Prices below were sourced from National Lumber in Newton, MA. There is no “board price”, meaning that a 24′ 2×10″ board will cost the same per foot as 32′ 2×10″ board. LVL prices are calculated PER foot PER size. The calculator will automatically switch your board from PINE to LVL when you exceed 20 feet long threshold on rafter length. If you need longer LVL, they can be custom ordered. LVLs come in 24′, 28′, 30′ and 32′ standard lengths. LVL is VERY expensive, but solves the limitation of 20 feet, in a common pine board. If you need rafters that are 20′ 1″ or longer, you will need an LVL (Laminated Veneer Lumber) engineered rafter board, which is this yellow color plywood-like board made for structural purposes. Rafters LONGER than 20 feet: Home improvement stores DO NOT sell pine boards longer than 20 feet. Lumber size/ width (2×8″, 2×10″ or 2×12″ boards) will be used to estimate cost of each rafter, as well as total cost (excluding local sales tax). Rafter spacing (and roof length) will be used to determine quantity of rafters needed for your project. If your roof pitch is in degrees, use our roof pitch calculator to convert degrees to “pitch” value. Example: If your roof rises 5″ for every 12″ of run, enter 5 as roof pitch. Enter desired overhang length – this will affect your rafter length and lumber needed for the job.ģ) Enter roof pitch / slope: Roof pitch is the value of roof rise over roof run, using 12 as the base for roof run. Width or Span is the gable side of the roof, which is used in calculating rafter length and cost.Ģ) Enter overhang length: Most houses have overhangs (soffits) which are needed to protect the house exterior walls and foundation from water run-off from the roof. Use the diagram on the right to correctly enter your roof dimensions – this will help you calculate board length more accurately.ġ) Enter house footprint: Length is the roof eave ( gutter) side. Standing Seam Materials & Cost Calculator.Eventually someone will cut the ties, leave them out, nail them improperly, etc. Honestly if this was a real design my advice is always keep it simple and design those rafters to bear all the weight by themselves. But with unbalanced loads I suspect the heavier side will transfer some load to the lessor loaded side. If your loading on each side of the roof is balanced than it will be in either compression or tension. As far as the collar tie a lot depends on the loading. Never mind sorry I see that your wrote that it is a steel ridge beam so I assume it is structural. A frame trusses simply do not have enough stiffness. And I suspect it happens a lot more than people think. I can think of at least four instances where I have seen this. I've seen far too many A-framed rafters or trusses thrust the tops of exterior walls outward. If the ridge beam is not supported than you need to have continuous ceiling joists. I'd like to reiterate what another poster stated already. RE: Roof Rafters Question 1503-44 (Petroleum) 14 Jun 21 21:28 A birdsmouth at the top is not a good idea as it will greatly reduce the shear capacity of your rafter. I would add triangles (beveled plate) below the rafters at the steel beam as noted on your sketch. So, your rafter span would be the horizontal distance from the wall to the steel ridge beam. Also, as noted above, the rafter span is typically taken as the horizontal projection of the rafter. Your detail shows a steel ridge beam, so I would assume that beam is sized to carry the vertical loads at the peak and rafter thrust is not an issue for you (therefore no rafter tie or ceiling joist is needed). A collar tie is not required if other means are used to prevent separation due to uplift (like a ridge strap). It is not for dealing with rafter thrust, that is a rafter tie or ceiling joist, which is required to be in the lower 1/3 of the rafter (again per the IRC). In general (and using the definitions used by the IRC), a collar tie is placed in the upper 1/3 of the rafters and is there to prevent issues with separation due to uplift as noted above. There have been multiple posts on the subject of collar ties (and the differences in verbiage in different parts of the world).
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