Aluminum Roofing for Porches and Patios in New England

Can a porch roof use the same aluminum roofing as the house?

A porch roof can use the same Interlock aluminum roofing as the main house if its pitch is at least 3/12. That means the roof rises at least 3 inches for every 12 inches of horizontal run. Many gabled entry porches, wraparound porches with a moderate pitch and shed-roof porches on farmhouses meet that number. When they do, matching the porch to the main roof is usually the best-looking result. The same profile, whether Slate, Cedar Shingle, Shake or Mediterranean Tile, and the same color carry across the whole house, and the porch gets the same concealed fasteners and corrosion resistance as the rest of the roof. The pitch is the first thing to measure. If it falls below 3/12, the porch needs a different roofing approach no matter what the main roof is.

Why doesn't the Interlock system work on low-slope porch roofs?

The Interlock system is not suitable below 3/12 because shingle-style interlocking panels depend on gravity to move water down and off the roof. On a very shallow slope, water drains slowly, and standing water, snowmelt and ice can sit against the laps long enough to find a way in. That is a familiar problem in New England. Many porch roofs on triple-deckers, Victorians and older Colonials were built nearly flat, sometimes with a slight pitch of an inch or two per foot. In winter those roofs collect snow, and meltwater from the main roof runs onto them and refreezes. For slopes under 3/12, a low-slope membrane or another system designed for flat roofs is the right answer. We will tell you plainly if part of your house falls into that category, so you can plan both roofs together.

How do you check the pitch of a porch roof?

You can check porch roof pitch with a level and a tape measure. Place a 12-inch section of a level flat against the roofing, or against a rafter in an open porch ceiling, so it is perfectly horizontal. Then measure straight down or up from the 12-inch mark to the roof surface. That vertical measurement in inches is the rise per 12 inches of run. A reading of 3 inches or more means 3/12 or steeper. Under 3 inches means a low-slope roof. Phone apps with an inclinometer can give a rough number from the ground too, but a measurement on the roof or rafter is more reliable. If you would rather not get on a ladder, the pitch of every roof plane is something we measure during an in-home roof consultation.

What about freestanding patio covers?

Freestanding patio covers and pergola roofs usually use simpler aluminum products, such as corrugated sheet, insulated aluminum panels or louvered aluminum systems. These structures are often built at low pitch, sometimes close to flat, and they shelter outdoor space rather than heated living space. For that job, the priorities are different: light weight, shade, enough strength for snow, and reasonable cost. A full architectural roof system is rarely needed over a patio table. Snow load is the part New England owners should not skip. Patio covers here must be built to carry winter snow, and local building departments set the design loads, which vary between, for example, coastal Rhode Island and the hills of Vermont or western Massachusetts. Ask your local building department what permit and design load apply before building one.

How does snow behave on a porch roof?

Snow tends to slide off a metal porch roof once it starts to melt, and that matters because porch roofs often sit directly over entries, steps and walkways. A sheet of wet snow releasing from a porch over the front door can land right where people walk. Planning ahead helps. Look at where snow from the main roof lands, too, because a steep main roof can dump snow onto a lower porch roof. Snow retention devices can be considered over doorways, and gutters and downspouts should be laid out so meltwater does not drip onto steps and refreeze. Ice dams can also form where a porch roof meets the house, especially if warm air from the house reaches that area. Ice dams come from heat loss and ventilation, not from the roofing material, so they are worth looking at on their own.

Are there extra steps for historic homes or condominiums?

Historic homes and condominiums can need approvals before a porch roof changes. Porches are often among the most visible features of a Victorian or Colonial, and many New England towns have local historic districts with review of exterior changes. Check with your local historic district commission before you plan new roofing material or a change in color or profile. In Massachusetts, condominium buildings are governed under Chapter 183A, and porches and roofs are commonly common or limited common areas controlled by the association. Talk to your condo trustees or board before you commit to work on a porch roof. These steps do not change the pitch rule. A porch below 3/12 still needs a low-slope roof, even if the main roof is going to be Interlock.

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