One neat little detail that I was able to incorporate in the door was to reuse a wood frame window that I removed from our main house a while back when we updated to double pane vinyl windows. It was originally installed tall and narrow but it was just the right size to put in the top of the door turned on its side.

See what you think…

So what did it end up costing to build this little building? I will still have to go back and total up all of the receipts but I can tell you that the total for the materials was definitely less that $1500 total. The majority of the lumber, siding and foundation materials was just a little over $800 and two pickup truck loads from Home Depot. The roofing materials came from Lowes for right around $300. The sliding door track and hardware was just over $100 from a local specialty hardware store here in Portland called W.C. Winks. I had a few odds and ends of materials on hand already but not that much overall. The window was the main special thing I had on hand. The 1×3 trim was a real deal from our local Habitat for Humanity Restore. I think I paid about $12 for most all of what I needed. I borrowed the framing nail gun from my son-in-law which was a big help. I rented the siding nail gun from Home Depot and ending up keeping it longer than I had intended and had to pay something like $97 for it. I could have bought a new one from Harbor Freight for that amount or less. I already have an air compressor and the other tools that I need. I did pay for some of the labor since my youngest son is not fully employed at the moment and my painting friend needed the work too.

How long did it take to build? I spent about 4 hours shopping for the first big pile of building materials the day before we started in earnest. I think I built the framing table top on that first partial day too. The nearest Home Depot is only about 1 mile away so making two trips was not too big of a deal. I also have a pickup truck so that helps. It would have saved some time to have ordered the stuff from a local lumber yard and have had it delivered. With my son’s help we got to the top of the floor on the first full day. We had to do a little more digging than we had anticipated for that part. Also the woodshed is maybe 75′ from where we unloaded the building materials so we had a lot of carrying to do. Day two we had built the walls all the way to the top. Day 3 we had framed the roof and installed the roofing. On day 4 I had to get back to my day job while my son installed and fully caulked all of the exterior trim. The painting took about 1 day total spread out over two partial days. I also built the door over a few hours. The total construction time to get the little building to where it is now appears to have been about 9 total man days of effort. I will have to spend an hour or two to finish up the minor details I mentioned above and to clean out the sawdust and wood scraps out of the building. The interior is completely unfinished with nothing painted so it would take more time to finish the inside more if someone wanted to do that.

When the 4′ wide wall panels are attached to each other a double stud (vertical member) is created. In my design of this shed my rafters fall at 4′ on center so this means that they will always sit on top of a double stud. This also helps explain why I do not need a double top plate (the horizontal member at the top of the wall). By the way you will notice in the above photo that there is no top plate on the top of the walls. This is because I added a 12′ long top plate at the top of the wall panels when they were all in place. This next photo show pretty clearly how each of the homemade trusses sits on top of the single top plate directly above a pair of studs. It also shows how we attached 2×4 purlins (the horizontal cross members laying on top of the trusses). Flat 2×4 purlins are capable of supporting the type of roof sheathing that I chose to use which needs to have purlins rather than rafters that are closer together.

The type of roofing I used was a product that I found at Lowes called Ondura roofing. It is a composite material in a corrugated form. The sheets are 48″ x 79″. I designed my rafters very carefully so that I could use full sheets at 79″ long. This meant that my roof overhang had to be a little smaller than I might have liked but it works out OK. This next photo shows a view of the completed roof.

I wanted the floor system to be relatively low profile so as to keep the overall height of the building low. Rather than placing beams on the pier pads and then laying joists across them I took a somewhat more complicated approach where I used 4×6 beams, attached 2×4 ledgers to the bottom of each beam and then added 2×4 joists between them. The drawing below shows the arrangement. I could have used only 3 beams and used 2×6 joists. I would not have had enough height on the beams to have used the ledger approach but metal joist hangers would have been fine. The following photograph shows a part of the actual floor frame.

Each of the wall panels were sized such that the bottom of the 4′x8′ Hardiboard sheet would overlap down over the floor frame. This meant that each of the vertical members had to be cut to size. There were 3 different types of panels. One panel was a full width panel. The other two were designed so that the 4′x8′ Hardiboard sheet would overlap another wall panel at the corner. This meant that I had both a left hand and right hand version of the panels. The main thing that I would like to point out in this post is how I prefabricated the wall panels.

