hobby so he and I collaborated on the design and construction of a workshop in his side yard. Art wanted a shop that was long and narrow to accommodate the beautiful wooden canoes and kayaks he builds. So the new building needed to be 8′ wide by 20′ long. Art also wanted to have an abundance of natural light inside as well as some passive solar heat when it was available. He originally thought about having large windows on the south side of the shop but that side faces the neighbors yard. I suggested using polycarbonate panels to make at least some of the roof into a skylight instead. We eventually decided to use polycarbonate panels for the whole roof. Art also wanted to have a generous overhang all the way around the building. He wanted the ceiling height to be generous so that he could store a boat or two up near the ceiling. The design that we came up with and built is described here along with photos of the progress.

The foundation was very simple and consisted of 2 parallel 4 x 8 beams resting on adjustable concrete pier pads as shown in the following photo.

Art and I constructed a 4′ x 10′ work table out of a sheet of plywood and some 2 x 4 that we could use as a template for building both the floor panels and the wall panels. The following photos show the work table with a partially constructed floor panel in place. Notice the 2 x 4 blocks that have been screwed down to the table to facilitate quick placement of the floor framing members. In the background you can see that the first floor panel has already been positioned on the supporting beams. These panels were going to be insulated so they were built with OSB sheathing that was for the bottom side of the panel. The panels were then flipped over before attaching them to the support beams. It was easy to nail or screw through the OSB into the support beams to hold everything together. We used construction adhesive and nails to attach the OSB to the floor panel framing which was made out of 2 x 6 lumber. Art installed fiberglass insulation in the floor panel cavities and added 3/4″ plywood for the sub-floor. The 3/4″ plywood was installed length wise of the shop which helped tie the floor panels together. The weather was nice enough that Art and I could build and install the floor panels in the same session.The whole floor had to be covered up with a tarp to protect it from the rain that came in shortly after getting the plywood sub-floor in place.

The weather turned uncooperative so prefabrication of the wall panels and the roof rafters moved into Arts garage. The wall panels were each prefabricated on the same 4′ x 10′ work table that was used to frame the floor panels. Of course the locating blocks were moved a bit. Both the floor panels and the wall panels were designed with a similar ladder type of construction so the changes to the template were actually minimal. The wall panels were built taller to give more overhead space in the shop according to one of the original design objectives. The wall panels were sheathed with a rough sawn plywood and they had a tail that hung down below the bottom of the wall panel so that it would cover the edges of the floor panels and could be fastened to them. The following photo shows the assembly line in the garage with the work table and a stack of finished panels ready to install when the weather got better.

As soon as the weather got better Art and I and Art’s son-in-law were able to start installing the wall panels.

This design a bit unique in that it has a barrel vault roof line. I designed it so that the roof could be covered with 12′ sheets of corrugated polycarbonate material that spanned all the way from one side to the other of the workshop. The panels were flexible enough to bend to the barrel vault shape. Art used his band saw to cut the curved rafters out of 2 x 12 lumber. The rafters are spaced 4′ apart so that they are supported on top of the double vertical 2 x 4 studs where the wall panels come together. I designed the wall panels so that the sheathing plywood also extends above the top of the wall panel framing to close in the space between the rafters. If you look closely at the previous photo and the following one you will see that there is a notch in the plywood for placing the rafters. The plywood at the top of the wall panels on the ends of the workshop were cut to fit the curve of the rafters that are placed at the ends of the building.

The following photograph shows how we added 2 x 4 purlins length-wise of the building on top of the curved rafters. Notice too that the purlins closest to the tops of the wall panels are placed so that they can be attached to the top of the wall sheathing plywood helping to tie down the roof system to the walls. You can also see how the polycarbonate sheets have been placed across the purlins. The sheets were fastened down using special screws that have a rubber washer attached to them. Clear sealer was also used at each joint where the polycarbonate sheets overlap each other to help make sure they are water tight.

This next photo shows the outside of the building pretty much complete except for final painting – which had to wait for better weather. You can see here how the curved rafters and the polycarbonate roofing extends out to provide an overhand that is almost 2′ deep. You can also see the row of windows that have been installed on the north side of the building. These windows were custom fabricated by a local supplier to fit exactly within one of the spaces in the ladder like layout of the wall panels. The building was also dressed up a bit with 1 x 3 trim. The double front doors and the single side door were fabricated out of the same plywood as the wall panels. In fact they were made out of the piece of plywood that was cut out of the wall panel to make the door opening.

This next photo is a nice shot of part of the interior that shows the windows from the inside. It also shows the 1/4″ birch plywood interior sheathing that Art installed as well as one of his nice wooden boat projects. Art installed fiberglass insulation in the walls before installing the 1/4″ plywood.  A less than obvious detail is that I specifically designed the wall panels so that a full sheet of 1/4″ plywood would fit from the floor to the bottom of the rafters without having to be cut to length. I thought that was a nice extra touch.

The nearly completed 8′ x 20′ workshop as shown in the two following photographs has plenty of room for Arts equipment and storage. It is well lit and inviting and has extra overhead storage space that makes for more room below. Art has since completed painting the outside and has added bamboo flooring. He contemplates adding a layer of clear plastic film to the bottom side of the curved rafters or the purlins to provide extra insulation. If you look closely in the first photo you can see part of my little red barn in the background.

This is a brand-new Blog site that will focus on Do-It-Yourself(DIY) Prefabrication(Prefab) construction techniques. The techniques that will be presented here can be used to build various kinds of structures including simple backyard buildings as well as more complicated structures. The materials presented here will in some sort of logical order with one post building on the content of the previous posts. For that reason it is a good idea to read them in order from the oldest to the newest.