Snow changes the problem
In most climates, rain arrives, runs off, and is gone within hours. In snow country, water can sit on a roof, deck, or terrace for months as snow and ice, melting and refreezing as days warm and nights cool. That changes how roofs, waterproofing, and building envelopes are loaded and how they fail.
Snow country conditions occur in parts of all three states we serve: California, Arizona, and Montana. We are snow country building specialists, and Gregg de Haan specializes in high alpine waterproofing, roofing, and general construction.
This article explains, in general terms, why construction in mountain environments fails differently, and what an investigation looks at. Many of these failures involve the same systems found anywhere: roofing, flashings, waterproofing, decks, and drainage. What differs is the duration of exposure, the loads, and the temperatures they must withstand.
Snow loads and sliding snow
Roofs in snow country are designed for snow loads set by the local jurisdiction, which can be far higher than at lower elevations. Drifting adds load where roofs step down or meet walls, and uneven melting can leave one side of a roof carrying more than the other. These are design questions for licensed design professionals, and an investigation notes where observed conditions may call for their review.
Sliding snow is its own hazard. Snow and ice that release from a steep or metal roof can damage lower roofs, decks, gutters, vents, and anything at the eave below. Snow retention devices, roof geometry, and the placement of entries and walkways all affect where that snow lands.
Penetrations and rooftop equipment face the same forces. Vents, chimneys, and plumbing stacks in the path of moving snow can be bent or sheared, opening a leak that appears only after the next thaw.
Decks, balconies, and canopies collect snow as well. Their framing, attachments, and waterproofing must handle both the weight and the long saturation that follows.
Ice dams and the warm roof
Ice dams form when heat escaping from the building warms the roof deck and melts the snow above it. The meltwater runs down to the colder eave, refreezes, and builds a ridge of ice. Water trapped behind that ridge can back up under shingles and other water-shedding roofing.
The causes usually sit inside the building: attic air leakage, gaps in insulation, warm ducts or equipment in the attic, and recessed fixtures that leak heat. Ventilated or cold roof assemblies keep the roof deck closer to outdoor temperature, which reduces melting.
Codes in areas prone to ice damming generally require an ice barrier underlayment at the eaves, extending up the roof past the exterior wall line. That membrane is a second line of defense, not a cure for the heat loss that causes ice dams.
Ice dams can also form at valleys, skylights, dormers, and roof-to-wall intersections, where snow collects and heat loss concentrates. Gutters packed with ice add weight at the eave and can pull away from the fascia.
Freeze-thaw and water that expands
Water expands by about 9 percent when it freezes. In concrete, masonry, stone, and mortar, water held in pores and cracks expands with each freeze, and repeated cycles break the material apart. Scaling of concrete surfaces and spalling of masonry faces are common results.
Concrete exposed to freezing is commonly specified with entrained air, which gives freezing water room to expand. Drainage, slope, and protection from deicing salts also matter. Where water is allowed to stand on flatwork, steps, or ledges, freeze-thaw damage tends to concentrate.
Sealant joints, coatings, and deck membranes face a related problem. Wide daily temperature swings make materials expand and contract repeatedly, and joints that open slightly let water in to freeze. Products installed outside their rated temperature range may not perform as intended.
Freezing soil can also move the ground. Footings set above the local frost depth, or slabs over wet, frost-susceptible soil, can heave as the ground freezes and settle as it thaws.
Roofing and waterproofing at altitude
High alpine roofs and terraces carry snow for long periods, so roofing and waterproofing must tolerate prolonged saturation, not just passing rain. Details that rely on quick runoff, such as low upturns, shallow slopes, or sealant-dependent flashings, are challenged in ways a lower building rarely sees.
Ultraviolet exposure increases with elevation, and roofing, coatings, and exposed membranes age faster under strong sun. Gutters, valleys, and edge metal take the load of ice and sliding snow. Decks and balconies may hold snow against door thresholds and wall transitions for weeks.
Below grade, snowmelt saturates soils in spring, raising the demand on subgrade waterproofing and site drainage. Snow piled against walls by plows or roof shedding can keep the base of a wall wet long after the surrounding ground has dried.
Certain details draw particular attention in alpine construction. They are where long snow cover, ice, and meltwater concentrate.
- Eave and valley protection against ice
- Upturn heights at door thresholds and deck edges
- Snow retention devices and their attachment to the roof
- Flashings at chimneys, vents, and rooftop equipment
- Drain outlets that must stay open under snow and ice
Short seasons and schedule pressure
Mountain building seasons are short. Foundations, framing, roofing, and dry-in often must be finished before the first heavy snow. That pressure compresses schedules and stacks trades on top of one another.
Cold-weather work raises its own questions. Concrete must be protected from freezing while it gains strength, and many membranes, adhesives, and sealants have minimum application temperatures set by their manufacturers. Materials left exposed through a winter, or installed over frost or moisture, may not perform as intended.
The building trade faces many challenges, including tight schedules, adverse building environments, fiscal constraints, and challenging design. In snow country, those challenges tend to arrive together.
Winter protection is part of the work. Temporary enclosures, heat, and covers protect work in progress through the cold months. When that protection falls short, framing and sheathing can be wetted repeatedly before the building is closed in.
Investigating a snow country building
Some snow country conditions can only be observed in season. Ice dams, drifting, and meltwater paths appear in winter and spring, while access to roofs and foundations is often easier in summer. An investigation may need more than one visit to see both.
Field work follows the same principles as any forensic investigation: careful observation, measurement, testing where useful, and thorough documentation. We use state-of-the-art cameras and video documentation techniques to provide trial-ready exhibits. We also take field samples to store at our office in case they are needed at trial.
We generate comprehensive field reports, photo documentation, conceptual repair scopes, and cost estimates. Gregg de Haan also specializes in plan reviews as they relate to waterproofing above and below grade, where many snow country risks first appear on paper.
Records from a building’s first winters can be valuable. Photographs of snow and ice patterns, snow removal logs, and reports of when leaks appeared help connect conditions to their causes.