8.2 Tear-Off vs. Recover, Reroofing Rules & Preparing the Site (MRC R908)
Key Takeaways
Under 2015 MRC R908.3.1.1, a recover is not allowed if the existing roof is water-soaked or deteriorated, is slate, clay, cement, or asbestos-cement tile, or already has two or more applications of roofing.
A roof replacement removes existing roof coverings down to the deck, but an existing ice barrier membrane adhered to the deck may stay and be covered with a new layer of ice barrier (R908.3).
Metal panels, metal shingles, and clay or concrete tile may be installed over wood shakes under R908.4, and a recover over wood shingles or shakes that creates a combustible concealed space needs a gypsum, mineral fiber, glass fiber, or other approved cover over the whole surface.
The roof structure must support the roof covering and the material and equipment loads during installation (R908.2), and damaged slate or tile and aggregate surfacing may not be reinstalled (R908.5).
Rusted, damaged, or deteriorated flashings, edgings, outlets, and vents must be replaced, and flashings reconstructed per the manufacturer's instructions (R908.5–R908.6).
Key Reroofing Definitions
- Roof replacement: removing the existing roof covering down to the deck and installing a new covering.
- Roof recover: installing a new covering over an existing one.
- Reroofing: either process. R908.1 requires reroofing to meet Chapter 9's materials and methods, with two exceptions. First, reroofing need not meet the 1/4:12 minimum slope for membrane roofs that already provide positive drainage, meaning drainage within 48 hours of precipitation. Second, secondary overflow drains or scuppers need not be added to an existing roof that provides positive drainage.
When a Recover Is Not Permitted (R908.3.1.1)
In the 2015 MRC, a recover is not permitted where any of these conditions exists:
- The existing roof or roof covering is water-soaked or has deteriorated to the point that it is not an adequate base for more roofing.
- The existing roof covering is slate, clay, cement, or asbestos-cement tile.
- The existing roof has two or more applications of any type of roof covering.
Where none applies, R908.3.1 allows a recover when the new covering is installed following the manufacturer's approved instructions. Stand-alone systems that carry roof loads directly to the structure, such as some standing-seam metal systems, do not require removing the old roofing. A new protective coating over existing spray foam roofing is also allowed without tear-off.
Wood Shakes and Shingles
The 2015 list of prohibited recovers does not include wood shakes. R908.3.1 allows metal panels, metal shingles, and clay or concrete tile over existing wood shake roofs when applied under R908.4. R908.4 requires the entire existing surface to be covered with gypsum board, mineral fiber, glass fiber, or other approved materials, securely fastened, where the recover creates a combustible concealed space over wood shingles or shakes. Asphalt shingles still require a solidly sheathed deck (R905.2.1), and shingle manufacturers generally do not allow application over shakes. In practice, an asphalt reroof over shakes means tearing off, or installing new solid sheathing and meeting the manufacturer's rules.
Roof Replacement and the Ice Barrier Exception (R908.3)
A replacement removes the existing layers down to the deck. Exception: where the existing assembly includes an ice barrier membrane adhered to the deck, it may stay in place and be covered with an additional layer of ice barrier under R905. Self-adhered membranes often cannot be removed without destroying OSB, so this exception saves deck.
Loads During Reroofing (R908.2)
The roof structure must support the roof covering system and the material and equipment loads during installation. In practice:
- Count the existing layers. A recover adds weight, and the Michigan snow load may already be high (Section 7.1).
- Distribute bundle loads over framing and away from unsupported spans. MIOSHA also bars storing materials within 6 feet of an unguarded edge during roofing (Section 6.2).
- Don't stack tear-off debris on the roof. Remove it as work progresses.
Reinstalling Materials and Flashings (R908.5–R908.6)
- Existing slate, clay, or cement tile may be reinstalled, but damaged, cracked, or broken pieces may not.
- Existing flashings, edgings, outlets, vents, and similar devices that are rusted, damaged, or deteriorated must be replaced.
- Aggregate surfacing may not be reinstalled.
- Flashings are reconstructed per the manufacturer's installation instructions. Metal flashing to which bituminous materials will be adhered must be primed first.
The Tear-Off Decision
Even when a recover is legal, a tear-off lets you inspect and repair the deck, install ice barrier on the deck, replace flashings properly, and avoid the extra weight. Many manufacturer warranties are stronger on tear-offs. Explain the options to the owner in writing.
Preparing the Site and Roof (PSI's Installation Tasks)
PSI's "roof system preparation" tasks, and how to meet each one:
| Task | Practice |
|---|---|
| Determine whether tear-off is required, then tear off and dispose of debris | Apply R908.3.1.1. Test suspect asbestos first. Contain lead-painted trim debris (Section 2.3). Use barricaded drop zones or chutes (Section 6.5) |
| Cover skylights and other openings for fall protection | Secured, marked covers able to hold twice the load, or guardrails (Section 6.2) |
| Confirm other trades' work is ready | Chimney tuckpointing or crown repair, removed satellite dishes, electrical work for PV, and replaced bath fan and vent terminations |
| Protect surrounding areas | Tarps and plywood over landscaping and AC units, driveway protection under dumpsters, attic protection where debris can fall through board gaps, and interior protection when needed |
| Identify and correct inadequate framing or sheathing | Replace rotted deck to framing centers, and obtain a design professional's repair for damaged trusses (Section 8.1) |
| Manage live and dead loads during tear-off and installation | Spread loads, and do not overload framing or the Michigan snow design (R908.2) |
| Install roof deck sheathing | Proper grade, span, clips, and nailing (Section 8.1) |
| Identify and correct unacceptable decking, membrane, and drainage areas | Replace wet insulation and membranes on low-slope areas, and correct ponding (Section 10.3) |
| Install roof-to-wall transitions, curbs, platforms, and pitch transitions | Flash each per Chapter 11 |
Daily Dry-In
Tear off only what the crew can dry in the same day. Watch the forecast, keep tarps ready, and secure loose materials against wind (MIOSHA R 408.40119). An open roof overnight risks interior damage, and some liability policies limit water-damage coverage when the contractor fails to keep the building weather-tight.
Under the 2015 Michigan Residential Code, which existing roof may receive a recover of new asphalt shingles, assuming the manufacturer allows it and the structure can carry the load?
One layer of sound asphalt shingles on a solid deck
Two layers of asphalt shingles in good condition
One layer of slate
One layer of water-soaked, curling shingles
During a full tear-off, a roofer finds a self-adhered ice barrier firmly bonded to the eave sheathing. What does R908.3 allow?
It must be scraped off completely because a replacement means removal to the bare deck
It may remain in place if it is covered with an additional layer of ice barrier membrane
It may remain only if the deck is replaced
It may remain and be covered with standard felt underlayment
Which statement about wood shake roofs is accurate under the 2015 MRC reroofing rules?
Every roof covering may be applied over wood shakes without preparation
The 2015 MRC lists wood shakes among the coverings that can never be recovered
Metal panels, metal shingles, and clay or concrete tile may be installed over wood shakes under R908.4, which requires covering the old surface where a combustible concealed space is created
Wood shakes may be recovered only with another layer of wood shakes
Sections you finish are checked off in the contents.