Inputs
Enter your deck size and wind assumptions, then calculate uplift.
Example Data Table
Use these sample scenarios to sanity-check your inputs.
| Scenario | Length | Width | Height | Wind | Exposure | Deck type | Net uplift pressure | Total uplift force |
|---|---|---|---|---|---|---|---|---|
| Typical backyard | 12 ft | 10 ft | 10 ft | 90 mph | C | Flat solid | ~24–28 psf | ~2,900–3,400 lbf |
| More exposed corner | 16 ft | 12 ft | 12 ft | 100 mph | C | Edge exposed | ~35–42 psf | ~6,700–8,100 lbf |
| Coastal / open terrain | 6 m | 4 m | 3 m | 140 km/h | D | Canopy-like | ~2.5–3.5 kPa | ~60–85 kN |
Examples are ranges because coefficients vary by detailing and code assumptions.
Formula Used
The calculator estimates wind velocity pressure and converts it into an uplift pressure on the deck plan area. Uplift force is pressure times area.
- Exposure coefficient: Kz = 2.01 × (z/zg)^(2/α), using a minimum height of 15 ft for stability.
- Velocity pressure: qz = 0.00256 × Kz × Kd × Kzt × V² × I (psf), where V is wind speed (mph).
- Net uplift pressure (magnitude): p = qz × G × Cp.
- Total uplift force: F = p × A, where A is deck area.
- Anchor check: Required capacity = F × SafetyFactor, compared against Anchors × CapacityPerAnchor.
How to Use This Calculator
- Select units, then enter deck length, width, and height.
- Enter the design wind speed for your area.
- Choose an exposure category that matches your site.
- Pick a deck type, or enable a custom Cp value.
- Set anchor count and capacity to check connections.
- Press Calculate Uplift to view results above.
- Download CSV or PDF to keep your scenario summary.
Why wind uplift matters for garden decks
Wind does not only push sideways; it can pull upward on exposed deck surfaces. Uplift is driven by velocity pressure and roof‑like suction at edges and corners. This calculator turns basic site inputs into an estimated net uplift pressure, then multiplies by plan area to produce a total uplift force you can compare against hold‑down capacity. Because force equals pressure times area, a 16×12 deck has 60% more area than a 12×10 deck.
How speed, height, and exposure change pressure
Wind pressure scales with the square of wind speed, so increasing speed from 90 to 100 raises V² by about 23%. Height and exposure adjust the coefficient Kz; open terrain typically increases Kz compared with wooded areas. Use the exposure selector to represent suburban (B) versus open (C) conditions for quick sensitivity checks. A taller deck usually increases Kz for uplift.
Interpreting Cp and deck type selections
The uplift coefficient Cp represents how strongly the deck shape and detailing attracts suction. A flat solid surface uses a moderate Cp, while edge‑exposed or canopy‑like conditions use higher values to reflect corner amplification. If you have a project‑specific coefficient, enable the custom Cp option to match your assumptions.
Anchorage check and safety margin
Total uplift force is compared to the combined allowable capacity of your anchors. The safety factor inflates demand to provide a planning margin and highlight connection weak points. If the status shows CHECK, increase anchor count, select higher‑capacity hardware, or reduce exposure by adding shielding and improving edge detailing. Example: total uplift 3200 lbf with factor 1.5 targets 4800 lbf capacity.
Scenario workflow and exporting results
Run multiple scenarios to bracket realistic and conservative cases. Start with typical values, then test higher speeds, more exposed categories, and higher Cp options. Download CSV or PDF after each run to document the assumptions and share a consistent summary with installers, inspectors, or a design professional.
FAQs
1) What wind speed should I enter?
Use the design wind speed used for local planning or permitting. If you only know typical storms, test several speeds to see sensitivity. Pressure rises with V², so small increases can noticeably raise uplift.
2) Which exposure category fits most gardens?
B suits sheltered yards with trees and nearby buildings. C fits open fields or large clear lots. D is for coastal or flat unobstructed water‑adjacent terrain. When unsure, try the more exposed option for a conservative check.
3) Why does the calculator use a minimum height?
Very low heights can produce unstable Kz estimates in simplified equations. A minimum height stabilizes the coefficient while keeping results practical for small decks. If your deck is elevated, the entered height drives a higher Kz.
4) How do I choose the deck type option?
Pick the option that best matches edge exposure and airflow below the deck. Typical solid decking is “Flat solid.” Use “Edge exposed” for corner‑prone layouts. Use “Canopy‑like” for highly exposed platforms with strong suction potential.
5) What does PASS or CHECK mean?
PASS means selected anchors provide at least the safety‑adjusted required capacity. CHECK means uplift demand exceeds capacity. Increase anchor count, increase allowable capacity per anchor, or revise assumptions and detailing to reduce uplift.
6) Is this suitable for final structural design?
It is a planning tool for comparisons and documentation. Final design should follow applicable codes, local wind maps, and manufacturer data for connectors. Use the outputs to guide questions and to communicate scenarios to a qualified professional.
Reminder: Local requirements vary. Use this as a planning tool.