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2x8 ceiling joist span - CEILING JOIST SPANS FOR COMMON LUMBER SPECIES (Uninhabitable Attics With Limited Storage, Live Load = 20 pounds per squ

A #2-2×10 joist can span between 11’-5” and 18’-0”, as

In a 2×8 Ceiling Joist, the letter "8" is pretty important. It's the depth of the Ceiling Joist. So, the span of 2×8 can be estimated by a rule of thumb i.e. 1.5 times the depth. So, a 2×8 Ceiling Joist can span a length of 1.5 x 8 equal 12 feet.Depending on various factors, the maximum span for a 2×8 floor joist is 16′ 6”. The maximum span for roof rafters is 23′ 9”. For headers, the maximum span is 11′ 2”. What size should ceiling joists be? Standard Size of Joists Though there is no standard joist size for the ceilings in all buildings, most average homes use ceiling ...The size of the lumber used for floor joists is the single greatest determining factor in terms of how far a joist can span. The joist span tables start with 2×6 lumber and it goes all the way up to 2×12. For example, a 2×6 Southern Pine joist can span 12’. A 2×12 joist of the same species and quality can span nearly 25’. It is used as floor joist, deck beam ceiling joist, pitch roof rafter, flat roof rafter, purlin and Binder. There are different depth of deck beam made of timber are used in floor construction such as 2×6, 2×8, 2×10 and 2×12 etc made of different species of wood (southern yellow pine & Douglas fir) and different grade such as grade – 1 ... The allowable span of ceiling joists that support attics used for limited storage or no storage shall be determined in accordance with Section R802.4. TABLE R502.3.1(1) FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES (Residential sleeping areas, live load = 30 psf, L/Δ = 360) a. JOIST SPACING (inches)The size of the lumber used for floor joists is the single greatest determining factor in terms of how far a joist can span. The joist span tables start with 2×6 lumber and it goes all the way up to 2×12. For example, a 2×6 Southern Pine joist can span 12’. A 2×12 joist of the same species and quality can span nearly 25’.The most common lumber sizes for floor joists are 2x6, 2x8, 2x10, and 2x12. Larger joists can span across wider areas. For example, a 2x6 joist would have a 12-foot, 6-inch maximum span, and a 2x10 joist would have a 21-foot maximum span. Additionally, wood species and grading determines how far apart floor joists can be spaced.The allowable span of ceiling joists that support attics used for limited storage or no storage shall be determined in accordance with Section R802.4. TABLE R502.3.1(1) FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES (Residential sleeping areas, live load = 30 psf, L/Δ = 360) a. JOIST SPACING (inches)According to the International Residential Code 2021 (IRC), the maximum length a 2x6 can span as a floor joist is 12’-6”, as a ceiling joist is 20’-8”, as a rafter is 18’-0”, as a deck board is 24', and as a deck joist is 9’-11”. These values are only possible if the members are made with the SS grade (structural select) Duglous ...Thus 2″×6″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 14 feet when spaced 16 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12. What size ceiling joist for a 15′ The provisions of this section shall control the design of truss roof framing when snow controls for buildings, not greater than 60 feet (18 288 mm) in length perpendicular to the joist, rafter or truss span, not greater than 36 feet (10 973 mm) in width parallel to the joist, rafter or truss span, not more than three stories above grade plane ...... roof and ceiling, but do not support roof joists, roof rafters or roof trusses ... rafter span of 4.9 m and a maximum roof truss span of 9.8 m. Lintel spans ...The maximum span for a 2×6, 2×8, 2×4, 2×10 & 2×12 ceiling joist depending on different size of Lumber, species of wood, grade of wood, spacing between the joist, expected …As an example, this means that a single floor joist with a span of 9’ would have a span of 11’ 2” when doubled. You can even triple the 2×8 floor joists for an even greater span. Ceiling. Ceiling joints have different spans depending on the location. For an uninhibited area with limited storage, the span for ceiling joints will range ...Douglas fir maximum horizontal roof rafter span for Lumber Grade Selected Structural and No. ... 