The Long Life of a Roof, and the Short Life of a Neglected One
A roof is bought once and consumed slowly. What decides whether it reaches the end of its warranted span is less the material than the small attentions paid to it along the way.
Among the components of an ordinary American house, the roof occupies a peculiar position. It is among the most costly things a household will ever buy for the building, it is replaced perhaps twice in the tenure of a single owner, and it is almost never looked at. A furnace announces its decline. A water heater fails in a manner impossible to ignore. A roof simply ages, in full view of the street and entirely out of view of the people beneath it, and then one spring it is finished.
The literature of the trade speaks of a service life, and manufacturers write warranties in terms of decades. Both are honest figures, and both describe a roof that is properly ventilated, properly flashed, and periodically attended to. The distance between the warranted span and what a particular roof actually delivers is not chiefly a matter of the shingle purchased. It is a matter of four conditions, none of them expensive to maintain and all of them commonly ignored.
The First Condition: Ventilation
A roof is cooled from beneath. Air enters low, at the soffit, passes up through the rafter bays, and leaves high, at the ridge. When that circuit is open, the underside of the deck stays near the temperature of the outside air, and the shingles above it age at the rate their maker intended. When it is blocked, by insulation stuffed into the eaves, by a bath fan discharging into the attic, by a ridge vent painted shut or never installed, the space becomes an oven in summer and a condensing chamber in winter.
The consequences run in both directions. Heat cooks the asphalt from below and shortens the life of the covering. Moisture condenses on the cold underside of the deck, wets the sheathing, rusts the fasteners, and in time delaminates the plywood the shingles are nailed to. A roof over a poorly ventilated attic can fail well short of its warranty while looking, from the street, entirely respectable.
The Second Condition: Water That Leaves
The covering sheds water. The gutter and the downspout are what carry it away, and they are the part of the system a homeowner can actually reach. A blocked gutter holds standing water against the fascia and the first course of shingles. In a hard freeze it holds ice, and ice that cannot drain backs up under the covering and finds the deck.
The remedy is seasonal and requires no skill: clear the troughs, run water through each downspout, and confirm that what leaves the downspout is carried well clear of the foundation rather than delivered into the corner where the wall meets the ground. A household that does this twice a year, in late spring and again after the leaves are down, has removed one of the two most common causes of premature roof failure.
The Third Condition: The Seams
Roofs seldom fail in the middle. They fail where one plane meets another, where a chimney or a vent stack or a dormer interrupts the field, and where the covering terminates at a wall. These junctions are sealed with flashing, thin formed metal that does the actual waterproofing while the shingles above merely shed. Flashing that has lifted, corroded, or been sealed with caulk instead of replaced is the origin of a great share of the leaks that homeowners discover as a stain on a bedroom ceiling.
This is inspection work rather than maintenance work, and it is properly done from the roof by someone who knows what a correctly lapped step flashing looks like. In most cases the sound course is an inspection every few years by a roofing contractor of established local standing, with any finding addressed while it is still a seam and not yet a ceiling. The economics favor this arrangement heavily. A flashing repair is a modest bill; the same failure discovered two winters later has usually taken sheathing, insulation, and drywall with it.
The Fourth Condition: What Grows and What Overhangs
Trees are the slowest of the four problems and the easiest to forget. A limb that overhangs the roof deposits debris in the valleys, holds moisture against the covering, shades the surface into moss and algae, and in a high wind becomes an instrument of considerable damage. Trimming back the canopy so that nothing rests over the roof plane costs a fraction of what a single fallen limb costs, and it removes the shade that keeps a roof damp between rains.
The Arithmetic of Attention
None of this is complicated, and that is precisely why it is neglected. The four conditions can be reduced to a short annual habit: keep the attic breathing, keep the water moving, have the seams looked at by someone competent, and keep the branches off. A household that holds to it will generally get the span it paid for. A household that does not will replace a roof early and will usually be told, correctly, that the failure was not the manufacturer's.
The Chronicle observes, as it has in other matters of household economy, that the expensive failures in an American house are rarely sudden. They are ordinary failures that nobody looked at in time.