Is it cheaper to shingle over shingles?

Yes, on the day. You avoid tear-off at roughly $50 per square plus disposal. Over a full ownership cycle it is often not cheaper, because the deck goes uninspected and the next replacement has two layers to strip instead of one.

Will roofing over shingles void my warranty?

It can, and this is worth checking in writing before the work rather than after. Adopted code itself points to manufacturer instructions as one of the conditions under which a recover is permitted, so installing outside those instructions puts both code compliance and the product warranty at risk at the same time.

National guide

Can you put a new roof over old shingles?

Updated Sep 20262 sources

The short answer

Sometimes. Adopted code permits a roof recover under stated conditions, but bars it outright where the existing roof already carries two or more layers, where the old covering is water soaked or too deteriorated to serve as a base, and where the existing covering is slate, clay, cement or asbestos-cement tile. It saves tear-off cost and gives up the chance to inspect the deck.

What an average can't tell you

A national average compresses very different roofs into one number, and most of what sets your price is invisible to it. It cannot tell you how many square feet of roof you actually have — which is not your floor area, and is the single biggest driver of the total — or what covering is going back on, and those two choices alone move the figure more than anything else on the page.

It also cannot see how many layers have to come off before anything new goes on, how steep the roof is, how many storeys the crew is working above, or whether the decking underneath has rotted — which nobody knows, including the contractor, until the old roofing is off. Even within one metro, labor pricing and disposal fees shift in ways a single average flattens out.

Those are answerable questions, and they are exactly the estimator’s inputs. It starts from sourced national cost data and recomputes the range for your area, covering, pitch, height, and tear-off — the factually correct next step after any national average.

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When code allows it, and when it does not

The permissive half is real: adopted code states that the installation of a new roof covering over an existing roof covering shall be permitted where any of the following conditions occur, and then lists them - including installation in accordance with the covering manufacturer's approved instructions.

The prohibitions are the part that gets left out of most online answers. A recover is not permitted where the existing roof has two or more applications of any type of roof covering, nor where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing, nor over slate, clay, cement or asbestos-cement tile.

The code text quoted here is the Illinois Building Code 2021, Section 1512, as published by UpCodes. It is cited as what one named jurisdiction has adopted - not as a national rule. Reroofing provisions derive from model codes that most states adapt, so the shape is widely similar, but the specifics genuinely vary and your jurisdiction is the only authority on your roof.

Adopted code states that the installation of a new roof covering over an existing roof covering shall be permitted where any of the following conditions occur.

SOURCED

up.codes

The real trade-off, beyond whether it is allowed

Going over saves the tear-off line - around $50 per square - and the disposal that goes with it, which on an average roof is a meaningful fraction of the job. That is the entire case for it, and it is a legitimate one when money is tight and the existing roof is sound and singly layered.

What you give up is knowledge. Tear-off is the only opportunity to see the deck, and decking replacement runs $2 to $8 per square foot when it is needed - a cost that does not disappear because you covered it, it just arrives later with more damage attached. You also add weight, and you make the next replacement more expensive because that one will have two layers to strip.

The judgement most roofers converge on is that a recover is a reasonable economy on a sound roof you intend to sell within a few years, and a false economy on a roof you plan to live under for the next two decades.

A recover trades a known saving now for an unknown deck condition later, which makes it a better fit for a short holding period than a long one.

OUR TAKE

Basis: A judgement resting on two sourced figures - tear-off at around $50 per square, and decking replacement at $2 to $8 per square foot when found - plus the sourced fact that hidden decking damage is only discovered once the old roof is removed.

Get a local answer

National ranges only go so far — labor rates, tear-off rules, weather, and insurance practice move the numbers in every metro. See the local guides, each with a cost estimator:

Sources

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