Roof Jack Calculator

Calculate the number of roof jacks (temporary roof brackets), scaffold planks, and nails needed for safe steep-slope roofing work by roof area, pitch, and bracket spacing

Calculate the number of roof jacks needed for your roof

Quick presets

ft
ft

Roof Area

866 sq ft

8.7 squares • 59 linear ft

PRO

Professional Calculator

Extended parameters for precise calculations

sq ft

Estimated Materials

60 bundles

Roof Area

1,792 sq ft

Squares

17.9

Detailed Breakdown

Roof Area1,792 sq ft
With Waste1,971 sq ft
Roofing Squares17.9
Bundles60
How to Use This Calculator
The Roof Jack Calculator helps DIY homeowners and roofing contractors determine the correct number of temporary roof brackets, scaffold planks, and fasteners needed for safe work on steep roofs. Roof jacks are essential safety equipment for pitches 6/12 and steeper, and this tool takes the guesswork out of planning by calculating exact quantities based on your roof dimensions and OSHA-compliant spacing.

Count tab: Enter your roof face dimensions — the length from eave to ridge (up the slope) and the width along the eave line. Select your roof pitch and choose the bracket spacing. Steeper roofs require tighter horizontal spacing (4 feet) and more frequent rows up the slope (every 6 feet) because workers need more support points and the forces on the brackets are greater. The calculator outputs the total bracket count, number of rows, and brackets per row. It accounts for the first row starting above the eave and additional rows spaced up to the ridge area.

Equipment tab: Select the bracket type — adjustable brackets are the best all-around choice because they accommodate any pitch from 4/12 to 12/12 with a single set. Choose the scaffold plank size (2x10 is the recommended minimum) and length. The calculator determines how many planks you need per row to cover the full roof width, including the required 12-inch overlap at bracket points and 6-inch overhang at the ends. It also calculates the total 16d duplex nails needed — 3 per bracket — and reminds you that duplex (double-head) nails are strongly preferred for easy removal.

Cost tab: Compare the total cost of purchasing versus renting the roof jack brackets. Purchase cost includes the brackets, planks, and nails as a one-time investment. Rental cost covers the bracket rental fee for your planned duration plus the planks and nails you still need to buy. The optional fall protection add-on includes a harness, lanyard, and roof anchor, which OSHA requires for steep-slope work. The cost comparison helps you make an informed decision based on whether this is a one-time project or an ongoing need.

The Formula
The roof jack calculator uses these formulas:

Brackets Per Row Brackets per row = FLOOR(Roof width / Horizontal spacing) + 1 Example: 40 ft / 4 ft + 1 = 11 brackets per row

Number of Rows Usable slope = Roof length - 2 ft (offset from eave) Number of rows = FLOOR(Usable slope / Row spacing) + 1 Example: (20 - 2) / 7 + 1 = 3.57 → 3 rows

Total Brackets Total brackets = Brackets per row x Number of rows Example: 11 x 3 = 33 brackets Add 10% spare: 33 x 1.1 = 37 brackets (round up)

Scaffold Planks Per Row Planks per row = CEIL(Roof width / (Plank length - 1 ft overlap)) Example: 40 / (10 - 1) = 4.4 → 5 planks per row Total planks = Planks per row x Number of rows Example: 5 x 3 = 15 planks

Nails Nails per bracket = 3 (16d duplex) Total nails = Total brackets x 3 Example: 37 x 3 = 111 nails (~1 lb of 16d duplex)

Purchase Cost Bracket cost = Total brackets x Price per bracket ($10-$15 adjustable) Plank cost = Total planks x Plank price ($8-$15 per 2x10x10) Nail cost = 1-2 lbs x $6-$8/lb for 16d duplex Fall protection kit = $100-$250 (harness + lanyard + anchor) Total purchase = Bracket cost + Plank cost + Nail cost + Fall protection

Rental Cost Bracket rental = Total brackets x Daily rate x Days Plank cost = same as purchase (not rented) Total rental = Bracket rental + Plank cost + Nail cost + Fall protection
Example Calculation
Example: Roof Jack Setup — 40 ft Wide x 20 ft Slope, 8/12 Pitch in Ohio

Dave is re-shingling one side of his roof and needs to set up roof jacks for the 8/12 pitch. The roof face is 40 feet wide along the eave and 20 feet from eave to ridge up the slope.

Step 1: Count Brackets
• Horizontal spacing: 4 ft (recommended for 8/12)
• Brackets per row: 40 / 4 + 1 = 11 brackets
• Usable slope: 20 - 2 = 18 ft
• Row spacing: 7 ft (standard for 8/12)
• Number of rows: 18 / 7 + 1 = 3.57 → 3 rows
• Total brackets: 11 x 3 = 33
• With 10% spare: 37 brackets

Step 2: Select Equipment
• Bracket type: Adjustable at $12 each
• Plank size: 2x10
• Plank length: 10 ft
• Planks per row: 40 / (10 - 1) = 4.4 → 5 planks
• Total planks: 5 x 3 = 15 planks
• Nails: 37 x 3 = 111 nails (~1 lb of 16d duplex)

