How many layers of shingles a Michigan roof can have

What the replacement section says

The code draws a line between replacing a roof and putting a new covering over an old one. Replacement is section R908.3 of the 2015 International Residential Code, which Michigan adopts as its residential code. It says roof replacement includes removal of the existing layers of roof covering down to the roof deck. That sentence gives no count of layers: a replacement takes everything off.

One exception in that section matters in Michigan, where an ice barrier is required along the eaves. An existing adhered ice barrier membrane may stay in place and be covered with an additional layer of ice barrier membrane. A roofer who leaves a strip of old membrane at the eaves after a tear-off is following the code. We read the Michigan rules that amend the residential code and found no change to R908, but that is a medium-confidence statement, so ask the building department what it inspects against.

When a new covering can go over the old one

A second path is called a re-cover. Section R908.3.1 permits a new roof covering over an existing one where the new material is installed according to the manufacturer’s approved instructions. The same section lists cases that need no tear-off at all, such as a standing-seam style separate system, and says coating over a sprayed polyurethane foam roof needs no removal either. Those cases are tied to specific systems, and the shingle question sits under the general rule.

That general rule has limits, and section R908.3.1.1 lists them. A re-cover is not permitted when any of these is true:

• the existing roof is water soaked or deteriorated so that it is not adequate as a base for the new covering;
• the existing covering is slate, clay, cement or asbestos-cement tile;
• the existing roof has two or more applications of any type of roof covering.

The list has no square-footage test, no age and no percentage.

What the third condition means for layers

The third condition is the one people mean when they ask about layers, though the code does not word it as a layer count. It bars a re-cover where the existing roof “has two or more applications of any type of roof covering.” Our reading is that this leaves room for exactly one existing application to be covered, which makes two layers the most a re-cover can produce and rules out a third. That is our reading of the text: the code states a prohibition, and the permission is what is left when you subtract it. A common summary on other pages, “Michigan allows two layers,” matches that reading only if two conditions also hold: the first layer is sound, and the new covering follows the manufacturer’s instructions. It also does not say what happens if you cannot tell how many layers are on the roof. If the count is unknown, ask for a look at the roof edge or the attic side of the deck before the quote is final.

The roofs a second layer can never go on

Two of the three bars have nothing to do with layer count. A roof that is water soaked or deteriorated cannot take a re-cover however many layers it carries, because the old surface has to serve as the base. A roof of slate, clay, cement or asbestos-cement tile cannot take one either.

For a homeowner the first bar is the practical one, because someone has to judge it before the quote is written. Ask the roofer how they decided that the deck and the existing layer are sound enough to cover, and whether they looked at the underside from the attic. A company that proposes a re-cover over a leaking roof has a hard question to answer under R908.3.1.1.

Where the sources stop

We read the 2015 text through the Michigan adoption rule, R 408.30500, and LARA’s code books page, which lists that edition as current. We did not find a Michigan source that explains how a building department counts layers in the field, or one that says what an inspector does when a roof turns out to carry more layers than the permit application stated. Those are local practices, and the inspectors you can phone are the ones who know them.

Flashings do not get covered

On either path, the metal around the edges and openings is handled separately. The code says existing flashings, edgings, outlets and vents that are part of the roof assembly are to be replaced where they are rusted, damaged or deteriorated, and that flashings are reconstructed according to the manufacturer’s instructions. A proposal to shingle over rusted valley or wall flashing has no support in the text. For the chimney side of this, see our chimney flashing page.

Permits, inspection and the 25 percent question

Michigan’s amended permit section lists the work that needs no building permit, and roofing, re-roofing and roof repair are not on it. Enforcement is local. LARA’s jurisdiction list shows building enforcement at the city level in Detroit, Grand Rapids, Warren, Flint, Ann Arbor, Lansing, Kalamazoo, Saginaw, Midland and Portage, so your building department decides whether a shingle replacement needs a permit and what it inspects. Do you need a permit to replace a roof in Michigan covers it in full.

You may have seen a “25 percent rule” that says a roof must be fully replaced once a quarter of it is damaged. We looked for one in the Michigan rules and the 2015 text and found none. If a company or an insurer cites it, ask for the section number in writing.

What to ask in a quote

The quote should say, in plain words, whether the job is a tear-off to the deck or a re-cover, and how many existing layers the roofer found. If it is a re-cover, ask why the existing roof qualifies under the three bars above, and whether the manufacturer’s instructions allow the new shingle over the old.

If it is a tear-off, ask what happens to the ice barrier at the eaves, since the exception lets an adhered membrane stay. Ask who pulls the permit, and which code edition the quote follows, a question that has a real answer because of the 2015 versus 2021 code dispute. The roof replacement page shows how the rest of a replacement job fits together.