What does joist tape do?
It forms a waterproof layer on the top of a timber joist, where water collects under the board and around fixings. A DIYer who covered joist tops before laying composite says the frame will otherwise rot long before the decking does. Ecoscape says joist tape waterproofs timber joists, and Composite Prime recommends it.
What width of joist tape do I need?
NeoTimber’s tape is black, non-butyl, self-sealing with a polymer acrylic adhesive, sold in 20 m rolls in three widths.
| Width | For |
|---|---|
| 50 mm | single joist tops |
| 82 mm | noggins |
| 100 mm | double joists |
How do you fit it?
Lay it on dry, clean joist tops before any board goes down, and cover noggins and double joists with the wider widths. A UK builder complements it with bitumen paint on cut ends and cuts treated with preservative. He splurged on premium tape at about £12 a roll and says he’ll only know in 20 years whether it paid off.
When can you skip it?
On aluminium and recycled plastic joists, which don’t rot. Cladco, Envirobuild and Millboard all sell those. Tape also doesn’t fix a frame that stays wet: keep air moving, give the frame a slight fall and keep it clear of the ground. See the frame guide and joists.
Is it the same as anti-slip tape?
No. Anti-slip decking tape is a different product that sticks on the boards’ surface. We haven’t sourced test results for it, so see our non-slip guide for what is measured.
Questions
What is decking tape?
In this guide, joist tape: a self-adhesive strip over the top of timber joists to protect them from water under the boards. The same words are sometimes used for anti-slip tape, which we haven't tested or sourced.
Do I need joist tape for decking?
On timber joists it adds protection, and Composite Prime recommends it. Plastic and aluminium joists don't rot, so they don't need it. It doesn't replace airflow and drainage underneath.
How much does deck tape cost?
A UK DIYer paid about £12 a roll for premium tape on his deck, as he said on video. Prices vary by brand and width.
Sources
- Decking Joist Tape - NeoTimber
- A Guide On How To Fit Composite Decking Pedestals - Ecoscape
- HD Deck Pro Fitting Guide and Composite Prime Care & Maintenance Guidelines (Taylor Maxwell, 2022)
- Installer video: REALITY CHECK! How much does timber decking actually cost in the UK? (Gosforth Handyman)
- Installer video: Watch This If You're Thinking About Composite Decking (Home RenoVision DIY)
- Installer video: How To Build A Sub Frame For A Decking Project Including Tips (Gareth Wilson)