The first thing to do is measure up your outside wall 8’2″. This will be the bottom of your porch roof. You should measure up from the bottom of the sill plate. Make a mark on each side of the house. Snap a chalk line across the house.
Now screw a 2×6 into the outside wall following your chalk line on the bottom of the 2×6. Extend the 2×6 about 8′ past each corner. This is to serve as the porch corner wrap.
Now you have to determine where you want the top of your porch roof to be. It is strongly recommended to keep the pitch at least 6″ under windows. Do not go less than a 3 1/2 pitch. This mean 3 1/2 feet of pitch for every 12 feet of run. Now measure the wall or walls you are installing your porch roof on. Divide the this length by 2. This is the number of trusses you have to order to install your porch roof. Order your porch trusses from your local building supply store.
Now it is time to install your posts and beam that is going to support your trusses. The building supply store will give you a sheet of the measurements you need to place your beam. Mark these measurements on the ground and mark from the corner of the wall every 8′. Do not forget the posts 8′ from the corner posts 8′ past the house’s edge. You will also want a post 8′ back from the outside post. Make a special note of where the middle posts are placed. You don’t want to put the posts in front of the door or off center. Adjust these post placements accordingly. After you have the placement figured out, rent a skid steer with a drill auger attachment and drill holes where the posts will go. Then fill the holes with concrete and level off with a small 2×4. Let the concrete set up for at least 8 hours before performing the next step.
Now it is time to get your posts set. Attach a 2×4 at about waist height that is about 10′ long. Attach the post at the measurement that the truss company gave you. Screw the post to the board and plumb the post. Mark the bottom of the post and temporarily set the post to the side. Take the post bracket and mark the holes in the bracket of the concrete pad. Use a hammer drill with a 1/4″ bit and drill holes. Put the bracket into place and hammer in concrete nails attaching the bracket to the pad. Then put the post back on the bracket, bend up the side tab, and screw the post to the bracket. Re-attach the 2×4 and plumb the post. Add another 2×4 at an angle down from the top to keep the post plumb. Repeat on the other corner and run a string line from the outside of the posts.
Now use the outside posts to measure from and measure your 8′ increments again. This will be the edge of your post. Plumb the post from the mark, mark the bottom of the post, and install the bracket and attach the post to the bracket. Use 2×4’s in at an angle into the ground to keep the post plumb and on the string line. Repeat this step until all posts are stable. Now attach a 2×4 to the edge of the 2×6. Make sure the 2×4 is flush with the top of the 2×6. Now attach the 2×4 to the corner post. Use a level to make sure that the board is straight. Mark along the top of the 2×4 and all around the post. Repeat this on the other corner post and run a string line where the marks are. Mark every post along the string. Then measure down 11 3/4″. This will be bottom of your header that holds up you porch. If you are using LVL laminated beams, measure down 12 1/8″. Now cut the posts off at this height.
Next, install your brackets for your double beam on top of each post. Drill holes for the bolts and hammer the bolts in. Lag bolts that go through both sides are recommended. Now nail your 2×12’s or 12″ LVLs together in a triangle nailing pattern. Cut each beam to go between two posts. You will need a few people for the rest of this step. Carefully lift the beam and set it into the brackets. DO NOT SECURE YET!!! Continue this process until all the beams are in. Note that the outside brackets are 90 degree brackets. Now that the beams are in, screw the beam to the brackets through the screw holes. Then nail the beams together on the top at an angle.
You are finally ready to install your trusses! This is pretty simple. Start right at the corner and measure every 24″. Put a truss on the side that is going away from your initial measurement. Rest the trusses on the 2×6 runner board. The trusses on the corner will have a gap at the corner where a hip will need to go. Cut the pitch on the top of a 12′ 2×6. For your seat cut, hold the 2×6 where it plains through with the roof. You do this by putting your level across the top of the trusses into the 2×6. This mark is how much you need to cut off the bottom for the rafter to sit properly. The seat cut should be the same width as the beam it sits on. Cut your seat cut and double check to make sure the 2×6 plains through. This is called a hip. Repeat this for the other side. You will then have to fill in a rafter on each side of the hip in order to continue the roof line.
Attach the trussed with screws or nails.
Now it is time to sheet the roof. Using a nail gun will make quick work of this. Make sure you stagger the sheets and use H-clips between the sheets for strength. See the diagram below. Use my roofing instructions to properly install a water proof roof on the porch.
You are now ready to remove the runner board. Unscrew it and add the hanger brackets for the trusses. Use all the holes as this is required by code.
Normally, you will finish the ceiling with soffit, and install a deck or patio for the porch. Please very my other Home Tips for articles on these subjects.
