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What Is the Best Thing to Put Under a Deck? Gravel

Gravel over landscape fabric is the standard answer: it drains, suppresses weeds and keeps the space dry. Solid plastic sheeting causes the problems it prevents.

By Zakaria 2 min read Save to Pinterest — opens Pinterest in a new tab
A close view of angular grey crushed stone spread as a ground covering
Photo: Pexels, Pixabay Content License, via Pixabay
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Gravel over permeable landscape fabric. It drains, it suppresses weeds and it keeps the space dry — which is what actually protects the joists. Plastic sheeting does the opposite of what people expect.

What goes down, in order

  1. Clear the ground, including perennial weed roots — fabric will not defeat established bindweed or couch
  2. Grade a slight fall away from the house
  3. Permeable landscape fabric, overlapped and pinned
  4. Gravel, a couple of inches, spread evenly

Plastic sheeting is the common bad advice

It stops water draining into the ground, so moisture collects on top of it and sits there, and the soil beneath goes stagnant. That raises humidity in the enclosed space — exactly the condition that rots joists.

Ventilation beats ground covering

This is the part people skip. Air moving under a deck dries the joists after rain.

  • Slatted or louvred skirting, or deliberate gaps at intervals
  • Not solid skirting, which holds damp air against the timber
  • A completely sealed underdeck is a rot problem waiting to happen

You can have a tidy, animal-proof underdeck and still have airflow. Those are not in conflict.

Weeds

Fabric stops weeds from below. It cannot stop seed blowing in and germinating in leaf litter that accumulates on top of the gravel.

So the maintenance is clearing debris, not improving the membrane. Low decks with little clearance are the awkward case: too little light for much to grow, and too little access to clear what does.

Animals

Use the same L-footer trick as for fences

Attach wire mesh to the bottom of the skirting and run it outward along the ground, just below the surface. Digging animals start right against the barrier and will not step back a foot to go around it.

Leave an access hatch. At some point something will need retrieving, inspecting or repairing under there, and cutting into finished skirting is a miserable job.

Common questions

What is the best thing to put under a deck?

Gravel laid over a permeable landscape fabric is the standard answer for a raised deck. The fabric suppresses weeds growing up, the gravel lets rain drain away rather than pooling, and together they keep the space beneath dry, which is what protects the joists. The one thing not to use is impermeable plastic sheeting, which traps water underneath and creates exactly the damp, airless conditions that rot timber.

Can you put plastic sheeting under a deck?

It is a common suggestion and a poor one for most decks. Plastic stops water draining into the ground, so moisture collects on top of it and sits there, and the soil beneath goes stagnant. That raises humidity in the enclosed space under the deck, which is the opposite of what the timber needs. Where a vapour barrier is genuinely wanted, such as under a very low deck over bare soil in a specific design, it needs to be part of a drainage plan rather than simply laid down.

How do you stop weeds growing under a deck?

Clear the ground first, including perennial roots, then lay a permeable landscape fabric and cover it with gravel. Fabric alone stops weeds coming up from below but will not stop seed blowing in and germinating in debris that accumulates on top, so the gravel layer and occasional clearing of leaf litter matter too. Low decks with very little clearance are the hardest, because there is no light for weeds but also no access to clear them.

Does the space under a deck need ventilation?

Yes, and it is more important than what is on the ground. Air moving under a deck dries the joists after rain, and a deck enclosed tightly with solid skirting holds damp air against the timber. Slatted or louvred skirting, or gaps left deliberately at intervals, allow airflow while still keeping the space tidy and stopping animals nesting. A completely sealed underdeck is a rot problem waiting to happen.

Should you slope the ground under a deck?

Yes, a slight fall away from the house helps considerably, because water that reaches the ground beneath should leave rather than pool. On a deck attached to a building this matters more, since standing water against foundations is its own problem. Grading the ground before laying fabric and gravel is easy at build time and awkward afterwards, so it is worth doing while the structure is still open.

What about animals getting under a deck?

Skirting with a buried mesh apron is the usual answer. Attach wire mesh to the bottom of the skirting and run it outward along the ground just below the surface, in the same L shape used to keep digging animals out from under fences, since animals dig where the barrier meets the ground rather than stepping back. Leave an access hatch somewhere, because at some point something will need retrieving or inspecting under there.

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