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.

Old House Journal - - Contents - BY MARY ELLEN POL­SON

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.

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