Dedication Roofing gets this question every autumn, and for most Salt Lake Valley homes the answer is reassuring: your roof was designed against a specific snow load, and if it was built to code and nothing has been added to it since, it carries what it was built to carry.
Snow load is a published number, not a guess. West Jordan sets a minimum ground snow load of 28 pounds per square foot for elevations at or below 4,239 feet, with the roof snow load itself calculated under Chapter 7 of ASCE 7-16. Neighbouring cities publish their own figures. The roofs that get into trouble almost never fail because an unusual amount of snow fell. They fail because something changed on the roof, or because two small details at the eave were never detailed correctly.
What actually changes the maths
The snow is only half the equation. The other half is dead load: the permanent weight of the roof assembly itself. Snow load is what the structure has left over once it is carrying its own roof.
That is why adding a second layer of shingles over the first is a structural decision and not only a budget one. Salt Lake City makes this explicit. The city requires a permit for roofing repairs and replacements, and the application runs through its Re-Roofing Questionnaire, which asks three questions that decide whether an engineer has to be involved:
- Will the existing roofing be removed? If not, how many layers are already up there?
- Will the added roofing weight exceed 3 pounds per square foot? Anything over that threshold triggers structural verification.
- Does the building have unreinforced masonry parapets or rooftop appendages such as chimneys, tanks or signs? On commercial buildings that triggers design calculations for bracing and anchorage, with one and two family dwellings excepted.
Three pounds per square foot is not much. A second layer of architectural asphalt can put an assembly past it, which turns a straightforward re-roof into an engineered one, with the cost and delay that implies. It is worth knowing before you accept a quote for an overlay, not after.
The overlay question, honestly
Building codes generally limit steep-slope residential roofs to two layers of shingles, and that is the standard applied across Utah. An overlay is genuinely cheaper, because it removes tear-off labour and disposal from the job. But it carries two costs that do not appear on the quote.
The first is the dead load above. The second is that the decking underneath cannot be inspected once it is covered. Rot, previous leaks and damaged underlayment stay where they are. On a roof that has already been through Utah freeze-thaw cycles, that is the part worth seeing.
Dedication Roofing weighs the existing assembly before recommending an overlay rather than defaulting to whichever option is cheaper on the day. Sometimes an overlay is the right call. Sometimes it quietly spends your structural margin.
The two details that fail before the structure does
In practice, Utah roofs rarely fail structurally under snow. They fail at the eave, and they do it through ice dams. Two code requirements address that, and both get missed.
The ice barrier has to reach past the wall
Utah residential code requires an ice barrier running from the eave edge to a point at least 24 inches inside the exterior wall line. That measurement starts at the wall, not at the eave, because the wall is where the heated envelope ends and the cold overhang begins. Salt Lake County sits in Climate Zone 5B, so this is not optional detailing here. We wrote about this separately in what Utah code actually requires for ice and water shield.
Ventilation is what stops the ice forming
An ice dam is a ventilation failure before it is a roofing failure. Warm air escaping into the attic melts snow on the upper slope, the meltwater runs down to the cold eave and refreezes, and the ridge of ice that forms holds the next round of water against the roof until it finds a way under the shingles.
Code requires net free ventilating area of 1/150 of the attic floor, reduced to 1/300 where at least 40 percent and not more than 50 percent of that area sits in the upper portion of the attic, with those upper ventilators no more than 3 feet below the ridge. That upper-and-lower split is the entire mechanism: exhaust high, intake low, and the attic stays close to outside temperature. Ridge vent installed over blocked or solid soffit does not achieve it, and it actively makes the attic wetter by pulling replacement air out of the house through ceiling gaps.
What to look at before the first heavy snow
- How many layers are up there. If you do not know, it matters more than anything else on this list.
- The ridgeline, sighted from across the street. A ridge that dips or a slope that reads as wavy rather than flat is worth a professional look.
- Whether you had ice dams last winter. Ice dams repeat. The conditions that caused them do not fix themselves.
- Whether the soffit is open. Blocked or solid soffit panel with a ridge vent above it is the most common ventilation fault we find.
- Staining on upstairs ceilings near exterior walls. That is the ice dam signature, and it shows up inside before it shows up outside.
None of this requires getting on the roof yourself, and we would rather you did not. A roof inspection from Dedication Roofing is free, comes with photographs of what we found, and takes about as long as a coffee. If the roof is fine, we will tell you it is fine.
Common questions about snow load
How much snow can a roof in Utah hold?
Utah cities publish a minimum ground snow load that roofs are designed against. West Jordan sets a minimum of 28 pounds per square foot for elevations at or below 4,239 feet, with the roof snow load calculated under Chapter 7 of ASCE 7-16. A home built to code and unaltered since carries the snow it was designed for. Problems usually come from weight added to the roof later, not from unusual snowfall.
Does adding a second layer of shingles affect snow load?
Yes. A second layer of asphalt shingles is permanent dead load on a structure that also has to carry snow, so it reduces the margin left over. Salt Lake City sets the threshold explicitly: added roofing weight over 3 pounds per square foot triggers structural verification on the permit application. Building codes also generally limit steep-slope residential roofs to two layers of shingles across Utah.
Do I need a permit to re-roof in Salt Lake City?
Yes. Salt Lake City requires a permit for roofing repairs and replacements, and the application runs through the city Re-Roofing Questionnaire. It asks for the existing and proposed roofing materials, the deck type, whether the old roofing is being removed, how many layers remain if it is not, and whether the added weight exceeds 3 pounds per square foot. Dedication Roofing pulls the permit so the filing is not the property owner problem.
What causes ice dams on Utah roofs?
An ice dam is a ventilation failure before it is a roofing failure. Warm air escaping into the attic melts snow on the upper slope, the meltwater runs to the cold eave and refreezes, and the ridge of ice that forms holds the next round of water against the roof until it works under the shingles. Utah code requires net free ventilating area of 1/150 of the attic floor, reduced to 1/300 where 40 to 50 percent of that area sits in the upper portion with those upper ventilators no more than 3 feet below the ridge.
How far does the ice barrier have to extend?
Utah residential code requires an ice barrier from the eave edge to a point at least 24 inches inside the exterior wall line. The measurement starts at the wall rather than the eave, because the wall is where the heated envelope ends and the cold overhang begins. On a house with a wide overhang the membrane has to run correspondingly further up the roof.
