Putting a weed membrane under your deck? Enter the deck size and the roll size. You get the number of rolls and the area to cover, with extra for overlaps.
Your shopping list
2Rolls to buy
13.2 m²Area to cover
12 m²Deck area
Lay the membrane flat and pin it down before you build the frame. Extra of 10% is included.
How to use the Weed Membrane Calculator for Decking
- Enter the deck length and width in metres.
- Pick the roll size you plan to buy.
- Read the rolls to buy and the area to cover.
The math behind it
Area = length x width
Area to cover = area x (1 + extra %)
Rolls = area to cover / area of one roll, rounded up
A worked example
What we typed in
- Deck length: 19.69 ft
- Deck width: 13.12 ft
- Roll size: 1 x 10 m roll (108 sq ft)
- Extra for overlaps and edges: 10%
What we got
- Rolls to buy: 3
- Area to cover: 284.17 sq ft
- Deck area: 258.33 sq ft
Tips from the job site
- Overlap the sheets by at least 10 cm so weeds cannot come through the joins.
- Lay the membrane before the frame and cover it with gravel if you can.
Common questions
How much weed membrane do I need for a deck?
Work out the deck area and add 10% for overlaps. A 4 x 3 m deck needs 13.2 m2 of membrane.
Do I need a weed membrane under decking?
It helps stop weeds. Many UK deck builds lay a membrane and a gravel layer under the frame.
See all Deck Calculators.
Last checked: (worked example and form display).