In a strong typhoon, the sequence is usually the same. The roof lifts at an edge, wind gets underneath, the sheets peel off, and then several days of rain fall directly into a house that is otherwise structurally sound.

The contents are lost, the ceilings collapse, the electrical is ruined, and the repair bill is many times the cost of the fixings that would have held it down.

Why wind is not on the hazard report

A CheckHazard screening reports mapped flood, landslide, storm surge, volcanic proximity, terrain, faults, and waterway distance. It does not rate wind.

Wind loading is a structural design matter. The National Structural Code of the Philippines sets the design wind speeds by zone, PAGASA provides the underlying wind information, and a licensed structural engineer applies them to a specific building on a specific site with a specific exposure.

We would rather say that than print a wind rating we cannot source at point level. The same principle governs tsunami and sinkholes. See a layer came back blank on your report.

What the wind actually does

Uplift, not push. Wind flowing over a roof creates suction above it. The roof is being pulled up more than it is being pushed down, which is why fixings matter more than weight.

Edges and corners are worst. Suction is highest at eaves, ridges, and corners. That is where failure starts.

Internal pressure makes it worse. If a window or door on the windward side fails, the wind gets inside and pushes the roof up from below while suction pulls from above. A broken window is a roof problem.

Debris does the breaking. Most window failures come from something flying into them, not from wind pressure alone.

What to look at on a viewing

1. How is the roofing fixed? Screws with washers into purlins are a different thing from plain nails. Ask what was used and at what spacing.
2. How are the purlins fixed to the trusses, and the trusses to the walls? This is the load path, and it is only as strong as its weakest connection. Straps or ties beat nails.
3. How far does the roof overhang? Long unsupported overhangs are lifting surfaces.
4. What is the roof pitch and shape? A hipped roof, sloping on all sides, generally performs better in wind than a simple gable end. Very low pitches generate high uplift.
5. Are there extensions or additions? Additions are usually the weak point, and they can pull the original apart when they fail.
6. What protects the openings? Shutters, storm bars, or nothing.
7. What is the condition? Rust at the fixings means the fixings are not what they were.
8. Is there anything to hit it? Overhanging branches, loose sheets on a neighbouring structure, unsecured roofing nearby.

Ask these questions

• Who built or last replaced the roof, and when?
• Are there stamped plans and a permit?
• Was it repaired after a storm? Which one, and what was done?
• Has a structural engineer looked at it?

Where it matters most

Everywhere in the country, and most of all on the eastern seaboard and the northern islands: Batanes, Cagayan, Isabela, Aurora, Quezon's Pacific coast, Catanduanes, Camarines Norte and Sur, Albay, Sorsogon, Northern and Eastern Samar, Leyte, Surigao, and Siargao.

Rolly in 2020 and Odette in 2021 both removed roofs at scale. Batanes has been building for this for centuries; see buying in Batanes.

Checklist

1. Screen the coordinates for the mapped layers, and note that wind is not one of them.
2. Inspect the roof fixing, the purlin and truss connections, and the overhangs.
3. Ask what the roof is, who built it, when, and whether there is a permit.
4. Check openings for shutters or protection, and look for debris sources nearby.
5. Look for rust at fixings and at the sheet edges.
6. Hire a licensed structural engineer for any property on an exposed coast.
7. Confirm that your insurance covers typhoon damage. See what calamity insurance excludes.

If you are building

Say the word "uplift" to your engineer and ask to see the connection details on the drawings. A roof designed with a continuous load path from sheet to purlin to truss to wall to foundation costs very little more than one that is not, and it is the difference between a repair and a rebuild.

The honest limit

PAGASA is the authority on wind and weather, and the National Structural Code governs design. A hazard screening does not rate wind and cannot assess a roof. That is a licensed structural engineer's job, and on the eastern seaboard it is the most valuable inspection you can buy.

CheckHazard does not replace a professional geotechnical or engineering survey.