2 x 8, 12, 21' - 7'', 19' - 11'', 18' - 8''. 16, 19' - 7'', 17' - ...Ceiling Joist Span Chart—Attics with Limited Storage Page 4 Allowable ceiling joist spans (R802.4): Spans for ceiling joists shall be in accordance with Tables R802.4(1) and R802.4(2). For other grades and species and for other loading conditions, refer to the AF&PA Span Tables for JoistsMaximum floor joist span for No. 1 and No. 2 Grade of Douglas fir are indicated below. Max. dead load (weight of structure and fixed loads) 10 lbs/ft2 . Live load is weight of furniture, wind, snow and more. 1 psf (lbf/ft2) = 47.88 N/m2.A #2-2×10 joist can span between 11’-5” and 18’-0”, as a rafter between 13’-9” and 21’-7”, and as a beam 3’-6” and 13’-0” or more. The span depends on spacing, lumber species, and grade, and for a beam, the lamination thickness, as well as numerous other factors. In this guide, we’ll identify what span means, how far ... Floor Joist Span. Floor joist span is the distance that a structural member such as a joist can span, from one end to the opposite end. A variety of factors play into joist span, including but not limited to: distance covered, width and thickness of the joist, type of material, and spacing between the joists.But the 2015 IRC included a new one (Table R507.5) that will make it easy for deck builders to spec a joist size for a given span and joist spacing. The table includes spans for common lumber species used for deck framing like southern pine, Douglas fir, hem-fir, redwood, western cedar and other species. The table accounts for wet service ...Span Tables. Use the span tables in the links below to determine the maximum allowable lengths of joists and rafters. These tables provide maximum spans for the #2 grades of four common species of lumber (Southern Pine, Douglas Fir, Hem-fir, and Spruce-pine-fir (SPF). Determine Maximum Joist and Rafter SpansIn general, a 2×8 will span 1.5 x 8, so 12-feet. Based on all factors though, a 2×8 joist span is 7′-1" to 16′-6". There are different factors that affect how far a 2×8 can span, including use or location, species of wood, grade, the spacing between joists or rafters, and load.A 14”, 16”, and 18” deep will all span 30’, but 16” and 18” are typically doubled or tripled for greater loads. 3-1/2” 2.1E 3100 at 7-1/4” deep will span 20’, a 9-1/2” up to 26’, and other depths 30’. A 7” 2.1E 3100 at 24” deep can potentially span up to 60’ depending on load and construction variables, and ...26 հնվ, 2021 թ. ... 2x6 ceiling joists span 24' 12' to center supporting wall, plaster ceiling from 1960's. 2x6 framed rafters 4/12 pitch. Removing a supporting ...But the 2015 IRC included a new one (Table R507.5) that will make it easy for deck builders to spec a joist size for a given span and joist spacing. The table includes spans for common lumber species used for deck framing like southern pine, Douglas fir, hem-fir, redwood, western cedar and other species. The table accounts for wet service ...In these cases, 2-inch by 10-inch lumber is often used for ceiling joists, although trusses may be more practical. Spans for joists greater than 20 feet that are parallel to the rafters require a 12-inch joist spacing when using 2-inch by 10-inch #2 Douglas and hemlock fir or southern pine, or 16-inch spacing when using 2-inch by 10-inch #2 ...2-2x4. 6'-11". 5'-3". 2-2x6. 9'-11". 7'-6". 2-2x8. 12'-10". 9'-8". 2-2x10. 16'-8". 12'-7". 2 ... CEILING JOIST SPANS FOR COMMON LUMBER SPECIES. (Uninhabitable ...One of the contractors commented on the span of the 22' long 2x8 attic ceiling joists, saying they should have been supported by a beam and not these 2x8 blocks that are currently connected in the middle of the 22 foot span. The attic is not going to be used for storage, it will only have blown in insulation.Building Control Subject Ceilings and flat roofs BCG008 · Timber sizes and construction details · MAXIMUM CLEAR SPAN OF CEILING JOISTS IN METRES · MAXIMUM CLEAR ...4. 