What is the 25% rule for roof replacement building code in Michigan?
Short answer
No formal 25% rule exists for roof replacement under current Michigan building code standards. Historically, model codes used a 25/50 rule where work valued under 25% gave local officials discretion, but modern residential codes apply whole-assembly tear-off rules regardless of damaged roof area percentages.
Status and Historical Origins of the 25% (michigan.gov) Rule in Michigan Building Regulations#
Prior to the late 1970s, three model building codes evaluated rehabilitation projects using a standard called the 25/50 rule (ced.msu.edu). This metric depended entirely on the estimated cost of proposed work calculated as a percentage of the total building value.
Under that historical framework, local building officials held discretionary authority if the rehabilitation cost was lower than 25 percent (ced.msu.edu) of the building value. If the rehabilitation value fell between 25 percent and 50 percent, the entire scope of the proposed work had to conform to modern building codes. Whenever the project cost exceeded 50 percent of the total building value, officials required the entire building to be brought up to current code standards.
Model codes eventually shifted away from this cost ratio approach. Historically, percentage rules were used under model building codes to determine compliance requirements for building rehabilitation. Instead, most Michigan jurisdictions limit asphalt shingles to a maximum of two layers, requiring a full tear-off if two layers exist.
Current Michigan Building and Residential Codes Governing Roofs#
Residential and commercial structures in Michigan operate under different state-adopted code editions. Residential building work throughout the state is governed by the 2015 Michigan Residential Code, which took effect on February 8, 2016 (michigan.gov).
Other construction projects follow different regulatory documents:
- The 2021 Michigan Building Code serves as the current baseline for commercial construction, effective April 9, 2025 (michigan.gov).
- The 2021 Michigan Rehabilitation Code took effect on April 9, 2025.
Roofing systems on existing properties must align with the specific code edition active for that building type. When dealing with repairs or replacements, the relevant provisions depend on whether the structure falls under the residential standards or the rehabilitation code for commercial real estate.
Statewide Code Uniformity and Local Municipal Authority Under Act 230#
Questions sometimes arise regarding whether local municipalities can establish their own percentage triggers for roof replacements. In 1999, the State of Michigan amended the code adoption process under the State Construction Code Act, known as Act 230 (ced.msu.edu). This statute mandates that local municipalities administer and enforce statewide codes uniformly.
Act 230 expressly prohibits local communities from modifying these state codes (ced.msu.edu). Under state law, municipalities must administer and enforce statewide codes without permitting local modifications. Municipalities across the state must administer and enforce these statewide codes consistently.
Requirements for Roof Coverings, Layer Limits, and Tear-Offs#
Instead of using percentage formulas, most Michigan jurisdictions limit asphalt shingles to a maximum of two layers. The 2015 Michigan Residential Code mandates that a roof replacement must include removing existing layers of roof coverings down to the roof deck (up.codes). Stripping the roof down to the wood deck sheathing allows contractors to inspect the structural base for rot, sagging, or water intrusion.
The standard progression for reroofing projects follows a strict structural sequence:
- Evaluate existing layers
- Strip shingles to deck
- Inspect wood sheathing
- Install new roof system
Layer restrictions determine whether a homeowner can install a recovery layer or must complete a full tear-off. Most Michigan jurisdictions limit asphalt shingles to a maximum of two layers (oneclickcode.com). When a residential roof already carries two layers of shingles, installing a third layer is prohibited, requiring a complete tear-off before any new shingles are installed.
Permit Requirements for Roof Repairs and Alterations#
Understanding permit thresholds helps property owners avoid costly stop-work orders during exterior renovations. Under Michigan administrative rules, property owners or their authorized agents must obtain a permit from a building official before undertaking any construction, enlargement, alteration, or repair regulated by the code (michigan.gov).
While small, non-structural maintenance tasks may occasionally qualify for exemptions depending on administrative scope, significant structural modifications or full reroofing projects require formal approval. This administrative requirement ensures that proposed construction or repair work is overseen by a building official according to applicable codes. Property owners should confirm local administrative filing steps through their municipal building desk before scheduling major exterior work.
