Under 2021 IRC Section R317.1, naturally durable or preservative-treated wood is required in nine listed locations, and Section R317.1.2 requires ground contact use wherever wood touches the ground or is embedded in concrete that does. Cuts and drilled holes must be field treated, and fasteners must resist corrosion.
Ground contact lumber is pressure-preservative-treated wood whose quality mark says it was treated for use in contact with soil or concrete in contact with soil. The end use is one of the items on the tag (Section R317.2.1). The code edition your jurisdiction has adopted, plus local amendments, governs, and this page is a preliminary reference.
Key facts
- 2021 IRC Section R317.1 requires naturally durable wood or wood preservative-treated to AWPA U1 in nine locations, from crawl space framing to wood columns on basement slabs.
- Wood framing members resting directly on concrete or masonry exterior foundation walls less than 8 inches from exposed ground must be durable or treated (R317.1, item 2).
- 2021 IRC Section R317.1.2 requires approved ground contact treated wood for any wood in contact with the ground or embedded in concrete in direct contact with the ground.
- Field-cut ends, notches and drilled holes in treated wood must be treated in the field under AWPA M4 (2021 IRC Section R317.1.1).
- Fasteners and nuts and washers for treated wood must be hot-dipped zinc-coated galvanized steel, stainless steel, silicon bronze or copper (2021 IRC Section R317.3.1).
- Each treated piece must carry the quality mark of an approved inspection agency showing seven items, including end use (2021 IRC Section R317.2.1).
When do you have to use pressure treated lumber?
You must use naturally durable or preservative-treated wood wherever one of the nine R317.1 conditions applies. Item 8 has a regional climate exception for sawn lumber.
2021 IRC Section R317.1: locations where decay protection by naturally durable or preservative-treated wood is required.
| Item | Location | Distance or condition |
|---|---|---|
| 1 | Crawl spaces or unexcavated areas inside the foundation periphery | Joists or bottom of a wood structural floor closer than 18 inches to exposed ground; girders closer than 12 inches; columns closer than 8 inches |
| 2 | Framing members, including columns, resting directly on concrete or masonry exterior foundation walls | Less than 8 inches from exposed ground |
| 3 | Sills and sleepers on a concrete or masonry slab in direct contact with the ground | Unless separated from the slab by an impervious moisture barrier |
| 4 | Ends of wood girders entering exterior masonry or concrete walls | Clearances of less than 1/2 inch on tops, sides and ends |
| 5 | Exterior wood siding, sheathing and wall framing | Less than 6 inches from the ground, or less than 2 inches vertically from concrete steps, porch slabs, patio slabs and similar surfaces exposed to the weather |
| 6 | Wood members supporting moisture-permeable floors or roofs exposed to the weather, such as concrete or masonry slabs | Unless separated by an impervious moisture barrier |
| 7 | Wood furring strips or framing attached directly to the interior of exterior masonry or concrete walls below grade | Unless an approved vapor retarder is applied between wall and wood |
| 8 | Structural supports of buildings, balconies, porches or similar appurtenances exposed to the weather | Where there is no roof, eave, overhang or covering that prevents moisture accumulation on the surface or at joints |
| 9 | Wood columns in contact with basement floor slabs | Unless on concrete piers or metal pedestals projecting at least 1 inch above the floor and separated from the pier by an impervious moisture barrier |
The sill-specific items are worked through in the sill plate guide. Items 1 and 4 come up in pier and beam foundations, where girders and floor framing sit close to the soil, and item 9 applies to a lally column base on a basement slab.
What is ground contact lumber, and when is it required?
Ground contact lumber is required when wood touches the soil or is embedded in concrete that touches the soil. Section R317.1.2 says all such wood shall be approved pressure-preservative-treated wood suitable for ground contact use.
The rule has three triggers:
- Wood in contact with the ground.
- Wood embedded in concrete in direct contact with the ground.
- Wood embedded in concrete exposed to the weather that supports permanent structures intended for human occupancy.
One exception: untreated wood used entirely below groundwater level, or continuously submerged in fresh water, does not need pressure treatment.
R317.1 and R317.1.2 are separate tests: the first asks whether wood is close to ground or moisture, the second whether it is actually in the ground or in concrete that is. A post set into a footing hole falls under R317.1.2. A sill resting on top of a dry foundation wall falls under R317.1 and is not normally in ground contact.
Can you use pressure treated lumber on concrete?
Yes, and in several cases you must. Wood resting on concrete is covered by R317.1 items 2, 3, 6 and 9, depending on where the concrete is.
- On an exterior foundation wall, less than 8 inches from exposed ground: item 2 requires durable or treated wood.
- On a slab in contact with the ground: item 3 requires it for sills and sleepers, unless an impervious moisture barrier separates the wood from the slab.
- Under a weather-exposed slab or roof deck: item 6 requires it for the supporting members unless a barrier separates them.
- Embedded in concrete: if that concrete is in direct contact with the ground, R317.1.2 requires ground contact use.