2×10: With 16-inch spacing, the maximum span is approximately 16-18 feet. There are different depth of ceiling joist are used in floor construction such as 2×4, 2×6, 2×8, 2×10 and 2×12 made of different species of wood (southern yellow pine & Douglas fir) and different grade such as grade – 1, grade – 2, grade – 3.Rafters: Flat ceiling rooms; attached and detached garages 35#LL + 10#DL. L/180. FLOOR JOISTS. 2 x 6. 2 x 8. 2 x 10. 2 x 12. 12”OC 16”OC 24”OC 12”OC 16”OC 24”OC ...*Maximum span based on a specified snow load of 1.5kPa. Ceiling Joists: When rafters are used ceiling joists not less than 2x4 (38x89) are permitted to be assumed to provide intermediate support to reduce rafter spans [OBC 9.23.13.7.]. Maximum span for spruce-pine-fir ceiling joists (SPF No1 or No2)*, (ft) Attic not accessible by a stairwayJoist Span Calculator. Select a load. There are six choices. The lowest is a plain ceiling joist with no storage (10 pounds per square foot). The highest is a fully loaded floor (70 pounds per square foot). Select the on center spacing for the joists. This is how far apart they will be. Most lay outs are on 16″ so the field is pre-selected.2-2x4. 6'-11". 5'-3". 2-2x6. 9'-11". 7'-6". 2-2x8. 12'-10". 9'-8". 2-2x10. 16'-8". 12'-7". 2 ... CEILING JOIST SPANS FOR COMMON LUMBER SPECIES. (Uninhabitable ...5602.3(1) and butted joists shall be tied together in a mann er to r sist such thrust. 5802.4 Allowable Ceiling Joist Spans. Spans for ceiling joists shall be in accordance with 780 CMR Tables 5802.4(1) and 5802.4(2). For other grades a sp e cie s a fo r o the r l oa din g on dit ion s, refer t o the AF&PA Span Tablesfor Joists and Rafters, or ...Allowable span tables are provided to simplify the selection of rafter and ceiling joist size for wood roof framing and cold-formed steel framing. Chapter 8 also provides requirements for the application of ceiling finishes, the proper ventilation of concealed spaces in roofs (for example, enclosed attics and rafter spaces), unvented attic ...Sistering two new 2x10's produces a beam 3" wide, while a new 4x10 is actually 3 1/2" wide. Sistering a new 2x10 to an old one (full 2"), which is what I'm doing in my bathroom, does produce a beam 3 1/2" wide, identical to a modern 4x10. But that's just identical for size. In my case, the sisters are select structural, and the original joists ...Table R502.3.1(1) shall be used to determine the maximum allowable span of floor joists that support sleeping areas and attics that are accessed by means of a fixed stairway in accordance with Section R311.7 provided that the design live load does not exceed 30 pounds per square foot (1.44 kPa) and the design dead load does not exceed 20 pounds per square foot (0.96 kPa). 21 օգս, 2015 թ. ... They are original 2x8, cracking, and sagging upwards of 3-4 inches. Further, the joists above the garage door have been notched to allow for the ...The sizing of the joist refers to the depth and width of the floor joists. The most common spacing for wooden floor joists is 16". According to the 2021 International Residential Code, spacing variations such as 12", 19.2", and 24" are also acceptable. For a particular span, this spacing distance can vary based on the species of lumber, grade ...Depending on various factors, the maximum span for a 2×8 floor joist is 16′ 6”. The maximum span for roof rafters is 23′ 9”. For headers, the maximum span is 11′ 2”. What size should ceiling joists be? Standard Size of Joists Though there is no standard joist size for the ceilings in all buildings, most average homes use ceiling ...Simplified maximum span tables for selected visual and mechanical grades of Southern Pine lumber in sizes 2×4 thru 2×12. Listed are 46 tables based on common loading conditions for floor joists, ceiling joists and rafters. View Joist & Rafter Tables Headers & BeamsJoist span tables - use these tables to determine maximum spans based on the species and grade of lumber, the size of the ceiling joists (2x4, 2x6, etc.), and the spacing of the ceiling joists. The ceiling joist tables below cover the following two design scenarios:Way back then, the wood was milled to 1 5/8" wide to 7 5/8" high. You say there is a wall "mid-way". Therefore, the span is 12'. So, with joists at 16" on center, they will