Each Roof Slope Ages on Its Own Schedule in St. Louis

A roof in St. Louis does not age evenly. The slope that faces the afternoon sun, the one that sits in shade through most of the winter, and the one that takes weather head-on from a storm front each wear differently, and the same shingle can look fine on one side and tired on the other. An inspection that reads the roof as one surface will miss the slope that is actually failing. Before you decide what to do next, it helps to know what each side of the house has been doing.

Why the slopes do not age together

Shingles fail through heat, cold, moisture and ultraviolet light, and each of those reaches a roof at a different strength depending on which way the slope faces and what stands in front of it. A south-facing slope gets direct sun for the longest part of the day. A west-facing slope takes the hard afternoon heat in July and August, when the surface of an asphalt shingle can climb well past the air temperature. A north-facing slope often stays cool and damp, with slower drying after rain and less sun to burn off the growth that settles on it. Each pattern leaves its own signs, and an inspector who knows them can tell you where to look first.

The south and west slopes

On the sun-facing side, the usual wear is granule loss and surface drying. Granules are the mineral grit pressed into the top of the shingle. They protect the asphalt underneath from ultraviolet light, and when they loosen, the shingle loses some of that protection. You will often see granules collect in the gutter below the downspout, or a bare dark patch on the lower courses where the shingle has been thinned by years of sun. Heat also softens the sealant strip that holds one shingle to the next, so a shingle that has lost its seal can lift in a windy week even though nothing else looks wrong. An inspection on this side should look closely at the sealant strips and the exposed tabs, not only at the overall color.

The west side also takes more thermal movement. Shingles expand in the afternoon and contract at night, and across many summers that cycle fatigues the nail heads and the sealant. A nail that has backed out a few millimeters can lift the shingle above it. Ask whether the inspector checked the nail line on the west slope and photographed it, since a popped nail is easy to miss from the ground.

The north and shaded slopes

The shaded side tells a different story. Moisture stays longer after a rain, and in a St. Louis winter it can sit on the surface through several freeze and thaw cycles. That is where algae, moss and lichen get a foothold, and the dark streaks people notice from the street are usually algae rather than a leak. Growth on the surface is a maintenance question first, but it also means the shingle is holding water longer than it should, and the lower edge of that slope is where ice tends to build at the eave. A roof that drains slowly in shade is also a roof where the nail line and the valleys need a closer look, because wet wood at the deck edge rots faster than dry wood does.

Shade also hides damage. A slope that never gets direct light can look sound from the yard while its underlayment and deck have been soft for years. When the inspector gets onto the shaded side, the useful questions are whether the surface is holding water in low spots, whether granules have washed into the valleys, and whether there is any sag along the eave line.

Storm side and wind exposure

Hail and wind do not respect the compass. They do tend to favor one side of a roof on a given day, and the side that takes the most force is the one facing the storm's approach. Many of the severe fronts that reach the St. Louis area arrive from the west or southwest, which means the windward slopes and their edges see more lift on a shingle, more impact from hail, and more wind-driven rain at the rake and ridge. A storm can leave the leeward side almost untouched while the windward side shows bruised granules and creased tabs.

That is why the storm date matters to the inspection. If you know roughly when the wind or hail came through and from which direction, you can point the inspector at the slope that took it. If you do not know, the inspector should still read every slope, but the one facing the last storm deserves the closest attention and the most photographs. Keep your own note of when the damage was first noticed, because a dated record is more useful than a memory of the weekend.

What to ask the inspector to photograph, slope by slope

Before the inspector leaves the roof, ask for a photo set that labels each slope by compass direction. The label is what lets you compare the photos later, against the next inspection or against a second company's quote. A useful set includes:

• A wide shot of each slope showing the full run from eave to ridge.
• Close shots of the sealant strips and tab edges on the sun-facing and west-facing slopes.
• Close shots of the nail line along the upper third of each slope, where thermal movement shows first.
• Photos of the valleys and low spots on the shaded side, with water lines or debris visible.
• Photos of the windward edges and rake, with any creased tabs or displaced granules marked.

Ask whether the inspector will mark the photos with the slope direction and the date. A photo without a label is hard to use six months later, when you are trying to tell what changed.

What the slope read does not tell you

A slope-by-slope inspection describes condition. It does not forecast how many years a roof has left, and it does not decide between repair and replacement on its own. A sun-faded south slope with sound sealant may be fine for several more seasons, while a shaded north slope with wet valleys may need attention sooner than its color suggests. The reading gives you the facts that make the next decision clearer, and it gives the roofer you choose a specific place to start. If the inspector cannot say which slope is weakest and why, ask for another look before you commit to a plan.

If you want the roof read slope by slope, call Keys Roofing at (314) 220-2333. The inspector will walk each side, photograph it by direction, and leave you a written scope with the measurements and photos in hand. Your insurer is your own to deal with, and the inspection gives you a record to work from while you do.