Three questions after a snow load failure
Every snow load investigation comes back to three questions. What snow load was the roof designed to carry? What load did it actually carry when it failed? And did the roof as built match the design, with the framing, connections, and bracing the design called for?
The answers decide whether a failure points to the design, the construction, the conditions, or the way the building was maintained, and often more than one. A roof can fail below its design load if it was built wrong, and a well-built roof can be overloaded by drifting or by snow left to accumulate.
We take construction defect and expert witness matters anywhere in Montana, from Bozeman and Big Sky to Missoula, Whitefish, and Billings. We are snow country building specialists, and Gregg de Haan specializes in high alpine waterproofing, roofing, and general construction.
How design snow loads are set in Montana
Montana adopts building codes statewide. Snow loads are determined by the building official. In certified cities and counties, the local building official provides them; elsewhere, Montana’s building codes program bases design snow loads on ASCE 7 ground snow loads, looked up with ASCE’s Hazard Tool. Montana law sets a minimum design roof snow load of 30 pounds per square foot after allowed reductions. Ground snow loads vary widely with elevation and location, so two buildings a few miles apart can be designed for very different loads.
A roof’s design load starts from the ground snow load and is then adjusted for factors such as roof slope, exposure to wind, and how warm the roof runs. Older editions of ASCE 7 also applied an importance factor for the building’s use; ASCE 7-22 instead maps ground snow loads by risk category. Design load calculations are typically made by a licensed engineer, and those adjustments are where many design questions arise.
The code edition matters too. The model 2021 International Building Code referenced ASCE 7-16, and the 2024 edition references ASCE 7-22, which moved ground snow loads to strength-level values. Montana’s 2024 codes took effect for the state program on September 26, 2026. A building is generally judged against the code and snow load rules in force when it was permitted, so identifying them is an early step.
Where roofs carry more than the average
Snow rarely sits evenly. Wind drifts it against higher walls, parapets, and rooftop equipment, and into valleys, so the load at a roof step or valley can be far higher than across the rest of the roof. Snow sliding off a steep upper roof can pile onto a lower roof or deck in a single event.
Rain on an existing snowpack adds weight quickly, and ice that builds at the eaves concentrates load at the edge. These conditions are part of what design snow loads account for, which is why an investigation compares the loads the design anticipated with the conditions the roof actually saw.
- Drifts at roof steps, parapets, and equipment
- Valleys and intersecting roofs
- Snow sliding onto lower roofs and decks
- Rain on snow and ice at the eaves
What fails, and how it shows
Structural distress from snow often appears before a collapse: sagging ridges or rafters, cracked drywall or plaster, doors and windows that start to bind, and new noises from the framing. Inside the roof, the weak points are usually members and connections: overstressed rafters or trusses, failed truss plates, hangers, or nails, and missing or inadequate bracing.
Field changes are a common thread. A truss cut to fit a duct, a header left undersized, or a connection never installed can leave a roof well short of its design. Comparing the framing as built with the approved plans is central to separating a design problem from a construction defect.
Ice dams are a different problem
Ice dams form when heat escaping through the roof melts snow that refreezes at the colder eaves. Water backs up behind the ice and works under roofing and flashing into walls and ceilings. The damage is usually from water rather than structural overload, though heavy eave ice adds load at the roof edge, and the two often appear in the same winter.
Air leakage, insulation gaps, ventilation, and eave protection all play a part. Roofing and sheet metal and waterproofing and building paper installation are among our investigative specialties, and Gregg de Haan specializes in high alpine waterproofing and roofing.
Investigating after the snow melts
Many snow load and ice dam matters are investigated after the snow is gone. Damage patterns, deflection, staining, and failed connections still record what happened, and plans, permits, and weather records help reconstruct the loads.
Our field personnel identify and document defects promptly, and we use camera and video documentation techniques to provide trial-ready exhibits. We take field samples to store at our office in case they are needed at trial, and we generate comprehensive field reports, photo documentation, conceptual repair scopes, and cost estimates.
Timing rules in Montana
In 2025 the Montana Legislature shortened the statute of repose for most damages actions arising from the design or construction of an improvement to real property (actions on written contracts are excluded) from 10 years to six years after completion, with one year for an injury that occurs in the sixth year (Mont. Code Ann. § 27-2-208).
For claims about a house or condominium unit, a claimant generally must serve written notice of the claim on the construction professional before filing, and the professional has 21 days to respond (Mont. Code Ann. § 70-19-427). Snow damage often surfaces a season or more after it starts, so the shorter period makes early documentation more important.
Shorter statutes of limitations can end a claim sooner. This is general information, not legal advice. Counsel determines how these rules apply, including to projects completed before the 2025 change.