Adding Equipment to a Roof Without Ruining the Roof

A strata approves a solar array on the roof of a ten-year-old building. The installer is competent, the system performs, and the energy savings arrive as projected. Four years later a suite on the top floor reports water at a ceiling, and the roofing contractor who installed and warranted the membrane declines the claim on the grounds that somebody else put forty penetrations through it.

Nobody involved did anything obviously wrong. The council got a good price on a good system. The installer mounted it properly by the standards of their trade. The roofer is within their rights.

The failure was in how the project was organised, and it is the same failure whether the equipment is solar, a heat pump, EV charging infrastructure, telecom hardware, or a replacement mechanical unit. Roofs are where equipment goes, and every one of those projects is also a roofing project whether or not anyone treats it that way.

The core problem

A waterproofing membrane is a continuous system. Its performance depends on being unbroken, and where it must be broken, on the termination detail at that break being built correctly.

Equipment installation puts holes in that system. Each hole is a detail that has to be flashed, sealed, and terminated to the same standard as the roof around it, and each one is a potential leak for the remaining life of the roof.

The equipment supplier’s expertise is in the equipment. They understand mounting loads, electrical requirements, orientation, and performance. Membrane termination detailing is a different trade, and the difference shows up years later, in the same way described in the post on skylight and roof curb flashing failures, where penetrations made outside the roofing trade produce failures that the roof itself would never have had.

Who makes the holes

This is the decision that determines most of the outcome, and it should be made before a supplier is selected rather than after.

The arrangement that works is to have the roofing contractor perform the penetration and flashing work, and have the equipment installer mount to what the roofer provides. The roofer sets the curbs or supports, flashes them into the membrane using details the membrane manufacturer approves, and hands over a watertight roof with mounting points on it. The equipment then goes on above the waterline.

That sequence costs more than letting the equipment crew do it all, and it keeps the warranty intact and puts responsibility for water in one place. Most membrane warranties require that penetrations be made by an approved applicator using approved details, so this is often not a preference but a condition of coverage.

Where an equipment installer makes the penetrations, the roofer will generally not warrant work they did not perform, and the strata is left holding a roof with divided responsibility and a leak that each party attributes to the other. That is the same structural problem the post on building envelope engineer versus contractor roles describes in a different context, and the fix is the same: decide who owns the outcome before the work, not during the dispute.

Ballasted systems trade one problem for another

Non-penetrating mounting systems hold equipment with weight rather than fasteners. Concrete ballast blocks or weighted trays sit on the membrane and resist wind uplift through mass.

They genuinely avoid new penetrations, which is a real advantage. They introduce two other considerations.

The first is load. Ballast is heavy by design, and it is concentrated at bearing points rather than distributed. On a roof structure with limited spare capacity, the ballast needed to hold an array against wind uplift can be the governing constraint.

The second is wear. Anything resting on a membrane and subject to thermal movement, vibration, or occasional shifting will abrade what it sits on. Protection layers and slip sheets address this, and they have to be specified and installed rather than assumed.

Neither system is automatically right. A penetrated system correctly flashed by a roofer under warranty is often the better outcome on a structurally tight building, and a ballasted system is often better where the structure has capacity and the membrane is near the start of its life.

Structure comes first

Every piece of rooftop equipment is load the building has to carry, and in Metro Vancouver that load is additive to snow load rather than an alternative to it.

The load is also concentrated. A mechanical unit sitting on four feet delivers its weight through four points, not across the roof deck. A solar array delivers wind uplift forces through its mounting hardware, and those forces are highest at roof edges and corners where wind pressures concentrate.

A structural engineer needs to confirm capacity before anything is ordered. This is not a formality on older buildings, where the roof structure was designed for the code loads of its era and may have had equipment added to it more than once already. The cumulative effect of three separate upgrades, each individually modest, is the scenario that structural review exists to catch.

Remaining service life is the number that matters

The question is how many years of service life remain, which a roof’s age only partly predicts.

Equipment installed on a roof with four or five years left will have to come off and go back on when that roof is replaced. Removal, storage, reinstallation, and recommissioning are real costs, and on a solar array they include electrical work and a period of lost generation.

That cost belongs in the decision now. Where a roof is approaching replacement, doing the roof first and the equipment second is frequently cheaper in total, and it gives the new equipment a full-life roof underneath it. The assessment framework in the post on roof recover versus tear-off is the right starting point for establishing where the roof actually sits.

Where a roof has most of its life ahead of it, proceeding makes sense, and the penetration work should be done to a standard that will outlast the equipment.

Maintenance access is designed in or lost

A roof needs to be walked, inspected, and maintained. Drains need clearing, seams need checking, flashings need looking at. Equipment that covers roof area makes that area unreachable without removing the equipment, and what happens in practice is that the covered area stops being inspected.

Array layouts should leave walkways to every drain, every scupper, every penetration, and every parapet flashing. That requirement reduces the number of panels that fit, and the trade is worth making, because a roof that cannot be maintained will fail earlier than one that can.

Shading is the related issue. Areas permanently shaded by panels stay damp longer, which encourages moss and organic growth, and debris collects under and around mounting hardware. Both accelerate deterioration of what is underneath, and both are manageable if the maintenance programme accounts for them. The seasonal approach set out in the post on roof drain and scupper maintenance needs extending to cover the new conditions.

Drainage changes

A flat roof is designed to move water across its surface to drains in a predictable way.

Panels change that. Water landing on an array runs off its lower edge rather than spreading across the roof, which concentrates flow into lines that the original drainage design never anticipated. Mounting rails and cable trays can act as small dams, holding water on the upslope side and creating ponding where none existed.

Neither effect is catastrophic on its own, and both are worth checking during design rather than discovering during the first atmospheric river. Where an array is large, reassessing drainage capacity and ponding behaviour is part of the engineering rather than an afterthought, for the reasons set out in the guide on ponding water warning signs.

Documentation the next roofer will need

Whatever gets installed, someone will work on that roof again, possibly decades later, and they need to know what is in it.

The as-built record should show where every penetration is, what detail was used at each one, who performed the work, and what warranty applies. Photographs during installation, before anything is covered, are worth more than a drawing produced afterwards.

Without that record, a future roofer inherits a roof with an unknown number of penetrations made by an unknown party under unknown terms. That uncertainty gets priced into every subsequent quote, and it makes a warranty claim harder to pursue when something does go wrong.

The decision sequence

Confirm the roof’s remaining service life and decide whether the roof goes first.

Get structural confirmation that the roof can carry the equipment and its mounting system, including wind uplift at edges and corners.

Decide who makes and flashes the penetrations, and check the membrane warranty terms before committing. Default to the roofing contractor doing that work.

Design the layout around maintenance access to drains, seams, flashings, and parapets, accepting fewer panels where necessary.

Reassess drainage and ponding with the equipment in place.

Require as-built documentation with photographs, and file it where the next council will find it.

Rooftop equipment is going to keep arriving on strata buildings, and most of it is worth having. Whether it becomes a problem is decided at the point where it is fixed to the roof, by people who were either brought into the project early or brought in afterwards to find out what went wrong.

Sources and further reading

• Canadian Roofing Contractors Association, CRCA Roofing Specifications Manual, rooftop equipment and penetration details, referenced 2026
• National Research Council Canada, National Building Code of Canada, structural loads and snow load provisions, referenced 2026
• BC Housing, Building Enclosure Design Guide, roof penetration detailing, referenced 2026
• Canadian Standards Association, CSA C22.1 Canadian Electrical Code, rooftop photovoltaic installation requirements, referenced 2026
• Allweathercoating roof assessment records, Metro Vancouver, 2026