Rim Board

Rim board is the engineered member that closes off the perimeter of an I-joist floor system. It caps the ends of the joists, ties the floor together, and carries the load from the walls above straight down to the foundation or wall below. Skip it or substitute the wrong thing, and you’ve broken the load path on an engineered floor.

Here’s the part many buyers get wrong. Rim board is a distinct, purpose-built product. Dimension lumber is not suitable for use as a rim board in BCI floor systems. That’s not a suggestion. The manufacturer’s installation guide says it plainly, more than once. Solid sawn 2x stock shrinks, and it isn’t depth-matched to the joist series, which means uneven bearing and a floor that doesn’t sit right.

Rim board does two structural jobs at once. It transfers wall loads through the floor system, and it laterally braces the joist ends. Dimension lumber is not suitable for use as rim board with BCI joists — the approved options are Boise Cascade Rimboard OSB or a BCI joist used as a rim joist. In Montana, where ground-snow loads run high and every pound of roof and wall load has to find its way to the foundation, a properly depth-matched, fully-nailed rim is what keeps that path intact.

Types and Sizes: OSB Rim vs. LVL Rim

Two families of engineered rim cover most floor systems. OSB rim board and LVL rim board. Both are built to match common I-joist depths so the floor closes off clean at the perimeter.

Western Building Center carries rim board in these configurations:

Item	Thickness	Depth	Length	Type
OSB Rim	1-1/8”	9-1/2”	24’	OSB Rimboard
OSB Rim	1-1/8”	11-7/8”	12’	OSB Rimboard
OSB Rim	1-1/8”	11-7/8”	24’	OSB Rimboard
Versa-Rim	1-1/8”	14”	24’	LVL (Boise Cascade)
Versa-Rim	1-1/8”	16”	24’	LVL (Boise Cascade)

Those depths — 9½”, 11⅞”, 14”, and 16” — are the standard I-joist depths the rim is sized to match. BCI joists come in 9½”, 11⅞”, 14”, and 16” depths, with deeper sizes available, and Versa-Lam LVL is designed to match.

The choice between OSB rim and LVL rim comes down to load and fastener holding. LVL, LSL, and rim board are engineered by bonding wood elements with waterproof adhesives to create stable, uniform members — LSL offers excellent fastener-holding for rim board and tall studs, while LVL provides high strength. For taller floor systems and heavier load transfer, the LVL Versa-Rim earns its keep. For standard residential floors at 9½” and 11⅞”, the OSB rimboard handles the job.

One detail that trips up framers: rim thickness changes how you handle the floor sheathing tongue. Do not install the tongue of floor sheathing flush with 1” thick Boise Cascade Rimboard OSB — the tongue is OK with 1⅛” and thicker Rimboard OSB. The rim board this market carries runs 1⅛”, so the tongue sits fine, but know the rule before you set sheathing.

Installation and Fastening

The rim does nothing for you sitting in a stack. It earns its structural role only when it’s nailed off correctly and braced as the floor goes together.

Nailing schedule first. Rim board is nailed to BCI joists with a 2½” (8d) nail into each flange. Two things the guide is firm about: do not nail closer than 1½” from the edge of the joist, and do not use 16d common nails. And to limit splitting the flange, start nails at least 1½” from the end.

Timing matters as much as the nail count. The rim isn’t an afterthought — it goes in as the floor is set. All rim joists, rim boards, x-bracing, blocking panels and hangers must be completely installed and properly nailed as each BCI joist is set. Don’t allow workers on the joists until all hangers, rim joists, rim boards, blocking panels, x-bracing and temporary strut lines are installed — serious accidents result from insufficient attention to proper bracing during construction.

Storage and Moisture — Don’t Skip This in Montana

Engineered rim board and the I-joist system it works with are dry-use products. Full stop. BCI joists and Versa-Lam LVL shall be installed in dry-use applications only, per their respective ICC-ES/APA ESR evaluation reports. The governing report is ICC-ES/APA ESR-1336.

That makes storage a real issue here. Framing season overlaps with rain and spring snowmelt, and these products can’t take the weather. The requirement is specific: products must be wrapped, covered, and stored off the ground on stickers at all times prior to installation, in an environment free from moisture from any source.

Ignore that and you’re not just risking a swollen, damaged member. You’re voiding the coverage. Failure to correctly store, use, or install these products in accordance with the Boise Cascade EWP Installation Guide will void the limited warranty. The flip side is worth knowing: all Boise Cascade BCI joist, Versa-Lam LVL, and AJS joist products are covered by a limited lifetime warranty for the expected life of the structure. Store it right, and you keep that.

Frequently Asked Questions

Can dimension lumber be used as rim board in an I-joist floor? No. Dimension lumber is not suitable for use as a rim board in BCI floor systems. The approved options are engineered rim board — Boise Cascade Rimboard OSB or a BCI joist used as a rim joist. Solid sawn 2x shrinks and isn’t depth-matched to the joists, which causes uneven bearing.

What depths does rim board come in? Rim board is sized to match standard I-joist depths. Western Building Center carries it in 9½”, 11⅞”, 14”, and 16” depths — the same depths the BCI joist and Versa-Lam LVL lines are built around.

What’s the difference between OSB rim board and LVL rim board? Both are engineered with waterproof adhesives for uniform performance. LSL offers excellent fastener-holding for rim board, while LVL provides high strength. The LVL Versa-Rim handles taller floor systems and heavier load transfer; OSB rimboard covers standard residential depths.

What nails are used to fasten rim board? Nail rim board to the BCI joists with a 2½” (8d) nail into each flange. Do not use 16d common nails, and don’t nail closer than 1½” from the edge of the joist.

Can rim board get rained on before installation? No. These are dry-use products. They must be wrapped, covered, and stored off the ground on stickers at all times prior to installation, in an environment free from moisture. Failing to store and install per the guide voids the limited warranty. In Montana’s wet framing season, keep it covered and off the deck.

Does rim board thickness affect the floor sheathing? Yes. Do not install the tongue of floor sheathing flush with 1” thick Rimboard OSB — the tongue is OK with 1⅛” and thicker Rimboard OSB.