Your roof’s snow capacity is set by its framing and sheathing, not by the roofing material on top. That is why weight matters: an Interlock aluminum roof adds about 0.41 psf — a fraction of what slate weighs — so it consumes almost none of your structure’s capacity. It also sheds snow rather than holding a saturated layer against the deck.
The short version
- Snow capacity is a structural property — the covering is a small input, not the answer
- Interlock aluminum installs at 0.41 psf (shingle and diamond), 0.58 psf (shake), 0.59 psf (tile) — per ICC-ES report ESR-1790
- Natural slate is heavy enough that replacing it often requires structural reinforcement first
- Inland and hill-country New England carries materially heavier design loads than the coastal plain
- Metal sheds snow — so plan snow guards, and plan where it lands
What actually carries the snow on your roof
The framing, sheathing and their condition carry the load. The roof covering adds dead weight and changes how snow behaves on the surface — but it is not what holds the roof up.
Engineers split it into two parts. Dead load is the permanent weight of the structure and everything fastened to it, including your roof covering. Live load is everything temporary — and in New England, that mostly means snow. Your rafters or trusses, their span and spacing, and the thickness and condition of the sheathing determine how much live load is available.
This is why “how much snow can my roof hold?” is a structural question, and why any roofer who answers it casually, without looking at your framing, is guessing. On an older home the honest answer often is: we need to look first.
Why roof weight matters more than homeowners think
Every pound the covering adds is a pound of snow capacity you give up. That makes the weight of your roofing material a winter-safety decision, not just a construction detail.
The verified numbers for Interlock’s aluminum systems, from ICC-ES evaluation report ESR-1790:
| System | Installed weight |
|---|---|
| Aluminum Shingle / Diamond | 0.41 psf |
| Aluminum Shake | 0.58 psf |
| Aluminum Hidden Fastener Tile | 0.59 psf |
| Steel equivalents | 0.85 – 1.16 psf |
For context, natural slate is heavier by a wide margin — heavy enough that homeowners replacing a slate roof are frequently told the framing needs reinforcing before anything goes back on. Aluminum sits at the opposite end of that scale, which is precisely why it suits the century-old framing common across New England: you can keep the look of a slate roofline without asking the structure to carry a slate roof.
There is a second structural figure worth knowing. ESR-1790 records an allowable positive (gravity) load of 52 psf for Hidden Fastener Tile panels installed over spaced sheathing at 15 inches on center. Positive load is otherwise limited by the adequacy of your framing and sheathing — which brings us back to the same point: the structure decides.
Snow load is not the same across New England
Design snow loads climb with elevation and distance from the coast. A house in the Worcester hills, the Berkshires or Vermont’s Northeast Kingdom is designed for materially more snow than one on the Boston coastal plain — and it holds that snow longer.
That difference is not subtle, and it is the reason a single regional answer is useless. Inland homes see more accumulation and far more freeze-thaw cycling per season; coastal homes see less snow but more wind-driven weather and salt. Cape Cod and the islands are a different problem again.
If you want the specifics for where you live, our county pages carry the local detail — Worcester County, Berkshire County and Caledonia County, Vermont are the hill-country examples.
Shedding versus holding — what happens after the storm
A smooth, four-way interlocked surface releases snow instead of holding a saturated layer against the deck. Less time under a wet load is less stress on the structure, and less meltwater working its way around the covering.
The mechanism is simple. Interlock panels lock on all four sides, so across the field of the roof there is no exposed lap seam — no open horizontal joint for water travelling up the slope under an ice dam to get beneath. On a shingle roof, those lap seams are exactly where backed-up meltwater finds its way in.
Ice dams: what actually causes them
Ice dams are driven by heat escaping through your roof deck — not by the roof covering alone. If you fix nothing else, fix that.
Here is the sequence. Warm air from the living space leaks into the attic. It warms the underside of the deck. Snow melts from beneath, runs down the slope, and reaches the cold overhang beyond the heated envelope, where it refreezes. That ridge of ice grows, and meltwater ponds behind it — then works into whatever seams it can find.
Which means the real fixes are air sealing, insulation and ventilation. A roof covering that eliminates exposed lap seams removes one path the water can take, and a surface that sheds snow gives the cycle less to work with. But no roofing material substitutes for an attic that is sealed and vented properly, and anyone who tells you otherwise is selling you the wrong thing.
Snow guards — controlling where it comes off
Metal sheds snow, so decide in advance where it lands. That is a design conversation, not an afterthought.
Snow and ice can build up and release suddenly. Before installation we look at what sits below each slope: entries, walkways, driveways, gas meters, landscaping, the spot where people actually walk. Snow guards and snow rails restrict how much releases at once and are specified where they are needed.
Two things worth knowing: snow guards can themselves contribute to build-up on the roof, so placement is a judgement call — and they are a service item, arranged with your installer, not a warranty matter.
What we look for on a New England roof inspection
We inspect down to the deck before recommending anything. On a winter-exposed roof that is not a formality.
We are looking at deck condition and thickness, how many layers are already up there, framing span and spacing, ventilation and insulation at the eaves, and the state of the flashings. That inspection also determines whether installing over your existing roof is even an option — local building codes commonly permit roofing over only one existing layer of asphalt shingles, and the deck has to be sound underneath.
If the structure needs attention, you want to know that before a roof goes on, not during the first February thaw.
Frequently asked questions
How much snow can a roof in Massachusetts hold? It depends on the framing, span, sheathing and the design load the house was built to — not on the roofing material. Design loads are higher inland and in hill country than on the coast. It requires an inspection to answer honestly for your home.
Is a metal roof heavier than asphalt shingles? No. Interlock’s aluminum systems install at roughly 0.41–0.59 psf depending on profile (ESR-1790), which is very light for a permanent roof covering — a fraction of the weight of natural slate.
Do metal roofs make ice dams worse? Ice damming is driven by heat loss through the deck. A four-way interlocking panel removes the exposed lap seams that backed-up meltwater typically travels under, and the surface sheds snow rather than holding it — but attic air sealing, insulation and ventilation remain the primary fix.
Does snow slide off a metal roof? Yes, and often suddenly. That is generally good for the structure and something to plan for at ground level — see snow guards above.
Do I need snow guards in New England? Frequently, yes — particularly above entries, walkways, driveways and utility connections. We assess it per slope during the estimate.
Interlock Metal Roofing – New England is the exclusive certified installer of Interlock® aluminum roof systems across Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont. Product engineering, specifications and full system detail are published by the manufacturer, Interlock Roofing Ltd.. Coverage is provided under the Guardian Warranty.
