Portland’s ground snow load runs 50 psf, the figure a Maine building permit and a truss drawing actually use, and that number is not what lands on your rafters. The code trims it down before it ever reaches the roof, and a separate wind map sets the 112 mph gust your sheathing and fasteners are built for. Check both figures against your building department’s plan review before you order shingles, because the ground number is a starting point, not a finished spec.
What is the ground snow load in Maine?
Ground load versus roof load
At Portland, the design ground snow load is 50 psf under ASCE 7-16, the edition of the American Society of Civil Engineers’ standard that IRC/IBC 2021 makes applicable in most states. This is the figure a permit application, a plan review and the truss drawings a builder orders all use directly. It is not, by itself, the load that ever reaches a rafter.
That distinction matters because a ground snow load is exactly what its name says: the weight of snow sitting on open, level ground near Portland. The code does not hand that number straight to a truss designer. It runs it through exposure, thermal and slope factors first, because a roof loses snow to wind, gains or loses heat through the attic underneath, and sheds snow faster as pitch increases. For an ordinary heated house with a sloped roof, that conversion lands the working roof snow load at roughly 35 psf, well below the ground figure that started the calculation.
A newer edition, a different basis
ASCE has also published a newer edition, ASCE 7-22, which maps the same point in Portland at 83 psf. That is not a claim that more snow is falling or that houses built to the older number are undersized. The 83 psf figure is a strength-level value, used with a 1.0 load factor, while the 7-16 figure is a nominal value used with a 1.6 load factor. The two numbers answer different arithmetic questions rather than the same question twice, and only a handful of jurisdictions are beginning to adopt the newer edition. Because Maine’s own code, covered below, is built on the 2021 IRC, it is the ASCE 7-16 figure that applies today, not the newer one.
This figure is measured at Portland, and Maine’s terrain does not hold still around it. The mountainous interior is mapped as a CS, or case-study, region, meaning the national map assigns it no value at all. A project up there needs a site-specific snow study rather than a number borrowed from lower ground. Anyone building outside the immediate Portland area should confirm with a roofing contractor or the local building department which figure actually applies to that address before a truss package gets ordered.
How much snow can a roof hold in Maine?
There is no single answer to this, because the same roof carries a different load depending on where the snow sits and what it has turned into. Start from the ground figure at Portland: 50 psf under ASCE 7-16, converted to roughly 35 psf on an ordinary heated sloped roof once exposure, thermal and slope factors are applied. That 35 psf is a baseline, not a ceiling.
Where drift changes the math
Snow does not sit evenly across a roof. Wind pushes it off open slopes and piles it against anything that breaks the wind: a parapet, a chimney, a taller wing of the same house. The classic failure point is a lower roof next to a taller one, where drift off the upper roof can pile several times deeper than open-field snow just a few feet away. A valley between two roof planes and the low side of a dormer behave the same way. Drift load, not the flat design figure, is where most roof overload problems actually show up, and it is entirely local to the shape of the building rather than something a single ground snow number can predict. Drift is not unique to Maine’s coast and hills either. Flat, open ground creates its own version of the same problem in a plains state such as South Dakota, where there’s no hillside to blame but the wind still finds a place to dump the load.
Why depth alone tells you nothing
A foot of snow is not a fixed weight. Fresh, dry powder runs roughly 5 to 7 pounds per square foot for every foot of depth. Once that snow settles, gets rained on, or partially melts and refreezes, the same foot of depth can weigh two to three times as much. An ice layer on top adds still more, and it adds it exactly where meltwater has been sitting rather than draining off. That is why a foot of snow that fell in January and has been through a few freeze-thaw cycles by March is a heavier roof load than a foot that fell yesterday, even though a tape measure would call them identical.
Watch the building itself for warning signs rather than trying to estimate weight by eye: interior doors that start sticking or won’t latch, new cracks running across ceiling drywall, or a ridge line that reads as visibly sagging from the yard. Any of those is a reason to call a licensed engineer or the local building department, not a reason to climb up and look closer. If snow needs to come off, a roof rake worked from the ground removes the load without putting a person’s weight on top of it, which only adds to what the roof is already carrying.
What wind speed must a roof withstand in Maine?
What the number actually measures
At Portland, the basic design wind speed is 112 mph under ASCE 7-16, the edition IRC/IBC 2021 makes applicable in most states. That figure is a three-second gust measured at 33 feet in open, Exposure C terrain, for Risk Category II buildings, which covers an ordinary house. It is not a sustained wind speed, and it is not the number a weather forecast reports when it talks about a storm’s wind speed. Those are two different ways of measuring wind, and comparing a 112 mph gust design value to a hurricane’s headline sustained speed will make the code look weaker than it actually is.
ASCE’s newer 7-22 edition maps the same point in Portland at 110 mph, a close figure rather than a meaningfully different one, and it changes nothing about what existing construction is rated for. Because Maine’s own code is built on the 2021 IRC, it is the ASCE 7-16 figure that applies today, not the newer one.
