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Gravel and pavers under the deck
Gravel under a deck is groundcover, not an underside assembly. IBHS Base strips vegetation and combustible mulch from under an elevated deck to mineral soil, and allows noncombustible hardscape. Where Oregon R327 is adopted, R327.3.4.4 still wants enclose-to-grade or a protected underside. Gravel is not that menu.
You are under the deck with a rake. Bark, weeds, and a stored cooler sit in the shade. That is fuel, not a finish.
DET-005’s mesh pair lives on the under-deck finding. This page is the ground. Do not use a house-level hub graphic as a gravel spec.
Why it matters
Embers and hot gases lodge under decks. Fuel on the soil lights the joists. Hardscape cuts that fuel. It does not replace Type X, a 1-hour assembly, or walls to grade.
How the jobs split
| Job | What finishes it | What does not |
|---|---|---|
| Ground under the deck (IBHS / CAL FIRE) | Mineral soil or noncombustible hardscape | Bark, rubber mulch, stored stuff |
| Underside (R327.3.4.4) | Enclose to grade or protect | A gravel bed |
| Screen, if used | Vertical plane to grade | Horizontal mesh under boards |
| Five-foot band around the posts | Zone 0 / IBHS 0–5 foot zone from outermost posts | The 200 sq ft lumber exception |
The paths
1. IBHS ground. Bare mineral soil or gravel, pavers, river rock, DG, steppingstones, concrete. Nothing stored. Four feet or less gets 1/8 inch mesh at the outer edge.
2. Oregon underside. Numbered R327.3.4.4 menu. No 12-foot out. See the 12-foot rule.
3. CAL FIRE. Ember-resistant zone under the footprint and five feet out. Hardscape.
What people mix up
- Gravel as a skip of R327.3.4.4.
- Bark “because it is in the shade.”
- Horizontal mesh plus gravel as a complete deck.
How to check
- Look at the soil. Inorganic, or not.
- Look at the joists. Enclosed or protected, or not.
- Look at the side. Vertical screen to grade if you screen.
- Walk five feet from the posts.
Limits
This page does not spec a gravel size. FireApproved is not the AHJ. IBHS is a designation.
Related records
Questions
If I put gravel under the deck, can I skip the underside protection?
No. R327.3.4.4 still wants the underfloor enclosed to grade or the exposed underside protected. Gravel is groundcover. It is not gypsum, a 1-hour assembly, or enclose-to-grade walls.
Is bark mulch OK if it is under the boards?
IBHS Base removes wood and rubber mulch to mineral soil under an elevated deck. Bark mulch also fails the 0–5 foot Zone 0 rule. See the bark-mulch finding.
Do I still mesh the sides if I gravel the ground?
If you screen, close the vertical opening to grade. Horizontal mesh under the boards is the installation mistake. IBHS also encloses decks 4 feet or less with 1/8 inch mesh at the outer edge.