Role of Ordinance or Law Insurance Coverage in Mandated Code Upgrades#
When storms damage an older roof, upgrading the assembly to modern standards can create unexpected expenses. Building code upgrade coverage, commonly referred to as ordinance or law coverage, pays for the additional costs incurred during the construction, demolition, or repair of a damaged covered structure resulting from changes in laws and modern regulations (progressive.com).
Standard homeowners insurance policies often cover only the cost to replace what was physically damaged based on previous building standards. If local code officials mandate that an entire slope be stripped down to the sheathing or require updated ventilation and drip edges, base policies might not pay for those mandated improvements. Ordinance or law endorsements bridge this financial gap by covering the necessary code upgrades, protecting property owners from out-of-pocket structural expenses during a covered insurance claim.
To determine how current codes apply to your property, take these specific steps this week:
- Review your current homeowners insurance policy declarations to confirm whether you have ordinance or law coverage endorsements.
- Check your roof's edge profile to determine if your home already has two layers of shingles installed.
- Schedule a comprehensive inspection with a licensed contractor to evaluate your roof decking, attic ventilation, and underlayment before planning your project.
| Percentage of Building Value (PV) | Scope of Work Compliance | Building Official Authority |
|---|---|---|
| Lower than 25% | Discretionary based on official determination | Flexibility to determine extent of required code conformity |
| 25% to 50% | Entire scope of proposed rehabilitation work must meet code | Mandated enforcement across the proposed project scope |
| Greater than 50% | Entire building brought up to current building codes | Mandated full-structure code conformity |
| Code Title | Effective Date | Primary Regulated Scope |
|---|---|---|
| 2015 Michigan Residential Code | February 8, 2016 | Residential detached homes, townhouses, and residential roof replacements down to roof deck |
| 2021 Michigan Building Code | April 9, 2025 | General commercial construction and larger multi-family structures |
| 2021 Michigan Rehabilitation Code | April 9, 2025 | Alterations, additions, and repairs for existing commercial buildings |
Michigan Roof Replacement vs. Tear-Off Code Evaluator
In Michigan, many property owners mistakenly assume the '25% rule' (found in states like Florida or older model codes) forces a full roof replacement if over 25% of the roof is damaged. Under the Michigan Residential Code (MRC R908.3), a full tear-off down to the roof deck is required if the roof already has 2 or more layers of existing roofing, or if the underlying decking/sheathing is deteriorated. This tool calculates the percentage of your roof area affected and evaluates Michigan's actual code triggers for a full tear-off vs. a localized repair or overlay.
Percentage of Roof Area Affected:
Full Tear-Off Mandated by Michigan Code (1 = Yes, 0 = No):
Minimum Work Area:
Frequently Asked Questions
What is the 25% rule for roofing?
Historically, model building codes used a 25/50 cost-ratio rule where work costing less than 25% of building value gave local officials discretion, work between 25% and 50% required the full scope of work to meet code, and work exceeding 50% required the entire building to meet code. Contemporary Michigan codes do not use a 25% surface area rule; instead, replacements require removing existing coverings down to the roof deck, and most jurisdictions limit asphalt shingles to two layers.
Disclaimer
This content is general information about roofing and home-exterior work and is not a substitute for an on-site inspection. Contact Horizon Roofing & Construction for advice specific to your home.
Sources
- www.michigan.gov - michigan.gov
- IMPLEMENTING A BUILDING REHABILITATION CODE IN ... - ced.msu.edu (2001-08-01)
- [PDF] department of licensing and regulatory affairs - State of Michigan - michigan.gov
- What Is Ordinance or Law Coverage? | Progressive - progressive.com
- Chapter 9 Roof Assemblies: Michigan Residential Code 2015 | UpCodes - up.codes
- Michigan Roofing Codes | OneClick Code - oneclickcode.com