How snow weight, drifting and roof shape affect a Palouse roof, and who confirms the design figure for an address.
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Snow load is the weight of snow on a roof, and it changes with the depth, the moisture, the wind and the shape of the roof. Drifting and sliding concentrate the weight where roof planes meet. The building code sets a design figure for each address, and the local building official confirms it.
Snow load is one of the first things a homeowner worries about on the Palouse, and one of the easiest to misunderstand. The weight of snow on a roof is not a simple function of how deep it looks from the street. It depends on how much water the snow holds, how long it stays, which way the wind blew it, and where it piled up against the roof's shape. A deep, dry snow in an open field can weigh less than a thin, wet layer that has refrozen on a shaded roof, and the difference matters for the structure below.
Moscow and Pullman publish their own design criteria, and they are not the same. The city of Moscow's building code adopts a local amendment to the international building code that addresses snow buildup at valleys, parapets and roof offsets. Pullman, Washington, publishes its own criteria under Washington's amendments. A design figure for one address is set by the code in force there, and the building official confirms it. This page does not print a snow load figure, because the sources available do not agree on one for Moscow, and it would be wrong to pick one.
What a homeowner can do is understand where snow concentrates, check the condition of the roof and attic, and ask the right office the right question. Roof care for snow is mostly about inspection, drainage, ice management and keeping the roof's weak points sound before winter. A technician can look at the roof, say where the load is likely to build up, and recommend the next step. Phones are answered 24/7, and a visit the same day happens only when a technician is free.
The design snow load for a building is set by the code in force at its address and confirmed by the local building official. The actual load on a given day depends on the depth, moisture and drifting of the snow, which is why the design figure and the real weight are different things.
The design figure is a number the code asks the structure to carry, and it is chosen with the local climate in mind. The actual load is the weight of the snow on the roof at a given time, which can be above or below the design figure depending on the storm and the wind. You cannot judge either one from the street, and you should not try to calculate it yourself from the snow depth.
To find the figure for your address, contact the building office for your jurisdiction. In Moscow that is the Building Safety Division. Outside city limits, the county building official confirms the figure. In Pullman and the Washington side of the map, the Washington rules apply, and the city's published criteria are the place to start.
Wind moves snow off exposed slopes and deposits it in the lee of walls, dormers, chimneys and parapets. Where two roof planes meet, the drift can be deep and concentrated, and the snow stays longer in shade.
A valley is a low point between two roof planes, and it collects snow sliding from both sides. A dormer or an addition creates a wall that catches drifting snow on the lee side. A parapet on a low roof holds the snow in place like a dam. The local building code recognizes these conditions, and they are the first places a technician checks.
Shade matters too. A north-facing slope or a draw below a hill stays cold and holds snow longer than a sunny slope. Because the Palouse has rolling hills, two roofs a short distance apart can behave very differently, and the technician looks at each roof's exposure rather than assuming the same pattern across the town.
Snow can damage a roof when the structure is overloaded, when meltwater is trapped under ice, or when a slab releases onto the eave. Signs include sagging, cracking framing, doors that stick and water stains after a thaw.
The most dangerous signs are structural: a ridge or rafter that sags, a crack in a beam or a joist, or a wall that moves when snow is removed. If you see any of these, keep people out of the area below and call for an assessment at once. Do not climb onto the roof to check it yourself, and do not try to remove snow from a damaged area.
Water damage is more common and slower. A stain on a ceiling near a valley or an outside wall after a thaw points to meltwater that has found a path under the roof covering. The stain is a sign that the roof's drainage or its seal has failed somewhere, and the technician will trace the path back to its source.
Removing snow from a roof is risky, and it is best left to a professional who can work safely at height. A roof rake from the ground can help clear an eave on a low roof, but climbing onto a snow-covered roof is the dangerous part.
Removing all the snow can damage the roof covering and the gutters, and it can leave the roof bare and exposed to the next freeze. Partial clearing from the ground, particularly at the eave where ice is forming, is a common measure. It should be done with care, and the person clearing should keep clear of the falling snow and the eave.
A technician can advise whether snow removal is needed at your address and whether the roof can take it safely. The decision depends on the snow load, the age of the structure and the condition of the roof, and it is not a question that a homeowner should answer by guessing.
Do not climb onto a snow-covered or icy roof to clear it, and never stand on a roof edge to knock snow or ice off. Keep people, pets and vehicles away from the area below the eave when snow or ice is loosening, and do not try to chip ice from the gutter with a metal tool while standing on a ladder. If you see sagging framing, a crack in a beam or a wall that moves, leave the building, keep others out and call for an assessment at once. A roof rake used from the ground at a low eave is a safer option than any work on the roof itself.
The technician looks at where the roof changes direction, such as a valley, a dormer, a parapet or an addition's roof meeting the main house. These junctions are where snow drifts and slides, and where the weight of a single storm can concentrate. Identifying them first tells the technician where to look for the structural and drainage risks.
