Glendale, CA · July 2020 – February 2021 · Glendale Water & Power / City of Glendale

A flat roof lets you choose the angle. Winter shows you which to change.

A 1938 Glendale house with a flat built-up roof and no pitch to work with. The modules went up on tilt frames, each with its own microinverter, and the system ran through the fall. In January the monitoring showed two modules lagging the rest, and a morning on the roof put them right.

On a flat roof the array's tilt is a design decision, not something the house hands you, and the mounting has to go through the membrane on sealed, flashed stands. The payoff is that every module can be aimed. The catch is that the aim is only tested in winter: a module clipped by the shadow of the frame in front of it produces normally under a high October sun and falls behind in January. Per-module monitoring is what makes that visible, and a tilt frame is what makes it adjustable.

At a glance

House

Built 1938, single story

Roof

Flat built-up roof; small pitched sections at the eaves

Mounting

Tilt frames on flashed, sealed roof stands

Modules

Canadian Solar

Inverters

Microinverters, one per module

Monitoring

Per module

Service call

January 2021 — two modules re-angled

Utility / AHJ

Glendale Water & Power / City of Glendale

The story

The house was built in 1938 and its main roof is flat: a built-up membrane with a gray surface, a few vents and skylights, and a strip of pitched shingle at the eaves where the original roofline shows. There is no south-facing slope to lay modules on. Whatever angle the array gets, the installer gives it.

That is the whole character of a flat-roof job. On a pitched roof the modules lie flush and the roof decides how they face. Here the modules sit on tilt frames, so they can be aimed, and the frames stand on posts that pass through the membrane. Every one of those posts is a hole in a roof whose only job is to keep water out, and each one is flashed and sealed before a rail goes near it.

The permit path was Glendale's, and the order is not the one most cities use. The application and the plans go to Glendale Water & Power first, for the utility's signature on the application and its stamp on the drawings, and only then to Building & Safety for plan check. The interconnection agreement came back approved in the middle of September, the permit set followed at the start of October, and the modules went up in the middle of the month.

One question the plans have to answer is worth passing on because it surprises people with older houses: does the home have fire sprinklers? The answer for a 1938 house is almost always no, and the plans have to say so. It took one email, but it was on the critical path.

The system ran through the fall without a call. Then in the third week of January the monitoring showed something the roof had not: two modules were producing noticeably less than their neighbors. Not failed — lagging. In October the sun is high enough that a few degrees of tilt make little difference. In January it is low, and a module aimed a little off, or shaded by the edge of the next frame for part of the morning, falls behind.

We wrote to the homeowner on the Monday and went up on the Tuesday morning. The angle of the two modules was changed so they cleared the low sun, and the monitoring has shown every module in line since. From the reading to the fix was one day and one visit.

None of this is free. Tilt frames on a flat roof are more work than a flush array on a pitched one: more penetrations, each one a place where the roofing has to be right, and rows that have to be spaced so one does not shade the next in winter. A flat roof hands the installer the aim and the spacing rather than settling them for him. What makes that safe to take on is the monitoring, which turns a winter question into a Tuesday morning.

If your roof is flat, the question for your installer is not only what angle the modules will sit at. It is how the stands go through the membrane, how the rows are spaced for a January sun, and whether the monitoring will show you a single module falling behind.

How it ran

Filed in July, installed in October, and one service visit in the first winter.

What we did

• Designed a tilted array for a flat built-up roof with rows spaced for the winter sun.
• Set the roof stands through the membrane with flashing collars and sealant at each post (C-39).
• Installed the modules, microinverters and rooftop conduit runs (C-10).
• Took the application through Glendale Water & Power and then City of Glendale plan check, in the order the city requires.
• Watched the monitoring after commissioning and caught two lagging modules in the first winter.
• Went back and re-angled the two modules within a day of noticing.

System specifications

Is your project like this one?

• Your roof is flat or nearly flat and you have been told solar will not work.
• Your house is from the 1930s or 1940s and you worry about holes in the roof.
• You want to know what happens after the system is switched on.
• You are on Glendale Water & Power and want the filing order explained.
• You want per-module monitoring rather than a single inverter reading.

Cali Energy in Glendale

Frequently asked questions

Can you put solar on a flat roof?

Yes. The modules sit on tilt frames rather than flush on the roof, so the installer chooses the angle and the direction. The frames stand on posts that go through the roof membrane, and each post is flashed and sealed. Rows are spaced so that one does not shade the next when the sun is low in winter.

Why did two modules underproduce?

Because the winter sun sits low, and on a tilted array a module aimed a few degrees off, or clipped by the shadow of the frame in front of it, falls behind its neighbors in the morning. In summer the same two modules were within normal range. Per-module monitoring showed the gap in January, and the fix was a change of angle on those two.

How do you seal the posts on a built-up roof?

Each post sits in a flashing collar that is bonded to the membrane, and the collar is filled and capped with sealant around the post before the rail goes on. The point is that water reaching the post runs off the collar rather than down into the roof. On an older built-up roof this is the part to ask to see.

What is the permit order in Glendale?

Utility first. The solar application and plans go to Glendale Water & Power, which approves the interconnection agreement and stamps the plans, and the building department only opens its plan check after that. Filing with the city first does not save time; the application waits for the utility either way.

What this would look like on your roof

Related

• One house, one crew, three permits — and the last one held the switch Glendale, CA · 20.8 kW · tile off, shingle on, panel rebuilt, three finals Solar
• On a flat roof, the array has no angle unless you give it one Northridge, CA · 6.88 kW DC · tilted racking Solar
• Thirty-four modules, tilted up, and one request for photographs Northridge, CA · 12.41 kW DC · tilt-up racking Solar
• Eight modules nobody can see Chatsworth, CA · flat parapet roof · 2.5 kW AC-CEC Solar

This timeline reflects this property and this permitting path. Updated September 2026.