This project tasked our team with helping design and construct a new porch with wheelchair access for a family with a special needs boy. The current porch is dilapidated and in serious need of replacement. The end goal of this project is to deliver the family a safe and structurally sound front porch that can be enjoyed for many years to come. The porch will be slightly larger than the current porch on the front of the house, featuring railing, a non-slip wheelchair ramp, space for a porch swing, and potential for a future add-on. Due to the size of this project, it was split among 3 groups dealing with the foundation, railing/ramp, and roofing. My group specifically is assigned with designing the roof of the new porch.
The family’s current porch is in very bad condition, posing safety risks to their young boy. The roof is too shallow, causing the front door to hit it when opening, and the boy has the potential to end up in a wheelchair, which is unaccommodated by the current porch. Additionally, the family would like the ability to hang a porch swing and eventually add on to the new porch. The new porch overall aims to bring safety, wheelchair accommodation, and the opportunity of expansion to the family that the current porch does not have. Specifically, we aim to design the roof to allow the front door to open unobstructed, support a porch swing, and make it easy to build off of if desired, ultimately tying together the foundation, railing, and ramp into a complete porch for the family to enjoy.
Size:
Roofing Material:
Accommodations:
Safety:
We began by researching how roofs are generally framed, including the sizes of wood used, the different potential layouts, and the connections between each piece of lumber. After having gained a basic understanding of how to frame the roof, we took to brainstorming potential designs we could use in our specific setting. We researched two main types of roofs, one type being a lean-to and the other being an open gable (imaged to the right).
We then researched the different roofing codes, specifically the required slope for the roofing material we are to use. In addition to this, our team also looked at potential loading requirements for a porch swing and snow load. That is, we looked at the static & dynamic loads that our roof might experience and factored these into designing a safe way to mount the porch swing to the roofing structure. The snow load that we found to design for was ~ 15 pounds per square foot, which was well within our capabilities for this project. With all of that settled, we began illustrating concepts for our roof.
This was our first design, where we tried to focus on what materials and wood sizes we were going to use for the main roofing structure. Here, the design is based on a lean-to and includes several 4×6 beams that sit on 6×6 posts as the main infrastructure of the roof. There are 2×6’s being used as the rafters to connect the front and back of the porch that the metal roofing can attach to. Notice that the ends and middle of the rafters are two 2×6’s that are “sistered” up to increase load-bearing capability and overall stability. There are also supports on the beams that attach to the 6×6 posts, and we believe that the rafters will be sufficient at holding a porch swing, given some extra reinforcement that isn’t shown. We are unsure of the orientation the family wants the swing to be. Regardless, one thing this concept does not address is how to connect the porch roof to the existing roof, while unobstructing the front door.
Pros
Cons
Our second design featured a more complex structure, that being based on an open gable. This roof focused less on the internal framing and materials used and more on the aesthetic design that we would go after. As imaged to the right, there are 4 posts that support this open gable design, which has a central beam that ties into the house structure. This center beam is then the focal point by which the rafters and roof are attached, and the roof is sealed off using caulk or a similar material to prevent water from infiltrating.
Pros
Cons
For our third design, we primarily built off the first concept design. It follows the same type of lean-to construction, but it focuses on the roofing connection and the potential solution to that issue. Here, we can see that the porch roof extends above and slightly over the house roof, featuring a gutter that is sealed between the two roofs to catch any rainwater from splashing down onto the porch. This gasketing could be similar to a caulk or outdoor adhesive material.
Pros
Cons
Our team has opted to go with the third concept design, where the structural layout of concept 1 is combined with a roof that extends over the existing house, coupled with the addition of gutters to catch any rainwater.
After discovering the structure was not going to be inspected, we felt confident in going with a 1:12 slope (with proper sealant) for the roof.
As aforementioned, this design is primarily based on a lean-to model and will extend ~1.5 feet over the existing house roof, with a 5ft overhang on the front and left side to cover the wheelchair ramp that wraps around. The back posts had to be moved 6 inches forward to accommodate our gutter system that we plan to install on the house.
Diving more in-depth into our roofing design, we plan to feature the following:
Our first analysis focused on determining the safety of the cantilevers present in our roof, those being the 5ft overhangs on the front and left sides.
The following presents a detailed calculation of the maximum cantilever moment acting on the roof framing. As the framing members demonstrate the capacity to resist this maximum bending moment with a safety factor of 5.5, it can be concluded that all cantilever elements within the roof system maintain a minimum safety factor of 5.5
Our second analysis focused on the header & rafter sizing that we chose for our design.
We came to the conclusion that double 2×8 headers and 2×6 rafters would be more than sufficient for our application based on roofing span tables, and discussion with Dr. Canfield and Dr. Henderson.
Supporting Links:
https://www.southernpine.com/wp-content/uploads/2023/11/SPtable17_060113.pdf (Rafter span table)
https://www.southernpine.com/wp-content/uploads/2023/11/SS_1-6L.pdf (header span table)
Our third analysis focused on the header design with a two-person porch swing added.
For this analysis, we calculated the internal shear and tensile stresses induced by the swing weight on the beam.
We concluded that a single 2×8 header would only provide a safety factor of 1.47, assuming a max swing weight of 560 lbf (as the swing has a maximum capacity of 500lb and the swing is estimated at 60lb). Shearing within the beam is not a worry, as there is a safety factor of 5.64.
Our design change is to increase the heading to two adjacent 2×8 beams, which will double the mass moment of inertia and thus increase our design safety factor to 2.94 for normal stress within the beam.
Our project didn’t feature any notable testing. However, we did physically try to test the stability of our porch swing beam by having multiple team members hang and pull on the beam simultaneously.
The beam had no noticeable deflection or undesirable movements despite our best efforts to do so. Given this, we assumed our swing beam would be safe to support a swing and any occupants.
Despite the scope of this project, the team thoroughly enjoyed the experience. Collaborating and coordinating with two other teams to construct the porch was both engaging and challenging. The process provided valuable insight into real-world scenarios, particularly in adapting to evolving customer requirements, managing cross-team communication, and overcoming unforeseen obstacles with limited resources.
Throughout the project, team members developed practical skills in using tools and, more importantly, gained a deeper understanding of the transition from design to execution. This process revealed several challenges that are difficult to anticipate during the planning phase, highlighting how discrepancies can emerge between initial designs and the final product. For instance, issues such as slight measurement inaccuracies and tool limitations required on-the-spot problem-solving and, in some cases, led to minor design adjustments.
Overall, the project was a highly rewarding experience. Every team member remained supportive, engaged, and committed throughout the process. Seeing the culmination of a semester’s worth of work come together in the final product was both satisfying and meaningful.
