Guide
Ohio ice barrier requirement: 24 inches inside the wall line
Updated
Ice damming is the reason Ohio roofs leak in February with no storm in sight. The code answer is specific, measurable and easy to check on a bid.
What the code actually says
In areas with a history of ice forming along the eaves causing a backup of water, the Ohio Residential Code requires an ice barrier for asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes. The barrier must consist of not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet used in place of normal underlayment (Ohio Administrative Code 4101:8-9-01, section 905.1.2).
Then come the two measurements that decide whether your bid is honest:
- It must extend from the lowest edges of all roof surfaces to a point not less than 24 inches inside the exterior wall line of the building. The 24 inch measurement is taken along the slope of the roof, from the point where the projected outside face of the wall intersects the roof deck.
- On roofs with a slope of eight units vertical in 12 units horizontal or steeper, the ice barrier must also be applied not less than 36 inches measured along the roof slope from the eave edge.
There is an exception for detached accessory structures and for roof assemblies terminating at a vertical wall over unconditioned floor areas.
Why deep overhangs cost more membrane
The measurement starts at the wall line, not at the gutter. A house with a two foot overhang needs the membrane to cover the overhang and then continue 24 inches past the wall, measured up the slope. On a low pitch that is easily two courses of membrane; on a steep roof the 36 inch rule adds more again. When one bid is noticeably cheaper than another, the ice barrier is one of the first places to look for the difference.
The other half of the problem is heat
The membrane manages the consequence of an ice dam. What causes the dam is warm air reaching the roof deck, melting snow that then refreezes at the cold eave. A roof replacement is the natural moment to deal with the cause as well:
- Ask whether the bid includes intake ventilation at the soffit as well as ridge exhaust. Exhaust without intake does not work.
- Ask about baffles keeping insulation clear of the soffit vents.
- Ask whether attic air sealing around fixtures, hatches and top plates is inside or outside the scope, and if outside, who does it.
- Ask about gutter and downspout condition, since a dam sitting in a clogged gutter is a different problem again.
- Get the ice barrier product name and course count written into the contract.
One useful detail if you are reroofing over an old membrane: the Ohio code allows an existing ice barrier membrane adhered to the roof deck to remain in place and be covered with an additional layer of ice barrier membrane (section 908.3, exception). That is the only layer the tear-off rule lets you keep. See tear-off versus layover.