support about 78 lbs. per square foot. (This is based on a No.2 grade Douglas Fir-Larch wood joist. Douglas Fir-Larch lumber is some of the strongest.The size of the lumber used for floor joists is the single greatest determining factor in terms of how far a joist can span. The joist span tables start with 2×6 lumber and it goes all the way up to 2×12. For example, a 2×6 Southern Pine joist can span 12’. A 2×12 joist of the same species and quality can span nearly 25’. Cold-formed steel roof framing constructed in accordance with the provisions of this section shall be limited to sites subjected to a maximum design wind speed of 110 miles per hour (49 m/s), Exposure B or C, and a maximum ground snow load of 70 pounds per square foot (3350 Pa). R804.1.2 In-Line Framing.01 հնս, 2013 թ. ... Rafter spans are tabulated for the most common roof loads. Snow ... 2x6. 2x8. 2x10. 2x12. 2x4 thru. 2x12. 2x4 thru. 2x12. The Southern Pine ...... roof and ceiling, but do not support roof joists, roof rafters or roof trusses ... rafter span of 4.9 m and a maximum roof truss span of 9.8 m. Lintel spans ...16 նոյ, 2020 թ. ... so a 2x8 can span 12 feet. on 16″ centers. not sure about a double one. ask a structural engineer.R502.3.1 Sleeping areas and attic joists.. Table R502.3.1(1) shall be used to determine the maximum allowable span of floor joists that support sleeping areas and attics that are accessed by means of a fixed stairway in accordance with Section R311.7 provided that the design live load does not exceed 30 pounds per square foot (1.44 kPa) and the design dead load does not exceed 20 pounds per ...These span tables assume installation of at least three joists or rafters that are spaced not more than 24" on center. The calculated spans assume fully supported members, properly sheathed and nailed on the top edge of the joist or rafter. Straight-line interpolation shall be permitted for intermediate spans and design values. 2. LUMBER DESIGN ...R802.4 Allowable ceiling joist spans. Spans for ceiling joists shall be in accordance with Tables R802.4(1) and R802.4(2). For other grades and species and for other loading conditions, refer to the AWC STJR. R502.3.1 Sleeping areas and attic joists.. Table R502.3.1(1) shall be used to determine the maximum allowable span of floor joists that support sleeping areas and attics that are accessed by means of a fixed stairway in accordance with Section R311.7 provided that the design live load does not exceed 30 pounds per square foot (1.44 kPa) and the design dead load does not exceed 20 pounds per ... Span Tables. Tables listing Maximum Spans for Southern Pine joists and rafters are detailed below. These 46 tables are based upon design values for visually graded Southern Pine dimension lumber that became effective June 1, 2013. For each application, a PDF download is available. Also see Using These Tables and five Examples showing how to ...Use “a” to determine joist size and “a”+”b” to determine beam a b and footing sizes. The length of “b” is restricted by both the length of “a” and the size of the joists. Example: a=8’, b=2’, Posting Spacing=10’ Refer to the Joist Span table. For an 8’ joist span, either 2x8s at 24” O.C. or 2x6s at 16” O.C. are ...Thus 2″×6″ size of ceiling joist made of #2 spruce – pine- fir can allow span up to 14 feet when spaced 16 inches apart with maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12. What size ceiling joist for a 15′But the 2015 IRC included a new one (Table R507.5) that will make it easy for deck builders to spec a joist size for a given span and joist spacing. The table includes spans for common lumber species used for deck framing like southern pine, Douglas fir, hem-fir, redwood, western cedar and other species. The table accounts for wet service ...2x6 2x8 2x10 2x12 Note: Deflection is limited to the span in inches divided by 240 for live load only. Maximum spans are inside to inside of bearings Lumber Span Tables for Spruce-Pine-Fir South (SPFs)** Ceiling Joists - 20 psf Live Load, 10 psf Dead Load, L/240 Deflection (Limited Attic Storage)a. Span exceeds 26 feet in length. 