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Use our Collar Tie Calculator to find roof tie tension, rafter thrust, roof pitch, timber stress, and tie spacing with ease.
A strong roof needs proper support. Collar ties help connect roof rafters near the ridge. They help resist the force that pulls rafters apart.
Our Collar Tie Calculator helps you find roof tie tension with ease. It uses roof span, roof rise, tie height, and design load. You can also check timber strength and tie spacing.
This tool gives clear results in a few steps. It helps builders, roofers, and DIY users understand basic roof tie forces.
A collar tie is a wood member that joins two roof rafters. It sits near the roof ridge. It helps resist rafter separation, often due to wind uplift.
A rafter tie serves a different role. It helps resist outward thrust at the lower ends of rafters. So, a Collar Tie Calculator and a Rafter Tie Calculator do not always serve the same purpose.
Our calculator uses a simple gravity-thrust model. It finds roof pitch, horizontal thrust, and tie tension.
1. Roof Pitch Formula
Roof pitch angle = tan⁻¹ (Roof Rise ÷ Horizontal Half-Span)
2. Horizontal Rafter Thrust Formula
H = (w × L) ÷ (2 × tan θ)
3. Collar Tie Tension Formula
T = H × (h ÷ y)
Where:
H = Horizontal rafter thrust
T = Tie tension
w = Design load per unit length
L = Horizontal half-span
h = Roof rise
y = Tie height above the wall plate
θ = Roof pitch angle
The final tie tension can also use this simple form:
T = (w × L²) ÷ (2 × y)
Use the same units in each formula. Our tool converts your inputs before it starts.
Follow these five simple steps:
Enter the horizontal half-span of your roof.
Enter the roof rise and tie height.
Add the design load per unit length.
Choose your units and optional timber check settings.
Click calculate to view the roof pitch, thrust, and tie tension.
You can also enter the net wood area and its allowed tensile stress. The tool will compare actual stress with the allowed value. You can also check tie spacing against its built-in 4 ft limit.
Let's look at a simple roof example.
Assume a roof has a 6 m half-span and a 3 m rise. The tie sits 2.4 m above the wall plate. The design load is 1 kN/m.
First, find the roof pitch:
θ = tan⁻¹ (3 ÷ 6) = 26.565°
Next, find the horizontal thrust:
H = (1 × 6) ÷ (2 × tan 26.565°)
H = 6 kN
Now, find the tie tension:
T = 6 × (3 ÷ 2.4)
T = 7.5 kN
So, the calculated tie tension is 7.5 kN.
For an optional timber check, assume a net area of 1,000 mm². Also, use an allowed stress of 10 MPa.
Actual stress = (7.5 × 1,000) ÷ 1,000
Actual stress = 7.5 MPa.
The result passes this simple check because 7.5 is less than 10.
Our Collar Tie Calculator makes basic roof tie math easier. It finds roof pitch, horizontal thrust, and tie tension. It also offers simple timber stress and spacing checks.
It can help with early estimates and basic learning. However, it does not check wind uplift or all roof safety needs. For full design, use a qualified engineer and the right building code.
A Wood Roof Tie (LRFD, NDS 2018) Calculator may be needed for a full wood design. A Rafter Tie Thrust Calculator can also help with lower roof tie forces. Each tool has a different purpose.
It finds roof pitch, horizontal thrust, and tie tension. It can also check timber stress and tie spacing.
A collar tie joins rafters near the ridge. A rafter tie joins them near the lower ends. They resist different roof forces.
The formula is T = H × (h ÷ y). Here, H is horizontal thrust, h is roof rise, and y is tie height.
Yes. It compares actual tensile stress with the allowed stress. This is a basic check, not a full wood design.
No. It uses a simplified gravity-thrust model. It does not calculate wind uplift or connection strength.
No. This tool only checks spacing against a fixed 4 ft limit. Always check the rules for your area and roof type.