Which Roof Slopes Hold Snow Longest, and What to Ask About Them

Snow stays on a roof for different lengths of time depending on which way each slope faces. A south-facing slope takes sun through the short winter days, so snow on it often slides off or melts within a day or two of a clear morning. A north-facing slope may get little direct sun for weeks in January, so its snow and frost can last long after the other slopes are bare. An inspection done before the first real snow of the season is a good time to note this, because the inspector can see the shingles, the valleys and the eave without anything covering them.

A simple check is to note which roof areas hold white the longest after each storm, and to compare that with what the inspector records. The yard is the cheapest place to start, since you can watch the roof from the sidewalk without climbing anything.

Why the slope facing matters in St. Louis

St. Louis winters cross the freezing line often. A week of afternoon highs in the thirties and overnight lows below freezing gives a roof many chances to melt and refreeze. Snow that melts on a warm afternoon runs down the slope, reaches the eave where the deck is colder, and freezes there. That is the start of an ice dam. Dams tend to form where the attic under the roof is warm and the eave overhangs with little heat reaching it, which often means the rooms directly below a heated attic.

The orientation question matters because the dam and the frost do not start in the same spot on every house. A south or west slope may thaw during the day and refreeze at night, which is hard on the edge of the shingles and on any flashing that sits in the path of the melt. A north slope may stay frozen through a whole cold stretch, which means its shingles and deck stay cold for longer and any moisture trapped under them has less chance to dry. Neither pattern is a leak on its own. Both are reasons to look at specific spots and to write down where they are.

What to ask the inspector to record

Ask for the orientation of every slope to be written on the report, not just labeled by letter on a sketch. Many reports name slopes "front," "rear," or "left," and a homeowner reading the report later may not know which direction those face. A short line such as "north slope over the back bedrooms" saves a phone call in the middle of February.

Next, ask what the inspector can see from the attic side of each slope. The underside of the deck on a north slope is often where frost shows up as white crystals or dark staining along the rafters. A band of staining on the deck near the eave can show that water has been moving there through more than one winter. Ask the inspector to photograph the rafter tails, the underside of the eave and the bottom edge of the sheathing on each side, and to note whether the attic insulation is pushed back from the top plates. Insulation pulled back and left open at the eave is a common reason a warm attic feeds ice at the edge.

Then ask about the valleys and the snow guards. A valley carries melt from two slopes at once, so it sees more water than either slope alone. Ask whether the valley metal is lifting, whether leaves or needles have packed into it, and whether any water staining sits below it on the ceiling. If the roof has snow guards, ask whether they are tight and whether they sit over a slope that gets little sun. Guards on a slope that stays cold for long stretches may need a different spot than the one the report assumes, and a loose guard can drop a sheet of snow onto a gutter or a walkway.

Inspection

Keys documents what it finds in writing, with photographs and measurements, and the written scope and photos go into the homeowner's hands. When a slope shows signs of ice damming or frost damage, the report should name the slope, the spot on that slope and what the photo shows, so you can compare it with what you see from the yard after the next thaw. Missouri law bars a roofing contractor from representing or negotiating a homeowner's insurance claim, and from saying anything about paying, waiving or covering a deductible. The report is a document you keep and take to your own insurer if you choose to, and the roofer does not carry the claim for you.

Keys attends the inspection as the contractor. The homeowner keeps the report, decides what to do about it and deals with their own insurer if a claim is involved.

What it costs

This page does not give a number for the inspection, because the price of any repair depends on what the inspector finds and on the house. Before the visit, ask the office to confirm whether the snow-slope check is part of the free inspection for your address and whether any repair estimate is billed separately. Keys can be reached at (314) 220-2333. If the answer is a repair, ask for it as a written scope with each item named, so the work on a north slope valley is not hidden inside a line that just says roof repair.

What to ask

1. Which direction does each slope face, and will the report say so by compass direction?
2. Which slopes show frost or staining on the attic side of the deck?
3. Is the attic insulation pulled back at the eave, and is there ventilation at the soffit?
4. Does any valley show lifting metal, debris or water staining below it?
5. Are the snow guards tight, and do they sit over a slope that gets little sun?
6. Can I have the photos of each slope and the attic underside as separate files?

Ask these before the first hard freeze, while the inspector can still see the shingles and the deck without snow in the way. When the snow comes, walk the yard after each storm and write down which roof areas hold white longest, so you have something to compare with the report at the next visit.