Wood box gutters were the premiere gutter design for the drainage of rain water from roofs in the United States from 1890 to 1925, and can still be found on houses today. Box gutters are actually built off of the rafters of the building, they are not hung from the building as metal gutters are. These wood gutters must be lined with metal. Traditionally, tin has been used most often because it's affordable and easy to work with. The downside is that it has to be painted at the time of installation and repainted every 8 to 10 years. Using copper to line box gutters is expensive, but once it's installed, it is maintenance free.
Cut mini notched rafters called "lookouts" from the 2- by 6-inch roofing lumber stock.
Nail each lookout to a rafter. The bottom edge of the lookout should rest on the top of the wall, extending passed the outside face of the wall and the edge of the roof. Successive lookouts must each be notched to create sufficient slope to ensure rainwater will readily flow downhill when the gutter is lined with metal.
Nail 1-inch thick lumber to the top of the notched edge of the lookout to support the bottom of the metal liner.
Nail a fascia strip to the outside end of the lookout. The height of the fascia strip determines the outside slope of the gutter and will vary per the individual building size.
Line the wood gutter with either tin coated steel sheeting or rolled copper. To calculate the gutter box size and determine the dimensions of the metal insert, use the "Load and Run Box Cutter Calculator" in Resources (please note this is a metric calculator so conversion may be necessary) with following the steps.
Open the calculator and enter the square footage of the side of the roof the water is flowing down in the box labeled "Roof Catchment Area."
Type the rainfall intensity for your location in the "Rainfall Intensity" box. You can get this information from your local weather bureau.
Type in your "Trial Box Gutter Width." This is an estimate of what you think the gutter width should be.
Type in an estimate of your "roof slope" in degrees.
Enter "16" in the box labeled "Box Gutter Slope." This number represents the average slope for a gutter.
Click "Calculate" to get the final dimensions of the inside metal gutter insert.
Create S joints where two sections of the metal have to be soldered together. An S joint is created by bending the flat edge over on each sheet of the metal where two sections are joined. Bend over a minimum of 3/8 of an inch.
Hook the two bent edges into each other to form the interlocking S joint and then flatten the joint with a rubber mallet.
Heat the metal with a torch and flow enough solder until the S joint is completely coated with solder. Solder in all downspout connections.
Bend the metal to fit the dimensions of the wood gutter.
Clean the surface of the tin using a rag and paint thinner or mineral spirits. Prime the metal with a coat of metal primer. Let it dry and paint a top coat of exterior paint within 24 hours of painting the primer coat on. Insert the metal liner into the wood gutter.