Hi @tjgriff
He’s probably not pissing in your pocket. If the spacing of the screw line doesn’t line up with the minimum spacing required of the tilt frames, without a lot of extra engineering, it genuinely might not get approved by the inspector. Tilt frames can be a bit tricky (especially in QLD) for a couple of reasons.
- Higher wind loading means more fixtures to the roof required. In Queensland in particular, regulations require the spacing between the fixings to the roof be quite tight, because it’s a high wind area. The tilts mean the wind can come up underneath the panels, and if they aren’t very secure, they can fly off the roof in wild wind conditions.
- More spacing between panels to avoid shading. Besides that though, you also need extra spacing between the rows of panels, so that the front row doesn’t shade the back row. Depending on your roof, that could mean losing panels. In which case, even though you get less generation per panel, if you could lay more panels you could get more generation overall.
Let’s assume that you can get the same number of panels on your roof (I’ve just found a flat roof in Brisbane to do an example for you). The difference between a 5 degree south facing VS 10 degree west facing is not a huge amount. I’ve used 10 degree west, because you probably wouldn’t be able to get much more of an angle than that due to those factors above (the higher the angle the worse those issues become).
91% efficient for 10 degree West
87% efficiency for 5 degree South
Bottom line = 27 kWh/day VS 25.9 kWh/day.
It wouldn’t be worth the extra cost of the tilt frame especially if you couldn’t fit the same number of panels.
Hope that helps!
Marty
Btw, you can play around with these different panel layouts yourself using Photonik.
Here’s some more details (AI assisted):
1) The key driver: wind loads (AS/NZS 1170.2)
Everything starts with wind actions.
- AS/NZS 1170.2:2021 defines regional wind speeds + pressure calculations for any structure
- It applies to buildings and “attached structures” → solar frames are treated as structural elements
- You don’t design for “a rule of thumb”—you calculate site-specific wind pressure
Core variables that affect a tilt frame:
- Wind region (A, B, C, D) → biggest driver
- Region A = non-cyclonic (e.g. Sydney, Melbourne)
- Region B/C/D = cyclonic → massive jump in loads
- Terrain category (TC1–TC4) → exposure (coastal vs suburban vs CBD)
- Height above roof + building height
- Topography (hills, escarpments)
- Shielding (nearby buildings)
These all combine into a design wind pressure (kPa) that your frame must resist.
2) Why tilt frames are treated more harshly than flush arrays
This is the big one.
Flush-mounted panels:
- Sit close to roof (< ~100–200 mm)
- Often treated similarly to the roof cladding
- Lower uplift coefficients
Tilt frames:
- Act like a mini canopy or free-standing structure
- Create:
- uplift (suction) on the back
- pressure on the front
- Result: much higher net forces
In engineering terms:
- Flush = “attached cladding”
- Tilt = often treated closer to “roof-mounted structure / canopy”
That distinction alone can double or triple loads.
3) Wind regions → what actually changes
The standard divides Australia into wind regions, and recent updates refined these regions .
Practical impact on tilt frames:
Region A (e.g. Sydney, Adelaide)
- Tilt frames are usually feasible with:
- moderate spacing
- standard ballast or fixings
Region B (SE QLD, northern NSW)
- Increased loads → often:
- more rails
- more fixings
- lower tilt angles required
Region C & D (cyclonic north WA, NT, FNQ)
- This is where things get strict:
- Tilt frames often:
- heavily engineered or
- not allowed by installers without certification
- You’ll see:
- very low tilt angles (e.g. 5–10°)
- or fully flush systems only
In cyclonic regions, uplift forces dominate design.
4) AS/NZS 5033 → makes wind compliance mandatory for PV
AS/NZS 5033 ties it all together:
- Requires PV systems to comply with AS/NZS 1170.2 wind loads
- Means:
- Installers can’t just use generic tilt kits
- Must use:
- manufacturer engineering tables or
- project-specific engineering
5) Specific tilt-frame design constraints you’ll see
These are the knobs designers actually adjust:
1. Tilt angle
- Higher tilt = higher wind load
- Common limits:
- ~10–15° in higher wind regions
- sometimes capped lower in cyclonic areas
2. Row spacing
- Prevents panels shielding each other
- But increases exposed area → trade-off
3. Fixings / ballast
- Either:
- mechanically fixed to structure
- or ballasted (common on flat roofs)
Higher wind region → much heavier ballast or more anchors
4. Edge zones (VERY important)
AS1170.2 has roof zoning:
- Corners and edges have much higher suction
- Tilt frames near edges often:
- require extra fixings
- or are excluded entirely
5. Height above roof
- Bigger gap = more wind gets underneath → higher uplift
- Low-profile tilt systems are preferred
6) Why installers often avoid tilt frames now
This is more practical than regulatory, but driven by the above:
- Wind compliance makes them:
- more expensive
- more complex to certify
- You lose density due to spacing/shading
- Panels are cheap → easier to:
- add more panels flat
- instead of tilting fewer panels
7) Subtle but important: classification problem
One tricky area (and where engineers spend time):
Tilt frames don’t neatly fit one category in the standard, so they may be modelled as:
- roof-mounted cladding (best case)
- canopy / awning
- free roof structure
That choice changes:
- pressure coefficients
- load paths
- resulting design
Bottom line
- Tilt frames are regulated primarily through wind loading (AS/NZS 1170.2)
- The moment you tilt panels, they behave like a small structure, not cladding
- Wind region (especially cyclonic vs non-cyclonic) dramatically changes feasibility
- That’s why:
- installers avoid tilt in many cases
- and why engineering tables are heavily region-specific
