What does ICC 500 mean for a storm shelter?

ICC 500 in one paragraph

ICC 500 is the “ICC/NSSA Standard for the Design and Construction of Storm Shelters”. It is published by the International Code Council, the body behind the building codes most US cities and counties adopt, and developed with the National Storm Shelter Association. It covers how tornado and hurricane shelters are designed, built, installed and inspected: structural design and testing, where shelters may be placed, how many people they hold, ways out, fire safety, ventilation and other essential features. It was first published in 2008 and updated in 2014, 2020 and 2023.

Why it matters to a homeowner

Since 2009, the International Residential Code and International Building Code have referred to ICC 500. In practice, that means your building department will often look to ICC 500 when you apply for a permit for a shelter. It also gives you a single, published yardstick to compare shelters against, instead of relying on adverts.

Residential and community shelters

ICC 500 separates two kinds of shelter:

• Residential: serves the people living in a home and holds no more than 16 people.
• Community: any shelter that is not residential, such as one at a school, workplace or mobile home park.

For a home tornado shelter, the National Storm Shelter Association summarizes the space requirement as at least 3 square feet of floor per person in a one- or two-family home. FEMA’s homeowner guide, P-320, uses the same 3 square feet per person for tornado safe rooms, and 7 square feet for hurricanes.

What the testing covers

A shelter has to resist two things: wind pressure and debris.

FEMA P-320 describes the tornado criteria in plain terms: a design wind speed of 250 mph wherever you live, and a debris test in which a 15-pound two-by-four is fired end-on at 100 mph. ICC 500 sets out the test methods. Walls, roofs, doors and other protective parts are tested for impact, and the standard also requires designs to resist debris falling or laying down on the shelter.

Doors are a big part of it. The 2023 edition limits the gap under a door to three-quarters of an inch and adds rules so that latches and electronic hardware do not block people from getting out. Labels showing compliance are mandatory on impact-protective parts, and the standard says what information those labels must carry.

What changed in the 2023 edition

FEMA’s summary of the 2023 edition lists several changes. The ones most relevant to homeowners:

• Tornado design now uses “tornado speed” and “tornado load” terms, following the 2022 edition of ASCE 7, the structural loads standard.
• The minimum mechanical ventilation for tornado shelters was reduced to 2.5 cubic feet per minute per person.
• Pressure testing gained pass or fail criteria, and impact testing gained a maximum deflection limit.
• Listing and labeling rules were moved into one chapter.

How FEMA P-361 and P-320 fit in

FEMA publishes two related documents:

• FEMA P-361, “Safe Rooms for Tornadoes and Hurricanes”, sets the design criteria for safe rooms, and goes beyond ICC 500 in places. The fifth edition was published in 2024. Its extra criteria apply when a shelter is built with FEMA grant money.
• FEMA P-320, “Taking Shelter from the Storm”, is the homeowner and builder guide, with safe room construction plans. Its sixth edition was issued in December 2024.

P-320 says prefabricated safe rooms must be listed and labeled to show compliance with both ICC 500 and FEMA P-361. That is why state programs often name all three documents.

FEMA does not approve products

FEMA’s residential safe room fact sheet says FEMA does not endorse, approve, certify or recommend any contractor, firm or product, and that businesses may not claim their products are “FEMA approved” or “FEMA certified”. If you see those words, treat them as a reason to ask more questions, not as a guarantee.

How to check a shelter

When you compare quotes for a tornado safe room or any other shelter, ask:

1. Which edition of ICC 500 and FEMA P-361 is it designed to?
2. Is the shelter, or its door and other protective parts, listed and labeled? Where is the label?
3. Which test lab did the testing, and can you see the report or listing?
4. Is there an engineer’s sealed drawing? State programs, such as Alabama’s tax credit, may ask for one.
5. How is it anchored, and does the installation match the tested design?

The ICC Evaluation Service runs a reports directory for products evaluated against ICC standards, which is one place to look up a listing.

A shelter is only as good as its weakest part and its installation. Our tornado shelter comparison explains the different types, our cost calculator gives typical installed prices, and we can find an installer who covers your area.