Step 3: Cost — Purchase Option
• 37 adjustable brackets x $12 = $444
• 15 planks 2x10x10 x $11 each = $165
• 1 lb 16d duplex nails = $7
• Fall protection kit (harness + lanyard + anchor) = $150
• Total purchase: $766

Step 4: Cost — Rental Option (7-day DIY)
• 37 brackets x $4/day x 7 days = $1,036 (or weekly rate ~$600)
• 15 planks (still purchased) = $165
• Nails = $7
• Fall protection = $150
• Total rental: $922 (weekly rate)

Step 5: Recommendation Purchasing is cheaper than a weekly rental and Dave keeps the equipment for future use. The 37 adjustable brackets and 15 planks provide 3 complete rows of scaffold platform across the full 40-foot width. Dave should install the bottom row first, work from that platform to install the second row, and so on up the roof. Remove brackets from top down as the final shingle courses are installed, sealing each nail hole with roofing cement.

Frequently Asked Questions

What are roof jacks and when do I need them?
Roof jacks are temporary steel brackets that nail to the roof deck through the sheathing into the rafters, providing a ledge to support scaffold planks. They create a horizontal working platform on a sloped roof surface, giving workers a safe place to stand, walk, and stage materials. Roof jacks are needed whenever the roof pitch is steep enough that workers cannot safely stand on the slope without support. OSHA requires fall protection or scaffold platforms for residential roofing on pitches steeper than 4/12, and most roofers start using jacks at 6/12 and above. At 8/12 and steeper, roof jacks are essentially mandatory because walking and working on the bare slope without a platform is extremely hazardous. Even on moderate pitches, jacks provide a stable working surface that increases productivity and reduces fatigue.
How many roof jacks do I need for my roof?
The number of roof jacks depends on your roof width, slope length, and chosen spacing. For horizontal spacing, place brackets every 4 to 6 feet along the eave direction. For vertical spacing, place rows every 6 to 8 feet up the slope. To calculate: divide the roof width by the horizontal spacing and add 1 for the bracket count per row. Then divide the slope length by the row spacing to get the number of rows. Multiply brackets per row times number of rows for the total. For example, a 40-foot wide roof with 4-foot bracket spacing needs 11 brackets per row. With a 20-foot slope length and 7-foot row spacing, you need 3 rows. Total: 11 x 3 = 33 brackets. Always have a few spares on hand in case you need to reposition for obstacles like pipes or vents.
How do I install and remove roof jacks without leaving holes?
Roof jacks are installed by sliding the flat mounting plate under a shingle course and nailing through the plate into the rafter below with three 16d duplex nails. The key is to install the bracket above a shingle course line so that when the bracket is removed and the final course is installed, the shingles cover the nail holes completely. Work from the bottom row up, installing brackets and planks as you go. To remove, pull the duplex nails with a hammer claw, slide the bracket out from under the shingle, and apply a dab of roofing cement or sealant into each nail hole. Then nail the covering shingle course down. When done correctly, the finished roof shows no evidence that brackets were ever used because all nail penetrations are hidden under overlapping shingles.
Can I use 2x8 planks instead of 2x10 for roof jacks?
A 2x8 plank can technically be used but is not recommended for most roofing work. The 7.25-inch width of a 2x8 provides a noticeably narrower platform compared to the 9.25-inch width of a 2x10, making it harder to maintain secure footing, especially on steep pitches where the plank is your primary standing surface. The 2x8 also has less bending strength, meaning it deflects more under load between bracket supports and has a lower maximum span. If you use 2x8 planks, reduce the bracket spacing to a maximum of 4 feet and limit the load to one worker per span. For any roof 8/12 or steeper, a 2x10 minimum is strongly recommended, and a 2x12 provides the safest and most comfortable platform. The cost difference between 2x8 and 2x10 planks is only $2 to $4 per 10-foot board, so the safety upgrade is essentially free.
Should I buy or rent roof jacks for a DIY roofing project?
For a one-time DIY roofing project, renting roof jacks is usually more economical unless you expect to do roof work again in the future. A typical rental for 20 adjustable brackets runs $60 to $100 for a week, compared to $200 to $300 to purchase the same brackets outright. However, you still need to buy the scaffold planks and nails regardless of whether you rent or buy the brackets. If you are a handy homeowner who maintains your own property, purchasing makes sense because steel roof brackets last a lifetime and you will likely need them again for future repairs, gutter work, or the next re-roof in 20 to 30 years. Contractors should always purchase — the brackets pay for themselves after two or three jobs. Consider that scaffold planks (2x10 or 2x12 lumber) can be reused for other projects after the roofing is done, so they are not a wasted purchase.

Related Calculators

Roofing Safety Calculator

Calculate fall protection equipment needs for roofing work

Shingle Calculator

Estimate shingle bundles, underlayment, and materials for your roof

Roof Pitch Calculator

Determine your roof pitch and convert between rise/run and degrees

Roof Area Calculator

Calculate actual roof surface area from building footprint and pitch

Roofing Labor Calculator

Estimate crew size and labor hours for a roofing project

Related Guides & Resources

Roof Replacement Guide How to Choose a Contractor Commercial Roofing Guide