Joist Tape Calculator
Butyl joist tape covers the tops of joists, beams and the ledger so water can't sit in screw holes and checks in the wood. Enter the deck length along the house, how far the joists run out, the joist spacing and the number of beams. The calculator counts the joists, adds up the linear feet of narrow joist tape, wide beam tape and optional rim tape for the ledger, and turns each into 50 ft rolls.
What you'll need
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FrogTape Pro Grade Deck and Joist Flashing Tape, 1.89 in x 50 Feet, Black
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$18.75Typical price:: $22.55
TAPEBEAR Joist Tape 4"×50' Deck Joist Tape Waterproof Butyl Sealant
$28.31
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BXI Flashing Roll Tape Membrane, 4 inches X 32 Feet Thick Waterproof Patch Seal Tape, Self-Adhesive SBS Modified Rubberized Asphalt, Deck Seam Joist Leak Sealant for Roof Window Gutter Repair Outdoor
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Flashing Kings 26 Gauge Galvanized Sheet Metal Flashing Roll (1, 12 in x 10 FT)
$49.00
Check price on AmazonPrices and savings as of Oct 1, 2026, 4:35 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Shopping for someone? See our backyard gift guide for deck builders & DIYers.
Joist tape for common deck sizes
Joists 16 in on center, one beam, rim tape on the ledger, 10% for overlaps, 50 ft rolls.
| Deck (along house × out) | Joists | Joist tape | Beam tape | Rim tape |
|---|---|---|---|---|
| 12 × 10 ft | 10 | 112 ft · 3 rolls | 1 | 1 |
| 16 × 12 ft | 13 | 172 ft · 4 rolls | 1 | 1 |
| 20 × 12 ft | 16 | 212 ft · 5 rolls | 1 | 1 |
| 20 × 16 ft | 16 | 276 ft · 7 rolls | 1 | 1 |
| 24 × 16 ft | 19 | 328 ft · 8 rolls | 1 | 1 |
Where the tape goes
Tape the top edge of every joist, the band joist and every beam before the decking goes on, and press it down firmly so the butyl seals around the screws driven through it. Trex Protect, for example, comes as 1-5/8 in joist tape, 3-1/8 in beam tape for doubled joists and beams, and 11 in rim tape for the ledger and rim joists, all in 50 ft rolls; the maker lists joists, rim joists, beams, stairs, stringers, blocking, the ledger and under joist hangers as places to use it.
The tape doesn't replace ledger flashing or treated lumber rated for ground contact where it is needed. Count the joists first with the deck joist calculator, and if you are building the whole frame use the deck framing calculator. Our joist tape buying guide compares the tapes.
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Frequently asked questions
- How much joist tape do I need for a deck?
- Add up the length of every joist, the band joist and any beams. A 16 × 12 ft deck with joists 16 in on center has 13 joists: 13 × 12 = 156 ft, plus 16 ft of band = 172 ft. With 10% for overlaps that is 189 ft, or four 50 ft rolls of joist tape.
- What width joist tape should I use?
- Narrow tape for single joists and wide tape for doubled joists and beams. Trex Protect, for example, sells 1-5/8 in joist tape, 3-1/8 in beam tape and 11 in rim tape for ledgers and rim joists.
- Is joist tape necessary?
- Building codes don't require it, but it keeps water off the top of the joists where deck screws go in and where checks open up — the part of the frame that rots first. It costs little next to replacing a frame under composite boards meant to last decades.
- Do you put joist tape on beams?
- Yes. Beams carry the joists and collect water at every joist crossing, so they get the wider beam tape. Trex lists joists, rim joists, beams, stair stringers, blocking and the ledger as places for its tape.
- How many feet are in a roll of joist tape?
- Trex Protect joist, beam and rim tapes come in 50 ft rolls (rim tape also in 25 ft). Check the label of the brand you buy and divide the linear feet by its roll length.
