Member and Load Inputs
Use metric units. Enter design values already adjusted for your material, service condition, and governing method.
Example Data
| Input | Example value | Purpose |
|---|---|---|
| Cantilever length | 1.20 m | Support to free edge. |
| Section | 50 mm × 250 mm | Single rectangular wood member. |
| Dead load | 0.80 kN/m | Decking and permanent materials. |
| Live load | 2.00 kN/m | Occupancy load assigned to one member. |
| Deflection limit | L/180 | Project-specific serviceability criterion. |
Formula Used
The calculator models a prismatic cantilever with a full-length uniform load and one vertical point load. The point-load distance, a, is measured from the fixed support. Service loads are used for deflection. Factored loads are used for the stress and bearing screens.
The beam equations are linear-elastic screening equations. They do not model connection slip, nonlinear behavior, creep, load redistribution, or a non-rigid fixed support.
How to Use This Calculator
- Enter the unsupported cantilever projection from the true fixed support.
- Enter the actual wood member width and vertical depth.
- Use suitable modulus and design values for your member.
- Assign line loads to the individual member being checked.
- Add any concentrated load and its distance from the support.
- Enter load factors that match your selected design approach.
- Choose a project-appropriate deflection ratio.
- Review bending, shear, bearing, and deflection together.
- Download the calculation record or print it as a PDF.
- Have a qualified professional verify the complete balcony system.
Balcony Cantilever Design Guide
Understand the Cantilever
A cantilever balcony projects beyond its supporting wall or beam. The support must resist vertical shear and a large fixed-end moment. The outer edge has no direct support. That condition makes member depth especially important. A deeper joist usually reduces bending stress and visible movement. This calculator screens one rectangular wood member. Preliminary only.
Load Paths and Reactions
Loads travel from decking and guards into joists. Joists deliver load to the supported backspan and connection. The calculator accepts dead load, live load, and one point load. A point load can represent a planter or concentrated feature. Enter its distance from the fixed support accurately. Loads near the tip create larger moments. The support reaction equals the total vertical loading.
Bending and Shear Checks
Bending stress is highest at the fixed support. The calculator divides fixed-end moment by the member section modulus. It compares that stress with your entered bending value. Shear also peaks at the fixed support. For a rectangular section, peak shear stress is 1.5 times average shear. The calculator compares this value with the entered shear limit. These checks assume sound, straight-grained wood. Knots, checks, notches, holes, and decay can reduce capacity. Wet service can also change suitable design values.
Deflection and Connection Review
Deflection uses service loads instead of factored loads. It estimates tip movement from the distributed load and point load. Excess movement can damage finishes and feel unsafe. It can also create drainage problems at the balcony edge. The selected span ratio sets the movement limit. Consider a stricter limit where brittle finishes occur. The calculator also estimates bearing stress at the support. Bearing length should match the actual compressed contact length. Verify ledgers, fasteners, flashing, hold-downs, and lateral bracing separately. Guard loads need their own dedicated connection review.
Practical Limits
Use consistent units throughout the inputs. Enter millimetres for member dimensions and metres for length. Use design values appropriate for the wood species and condition. Apply factors required by your governing standard. Confirm the wall can transfer forces into the building structure. Check uplift, lateral restraint, and water management. Obtain review from a qualified structural professional before construction. Field conditions can govern over simple member calculations. Good details protect both the balcony and the building envelope.
Frequently Asked Questions
1. What does this calculator check?
It screens one rectangular wood cantilever member for fixed-end moment, shear, bending stress, support bearing stress, and tip deflection. It does not design the complete balcony system or its connections.
2. Can I use this for a balcony ledger?
No. A ledger requires a separate connection design. Fasteners, edge distances, flashing, water protection, wall framing, uplift, and lateral forces need dedicated checks.
3. Why is the point-load position important?
A load farther from the fixed support creates more bending moment. It also usually creates more tip movement. Enter the actual distance from the fixed support.
4. Does the tool include member self-weight?
Not automatically. Include the member self-weight within the dead distributed load when it is material to the selected member and load assignment.
5. What design values should I enter?
Enter values appropriate for the actual species, grade, moisture condition, treatment, temperature, duration, size, and selected design method. A qualified designer should determine those values.
6. Why are deflection loads not factored?
Serviceability checks commonly use service-level loads. This tool follows that general separation. Confirm your project requirements because deflection criteria and load combinations vary.
7. Can the member pass while the balcony still fails?
Yes. The support, backspan, connection, guard, decking, drainage, flashing, lateral bracing, and building wall may govern even when the isolated member screen passes.
8. Is a lower utilization always better?
Lower utilization provides more reserve in this simplified check. It does not remove the need to verify every separate limit state and construction detail.
9. Can I use multiple point loads?
This version accepts one point load. Combine conservative point loads into an equivalent load only when a qualified engineer confirms that approach is appropriate.
10. What happens if the fixed support is flexible?
The actual tip deflection can exceed this estimate. A flexible support also changes force distribution. Model the real support and connection behavior separately.
11. Is this suitable for permit construction documents?
No. Use it as an early screening aid. Permit documents should be prepared or reviewed by the responsible qualified professional under the applicable local requirements.