Calculator
Formula Used
The calculator treats the dish as an exposed projected area.
Projected Area = π × Width × Height ÷ 4 × Area Percent
Wind Pressure = 0.5 × Air Density × Wind Speed²
Wind Force = Wind Pressure × Drag Coefficient × Exposure Factor × Projected Area
Overturning Moment = Wind Force × Force Center Height
Required Mass For Tipping = Moment × Safety Factor ÷ Lever Arm ÷ Gravity
Required Mass For Sliding = Wind Force × Safety Factor ÷ Friction Coefficient ÷ Gravity
The final required resisting mass is the larger of the tipping and sliding checks.
How To Use This Calculator
- Enter dish width and height from the clear face area.
- Choose the matching units for dish size, height, lever arm, and weight.
- Enter the design wind speed for the site.
- Set drag coefficient, exposure factor, air density, and safety factor.
- Enter the force center height and shortest base lever arm.
- Add mount weight, existing blocks, and block weight.
- Press calculate to see required ballast and extra blocks.
- Download CSV or PDF for your project record.
Example Data Table
| Dish Width | Dish Height | Wind Speed | Center Height | Lever Arm | Block Weight | Safety Factor |
|---|---|---|---|---|---|---|
| 1.2 m | 1.2 m | 120 km/h | 1.5 m | 0.45 m | 18 kg | 1.5 |
| 36 in | 36 in | 90 mph | 60 in | 24 in | 40 lb | 1.7 |
| 4 ft | 3.5 ft | 80 mph | 5 ft | 1.8 ft | 35 lb | 1.6 |
Dish Ballast Planning Guide
Why Dish Ballast Matters
A dish mount must stay stable when wind pushes against the reflector. Ballast gives the base enough downward force to resist tipping and sliding. The correct amount depends on dish size, wind speed, mount shape, roof surface, and safety margin. A small dish can still need heavy blocks when it sits high above the base.
What This Calculator Estimates
This tool converts the dish face into a projected area. It then estimates wind pressure from air density and wind speed. The pressure is multiplied by drag coefficient, exposure factor, and area. That gives the horizontal wind force. The force is applied at the entered height, so the tool can estimate overturning moment. It also checks sliding resistance from friction.
Planning Notes
Use measured values whenever possible. Enter the clear dish width and height. Use the center height from the roof surface to the dish center. Use the shortest effective base arm, because wind can act from a weak direction. Add safety factor for uncertainty. A higher factor is useful for exposed roofs, tall mounts, loose pavers, or uncertain block weights.
Reading The Result
The calculator shows wind pressure, wind force, overturning moment, required ballast by tipping, and required ballast by sliding. The final recommendation uses the larger requirement. Existing mount mass and existing blocks are subtracted from the required total. The result shows extra weight, total blocks, and additional blocks.
Good Field Practice
Ballast is only one part of safe mounting. The roof must support the dead load. Blocks should sit on suitable pads. The mount should not damage waterproofing. Cables should not pull the dish. Wind zones can vary across the same roof. Corners and edges often see higher uplift and speed. Local codes, manufacturer data, and a qualified installer should guide final work.
Useful Reports
Use the CSV button for spreadsheets. Use the PDF button for a quick record. Save the inputs with the result. That makes later reviews easier. Recheck the calculation when the dish size, location, base, roof surface, or design wind speed changes.
Limits To Remember
This estimate is a planning aid. It does not replace stamped engineering, roof approval, or installation instructions for critical sites. Always confirm local requirements first.
FAQs
1. What is dish ballast?
Dish ballast is added weight placed on a non-penetrating mount. It helps resist tipping and sliding caused by wind acting on the dish face.
2. Does this calculator replace engineering approval?
No. It is a planning tool. Use manufacturer instructions, local wind rules, roof limits, and professional review for final installation decisions.
3. Which wind speed should I enter?
Use the design wind speed required for your location or project. Higher speeds create much higher wind pressure because speed is squared.
4. What drag coefficient should I use?
Many dish estimates use values near 1.1 to 1.4. Use a manufacturer value when available, because shape and mounting details matter.
5. What is the base lever arm?
It is the effective distance from the tipping edge to the resisting weight center. Use the weakest wind direction for a conservative estimate.
6. Why does the calculator check sliding?
A mount can move sideways before it tips. Sliding resistance depends on friction, total downward weight, wind force, and safety factor.
7. Should I include existing blocks?
Yes. Enter blocks already installed. The calculator subtracts their weight and reports the extra blocks still needed.
8. Can ballast damage a roof?
Yes. Too much point load can damage roof surfaces or structure. Use pads, spread load properly, and confirm the roof can carry the weight.