So again, if you just use 50% more members, you'll have 2/3 as much load per member, and 2/3 as much deflection, and the L/240 deflection criterion becomes an L/360 deflection criterion.Īnd the upside of the above reasoning is that it has a chance of convincing a plans examiner without having to hire an engineer. Resources provide a simplified system to determine allowable joist and rafter spans in one- and two-family dwellings, and the companion supplements for tabulating allowable bending and modulus of elasticity design values for visually graded and mechanically graded dimension lumber. Then an added wrinkle is that the 20 psf live, 10 psf dead table doesn't have the correct deflection criterion, it's L/240 instead of L/360 for floor joists. So instead of checking 40 psf live, 20 psf dead, 8" o.c., we check 20 psf live, 10 psf dead, 16" o.c. If we halve the load, and halve the number of members, the load per member is still the same, and the allowable span is the same. Since the table doesn't cover 8" o.c., we need to be a bit more resourceful. The next simple multiple would be 8" o.c., which in practice you'd install as double members at 16" o.c. So you want to check whether a tighter spacing would work. On the table you referenced (the obvious first place to look), none of the 2圆 options work for a 12' span, even at the tightest spacing listed, 12" o.c. Bci® joistsI-joist size & span chart Beautiful laminate countertop with undermount sinkLvl chart lam boise span versa beam beams laminated joist lumber veneer engineered. That is, sister each hacked 2x8 with (2) 2圆 DF #1.Ĭlick to expand.You've missed the point of my post. Span boise lvl laminated beam joists bciBoise cascade tji span chart Tji joist span chart / better yet, with the help of boise cascadeBoise cascade bci span tables. That means instead of 1 member per 24", you need 3 members per 24". So you'll need to double the member count for the loading, and add another 50% to reduce the deflection. Now you have twice the load (40 psf live, 20 psf dead) and need 2/3 of the deflection (L/360) compared to the table parameters. It tells us that (if douglas fir is your preferred species) DF #1 2圆 24"o.c. Start with 2018 IRC table R802.4.1(2), which is a span table (for rafters) for 20 psf live load, 10 psf dead load, and L/240 deflection. With a bit of reasonable extrapolation, you can do this via the span tables. So you should just consider your hacked up 2x8s to be oversized nailers and install new members that will be sufficient for the load and span on their own. In which case you no longer have that grade. For example, if you start with a particular grade which might allow knots of a certain large size as long as they are at least 2" from the edge of the member, and you remove 2" from the bottom of the member, now you may have a large knot right at the bottom edge of the member. Hence I need a table.Īny advice on whether my plan to gain some height in the basement is a bad idea would be greatly appreciated!Ĭlick to expand.If you hack up your 2x8s, it's difficult to assign design values to them, as they will no longer be graded. Or rather than replace the existing joists, I will just sister each of the 2圆 joists to the existing 2x8 joists and trim off the bottom 2 inches of the 2x8's, thus getting at least as good as 2圆 joists at 12"Īccording to the IRC 2018, I can even use 2圆 Douglas fir-larch for this, but I was wondering if the LVL's will be even better (stronger and with less bounce). The reason I want to know thei is because I want to replace the basement ceiling (=kitchen floor) joists, which are 2x8 at 16", with 2圆 LVL joists at 12" so that my basement height will be 7' from finished floor to finished ceiling (after I finish it). SO I assume that Boise Cascade VERSA-LAM 2.0-3100 LVL can do better? Is it true? Using these guidelines will help keep product clean, shed rain, and promote air circulation to dry off any incidental moisture.The IRC 2018 table R502.3.1(2) shows for Douglas fir-larch (the strongest lumber listed), a 2"圆" with 12" spacing can span 11' 4" (!) for dead load = 20psf and live load = 40psf. PWT LVL products should be protected by keeping the products wrapped, off the ground, stacked, and supported appropriately. Moisture content for in service conditions will vary widely. For side or other combined bending and axial loads, see provisions in 2018 NDS. PWT LVL may swell, shrink, and change shape in response to moisture and adverse weather, even with the additional protection of factory applied sealants. For other end fixity conditions, contact Boise Cascade EWP Engineering. When PWT LVL leaves the manufacturing facility, its dimension tolerances are within the manufacturer’s limits and the product moisture content is between 6-10%. This slight deviation in dimensions is called tolerance. Due to the manufacturing processes there may be slight variations between the product and nominal dimensions. PWT Laminated Veneer Lumber (PWT LVL) is produced to specific tolerances based on manufacturing equipment capabilities.
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