The wind-borne debris question
Whether a given site falls inside a wind-borne debris region, where the code requires impact-rated glazing or approved shutters on new construction, is not something a single state-level wind figure settles on its own. That determination is address-specific. This coastal-adjacent Portland figure also isn’t a stand-in for the whole state: a state with a longer exposed ocean coastline further south, like Rhode Island, carries that kind of obligation across a much larger share of its land. Anyone planning new windows, doors or a re-roof near the Maine coast should ask the local building department directly whether the requirement applies before ordering materials.
What the number buys on a roof
What the 112 mph figure actually buys on a roof is a set of construction details, not a single spec: the wind rating printed on a shingle bundle, the nailing pattern that fastens it, the sheathing fastening schedule, and the uplift connectors, hurricane ties or straps, that tie the roof framing down to the wall framing. Edges, rakes and ridges fail first in high wind because that is where uplift pressure concentrates, which is why code nailing patterns are tighter at those locations than in the field of a roof slope. A roof that meets the wind speed rating on paper but is fastened to a lower standard in the field does not perform to the number on the drawing.
Does Maine require an ice barrier under the shingles?
An ice barrier is a self-adhering membrane installed under the shingles, run from the edge of the eave up the roof deck far enough to pass the interior line of the exterior wall below it. Its job has nothing to do with stopping snow from piling up. It exists to stop water, specifically the meltwater that backs up behind an ice dam, from finding a gap in the shingle layer and reaching the roof deck and the framing underneath.
Why ice dams form here
An ice dam doesn’t need extreme cold to form, it needs a temperature difference across the roof. Heat escaping from a heated attic or a poorly insulated ceiling melts the underside of the snowpack even while outdoor temperatures stay well below freezing. That meltwater runs downhill under the snow until it reaches the unheated overhang past the exterior wall, where it refreezes into a ridge of ice. The ridge dams up more meltwater behind it, and that water eventually finds its way under the shingles instead of off the roof edge. With Portland’s coldest-month average minimum running 15.6°F under NOAA’s 1991-2020 climate normals, attics stay cold enough for long enough each winter that this cycle is a recurring risk here, not an occasional event.
What the state’s own code requires
Maine’s own residential code, the Maine Uniform Building and Energy Code (MUBEC), chapter 5, based on the 2021 International Residential Code and administered statewide by the Maine Technical Building Codes and Standards Board, carries the ice barrier requirement that follows from that risk. Municipalities can’t weaken it, though enforcement is only mandatory in towns above 4,000 people. Smaller towns can decline to enforce it, but they can’t substitute a different code in its place. Check with the local building department for the exact eave and wall-line measurements that apply to a given roof pitch, since that detail is enforced at the permit and inspection level even where the underlying rule is set statewide.
The membrane only protects the roof deck once water is already trying to get past the shingles. It does nothing to stop the dam from forming in the first place. That takes air sealing at the attic floor, ductwork and can lights closed up and insulated over, and enough attic insulation that the underside of the roof deck stays close to outdoor temperature all winter. A roof with a correctly installed ice barrier and a leaky, under-insulated attic will still grow ice dams every year. It just won’t leak from them, at least not right away.
What roofing material suits Maine best?
The choice depends on how a material behaves against the loads already covered on this page: the 50 psf ground snow load and roughly 35 psf converted roof load at Portland, and the 112 mph design wind speed at the same point. Maine’s counties also split across two IECC climate zones, zone 6A covering 15 of the state’s 16 counties and zone 7 covering the remaining one, a heating classification that sets attic insulation levels and loops straight back into the ice-dam mechanism covered above. No single material changes the underlying loads a structure has to carry, and none of them wins on every count at once.
How the main categories differ
| Material | Snow behavior | Wind consideration | Weight added to roof |
|---|---|---|---|
| Architectural asphalt shingles | Holds snow on the roof rather than shedding it | Carries a published wind rating, performs only to the nailing pattern actually used | Minimal added dead load |
| Standing-seam metal | Sheds snow in a sudden slide rather than holding it | Panel and seam type carry their own uplift rating, separate from shingle ratings | Minimal added dead load |
| Slate | Holds snow, sheds little | Individual pieces can be dislodged by wind if fastening is inadequate | Substantial dead load added on top of the snow load |
| Concrete tile | Holds snow, sheds little | Heavier units resist wind uplift better on a per-unit basis | Substantial dead load added on top of the snow load |
Standing-seam metal’s snow-shedding behavior is the detail that gets missed most often. A metal roof doesn’t hold snow the way shingles do, it lets go of it all at once, and that slide can come off a slope with enough force to injure someone standing below or crush anything underneath it. Where the slide will land, over a doorway, a walkway, a deck, a parked car, is a design decision that has to be made before installation, not something discovered the first winter. Snow guards or a change in roof geometry over doors and walkways handle this, but only if someone specifies them.
Slate and concrete tile carry their own weight into the same structural calculation that already carries the snow load discussed above. That added dead load has to be accounted for in the framing design on top of, not instead of, the snow load, which is one reason a re-roof from asphalt to tile is a structural question, not just a material swap.
Fastening and the underlayment beneath it matter more than the material choice itself once wind speed is the governing factor. A shingle rated for a high wind speed that gets nailed to a lower nailing pattern than its rating assumes performs to the lower standard in an actual storm, not to the number printed on the wrapper. The same is true of standing-seam panels, whose wind performance depends on clip spacing and seam type as much as on the panel profile itself.