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CampingCalc

Roof Load Calculator: How much may solar, air conditioner and cargo box weigh?

Two glass solar panels, a rooftop air conditioner and a satellite dish quickly add up to 175 lb (80 kg) on the roof – for many vehicles the limit of the manufacturer's approval. This calculator adds up your roof items, shows the reserve to the permissible roof load and the new vehicle height.

Units

From the owner's manual or the coach manufacturer's figure. Without a figure: ask the manufacturer – don't guess.

Items on the roof

For the new overall height (bridges, parking garages, ferries). High-roof vans about 8.4–8.7 ft (2.55–2.65 m), Class C 10–11 ft (3.0–3.4 m).

Result

Roof load reserve

159 lb

61 lb of 220 lb used (28%)

Roof load61 / 220 lb
Total roof load
61 lb
Tallest item
2 in
  • The roof load figure applies to an evenly distributed load. Point loads (air conditioner, roof tent), mounting, driving dynamics and wind load must additionally be assessed by the manufacturer or a specialist shop.
Show calculation
  1. 1Solar panel 200 W (glass): 26 lb × 2 = 52 lb
  2. 2Mounts and cables: 9 lb × 1 = 9 lb
  3. 3Total roof load: 61 lb
  4. 4Reserve: 220 lb − 61 lb = 159 lb

 

How it's calculated

Roof load = Σ (weight × quantity) Reserve = permissible roof load − roof load New height = vehicle height + tallest item

The permissible roof load is a manufacturer figure – for base vehicles (cargo vans) usually as a dynamic load with roof rack, for coach bodies (fiberglass/sandwich roof) as an evenly distributed load. The values differ considerably by model; that's why the calculator contains no default value that could be mistaken for an approval.

Point loads (air conditioner over a roof vent cutout, roof tent on crossbars), mounting method, wind load and driving dynamics are separate questions. Installing heavy items belongs in the hands of the coach manufacturer or a specialist shop.

Worked example

Camper van with 220 lb (100 kg) permissible roof load and 8.5 ft (2.6 m) height gets two glass panels, a satellite dish and a roof rack with cargo box.

Inputs

  • Permissible roof load per manufacturer: 220 lb
  • Items on the roof:
  • Solarmodul Glas 200 Wp: 26.5 lb × 2 × × 1.57 in
  • Sat-Anlage: 30.9 lb × 1 × × 7.87 in
  • Dachträger: 26.5 lb × 1 × × 3.94 in
  • Dachbox (leer): 39.7 lb × 1 × × 15.7 in
  • Gepäck in Dachbox: 44.1 lb × 1 × × 0 in
  • Vehicle height without roof items (optional): 8.53 ft

Result

26 lb

Roof load reserve

Total roof load
194 lb
Tallest item
16 in
New vehicle height
9.84 ft

Calculation

  1. Solarmodul Glas 200 Wp: 26.5 lb × 2 = 52.9 lb
  2. Sat-Anlage: 30.9 lb × 1 = 30.9 lb
  3. Dachträger: 26.5 lb × 1 = 26.5 lb
  4. Dachbox (leer): 39.7 lb × 1 = 39.7 lb
  5. Gepäck in Dachbox: 44.1 lb × 1 = 44.1 lb
  6. Total roof load: 194 lb
  7. Reserve: 220 lb − 194 lb = 26.5 lb
  8. Height: 8.53 ft + 16 in = 9.84 ft

The variables explained

Permissible roof load
Manufacturer figure from the owner's manual or technical data sheet.
Weight per item
Manufacturer figures incl. mounts; presets are typical values.
Height
Height of the item above the roof for the new overall height.

Common mistakes

  • Confusing the roof load of the base vehicle with that of the coach body – for motorhomes with a coach body the coach manufacturer's figure applies.
  • Forgetting the luggage in the cargo box: the box weighs 33–44 lb (15–20 kg) empty, 110 lb (50 kg) and more loaded.
  • Ignoring the center of gravity: 175 lb (80 kg) on the roof noticeably increases body roll in curves.
  • Not updating the height: after installation note the new height clearly visible in the cockpit.

Assumptions and limits

  • Evenly distributed load; no assessment of point loads or mounting.
  • Preset values are typical manufacturer figures and must be checked.