A second layer of shingles over the old roof is a real option: widely recommended, cheaper up front, and the right call for some houses. It is also unavailable to a lot of Michigan homes. Michigan’s residential code requires existing roof coverings to be removed once a roof carries two applications, and two layers is common on older Michigan homes. Where an overlay is permitted, it costs manufacturer warranty coverage along with years of service life.

This assumes you have already decided to replace; if you are still weighing whether a replacement is the right call at all, start there. The question here is method: cover the roof you have, or take it down to the deck, the wood sheathing your shingles are nailed to.

Two Layers of Shingles Means the Roof Comes Off

Michigan enforces the 2015 International Residential Code, and no state amendment touches the reroofing section. Michigan Residential Code R908.3 requires existing roof coverings to come off before new roofing goes on where the roof already carries two or more applications, an application being one complete layer of roof covering installed at one time. One existing layer can leave an overlay on the table. Two means the roof comes off.

It also requires removal when the existing covering is water-soaked or deteriorated enough that it will not serve as a sound base for new roofing. Your roofer pulls the permit, and the local building department is the final word on what your roof carries.

Can you put new shingles over old shingles?

Sometimes. If the roof carries one layer, the shingles are lying reasonably flat, and the deck underneath is sound, an overlay is permitted. Fail any one of those and the old roofing comes off first.

How do I know how many layers my roof has?

A roofer can usually count them at the roof’s edge, where the shingle stack shows in cross-section; permit history at the building department is the other record. From the driveway you cannot tell, which is one of several things a roof inspection turns up that a look from the ground will not.

Key takeaway: One existing layer may leave you a choice; two or more applications means the roof comes off.

An Overlay Covers the Roof You Have; a Tear-Off Replaces It

What is roofing over existing shingles?

An overlay, also called a re-cover or layover, adds a new course of shingles over the roofing already on the house. The old shingles stay, as do the underlayment (the water-resistant sheet between shingles and deck) and most of the flashing (the metal that seals joints at chimneys and walls).

What is a roof tear-off?

A tear-off strips the roof to the bare deck and rebuilds: new underlayment, a new ice barrier along the eaves (the waterproof membrane at the roof’s lower edge), new flashing, new shingles.

Key takeaway: An overlay adds a layer over the roof assembly you have and leaves the deck, underlayment and most flashing unseen; a tear-off replaces the assembly.

A Tear-Off Is the Only Version Where Anyone Sees Your Roof Deck

Michigan roofs cycle through freeze and thaw and build ice dams, and both push water toward the eaves, where soft sheathing and rot show up first and where an overlay covers them over. Sheathing that has lost its nail-holding capacity, meaning it no longer grips a nail, will not hold new shingles any better than it held the old ones.

The deck inspection is much of what a tear-off buys, and a clean deck is where a good install starts, which is much of how installation quality shows up the following winter. Ask what happens if the crew finds soft sheathing once the shingles are off: what gets replaced, how it is priced, and whether that call is made with you or without you.

Ask how the crew protects the house. Catch-all tarping and roofing buggies are the answer you want to hear, and they are what Weather Vane Roofing’s crews use to keep siding, windows and landscaping clear of the debris. A good crew also strips in sections and does not leave a deck exposed overnight; get that in writing.

None of this is work to take on yourself; roof work is not a homeowner project, and a tear-off is the least forgiving version of it.

Key takeaway: An overlay hides the deck; a tear-off is the only method where anyone sees it.

Overlaying Costs You Warranty Coverage, Not Just Years

Some manufacturers’ limited warranties require the old layer to be removed, and the premium system warranties generally require a clean deck, which leaves an overlaid roof on basic materials-only coverage. Impact-resistance ratings may only have been evaluated on shingles applied directly to the deck. Read the warranty before settling on a method, and know what a manufacturer warranty leaves out either way.

Weather Vane Roofing’s lifetime workmanship guarantee on complete roofing jobs stands behind a clean-deck install.

Service life runs the same direction: the same shingle over old roofing does not last as long as one on a bare deck. The finish changes too, since a second layer follows the contour of the first, so old ridges and patched spots telegraph through.

Key takeaway: Overlaying narrows what the manufacturer will cover, not only how long the roof lasts.

Overlay Fits a Narrow Set of Michigan Houses

Overlay is the right answer for a narrow set of houses.

Your roof	Overlay possible?
One layer, flat shingles, sound deck, no leaks	Yes
Two or more applications	No, code requires removal
Soft or water-damaged deck	No
Curled, cupped or patched shingles	No
Switching asphalt to metal	No, the new material needs a bare deck

A short remaining ownership horizon pushes toward overlay; another twenty years in the house pushes the other way.

Is a second layer of shingles a bad idea?

Not automatically. It is the right choice less often than the price gap suggests, and the conditions above are the test. Changing materials settles it: a new metal roof goes onto a bare deck, which is a different question from whether a steel roof is worth repairing.

Key takeaway: One layer and a sound deck makes overlay a real option; anything else makes tear-off the only one.

Count the Layers Before You Collect Bids

Find out what your roof carries before anyone quotes you a method. Two applications and the decision is made for you, and every bid you collect should be a tear-off. One layer and you have a real choice, settled by the deck’s condition and how long you plan to own the house rather than by the gap between two numbers. For the money side, what a full replacement costs in Michigan has the ranges.

Schedule an Inspection

Layer count and deck condition cannot be read from the ground. Weather Vane Roofing will come out and tell you what your roof qualifies for, including a repair if that is the honest answer, backed by the $1,000 Repair Credit Guarantee. If you only want the layer question settled, ask Roofster.