Storm-Season Filter Checks for Rooftop AHUs in Brisbane Office Buildings

Severe storms can turn a routine rooftop plant check into a damage-control exercise. For Brisbane office buildings, rooftop air handling units often cop the first impact from wind-driven rain, debris and pressure changes, so a quick but careful inspection before and after a storm can help you spot problems early and keep the system in serviceable condition.

The goal is not just to look for obvious damage. Facility teams should check whether filters are wet, whether debris has bypassed the intake, and whether doors, gaskets and frames are still sealing properly. If you manage multiple buildings, a consistent inspection process makes it easier to compare what has changed from one event to the next.

Why rooftop AHUs need extra attention in storm season

Rooftop air handling units are exposed to conditions that indoor plant rarely sees. Heavy rain, gusting winds, airborne leaves and dust, and even brief loss of power can all affect how the unit performs once the weather clears.

Storm events can cause:

• •Wet or saturated filters that restrict airflow and may slump or deform
• •Debris lodged in louvers, grilles, fan sections or filter banks
• •Torn, lifted or compressed seals around access doors and filter housings
• •Water entry through poorly sealed penetrations, conduits or panel joints
• •Standing water in compartments where it should not be present

If the unit has pre-filters and finer final filters, inspect each stage separately. A damaged pre-filter can allow more debris to load the downstream filter faster than expected.

What to inspect before a storm arrives

A pre-storm inspection is about reducing the chances of water and debris getting into the unit in the first place. If severe weather is forecast, make time for a walkaround while access is still safe.

Check the exterior first

Start with the rooftop surroundings and the AHU housing itself.

• •Confirm the access doors are fully closed and latched
• •Look for loose panel screws, open knockouts or obvious gaps
• •Check that louvres, intake hoods and weather protection are clear of leaves and rubbish
• •Make sure nearby loose items cannot blow into the unit
• •Inspect visible seals for cracking, flattening or separation

If the unit has a visible filter access section, note whether the door sits flush against the frame. Even a small gap can let in wind-driven rain or dust during a strong storm.

Review the current filter condition

Before a storm, it is worth checking whether the installed filters are already heavily loaded. A filter near the end of its serviceable condition may be more vulnerable to collapse or bypass if it becomes wet.

Look for:

• •Excessive dust build-up on the upstream face
• •Wrinkling, bulging or bowing of the filter media
• •Damaged frames or bent retaining bars
• •Missing clips, fasteners or holding hardware
• •Signs of past moisture exposure, staining or odour

If you use pressure gauges or other monitoring, record the reading before the storm so you have a reference point afterwards. Follow the filter and equipment manufacturer instructions for interpreting readings.

What to inspect after a severe storm

Once the weather has passed and it is safe to access the roof, inspect the unit before restarting or returning it to normal operation. A visual check can save time later if you find water ingress, torn media or dislodged parts.

Look for wet filters and water entry

Wet filters are one of the most common post-storm findings. Any filter that has been soaked by rainwater, spray or pooled water should be assessed carefully.

Check for:

• •Damp, saturated or collapsed filter media
• •Water inside the filter housing or on the downstream side of the filter
• •Rust staining, swollen cardboard frames or softened seal material
• •Droplets or tracks showing where water entered
• •Signs that water ran around, rather than through, the filter bank

If a filter is wet, do not simply dry it and assume it is ready to go back in. Some filters are designed to be washable - check the product instructions. If the product is not designed for that use, it should be replaced according to the manufacturer guidance and the condition of the system.

Check for debris ingress

Storm debris can be surprisingly invasive. Leaves, bark, dust, insects, plastic and other loose material can accumulate in the intake path or inside the AHU.

Inspect:

• •Outside air intakes and pre-filter sections
• •Fan compartments and drain areas
• •Corners, ledges and channels where debris can collect
• •Any point where air can bypass the intended filtration path

Debris on the intake side may indicate that the weather screen or louvre has been compromised. Debris downstream of the filter is a stronger sign that the seal, frame or filter seating has been affected.

Inspect seals, gaskets and access panels

Damaged seals are easy to miss but can cause ongoing problems if they are not addressed. After a storm, inspect every accessible seal point around the filter section and access doors.

Look for:

• •Flattened or cracked gasket material
• •Gaps where a door no longer closes evenly
• •Torn weather seals or missing adhesive backing
• •Movement in filter holding frames or clamping rails
• •Water tracks that show air or rain has passed through a gap

If seals are no longer making full contact, the unit may allow unfiltered air or water to enter around the filter rather than through it. That is especially important in busy office buildings where rooftop units may run for long periods after weather has cleared.

How to decide what needs repair or replacement

Not every storm-related issue means the whole AHU needs attention, but some findings should be dealt with immediately. The decision usually comes down to the filter condition, the extent of the water ingress and whether the unit can still seal properly.

Replace or service the affected parts if you find:

• •Filter media that has torn, collapsed or separated from the frame
• •Visible bypass around the filter bank
• •A damaged filter frame or retaining system
• •Seals that cannot be restored by simple cleaning or refitting
• •Corrosion or contamination inside the housing

If the system uses specialised filters, including higher-efficiency products, handle them according to the manufacturer instructions. For critical spaces or plant with specific ventilation requirements, confirm site needs with the mechanical services engineer or building owner and refer to AS 1668.2:2024 where relevant.

If you are unsure whether a filter is still suitable, measure the filter size correctly before ordering a replacement. how to measure an air filter can help with the basics.

Building a practical storm-response routine

The most effective storm response is a simple one that your team can repeat. Keep it focused on the checks that matter most for rooftop equipment.

A useful routine includes:

• •Visual inspection before the storm if access is safe
• •Immediate post-storm roof and plant check once conditions allow
• •Filter, seal and housing inspection before the AHU is restarted
• •Recording any water entry, debris or damage found
• •Follow-up action for replacement filters, cleaning or repair work

If your building has multiple rooftop units, it helps to document which ones were checked, what was found and what was replaced. That makes later maintenance easier to plan, especially if the storm affected several areas of the site.

For teams that prefer support with ongoing maintenance, filter servicing and commercial filter servicing can help keep the inspection load manageable.

Keeping the right filters on hand

Storm season often exposes issues that were not obvious in calm weather. Having the right replacement filters available, or knowing where to source them quickly, can reduce downtime after a weather event.

Total Air Filtration is a family-owned air filter manufacturer and supplier based in Hillcrest, Brisbane QLD, and we can help with standard sizes, custom requirements and matching filters to the unit on site. Browse our products or explore custom air filters if your rooftop AHU uses an uncommon size or configuration.

If you need help with rooftop AHU filters after a storm, call 07 3800 3448 or request a quote.