Wind failure is progressive, which is why it is worth catching
A roof rarely goes all at once. It goes in a sequence, and every step in the sequence makes the next one easier.
It starts at a corner, where a length of edge metal loosens, or at a termination where the membrane was fixed into that metal. Air gets under the free edge. Once air is under the sheet, the wind has a handle on it, and what was a lifting force spread across a whole surface becomes a peeling force concentrated along one line. Peeling takes far less than lifting. That is why a roof can sit through years of hard weather and then lose a large area in a single night. Nothing changed about the wind. Something changed about the edge.
The useful consequence is that the cheap repair and the important repair are the same repair. Refixing a loose length of coping is a small item on a quote. It is also the thing that stops the next storm getting a handle on the membrane behind it.
The other consequence is that wind damage is worth looking for when nothing is leaking. A peeled and reseated lap does not let water in straight away and will not announce itself. Meanwhile the roof has lost the reserve it was built with, and the next wind arrives at a seam that is already open.
Repairs we will not make
We will not run sealant along a seam that uplift has opened. The bond failed along a line, and the repair has to restore the bond, which means opening the lap back to sound material and rejoining it by the method the roof was built by. Sealant over a released weld is a cosmetic answer to a structural problem.
We will not refix edge metal into a deck or a nailer that will not hold it. If the substrate has gone soft, wet or thin, putting the same fixings back into the same holes returns the roof to exactly the condition it was in the day before the storm.
And we will not treat debris damage as wind damage. A branch through the membrane is impact. It is found differently and repaired differently, and it belongs with the rest of the storm survey rather than with the perimeter work.
When people notice wind damage
After a named storm, usually with a photograph of metal hanging off an elevation. Sometimes after a tenant reports a banging noise overnight, which is generally a length of fascia no longer attached at one end. And sometimes months later, with a leak along one edge that turns out to be a lap opened in weather nobody wrote down.
If the wind took something visible off your building, assume it worked on what you cannot see as well, and have the perimeter checked while the crew is there.
Common questions
Why does wind damage start at the edges of a flat roof?
Because wind does not press down on a roof, it pulls up, and the pull is strongest at the corners and along the edges where the air separates as it goes over.
- The field of the roof sees the least, which is why it fails last
- Corners see the most, then the perimeter strip, then everything else
- The edge is also where the membrane is terminated by hand into metal
- So the highest load lands on the most hand made part of the assembly
That combination is why a roof can lose an edge in weather the rest of it barely noticed. It is also why perimeter work is worth more than its size suggests. Refixing a length of coping is a small repair, and it is standing between an ordinary storm and the sheet behind it being peeled inward.
The membrane lifted and then laid back down. Is that damage?
Yes. A sheet that has lifted was stressed at every point where it is held, and the points that let go are not visible now that it is flat again.
- Seams peel from one end rather than failing all at once
- A partly peeled lap reseats itself and looks exactly like a sound one
- Fasteners work back through their plates when the sheet billows
- A plate cutting the sheet from beneath leaves nothing to see on top
It is one of the few findings on a roof that has to be checked by hand. We probe seams along their length with a blunt tool, working in from the edge, and the failures show up as a soft run where the weld has released. A roof that looked untouched after a wind event and began leaking the following spring is almost always this.
Our roof ripples or flutters in the wind. Is that normal?
Some movement is normal on a mechanically attached roof and the system is designed for it. Movement you can see from the ground, or hear from inside, is worth looking at.
- The sheet billows between fastener rows, which is how the system works
- Billowing that has grown over the years means fixings are giving up
- Each cycle works the fastener back and the plate against the sheet
- It is progressive, so a roof gets louder before it gets open
The check is the fixings rather than the surface: a sample tested for withdrawal, and a look at the deck they are going into. Where the deck has thinned or corroded, refastening into the same holes achieves nothing, and the answer runs from a denser pattern to a different form of attachment.
Can the edge metal be refixed, or does all of it have to come off?
Usually a section, not the whole run. What decides it is whether the metal is straight, whether its fixings still have something to hold, and whether the membrane behind it survived.
- Sound metal that has pulled loose can often be reattached and resealed
- Bent or torn metal is replaced, because it will never sit flat again
- Matching an older profile is the part that takes time, not the fixing
- If the termination behind it has torn, the membrane work is the real job
Ask about the fixing detail rather than the finish. Edge metal is engineered as part of the roof rather than as trim, and the way it is anchored decides whether it is still there after the next storm. A neat line of sealant along a joint tells you nothing about what is behind it.
Does an open door in a storm really affect the roof?
It can, and on a large open volume building it matters more than people expect. Air coming in pushes up on the underside of the roof while the wind outside pulls on the top.
- A loading door left open on the windward side is the usual version
- A window or a rooflight failing does the same without anyone choosing it
- The two pressures add, so the roof sees more than the wind alone
- Warehouses, workshops and halls are where it shows
It is rarely the whole story, and it is the one item on this list that somebody on site can do something about on the day. If high wind is forecast, closing up the windward side costs nothing. Roofs are lost with every door shut as well, so treat it as a precaution rather than as protection.