Treatment categories and retention values are not given in the IRC sections used here, so take them from the tag and the building official. For a slab-on-grade house, see the monolithic slab guide.
Do you need to treat cut ends and drilled holes?
Yes. Section R317.1.1 requires field-cut ends, notches and drilled holes of preservative-treated wood to be treated in the field in accordance with AWPA M4. Section R507.2.1 repeats the rule for decks. Anchor bolt holes through a treated sill, cut joist ends and notches for hardware all count.
What must the pressure treated lumber tag show?
Treated lumber and plywood must carry the quality mark of an approved inspection agency under Section R317.2. Section R317.2.1 lists what the mark must contain.
2021 IRC Section R317.2.1: required information on the quality mark.
| Item | Information |
|---|---|
| 1 | Identification of the treating plant |
| 2 | Type of preservative |
| 3 | The minimum preservative retention |
| 4 | End use for which the product was treated |
| 5 | Standard to which the product was treated |
| 6 | Identity of the approved inspection agency |
| 7 | The designation "Dry," if applicable |
Item 4 is how you confirm a piece is suitable for ground contact. For decks, Section R507.2.1 adds that all preservative-treated wood products in contact with the ground shall be labeled for such usage.
An exception allows small pieces to be marked differently: lumber less than 1 inch nominal thickness, lumber smaller than nominal 1 inch by 5 inches or 2 inches by 4 inches, or lumber 36 inches or less in length. These are marked by stamping the faces of exterior pieces or by end labeling at least 25 percent of the pieces in a bundled unit.
What fasteners can you use with pressure treated lumber?
Fasteners, nuts, washers and connectors in contact with preservative-treated wood must resist corrosion. Section R317.3.1 says fasteners, including nuts and washers, shall be hot-dipped zinc-coated galvanized steel, stainless steel, silicon bronze or copper, and staples shall be stainless steel. Connectors follow the connector manufacturer's recommendations, and without them need at least ASTM A653 type G185 zinc-coated galvanized steel or equivalent.
Exceptions to R317.3.1:
- Steel bolts of 1/2-inch diameter or greater.
- Fasteners other than nails, staples and timber rivets may be mechanically deposited zinc-coated steel, ASTM B695 Class 55 minimum.
- Plain carbon steel fasteners in SBX/DOT and zinc borate preservative-treated wood in an interior, dry environment.
Deck fasteners and connectors
Section R507.2.3 sends deck fasteners to Section R317.3 and Table R507.2.3.
2021 IRC Table R507.2.3: fastener and connector specifications for decks.
| Item | Minimum finish or coating | Alternate |
|---|---|---|
| Nails and glulam rivets | Hot-dipped galvanized per ASTM A153, Class D for 3/8-inch diameter and less | Stainless steel, silicon bronze or copper |
| Bolts, lag screws, nuts and washers | Hot-dipped galvanized per ASTM A153, Class C (Class D for 3/8-inch diameter and less), or mechanically galvanized per ASTM B695, Class 55, or 410 stainless steel | Stainless steel, silicon bronze or copper |
| Metal connectors | ASTM A653 type G185 zinc-coated galvanized steel, or post hot-dipped galvanized per ASTM A123 with a minimum average coating weight of 2.0 oz./ft2 (total both sides) | Stainless steel |
Footnote b to the table requires stainless steel for fasteners and connectors exposed to salt water or located within 300 feet of a salt water shoreline.
What lumber does the IRC require for decks?
Deck wood must be No. 2 grade or better, and either preservative-treated in accordance with Section R317 or approved naturally durable lumber (Section R507.2.1). Termite protection is added where Section R318 requires it, and engineered wood products follow Section R502.
Joist sizes and spacing are in the deck joist span and spacing guide, and the drawing side is in the deck framing plan guide.
Is termite protection the same as decay protection?
No, but they overlap. Section R318 applies in areas subject to termite damage as indicated by Table R301.2. Section R318.1 allows one or a combination of six methods:
- Chemical termiticide treatment (R318.2).
- A termite-baiting system installed and maintained per its label.
- Pressure-preservative-treated wood in accordance with Section R317.1.
- Naturally durable termite-resistant wood.
- Physical barriers (R318.3) used in the locations specified in Section R317.1.
- Cold-formed steel framing.
So treated wood is one way to meet R318, not the only way. Where it is the chosen method, the quality mark (R318.1.1) and field retreatment (R318.1.2) rules match those in R317.
Summary
The 2021 IRC requires naturally durable or preservative-treated wood in the nine R317.1 locations, and ground contact rated wood where timber touches soil or is embedded in concrete that does (R317.1.2). Cuts and holes get field treatment, the tag must show the end use, and fasteners must be hot-dipped galvanized, stainless steel, silicon bronze or copper unless an exception applies. Adopted amendments and the product's own tag take priority over any summary.
Framing Plan is a preliminary drawing aid that draws joist layouts, beams and openings and exports PNG, PDF and DXF. It does not check treatment requirements, and the editor works in millimeters. Note the treatment and fastener callouts on your drawing, then open the framing studio to lay out the framing for your designer or plan reviewer.