Calculate how many hurricane ties your roof needs and the wind uplift load on each rafter-to-wall connection, then check whether your tie is strong enough.
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Hurricane Tie Formula
This calculator estimates quantities from a specified layout and compares supplied uplift demand with supplied connection capacity. Count mode assumes a member at each endpoint with spacing no greater than S:
For an arithmetic uplift comparison, use the engineer-supplied net ASD uplift pressure and tributary area for the exact connection:
This calculator does not derive design pressure from wind speed. Obtain the applicable net demand, tributary area and complete connection capacity from the project design documents. Wind exposure, roof location, internal pressure and load combinations matter:
Do not substitute a generic wind-speed factor for project design pressure.
Variables:
- Ties is the number of hurricane ties needed for the roof
- L is the roof length along the wall the rafters run past
- S is the maximum rafter or truss spacing (use a consistent unit with L)
- E is the number of ends you tie per member, 1 for one wall or 2 for both walls
- U is the uplift force on one connection, in pounds
- Pnet is the net ASD uplift pressure for the applicable load combination, in pounds per square foot; no additional dead-load subtraction is made
- A is the tributary area one connection carries, in square feet
- Callowable is the allowable uplift capacity of the complete specified connection on the same load basis
- Additional is the number of connections outside the regular spacing layout
- Specified ties per connection is a quantity from the plans, not an assumption that tie capacities add
Count mode estimates quantities from the plans. With members at both endpoints, use ceil(L/S) + 1 positions; rounding down misses a position when L is not divisible by S. Multiply by specified connected ends, add extra connections, then multiply by specified ties per connection. Spares are rounded up after applying the chosen percentage. Confirm irregular layouts, openings and actual endpoint details separately.
Uplift mode compares U = Pnet × A with the allowable capacity of the complete connection. Use engineer-supplied net ASD pressure and the correct tributary area for this exact location. Do not subtract dead load a second time or assume that adding ties multiplies capacity. This arithmetic is not a connector selection or code-compliance decision.
Hurricane Tie Capacity and Roof Coverage
Connector ratings depend on the exact current product, wood species, fasteners, installation geometry and combined loads. A product name alone does not establish an allowable capacity. Obtain the complete connection rating from approved design documents and current manufacturer data.
| Required source data | Check |
|---|---|
| Net ASD uplift demand | Correct roof location and applicable load combination |
| Tributary area | Specified for the exact connection |
| Complete connection capacity | Current approved wood, fasteners, geometry and combined loads |
Wind speed alone does not establish net uplift pressure. The table below illustrates arithmetic using supplied net ASD pressures and a specified 30-square-foot tributary area; these values are not design pressures for any building.
| Supplied net ASD pressure | Specified area | Arithmetic demand |
|---|---|---|
| 20 psf | 30 sq ft | 600 lb-force |
| 30 psf | 30 sq ft | 900 lb-force |
| 40 psf | 30 sq ft | 1200 lb-force |
Example Problems
Example 1: Count the ties for a roof.
A gable roof is 50 feet long with trusses spaced 24 inches (2 feet) on center, and you tie both ends. First find the number of trusses, then multiply by two ends:
Ties = (50 / 2 + 1) * 2 = 26 * 2 = 52 ties.
Order a few spares on top of that, since a tie with a missing or bent nail hole should be replaced rather than installed short.
Example 2: Compare supplied demand and capacity.
Suppose the design documents specify a net ASD uplift pressure of 40 psf and a tributary area of 30 square feet for one connection. The demand is:
U = 40 × 30 = 1200 lb-force per connection.
If the complete specified connection has an allowable uplift capacity of 1500 lb-force on the same basis, the arithmetic ratio is 1200 / 1500 = 0.8. This comparison does not establish that a particular tie or fastener arrangement is acceptable. Multiple ties require an approved detail; their ratings cannot simply be added.
Frequently Asked Questions
How many hurricane ties do I need?
Use the approved connection schedule to determine ties per connection and connected ends. For 26 regular member positions with two connected ends and one specified tie per connection, the base quantity is 52 ties. Additional connections and spares are separate. A quantity estimate does not prescribe a fastening detail.
Do hurricane ties go on the inside or outside of the wall?
Follow the exact manufacturer installation and project detail for connector orientation, wood members, fastener size, length, type and location. Installation side and fastener schedules are product-specific; do not assume that every hole must be filled or that either face is always permitted.
When is a hurricane tie required instead of just nails?
The applicable code, adopted edition and project conditions determine when prescriptive fastening or an engineered connector is required. A generic 200-pound threshold is not sufficient permission to use toenails. This calculator does not decide code exceptions or select the required fastening method.
