How to Construct a 30 x 40 Metal Building
Building a 30-by-40 foot metal pole barn takes only a few days and is relatively inexpensive. Purchasing a kit with pre-measured lumber and hardware takes much of the guesswork out of the process.
Grade the area where the metal building will be constructed by leveling and packing the dirt to make a level surface. This can be done by hand with a shovel and tamper for a very small area, or with a bobcat for a larger space. Check to make sure the space is level by placing two stakes and running a level string line between them (use a level to check and adjust it), and follow this for your grade line. A dirt floor is acceptable for this type of structure but you can add a gravel or concrete pad if you desire. For this instructional it is assumed a plain dirt floor is used.
Measure the exterior lines of the building on the ground using the chalk line. Begin by setting a wood stake in the ground at what will be a corner point of your structure. Stretch a 30 foot length of string out from this and pound another stake. Tie off your string, check it for level and adjust as necessary. Make a 90 degree angle turn and run a 40 foot level string measure, and add your third stake. Run the final 30 foot length, then finally tie the last two together, checking for level. You should have made a 30 by 40 foot rectangle. This is the outline of your structure.
Dig the holes for the posts. Posts for a large structure should be at least 4 feet in the ground. Check the local building code to find specific requirements for your area. If you are in an area with heavy ground moisture, use a few inches of gravel fill for drainage in the bottom of each hole, adding this to the depth you dig. Set the poles in place, brace them with 2-by-4 pieces of lumber wedged against each side, and check to make sure they are level. Secure the posts with concrete if desired. If the ground is firm, you can just fill the holes with soil around the posts.
Begin the frame construction by adding the stringers to the poles. Stringers are wider pieces of lumber that stretch between the posts at the top of the walls and support the structure. In some cases a larger piece of thick lumber called a 'header' will be required above a space if you are installing a garage door and it requires a larger load-bearing weight.Your kit will have a diagram of the size and placement of the stringers or headers if they are required. These will likely be attached with a bolt for durability. The hardware will be part of the building kit.
Install the roof trusses. Start with an end truss and anchor into place with the hardware provided. Trusses are anchored to the top of the walls with brackets and nailed in place. The truss is the pre-constructed angled roof sections that will support the roof, and there will be a series of them evenly spaced across the top of the structure. Brace the first trusses with poles or lumber as you frame them in place, then use the existing trusses to brace the remainder.
Add the purlins (the lumber pieces that support the weight of the trusses and provide an attachment point for the metal siding). These pieces are attached across the trusses and also horizontally between posts.
Screw the metal siding and roofing panels to the structure using the screw gun or screwdriver. Overlap them slightly at the edges according to your building plan kit. You can add storm clips to the structure if you are in a heavy weather area and you feel it is necessary, or if it is required by law. These can be purchased with your kit when you buy it. Storm clips are small metal plates that nail to the roof trusses anchoring the roof more solidly to the walls.
Things You Will Need
- Digging equipment such as a Bobcat
- Chalk line
- Wood stakes
- Screw gun or screwdriver
- Materials kit for 30-by-40 foot metal pole building