Commercial roof replacement, layer by layer, to the 2021 Illinois energy code
When a business roof is past repair, State Restoration Services takes it off down to the deck and builds a new one: insulation, cover board, a TPO, EPDM or modified bitumen membrane, and new flashing at every wall, curb and drain. We do it for property managers and owners of stores, offices, industrial buildings and apartment buildings across the Chicago suburbs.
- 1The deck: steel, concrete, wood or gypsum. Nobody sees all of it until the old roof is off, which is why damaged deck is priced per unit.
- 2Insulation boards in at least two layers with staggered joints, cut to a slope where water has to run toward a drain.
- 3A cover board: a thin, hard board over the insulation that takes foot traffic and gives the membrane a flat base.
- 4The membrane, TPO, EPDM or modified bitumen, attached the way its manufacturer's instructions call for.
- 5Wall flashing: the membrane is carried up the parapet and the metal coping goes back on over it.
- 6The drain: the new membrane is clamped into the drain bowl and the strainer is put back.
When a repair is no longer enough
Most leak calls on a flat roof end with a repair at a seam, a curb or a drain. A new roof is the answer when our survey finds one of the three conditions on the right. How that call is made, and when a coating is the cheaper way to buy years, is laid out on our commercial flat roof repair page.
- The insulation under the membrane holds water across large parts of the roof, so a patch on top would seal the wet board in.
- The membrane is worn out over the whole roof, not at one seam or one corner, and new leaks keep appearing in new places.
- The code does not allow another layer: the old roof is water-soaked or too deteriorated to build on, or the deck already carries two roofs.
The new roof has to meet today's insulation rule
On most flat commercial roofs the insulation sits entirely above the deck. When such a roof is replaced, the energy code treats the new one like new construction, so it must reach the insulation value set for a new building, even if the old roof had far less.
- The code
Illinois adopted the 2021 International Energy Conservation Code with state amendments for building permits applied for on or after January 1, 2024, as the National Roofing Contractors Association reported. The City of Chicago runs its own energy code.
- The value
R-30 continuous insulation for roofs with insulation entirely above the deck in climate zone 5, both for most buildings and for Group R residential buildings, as the University of Illinois Smart Energy Design Assistance Center sets out in its 2021 IECC commercial changes course.
- The trigger
The roof replacement section applies when the insulation is entirely above the deck, and the roof then follows the new construction provisions, as the International Code Council explains in Talking in Code: roof replacement requirements.
Sloped insulation still counts toward R-30
Where boards are cut to a taper to move water to the drains, the code lets the average R-value of the tapered layer count. The thinnest point has to be at least 1 inch, and the insulation goes down in at least two layers with staggered joints, except at a gutter edge, a drain or a scupper.
A thicker roof sits higher, so the plan also checks curb heights, edge metal and any door that opens onto the roof. Your village's building department confirms the edition and any local amendments when the permit is filed.
Nine lines to compare when you hold two bids
Two bids for one roof can be far apart because they describe two different roofs. Lay them side by side and look for each of these lines. Our free roof survey comes with a full photo report, so every line can be checked against the roof itself.
What the plan works around, building by building
The roof is the same kind of job on every building. What changes is who is underneath it while the crew works.
Stores and strip centers
Customer entrances and parking stay open. Work over a storefront can be moved to early mornings or a weekend so shoppers never walk under it.
Offices
Rooftop units serve people working below. The plan shows when each unit is flashed, so your HVAC contractor can be on site if a unit has to be lifted.
Industrial buildings
Loading docks keep working. Crews and material stay clear of the dock side while trucks are moving, as agreed in the schedule.
Apartment buildings
People live under the roof every day, so working one section at a time matters most here. Associations of townhomes and condos have their own page on association roof replacement.
One building, replaced in sections
On an occupied building the roof can be split into sections, and each one is torn off and rebuilt before the next is opened. Early starts and weekend phases are other options, and they can be combined.
We agree the order, the hours and which entrances stay open with you before the job starts, so tenants hear about it from you in advance.
When hail or wind is the reason for the new roof
Hail can crack insulation board and bruise a membrane without leaving a hole you can see, and wind lifts the roof edge and peels the coping. Our survey records the damage in photos and measurements, and we write an estimate for the carrier that follows the code.
A roofer in Illinois may not negotiate an insurance claim. The building owner can be represented on the claim by our partner, the licensed Illinois public adjuster State Adjusting Services, and the insurer decides the amount it pays. Whether a policy pays toward the extra insulation the code now asks for is a separate question, covered in our guide to code upgrade coverage on a roof claim.
Questions owners ask before replacing a commercial roof
Do you have to remove the old roof or can the new one go over it?
If the old roof is dry, sound and the only layer on the deck, a new roof can sometimes go over it with a cover board. If it is water-soaked, deteriorated or already has a second roof on it, the code requires a tear-off, and our survey shows which case your roof is in.
Does a commercial roof replacement have to meet the energy code?
Yes, when the insulation sits entirely above the deck. Under the 2021 IECC adopted in Illinois from January 1, 2024, the new roof then needs R-30 continuous insulation in climate zone 5, and tapered boards may count by their average value.
Can the building stay open during a roof replacement?
Yes. We schedule the work around your hours with early starts, weekend phases or one section of roof at a time, so entrances, loading docks and tenant space stay usable. The order is agreed with you before the crew arrives.
Which membrane do you install on a new commercial roof?
TPO, EPDM and modified bitumen on flat and low-slope roofs, and standing-seam metal on pitched commercial roofs. The choice follows the building: what it is used for, how it drains, what sits on the roof and how much foot traffic it gets.
Want this looked at?
We inspect for free, document what we find and prepare a code-compliant estimate you can hand to your insurer. Our partner, a licensed public adjuster, State Adjusting Services, can represent you on the claim.
Call (866) 992-2982. Free Inspection