This is a pre monsoon walk for a flat or low slope commercial roof in the Las Vegas valley. Run it in May or early June, and again after the first storm of the season.
The order is deliberate. Drainage first, because that is what fails here, then the perimeter, then the surface, then the equipment, then inside.
Before you go up
Do not go up alone, on a wet roof, or when a storm is forecast within the hour. Summer roof surfaces here run far hotter than the air, so go early in the day and take water with you.
Take a camera, a roof plan with the outlets numbered, and something to write on.
The drainage
| Look at | What a problem looks like |
|---|---|
| Outlets and sumps | Dust, grit and silt packed into the sump, water sitting in it |
| Strainers and domes | Missing, broken, lifted off, or crushed flat |
| Clamping rings | Bolts loose or missing, the membrane not gripped all round |
| Scuppers | A throat blocked where it cannot be seen from the roof |
| Overflows | None fitted anywhere, or blocked at the opening |
| Gutters and downpipes | Debris, sagging, a joint that has opened, staining below |
| Falls and low spots | Tide marks, silt lines, areas that hold water after a wash down |
| Downstream of the building | Where the water actually goes once it leaves the roof |
The perimeter
| Look at | What a problem looks like |
|---|---|
| Edge metal and coping | Open joints, lifted sections, staining down the wall below |
| Termination bars | Loose or missing fasteners, a bar that has pulled away |
| Parapet upstands | Membrane pulling away from the wall, a gap at the top |
| Ballast at the edges | Scoured away on the upwind side, piled on the downwind side |
| Corners | The first place wind lifts, and the first place a detail slumps |
The surface after a desert summer
| Look at | What a problem looks like |
|---|---|
| Sealant at every detail | Cracked, shrunken, pulled away or fallen out |
| Membrane texture | Harder, darker or more brittle than the surrounding area |
| Seams and laps | Edges that lift, a dirt line, a visible step |
| Coating condition | Chalking, thinning, worn through at high points and walkways |
| Splits and cracks | Short straight splits, often over a joint or a fastener line |
| Blisters | Raised areas, soft underfoot, larger than in the last photograph |
The equipment and the loose items
| Look at | What a problem looks like |
|---|---|
| Units and curbs | Flashing slipped, corners sealed with mastic, fixings through the membrane |
| Condensate discharge | Running onto the membrane, a permanently damp patch, staining |
| Solar arrays and screens | Debris packed at the upwind edge, ballast shifted, movement in a frame |
| Cable trays and conduit | Resting on the membrane, fixings through the roof |
| Loose material | Offcuts, panels, tools, packaging, anything a gust can pick up |
| Access panels and hatches | Open, propped, or no longer fastening shut |
Inside the building
| Look at | What a problem looks like |
|---|---|
| Ceilings below the roof | New stains, old stains that have grown, sagging tiles |
| Walls below parapets | Damp at high level, blown paint, staining at a corner |
| Plant rooms | Trays, buckets or diverters somebody has quietly accepted |
| Insulation in the void | Damp, compressed or stained material |
| Tenant reports | Anything reported last season that was never traced |
What to do with it
- Clear every outlet before anything else. This is the cheapest risk reduction on a desert roof.
- Fix the perimeter next. A roof lifts from its edge.
- Photograph every finding twice, wide and close. Wide to place it, close to show it.
- Book repairs in June, not July. Availability collapses once the storms start.
- Run it again after the first storm. The first storm shows you what the walk missed.
Want the reasoning behind these checks? Read what the desert climate does to a roof and what a maintenance program covers.
Walked by Date Roof
Common questions
When should this checklist be run?
In May or early June, before the first storms arrive, and again after the first significant storm of the season. Running it in August means finding the blocked outlet after the water has already stood on the roof for a night, which is the expensive version of the same discovery.
- Before the season, so there is time to fix what you find
- After the first storm, because the first storm reveals the weak points
- Not during a storm, and not on a wet roof
- Book repairs early, because every roofer in the valley is busy in July
The valley gets most of its rain in a handful of events, and those events arrive with wind and debris rather than as steady rain. A roof that copes with an inch over a day can fail with the same inch over twenty minutes, so the margin you are checking for is the drainage rate rather than the annual total.
What fails most often in a monsoon?
Drainage, almost always. Outlets blocked by a year of dust and grit, strainers missing, scuppers packed solid, and overflows that were never fitted. The membrane itself usually survives the storm that the drainage does not. The membrane itself usually survives the storm that the drainage around it does not.
- Outlets silted up with dust that never gets washed away
- Strainers missing, broken or lifted off and left
- Scuppers blocked at the throat where nobody can see
- No overflow anywhere, so a blockage becomes a structural load
- Gutters and downpipes that have not been cleared since the last season
Desert dust is the specific problem. In a wetter climate, regular rain keeps outlets moving. Here the grit accumulates for nine months and then meets the heaviest rain of the year in one afternoon. Clearing outlets in June is the single cheapest piece of roof maintenance available in this valley, and it is the one most often skipped. Work through every outlet on the roof plan and tick each one off by number, because the one that gets missed is always the one in the far corner nobody walks to.
Does heat damage show up before the storms?
Yes, and the pre monsoon walk is the right time to look for it. A summer of surface temperatures well above air temperature leaves membranes brittle, sealants cracked and laps opened, and the first wind driven rain finds every one of those openings.
- Sealant cracked, shrunken or fallen out of a joint
- Membrane noticeably harder or more brittle than last year
- Laps and seams opened at the edges
- Coating chalking, thinning or worn through on the high points
- Shrinkage pulling the membrane down and away from an upstand
Heat and water damage are usually discussed separately, but on a desert roof they are one sequence. The heat opens the path and the storm uses it. That is why a pre monsoon check is not only about drainage, and why a roof that looked fine in April can leak in its first storm of the year. Photograph the same details every spring from the same standing positions. Heat damage is gradual, and a single year of it is far easier to see in a comparison than on the roof itself.
What about wind rather than rain?
Wind is what turns a loose edge into an open roof. Check the perimeter, the edge metal, the ballast and anything light enough to move, because the storms here arrive with gusts that will find whatever is not fixed down.
- Edge metal and bars loose, lifted or missing fasteners
- Ballast scoured away from the upwind edge
- Loose materials, offcuts, tools and panels left on the roof
- Screens, signs and solar edges with movement in them
- Hatches and access panels that no longer fasten shut properly
A roof lifts from its edge, not from its middle, which is why perimeter fixings matter more than anything in the field. Anything loose on the roof is also a projectile for the building next door, and the clean up after a gust that moved a stack of panels is usually more expensive than the hour it would have taken to secure them. Walk the perimeter as a separate pass rather than as part of the general walk, because the edge is where the risk concentrates and it is the easiest part of the roof to pass by.
What should be fixed first if the budget is limited?
Drainage, then the perimeter, then everything else. Those two carry nearly all of the risk in a monsoon, and both are cheap compared with the interior damage that follows when either one fails during a storm. Everything else can reasonably wait until autumn, when the pricing and the availability are both better.
- Clear every outlet, scupper and gutter first
- Fit or replace missing strainers and clamping rings
- Secure loose edge metal and any lifted termination
- Remove anything on the roof that can move in a gust
- Then book the remaining work for autumn, when crews are available again
This is the ordering that holds whatever the roof is made of and whatever its age. A twenty year old membrane with clear drains and a secure perimeter will usually get through a season. A new membrane with a blocked outlet and a loose edge bar will not, and the repair bill afterwards will be for the ceiling rather than the roof. Write the deferred items down with a date rather than leaving them as a verbal intention, because an item deferred without a date is an item that quietly disappears from the plan.