Professional Guide

Best Weed Membrane for Decking: 2025 Expert Review

DR Joinery

Expert Joiner & Timber Specialist

Published 16 December 2025

Building a timber deck is a significant investment for any homeowner. You choose the right softwood or hardwood, you treat the cut ends, and you plan the layout perfectly. But often, the most critical step is the one that gets rushed: the ground preparation.

Living and working in York, where the ground is often damp and vegetation grows aggressively, I have been called out to fix too many 'wobbly' or rotting decks. Very often, the culprit is invasive weeds growing up through the structure, trapping moisture against the joists and accelerating rot. A simple weed membrane is the first line of defence.

In this review, I've analysed three landscape fabrics that I consider for different types of jobs. From a budget-friendly option for small garden patches to a heavy-duty commercial grade sheet for serious construction, here are the membranes that will keep your deck weed-free.

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Specs vs. The Real World

The Spec: "GSM Rating (Grams per Square Metre)"

The Theory

"Higher GSM always means a better product."

The Reality

Whilst density is important, for decking, drainage is equally vital. A super-thick membrane that pools water will cause your timber frame to rot. You need a woven fabric typically between 100gsm and 130gsm that breaths.

The Spec: "UV Stability"

The Theory

"You need the highest UV rating possible."

The Reality

Under a deck, the membrane is in the dark. UV stability is crucial for exposed flower beds, but for decking, puncture resistance and tensile strength are far more important characteristics.

My Top 3 Recommendations

Three options to cover different needs and budgets

LawnScape 1M x 10M Weed Control Membrane 105 GSM Heavy Duty

Budget Pick

LawnScape

This is a sensible entry-level fabric. At 105gsm, it offers adequate protection for standard garden weeds. It's ideal for smaller, localized decking projects where you aren't fighting aggressive ivy or brambles.

Price£6.19 (at time of writing)

Weight105 GSM

Size1m x 10m

The Good

Very affordable for small repairs or extensions
Woven mesh allows for good drainage (essential for timber)
Easy to cut and manipulate around posts

The Bad

105gsm is the minimum I'd recommend; may struggle against tough thorns
Narrow 1m width means more taping/overlapping required

Installer Tip:

Because this roll is only 1 metre wide, you will have plenty of joins. Ensure you overlap the edges by at least 150mm (6 inches) and peg them down securely. Weeds love to find the weak spot at a join.

Priced at £6.19 at the time of writing

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4m x 15m Pro-Tec Gold-Line 125gsm EXTRA Heavy Duty Weed Control Membrane

Quality Pick

Pro-Tec Garden Products

This is a serious bit of kit. The 'Gold-Line' indicates a higher specification, and the 125gsm weight is substantial. The real winner here for a joiner is the 4m width, which allows you to cover large deck footprints with minimal joins.

Price£39.99 (at time of writing)

Weight125 GSM

Size4m x 15m (Large Deck Ready)

The Good

Excellent 125gsm thickness prevents most invasive growth
Huge 4m width reduces the number of seams (fewer weak points)
Made from virgin materials for better longevity

The Bad

Significant upfront cost compared to budget options
The large roll can be heavy and awkward to manoeuvre solo

Installer Tip:

When laying a 4m wide sheet, wind can be a nightmare. Weigh down the corners immediately with your decking blocks or gravel before you try to peg it out, otherwise, you'll be chasing it across the garden.

Priced at £39.99 at the time of writing

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Pro-Tec 130gsm Commercial Grade SUPER Heavy Duty Weed Control Membrane

Problem-solving

Pro-Tec Garden Products

If you are dealing with ground that has a history of aggressive weeds like brambles or nettles, this 130gsm commercial grade fabric is the solution. It is incredibly dense and designed to withstand heavy traffic and sharp stalks.

Price£16.95 (at time of writing)

Weight130 GSM (Super Heavy)

GradeCommercial

The Good

Extremely tough 130gsm weave
Green colour helps blend in if edges are slightly exposed
25-year guarantee claims (below ground)

The Bad

Overkill for a simple raised deck on a patio
Thicker material is harder to fold into tight corners

Installer Tip:

Even with this heavy-duty membrane, you must clear sharp stalks first. However, if you are laying gravel on top of the membrane (which I recommend to hold it down and aid drainage), this thickness prevents the stones from piercing the fabric over time.

Priced at £16.95 at the time of writing

Check Price on Amazon

Frequently Asked Questions

Does weed membrane go over or under the decking frame?

It goes under the frame, directly on the ground (soil). You should clear the turf, level the ground, lay the membrane, and ideally cover it with gravel. Then, your timber frame sits on top (usually on concrete pads or posts). Never staple it to the underside of the deck boards; it will trap moisture and rot the wood.

Do I need gravel on top of the membrane?

Yes, I strongly advise it. The membrane stops the weeds, but the gravel holds the membrane in place, protects it from UV light (if light gets through gaps), and most importantly, it stops the membrane flapping about. It also looks much tidier underneath raised decks.

What happens if I don't use a membrane under my deck?

Light and water will still get through the gaps in your deck boards. Without a membrane, weeds will grow in the dark, damp environment under your deck. They will grow up through the gaps, trapping damp air against your timber, which drastically accelerates rot. In York's damp climate, this is a recipe for disaster.

Can I use a plastic sheet instead of woven membrane?

Absolutely not. Solid plastic sheeting (like damp proof membrane for houses) is impermeable. If you use that under a deck, rainwater will pool on top of it, creating a stagnant swamp under your timber. You must use a woven polypropylene fabric that allows water to drain into the earth whilst blocking sunlight.

Which GSM is best for decking?

For professional jobs, I look for anything over 100gsm. 100gsm is standard, 125gsm or 130gsm is excellent. Anything typically below 70gsm is flimsy and better suited for flower beds, not construction projects.

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