Recover or Replace: The One Line in the Energy Code That Decides Whether You Must Add R-30, State by State

In short

The energy code treats a roof replacement and a roof recover as two different events. A replacement, meaning a tear-off to the deck, on a roof whose insulation sits entirely above the deck must be rebuilt to today's insulation table: R-30 continuous in Nebraska and most of Minnesota, R-25 in most of Iowa, R-35 in northern Minnesota. A recover, meaning a new roof over the existing one, is exempt in all three states as long as the building's energy use does not go up. South Dakota and Wyoming have no statewide energy code at all.

That one distinction can add more than five inches of insulation to a re-roof. The polyiso manufacturers' own sample R-30 assembly is two layers of 2.6-inch board.

What the code actually says

The 2018 International Energy Conservation Code, which Nebraska enforces, defines the terms. Roof replacement is the process of removing the existing roof covering, repairing any damaged substrate and installing a new roof covering. Roof recover is the process of installing an additional roof covering over an existing roof covering without removing it. Roof repair is reconstruction or renewal of any part of an existing roof for the purpose of its maintenance.

Section C503.3.1 then says roof replacements shall comply with the insulation requirements for new construction where the existing roof assembly is part of the building thermal envelope and contains insulation entirely above the roof deck. Section C503.1 lists the alterations that need not comply, provided the energy use of the building is not increased, and roof recover is on that list, along with construction where the existing roof cavity is not exposed.

The ICC's own technical staff covered the uninsulated case in an August 5, 2019 column: if the existing roof has no insulation and the roof cavity is not exposed, there is no requirement. If the cavity is exposed, it must be filled with insulation to the extent it can be.

Effective dates and the rule in each state

The same physical job lands differently in each of A-1's five states.

• Nebraska: the Nebraska Energy Code is the 2018 IECC and ASHRAE 90.1-2016, adopted by LB 405 and in effect since July 1, 2020. Where a local jurisdiction has not adopted an energy code, the Department of Water, Energy, and Environment enforces it. Every county is climate zone 5A, and the 2018 table requires R-30 continuous insulation for roofs with insulation entirely above the deck. C503.3.1 and the recover exception apply as written above.
• Iowa: 481 IAC 301.25 adopts the 2012 IECC commercial provisions as the state's nonresidential energy code, effective September 10, 2025, and rule 301.23 applies it to buildings intended for human occupancy throughout the state. The 2012 edition predates C503.3.1. Its trigger is exposure: under the exception to section C101.4.3, reroofing is exempt where neither the sheathing nor the insulation is exposed, provided energy use does not rise, and a roof without cavity insulation whose sheathing or insulation is exposed during reroofing must be insulated above or below the sheathing. A tear-off exposes the insulation, so it is built to the 2012 table: R-25 continuous above the deck in climate zone 5A, which covers most of the state, and R-30 in the 6A counties in the north of the state, such as Winnebago, Worth, Allamakee and Webster.
• Minnesota: chapter 1323 adopts ASHRAE 90.1-2019 with state amendments, effective January 5, 2024, and it applies to alteration and repair as well as new work. Twenty-three northern counties, Aitkin, Beltrami, Carlton, Cass, Clearwater, Cook, Crow Wing, Hubbard, Itasca, Kittson, Koochiching, Lake, Lake of the Woods, Mahnomen, Marshall, Norman, Pennington, Pine, Polk, Red Lake, Roseau, St. Louis and Wadena, are climate zone 7 and need R-35 continuous above the deck on a replacement. Every other county is zone 6A at R-30, per the Polyisocyanurate Insulation Manufacturers Association's December 2023 fact sheet. 90.1's envelope alteration exceptions include roof recovering. Minnesota adds Exception 9 (rule 1323.0513): where structural capacity or rooftop conditions such as curbs, door heights, parapets or flashing heights prevent the full R-value on a replacement, the maximum insulation that fits must be installed, it must have the highest R-value per inch available, and the roof's R-value may never go down.
• South Dakota: no statewide mandatory energy code, per the Building Codes Assistance Project. What the state does require is in SDCL 11-10-5, amended by the 2026 Legislature (SL 2026, ch 59): if a city or county adopts a building ordinance for non-residential construction, alteration or repair, it must comply with the 2024 International Building Code. A regular-session act with no date of its own takes effect July 1 under SDCL 2-14-16. Energy rules apply only where a city has adopted an energy code of its own, so ask the local building office which edition, if any.
• Wyoming: no mandatory statewide energy code, per the same project. The State Fire Marshal requires plan review under W.S. 35-9-108 for state and local government buildings, schools, buildings over 5,000 square feet with public access and places of assembly, including alterations valued at $40,000 or more. Submissions since June 28, 2024 must comply with the 2024 International Building Code, Existing Building Code, Fire Code, Fuel Gas Code and Mechanical Code. No energy code is on that list.

