In this edition of DIY projects gone wrong I will explore porch and carport additions.
When I design a house or an addition to a house I use certain criteria to decide whether I need to use the services of a licensed Structural Engineer. If the design includes a beam over 20', a ceiling height more than 10' or lateral resistance that cannot meet the prescriptive requirements of the code then I use the services of a Structural Engineer. Many Home Inspectors find an incorrectly built porch and they immediately recommend having a Structural Engineer look at it because recommending the method to repair it is beyond the scope of a Home Inspectors license. In my structural design classes at the Arizona State University School of Construction and in the course of designing many custom homes I have learned how to design structural members that meet standard building practices. This does not mean that I never recommend a Structural Engineer look at something or I try to practice Structural Engineering myself. It just means that I am able to set the threshold of when a Structural Engineer is needed a little higher
The following pictures are of porch additions that were not done to standard building practices.
This carport uses the fascia as the ledger for the rafters. The problem with this is that the rafters now rely on the weight of the roof to hold them up. Most would conclude that the weight of the rafters push down on the top cord of the trusses and therefore push down on the wall. In reality the wall becomes a teeter totter point that lifts up on the top cord of the truss. This can cause the top cord of the truss to split or pull up on the ceiling causing cracks in the ceiling.
This next picture is the other end of the rafters. The steel columns sit on a block retaining wall. They are spaced close together, which is a good thing. The problem lies in the beam used to hold up the rafters. All beams should be oriented so that their longest side in cross section is vertical. If you look closely you can see this 2x sagging at the rafters that are not close to the columns.
There are two other issues with this carport. The rafters are 2x6's at 24" on center. They span at least 16 feet. The slope of the carport roof is about ¼" per foot. This carport is in Globe Arizona. In the Phoenix area we get snow about once every 100 years. In Globe they get it once or twice per year. If you stand back from the front of the carport you can see the bow in the roof.
The home owner had inherited the home when his parents passed away. When I showed him the bow in the roof he said "No wonder my dad never parked the car under it when it snowed." Placing the rafters on the top of the wall would have increased the pitch of the roof to allow the snow to melt and run off faster. Sizing the beam and rafters appropriately would have made this carport much safer.
In the next photo of a Phoenix home they didn't use the fascia as the ledger. They bolted the rafters to the ends of the truss top cords. This is a stronger connection but it still created the teeter totter effect. The 2x4 rafters are also too small for this patio.
This is the front porch of the same Phoenix home. Here they did use the facia as the ledger. This time they covered it with the plywood. This also made the porch roof slope too shallow to allow for proper drainage.
This patio has the beam vertical. The problem here is that the beam and rafters are undersized. The full weight of the patio is bearing on the nails. The post should be cut shorter and the beam should be sitting on top of the post. The hangers that are designed to connect the posts to the beams also help resist lateral forces. These nails will not resist any lateral forces.
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professional opinion almost became fatal and could be if not corrected. The home owner built a home office inside the garage. What they failed to take into consideration is that the combustion air vents for the gas water heater are on the oposite side of the garage from the home office. When the door and window to the office are closed the water heater only has one source of air to burn. It has to pull air through the vent. This causes a backdraft. The smoke stains on the back of the water heater indicate that a backdraft has happened at least once. The next time it happens it could turn the whole house into a nice little pile of ashes.