The attic is the place to see how the structure is handling the load. The technician looks for sagging rafters or ridge boards, cracked or split framing members, and daylight at the eaves. Wet insulation and dark staining on the decking point to moisture that has been trapped under the snow.
Snow that stays on the roof has to melt and drain somewhere. The technician checks whether the gutter and the downspout are clear, whether the eave detail lets meltwater leave, and whether a line of ice is forming at the edge. A blocked eave turns a drainage problem into a leak and a structural one.
The design figure for an address is set by the code in force there and confirmed by the building official. The technician will tell you whether a snow-load question affects the work, and will direct you to the right office for the number. For a job outside city limits, the county building official is the right contact, and for a job in Washington the Washington rules apply.
The inspection ends with a written list of what was found, what is urgent, and what should be checked after the next storm or thaw. That plan is the practical part of snow care. It gives the homeowner a short list of things to watch and a clear point at which to call back.
Drifting builds snow in the valleys, behind parapets and at the foot of a roof offset, and the load there can be far greater than the average across the roof. The building code addresses this directly in Moscow's amendment. For a homeowner the practical question is whether a valley or an offset has the framing and the drainage to carry the weight of a drift, and that is checked in the attic and at the eave.
Ice at the eave adds weight that is not spread evenly across the roof. Where meltwater refreezes at the edge, the ice can build into a ridge that holds more water behind it. The weight is local, but its effect on the gutter, the fascia and the roof covering can be large. Managing it is part of snow care, and it is covered on the ice dam service page.
A smooth roof can hold snow until it releases it all at once. The slab is a load that lands on whatever is below the eave. This is a different risk from the structural load itself, and it is managed by planning where the snow can go, using retention where needed. The metal roofing service page covers the options in more detail.
Low-slope roofs hold snow rather than shedding it, so the weight stays on the roof for longer and drainage becomes the main concern. Flat roofs on the Palouse are common on additions and on some commercial buildings, and they need a drain that can handle the meltwater, plus a structure that was designed for the snow that will sit on them. The check is practical as well as structural.
Tell us what's happening and we'll tell you honestly whether it's a quick fix, and what snow load and roof care should cost.
On the Palouse plateau, snow tends to stay on a roof longer than it does in the river valleys, and the eastern timbered towns hold their snow for a larger part of the winter. A house in Troy, Deary or Harvard may carry its snow for longer stretches than one in Clarkston or Lapwai, and the snow care plan should reflect that difference rather than assuming one standard for the whole map.
Moscow publishes a local amendment to the building code that addresses snow buildup at valleys, parapets and roof offsets, and that amendment is the most useful local reference for a homeowner with a complex roof. The building office can show you the relevant section and explain how it applies to an addition or a dormer on a particular house.
Pullman is about 14 kilometers from Moscow, and it is a separate city with its own design criteria under Washington's rules. Those criteria are not the same as Moscow's, and it would be wrong to read one city's requirements as the other's. A roof on the Washington side of the state line is designed and inspected under Washington's code, and the Idaho side follows Idaho's.
Stopping eave ice dams on Palouse roofs through attic insulation, air sealing and ventilation, and safe removal when water is already getting in.
A look at the roof, gutters and attic before the first snow, to find the loose flashing and blocked gutter that cause winter leaks.
Metal roof repair and installation, planned around how the panels shed snow onto doors, walks and parked cars.
Snow guards and retention hold snow on a metal roof so it does not slide off over doors, walkways and parked vehicles.
Not sure if you're covered? Check your ZIP code.
Design snow load is the weight a building code tells a designer to plan a roof for.
A metal roof suits a Palouse winter because its smooth surface lets snow slide off rather than build up.
The answer depends on the design figure set for your address and on the actual condition of the snow on the day. The design figure is set by the code in force and confirmed by the building official. This page does not print a figure, because the sources do not agree on one for Moscow. The building office can give you the figure that applies to your address.
Not every winter, and not in every case. Whether snow removal is needed depends on the roof's structure, its drainage and how much snow builds up in the valleys and offsets. A technician can look at the roof and tell you whether removal is needed. Removal from a roof is dangerous, and it should be done with care or left to someone equipped for it.
Moscow and Pullman are separate cities in separate states. Each publishes its own design criteria under its own code, and they are not the same. A roof on the Idaho side follows Idaho rules, and a roof on the Washington side follows Washington rules. A technician will tell you which applies to your address.
Keep people and pets out of the area below, and stay out of the building if the sag is serious or if you hear cracking. Call for an assessment at once. Do not try to remove snow or prop the roof up yourself. A structural question needs a person who can inspect the framing and say what is safe to do.
Ice at the eave can add weight locally and can trap meltwater under the covering, which can lead to leaks and damage to the fascia and gutters. Managing ice at the eave is part of winter roof care, and it is covered on the ice dam service page. A technician can look at the eave and recommend the right next step.
For a property outside city limits, the county building official confirms the design figure, and the county planning office can point to the right contact. In Lapwai and on the Nez Perce Reservation, ask both the Nez Perce County planning office and the Nez Perce Tribe which permit and code applies to your property.