The Porch and Its All Important Roof
A porch without a roof is merely a deck. Besides, the porch roof is an important defense against the elements.
Maintenance and repair of a wood porch start with keeping its roof sound: some field notes, and a visit to Abatron.
When it comes to porch repair, the posts, decking, rails, and balusters tend to get all the attention. For some reason the porch roof—which protects those vital elements from rain, wind, and snow—gets scant coverage. That’s a shame, because neglecting the roof puts the entire structure at peril.
Telltale signs of a deteriorating porch roof include curled or missing shingles, moss growth, metal that’s rusty or in need of a good coat of paint, and roofing tar applied as a stop-gap measure. Peeling paint on the ceiling boards underneath may be a sign of moisture buildup or a roof leak.
Any roof that’s aged a century or more has likely been repeatedly patched or covered with new materials without the old having been removed, warns Andrew Curtis of Full Circa, a restoration specialist. “What you typically see on historic houses in Oregon is three layers of roofing material.” While a deteriorated soffit or broken piece of the entablature may have been replaced, “no one ever goes down to the bottom layer to make repairs.”
The porch roof is more than shelter. It is the first defense against the effects of water and ultraviolet light, protecting all the structural and decorative elements that can be expensive to replace.
When faced with crumbling layers of roofing over a suspect roof deck (substructure), Curtis and his team usually do a tear-off—that is, ripping the roof down to the old support system. This removes all accumulated layers of shingles, which trap moisture.
Inevitably, Curtis’s team finds corroded terne metal and rotted deck sheathing, especially toward the edges of the roof; damage to rafters underneath the sheathing; and plugged or damaged gutters. Before starting repairs to the roof, the foundation for the entire porch and any supporting columns must be assessed for damage and structural integrity. Usually the entire porch structure temporarily must be supported, sometimes with an extensive shoring system held in place by scaffolding. This allows work on all parts of the porch to proceed at once.
After all of the roofing layers have been removed, the team has access to the structural framework beneath, which includes the rafters on which the roof proper rests, as well as ceiling joists that support the porch ceiling underneath. The roof structure as a whole rests on beams (the entablature), which are in turn supported by the foundation below. The ceiling joists are laid out turned on edge, usually 2x6 or 2x8 tall, creating a flat, level framework for the rest of the work. If there are integral gutters, the ceiling joists are extended out over the beam so that the profiles of the gutters can be cut in.
All of the weight of the porch roof rests on the rafters, which tie in to the plate (or bed moulding) on top of the beam. Repairs are made us-
ing the old timbers as a model for the new. (You may want to lay the old framework of rafters on the ground and test-fit new rafters before installing them.)
The pitch is calculated and adjusted for proper drainage, starting at the center of the porch roof. Since the pitch can be as little as 1/8" per foot, the Full Circa team often increases the slope of the gutters so that they’ll drain more efficiently—especially when internal gutters are intended to direct water toward vertical downspouts on the façade.
Once rafters are in place, the roof is sheathed with wood that closely matches the original in quality and thickness, whether it was an old form of plywood, or tongue-and-groove or shiplap. If the roof will be capped with metal, in most situations ½ " thick plywood goes on top of the sheathing.
Next, an ice and water shield goes down, extending into the (rebuilt) internal gutters. The shield is a bituminous, sticky-backed material that can be nailed without leaking. The metal—either copper or 18- to 22-gauge galvanized metal— goes directly over the ice and water shield.
Although either material is superior to the terne-plate of the past, galvanized metal must be primed before it goes down. Sheets are larger, creating fewer joints when riveted and soldered in place.
A less expensive reroofing method, called a torch-down, uses rolled asphalt roofing. The extra layer of plywood is omitted, and a granulated asphalt material goes down directly on top. “It has a presheet, also with a granulated asphalt base,” Curtis says. “You melt one to the other using a torch. That’s why it’s called a torch-down.”
On historic wooden houses, rarely does the roof alone need work; porch roof repairs are usually part of a project that extends to deck and columns.