No fasteners through the roof: how ballasted steel works.

Short answer: a non-penetrating rooftop system is held down by engineered ballast instead of fasteners. Weighted bases sit on membrane-compatible bearing pads, and the connected frame resists wind. The ballast is sized so the restoring moment beats the wind overturning moment with a safety factor — a stability calculation, not a weight guess. The trade is permanent added dead load on the roof structure.

Why the spec says it

The driver is almost always the roof warranty. A membrane warranty is issued by the manufacturer or the installing roofer, and it is written to protect them from work they didn't do. Drive an anchor through the assembly outside their scope and coverage can lapse — frequently not just at that hole but in a buffer zone around every penetration, and on some policies across the entire roof.

On a building that was re-roofed two years ago, that remaining coverage is worth more than the entire steel package. Which is why the requirement shows up most often on municipal, institutional, and school-board buildings: the asset manager is protecting a capital investment with a documented life, and "no penetrations" is the cheapest way to do it.

Two secondary reasons matter too. Leak risk — every penetration is a detail that has to be flashed correctly and maintained forever. And re-roofing — a ballasted system can be unbolted, lifted, set aside, and put back when the roof is replaced. Anchored steel has to be cut out and re-detailed.

How the ballast is actually sized

This is the part that separates an engineered system from a pile of blocks. The governing load case is usually wind, and it works like this:

• Wind produces an overturning moment. Uplift and lateral pressure act on the structure — a guardrail, a platform, whatever is up there — and try to rotate it about the edge of its base. Pressures come from the building code for your location, terrain exposure, and roof height.
• Ballast produces a restoring moment. Weight acting through the lever arm from the base pad resists that rotation.
• Restoring must exceed overturning, with a factor. We design to a safety factor rather than to break-even, so the system has margin against a gust above the design case.
• Bases share load through the frame. Posts tied together by a continuous top rail or frame don't act alone — an uplift at one post is resisted by its neighbours, so the effective per-post resistance is higher than a single isolated base. Ignoring this over-ballasts the roof; assuming too much of it under-ballasts a corner.

Roof corners and edges see substantially higher wind pressure than the field of the roof, so a system that's adequate in the middle can be under-ballasted at the perimeter. Uniform ballast everywhere is a red flag on a submittal. We ran exactly this calculation on a 420-lineal-foot install — the London guardrail case study walks through the per-base ballast math and the lever-arm assumptions.

Protecting the membrane you're standing on

A non-penetrating system still puts weight on a roof, and there are three ways to damage a membrane without ever drilling it:

• Point loadingpad sized to spread contact pressure
• Abrasionbase must not slide or rock
• Chemical incompatibilitypad material vs membrane type
• Water dammingbase must not block drainage
• Iceno ponding under walkways

All five are design decisions, which is why we confirm the membrane type — TPO, EPDM, modified bitumen, PVC — with the warranty holder before fabrication, not on install day. Getting the roofer's written sign-off on the pad detail is a fifteen-minute conversation that protects everyone.

The constraint people miss: dead load

Here's the trade-off nobody puts in the sales pitch. A ballasted system works because it's heavy, and that weight is permanent. On a modern building with capacity to spare, that's a non-issue. On a 1970s municipal building with open-web steel joists at a spacing designed for snow and not much else, the added dead load is the thing that decides whether the approach works at all.

So the roof structure gets checked — joist designation, spacing, and what the existing framing has left. Sometimes the answer is to spread the load differently; sometimes it's to accept fewer, heavier bases in locations that land near joist bearing points; occasionally it's that ballast genuinely won't work and the honest recommendation is an anchored design coordinated with the roofer, or landing the load outside the building on its own footings. The same load-path logic applies to supporting mechanical gear — covered in HVAC and equipment platforms.

What it's used for

Non-penetrating detailing isn't limited to guardrail, though that's where most people meet it first:

• Rooftop guardrail around a work area, a hatch, or an unprotected edge — the most common ballasted system, and the one with the clearest fall-protection driver. See fall arrest vs guardrails.
• Walkways from a hatch or access stair out to the equipment, keeping traffic off the membrane.
• Crossover platforms and stairs over ductwork, piping, or between two roof levels.
• Equipment support for light rooftop gear, where the unit weight is modest enough that a weighted frame is realistic.

What to ask a fabricator

If a quote says "non-penetrating", these four questions separate an engineered system from a catalogue assumption: What wind pressures did you use, and for what exposure and roof height? What safety factor is the ballast sized to? Did you increase ballast at roof corners and edges? And what pad material, confirmed against which membrane?

A supplier who can answer all four has done the work. One who can't is selling you a stock kit and hoping your roof looks like the one in the catalogue. More on how we design and install these on rooftop platforms & crossovers, and on vetting fabricators generally in picking a fabricator. For the fall-protection side, the criteria most facilities reference are in OSHA's 1910.29; Ontario work is governed by the OBC and the OHSA industrial regulation.

Frequently asked