Substantial damage and improvement: the 50% rule in a flood zone

It is the framework the Planning Board adopted on 24 September 2025 in the "Operational Guide for Substantial Damage and Substantial Improvement Determinations in Puerto Rico", prepared by the Geology and Hydrogeology Office in its role as State Coordinating Office of the National Flood Insurance Program. The thresholds it sets are not new: they come from Section 2.00 of Topic 1 of Planning Regulation Number 13. What the guide adds is how they are calculated, which costs count and which do not, who is responsible for what, and how to ask that a determination be amended.

The substantial damage rule applies to all structures located in special flood hazard areas, including those with flood insurance. It reaches damage from natural events and from human causes alike. And it does not depend on you declaring it: since the guide took effect, a substantial damage or improvement assessment is required as part of permit requirements in those areas, and the Floodplain Administrator and the Participating Community may review, require and audit permits.

• Presenting complete information on the repair or remodelling, including works costs, labour and the materials cost estimate.Verified against the official source
• Providing an appraisal of the structure by a professional appraiser based on market value, where permit officials or the floodplain administrator require it.Verified against the official source
• Sharing insurance adjuster claim information where permit officials or the floodplain administrator require it.Verified against the official source
• Including the file or permit number in the documentation for the risk, damage or substantial improvement determination.Verified against the official source
• Providing at the start of the project a completed elevation certificate certified by a surveyor or professional engineer authorised to practise surveying, on FEMA’s current form FF-206-FY-22-152.Verified against the official source

• An appraisal of the structure’s market value, excluding the land, prepared by a certified professional appraiser before the improvements begin.
• A construction cost estimate signed by a licensed engineer or licensed architect; evaluation tables from recognised industry organisations, updated estimating manuals and professional field tools are also accepted.
• The elevation certificate on FEMA’s current form FF-206-FY-22-152, and any additional certifications that apply: VE Certification, No-Rise Certification and floodproofing.

1. 1

   Step 1: The division that decides everything

   The determination is based on the relationship between the cost of replacing or repairing the structure to its pre-damage condition and that structure’s market value. If that ratio equals or exceeds fifty per cent, there is substantial improvement or damage. It is literally cost divided by value, times one hundred, against a 50% threshold. There is no discretion in the number; the argument, when there is one, is about the two figures that go into the division.

2. 2

   Step 2: What "market value" means here

   It is not the bank appraisal or the CRIM assessed value. The guide defines it as the price agreed between buyer and seller considering the building’s original quality, later improvements, year of construction and current condition. And it adds two precisions that change outcomes: the value must be determined by a certified professional appraiser before the improvements begin, and in the amendment procedure the guide expressly requires the appraisal to establish the structure’s market value prior to the event, excluding the land value. The lot does not count.

3. 3

   Step 3: Substantial damage and its cumulative version

   Substantial damage is damage where the cost of restoring the structure to its previous condition equals or exceeds 50% of the market value before the damage. But there is a second door many do not see coming: cumulative substantial damage. It refers to flood damage in two separate events over a ten-year period; the damage is considered substantial if the repair cost at the time of each of those events, on average, equals or exceeds twenty-five per cent of the market value before the damage. Two medium floods in a decade can weigh as much as one big one.

4. 4

   Step 4: Substantial improvement: remodelling counts too

   Substantial improvement is any extension, reconstruction, rehabilitation or other improvement project whose cost equals or exceeds 50% of the structure’s current market value. The guide names the project types that will require permits as improvements: remodelling, rehabilitation, additions or extensions, and repair and reconstruction. And here too there is a cumulative version: the sum of repair or improvement costs accumulated over a ten-year period, such that the structure reaches 50% and becomes obliged to comply with floodplain regulation. Doing it in pieces does not avoid it.

5. 5

   Step 5: Which costs go into the count

   The guide lists them. Included are: materials and labour; value donated by volunteers or material discounts; site preparation such as excavation or fill; demolition and disposal of demolition debris; costs of complying with other regulations, for example the ADA; elevating the structure where it sits below the applicable base flood level; works management and supervision; taxes on materials; exterior and interior finishes; and the structure’s utilities and service equipment. That the work is donated by a volunteer or the material came discounted does not lower the count: its value goes in anyway.

6. 6

   Step 6: And which costs stay out

   Excluded are: cleaning or removing rubbish or debris from the property; tools or techniques used to stabilise the structure; surveying plans and specifications; permit or inspection taxes; installing carpet over finished wood or vinyl floor; and exterior improvements such as landscaping, irrigation systems, pavements, fences, accessory structures, sanitary code upgrades and installing washers, dryers and cookers. Further, improvements meant to correct code violations should not be included in the cost, and historic buildings may be exempt from substantial improvement requirements.

7. 7

   Step 7: Where the estimate may come from

   The guide accepts four sources: a construction cost estimate signed by a licensed engineer or licensed architect; an evaluation table published by recognised construction-industry organisations; updated construction cost estimating manuals; and tools available to professionals in the field. Further, the owner may use their own cost estimates provided they submit adequate documentation justifying the results, and the Floodplain Administrator may set criteria for those estimates using professional good judgement.

8. 8

   Step 8: If the determination came out wrong

   There is an amendment procedure for substantial damage determinations. You file a formal letter addressed to the Planning Board or the Participating Community requesting the amendment, with the minimum documentation. That documentation is demanding: an explanatory memorandum signed and sealed by a licensed engineer or architect detailing the reason for the error in the original documentation — calculation error, omitted line items, incorrect values — with the technical justification and a comparison table between the original and amended documents; an updated appraisal of the property, currently dated, establishing the structure’s market value prior to the event excluding the land; a repair cost estimate prepared and signed by a licensed engineer or architect, itemised and explaining the differences from the previous estimate; and supporting documentary evidence such as recent photographs, sketches or plans and expert documents.

9. 9

   Step 9: What happens to the amendment request

   The request is deemed incomplete if it does not include the full set of documents, and incomplete ones do not proceed to evaluation until cured; if not cured within the established term, the request is denied and filed away. If complete, the Office’s technical staff verifies the formal and legal validity of the documents, compares the original file with the amended information and determines the technical consistency between the appraisal, the estimate and the memorandum. If the correction is warranted, a Revised Determination Letter of Substantial Damage or of No Substantial Damage is issued replacing the initial one; if not, a denial notice is issued with the technical or regulatory reasons. The guide does not publish what that "established term" for curing is, and we do not invent it.

The determination is handled with the corresponding permit office: the Planning Board or the Participating Community, and in municipalities the Floodplain Administrator. The amendment request is filed by formal letter addressed to the Planning Board or the Participating Community. The guide is published by the Geology and Hydrogeology Office on the Board’s Flood Portal.

• Using the CRIM assessed value or the bank appraisal instead of the structure’s market value without the land.
• Getting the appraisal after starting the improvements: the guide asks for it before.
• Believing it only applies if you have flood insurance: it applies to all structures in special hazard areas.
• Forgetting the cumulative rules: two events in ten years averaging 25%, or improvements summing to 50% in ten years.
• Putting into the cost items the guide excludes, such as debris, fences, landscaping or permit taxes.
• Leaving out the value of volunteer-donated work or material discounts: the guide includes them.
• Filing an incomplete amendment request: it does not proceed to evaluation and can end denied and filed away.
• Submitting the explanatory memorandum without a licensed engineer’s or architect’s signature and seal.

These are the government pages this guide is based on.

• Junta de Planificación de Puerto Rico (JP)

  Junta de Planificación

  portaldeinundacion.jp.pr.gov

• Planning Board Flood Portal

  jp

  portaldeinundacion.jp.pr.gov