Who this affects

Any owner of a low-slope commercial, school or public building in Nebraska, Iowa or Minnesota whose roof is near the end of its life and whose insulation sits on top of the deck. Built-up, modified bitumen and single-ply roofs over steel or concrete decks are commonly built that way, and a core sample shows whether yours is. Metal building roofs sit in their own row of the code tables, with different numbers.

Every one of A-1's five published case studies kept the existing roof in place. Colome's EPDM was cleaned, primed and coated, with only the delaminated areas cut back and rebuilt. The Monument's PVC was restored in place across three venues. The Was Ake' Building's 1994 standing seam roof was sealed under a membrane over the original panels. Woonsocket came closest to a tear-off: the saturated foam was cut out and replaced section by section, and the deck was never exposed. Freeman Shopping Center shows the other direction. In 2021 A-1 sprayed foam over a 43-year-old metal roof while fixing its leaks and condensation, and the foam added R-10. It went over the existing panels, the kind of job the replacement rule does not reach. A recover can add insulation. It just is not forced to.

The code is not the only reason owners recover. In the early 2000s a school district came to A-1 with an aging building whose roof contained asbestos. A tear-off would have disturbed it and brought costly remediation with it, and the district planned to build a new school within about ten years. A-1 sprayed foam over the existing roof to insulate and waterproof it, a roof meant to get the building by until the new school opened.

Classifying a particular job is the building official's call. Ask before the bid, not after the permit.

The catch: a wet roof cannot be recovered

The recover exemption only helps a roof that is allowed to be recovered. The model building code's reroofing section, as NRCA summarized for the 2018 International Building Code, requires removal down to the deck when the existing roof is water-soaked or deteriorated to the point that it is not an adequate substrate, or when it already has two or more layers. A protective roof coating is not counted as a layer.

So the moisture survey decides more than the repair. A roof with dry insulation can usually be recovered and stay outside the replacement rule. The same roof three winters later, with wet insulation across a third of it, may have to come off, and then it has to come back at R-30.

What to do this month, and this quarter

The decision gets made before anyone prices the job.

• This month: find out which energy code, if any, your building official enforces, and which edition. In Nebraska and Iowa there is a state default. In South Dakota and Wyoming there may be none.
• This month: get a moisture survey and core samples on the roof. They tell you whether a recover is allowed at all, and how much of the existing insulation is worth keeping.
• This quarter: if a replacement is unavoidable in Minnesota, ask the designer whether Exception 9 applies. Curb heights, door thresholds and parapets are the conditions the rule names.
• This quarter: if a recover is the plan, get the R-value the new system adds in writing, so the energy effect of the job is on record from the start. A-1's proposals usually state the R-value being installed, especially when added insulation is the reason for the job.

Where to find the primary sources

This post describes state energy and building codes as adopted and in effect on October 2, 2026. It is not legal, engineering or code-compliance advice. Local jurisdictions can adopt newer editions or amendments, and the building official decides how a specific roof project is classified. Confirm the code in force and the classification of your project with your local building department before design or bidding. The sources below carry the section numbers and dates.