I build a very simple framing table out of a sheet of 7/16″ thick OSB with a frame of 2×3 lumber around the edges. I supported the table with two standard folding plastic saw horses. I used a black Sharpie marking pen to draw lines on the table to indicate where framing members should be placed. I also drew a pattern for my rafter on the table. I screwed down a few short pieces of 2×4 block at strategic locations to help make it easier to quickly position the framing members when building a panel. It was then a pretty simple matter of placing all the framing pieces, nailing them together and then adding the siding sheet on top. In this case I was fortunate to be able to borrow a framing nail gun from my son-in-law that was very helpful for nailing the 2×4 lumber together. I also rented a siding nail gun for nailing the Hardiboard siding in place. If I did not have access to a framing nailer I probably would have used decking screws to assemble the frame. I find that it is easier to hold things in place if you can quickly attach members with a nail gun or a screw gun. Manually nailing the members would certainly be possible but harder to do on a table at the height of mine. If I were to manually nail the panels I would probably have set the table much lower – maybe directly on the floor. You will have to look closely in the photos below to see some of my lines. Hopefully the idea will be obvious enough. The second photo shows the frame members on the table just after they have been nailed together. Notice the nail gun.

Structural Insulated Panels (SIPS) typically have a solid core of insulation foam between skins of OSB or plywood. Adding wiring after the fact would be pretty hard. SIPS that use preformed expanded polystyrene foam (EPS) typically have wiring channels precut inside of them during the manufacturing process. The design process needs to specify where these wiring channels need to be located. SIPS that are made using polyurethane foam insulation that is foamed in place during the manufacturing process require a different approach. For this type of panel plastic electrical conduit and electrical boxes are pre-placed in the panel before the foam is injected. Obviously this approach also requires predetermination of the locations where the wiring should be located.

A good example of the prefabrication of some architectural details such as cupolas and dormers can be found at the following web link:

http://pennypincherbarns.com/Accessories.aspx

The overall design of a roof system may very well determine the feasibility of panelizing vs. pre-cutting. I worked for a while at a wood frame prefab shop in the late 80’s where we shipped quite a few house packages to Japan. The average floor plan in Japan was definitely smaller than in the United States. At that time the average family of 4 lived in about 400 square feet of space. What I observed with the projects that we built was that what these houses might lack in overall size was very definitely made up for by complexity of roofline. More often than not the designs had full hip roof lines. For those that are not familiar with that terminology it is simply a roof where all of the sides of the roof come down to the top of the walls. This type of roof is definitely more complicated in that the rafters that are required to make it are all different lengths and typically have compound angles cut at their top end. Certainly this type of roof could be prefabricated into panels but we found it was generally easier to carefully pre-cut and label all of the pieces and furnish a detailed drawing of their placement. Usually the plywood was not precut but it could have been.

If you are building a DIY project and you are the one that is building the foundation itself then you have somewhat more direct control of the overall dimensional quality of the foundation. If you are having someone else build it for you be sure to stress the importance of the dimensional accuracy. There are some design tricks that you can play though that make for a less critical dimensional relationship between the foundation and the prefabricated building.

One suggestion that I have in particular is that you consider some type of post and beam foundation system. In this type of system the floor framing members or prefabricated floor panels span across and beyond the supporting foundation beams. Consider the type of foundation shown in the following drawing.

I think you can see that the placement of the beam relative to the floor panel that is sitting on top of it is not particularly critical in the left-right direction as shown in the drawing. Of course the beam needs to be level along its length as well as level with the other beams in the foundation. It also needs to be long enough to support the floor panels out to their edges. Otherwise the location of the beam could vary considerably without hurting the overall structural integrity of the building. By the way this type of foundation system is what is used in Michael Jansen’s prefabricated small building plans.

One other aspect of floor systems that can contribute to making panelizing more difficult has to do with insulation, wiring and plumbing. Wall panels most typically have at least the outer skin attached. This leaves ready access to the inside of the panel so that wiring, plumbing and insulation can be installed from inside of the building. It is more convenient on the other hand for a floor panel to have the top skin installed. This makes access to the inside of the panel a little more difficult since it must be accessed from below. This might not be a problem if there is enough space underneath the floor. Still it can complicate the overall process of completing the floor part of the assembly. Supplying the floor system in a pre-cut only kit sometimes is worthwhile because many of these other installation problems can be avoided.

There is also potentially a very large difference between the bottom floor of a house and the other floor levels. If the bottom floor is built directly over the ground it is easier to provide support points at predictable increments that are small enough to make building pre-assembled panels feasible. You could easily build floor panels that are 4’ x 8’ in size if you could support the from beneath at least at their corners.

One other factor to consider when you are thinking about pre-cut or panelized floor systems has to do with how you will attach the panels together. Conventionally framed floor systems typically rely on the overlap of plywood sheets to fasten the various sections of the floor together. In a panelized approach some other means is required to fasten the panels to each other. This is easily enough accomplished if you have access to the panels from beneath. If, on the other hand, the panels are fully enclosed them some other technique is required. One approach is the type that Michael Janzen adopted in his pre-fab house plans (more information is available by clicking on the link on this site). In that design Michael uses a plywood spline between the panels and under the top level of the floor sheathing. This is very similar to the way that he attaches his wall panels together. Please refer to the following drawing repeated from an earlier post that shows the spline in red. Of the course the floor panels might be thicker than what is shown here.