When designing a porch, the goal is to make it look original to the home's construction. Create a porch that harmonises with the architectural style of the house in terms of roof shape, porch railings and foundational style. The porch should look appropriate from every angle and proportionate to the existing house. Plan to construct the porch roof to match the home's roof material to make the new project look seamless with the rest of the house.
Do the necessary research for porch building. Look through home design books and porch magazines to review types of porches that might work. Visit local authorities to inquire about local building codes. Obtain a building permit before starting any porch construction. Inquire about how far away from a neighbour's property line you will need to build the porch.
Measure the allowable space for the porch. Sketch a porch size that looks appropriate with the rooflines and facade of the house. Keep in mind that the rooflines of the porch will determine its architectural design. Draw the porch in exact detail to fit the house from every angle. Give every roof angle a slope of at least 30 degrees, so the roof will shed rain and snow.
Design the porch foundation. Decide whether you'll construct the porch framework on a concrete slab or wooden foundation. Sketch the steps, support posts and railings. Plan to build floor joists on 16-inch centres that will support an exterior-grade plywood flooring base and pressure-treated floor boards on top of the plywood.
Use graph paper to lay out the exact dimensions of the porch drawn with the house. Include exact window sizes and the space between the porch posts, for example. Make sure the roof areas of the porch don't cover any second-story window sills. Fit the porch's uppermost roofline under second-story windows to allow for a margin of at least 6 inches.
Plan the building steps and stages. Work from the foundation up to plan each phase. List all building materials needed for the foundation, framework, roof sheathing and roof materials. Include railings that fit the design period of the house. Include guttering and downspouts in the design to make the porch roof blend with the existing overhang areas of the house.
Install splash blocks at each end of the porch, so that water moving off the porch roof will be carried away from the foundation. Water can easily erode the pilings, footings or the concrete slab flooring of a porch over time.
Bolt the porch framework to the house versus using screws and nails only. The weight of the porch can easily cause the structure to pull loose from the house if you don't use a bolt system.