2012 IRC Table R802.4(1) -Ceiling Joist Spans for Common Lumber Species (Uninhabitable Attics Without Storage, Live Load = 10 psf, L/Δ = 240) Ceiling Joist Spacing 2 x 4 (inches) Species and Grade Dead Load = 5 psf 2 x 6 2 x 8 2 x 10 Maximum Ceiling Joist Spans Feet- Feet- Feet- Feet-19.2 Douglas Fir-LarchD. ROOF RAFTERS @ 16" o.c.. TABLE 1. TABLE 2. REFER TO TABLE 1 FOR SIZES. NUMBER OF. RAFTER SIZE. JOIST SIZE MAX SPAN. COLLAR TIES @ 16" o.c.. NAILS PER.01 հնվ, 2001 թ. ... Use this column when the roof slope is steeper than 3:12. Member. Size. O/C. Spacing. Floor Joists. Ceiling Joists ... 2” x 8”. 12”. 14' 2”. 25' 8 ...How far apart can you span a ceiling joist? (2×4, 2×6, 2×8) May 13, 2023 by Saad Iqbal. If you’re using a 2×4 simple wood ceiling joist, you can span it from 4 to 12 feet. The exact span for a ceiling joist depends on factors like type and grade of lumber, the spacing, the load. Normal spacing of ceiling joist is 16 inches or 24 inches on ...The joists span 17 feet, 6 inches (5334 mm). Find the required joist size using Douglas-Fir Larch #2 lumber and a joist spacing of 16 inches (406 mm). Solution: In Table R502.3.1(2), which is based on LL = 40 psf (1.92 kPa), find 16-inch (406 mm) joist spacing in the left hand column. Locate Douglas Fir-Larch #2 and under DL = 10 psf (0.48 kPa ...Dec 29, 2022 · So, the span of 2×8 can be estimated by a rule of thumb i.e. 1.5 times the depth. So, a 2×8 Ceiling Joist can span a length of 1.5 x 8 equal 12 feet. But in reality, this span can vary between 10’ to 21’ 7” For an uninhibited area with limited storage and it can go upto 14’ 2” to more than 26’ for an inhabited area without storage ... A #2-2×10 joist can span between 11’-5” and 18’-0”, as a rafter between 13’-9” and 21’-7”, and as a beam 3’-6” and 13’-0” or more. The span depends on spacing, lumber species, and grade, and for a beam, the lamination thickness, as well as numerous other factors. In this guide, we’ll identify what span means, how far ...Maximum floor joist span for No. 1 and No. 2 Grade of Douglas fir are indicated below. Max. dead load (weight of structure and fixed loads) 10 lbs/ft2 . Live load is weight of furniture, wind, snow and more. 1 psf (lbf/ft2) = 47.88 N/m2.According to the International Residential Code 2021 (IRC), the maximum length a 2x6 can span as a floor joist is 12’-6”, as a ceiling joist is 20’-8”, as a rafter is 18’-0”, as a deck board is 24', and as a deck joist is 9’-11”. These values are only possible if the members are made with the SS grade (structural select) Duglous ...14 հոկ, 2022 թ. ... Can anyone help me with the maximum span of 3x2's? 2. If I add extra wooden “joist hangars” from the rafters to the ceiling joists, is this ...Simplified maximum span tables for selected visual and mechanical grades of Southern Pine lumber in sizes 2×4 thru 2×12. Listed are 46 tables based on common loading conditions for floor joists, ceiling joists and rafters. View Joist & Rafter Tables Headers & Beamsto the span in inches divided by 360, and is based on live load only. The load duration factor, C D, is 1.0. Listed spans are for wet-service conditions, pressure-treated Southern Pine floor/deck joists, MC > 19%. Check sources of supply for available grades and sizes. Maximum spans were calculated using design values effective June 1, 2013.But the 2015 IRC included a new one (Table R507.5) that will make it easy for deck builders to spec a joist size for a given span and joist spacing. The table includes spans for …The 2x8 plus the 2x6 with No. 1 grade joists will give you about 68 lbs. per square foot (depending on species of wood where you live) for a 16' span and about 56 lbs. per square foot for an 18' span. I'm assuming there is an existing ceiling you don't want to disturb, so be sure to install the new joists "crown" up.What is the maximum span for a 2X8 ceiling joist? But first, generally, how far can a 2×8 span without support? Depending on various factors, the maximum span for a 2×8 floor joist is 16′ 6”. The maximum span for roof rafters is 23′ 9”. For headers, the maximum span is 11′ 2”. How do you make a double 2X8 beam?a. Span exceeds 26 feet in length. 2012 IRC Table R802.4(1) -Ceiling Joist Spans for Common Lumber Species (Uninhabitable Attics Without Storage, Live Load = 10 psf, L/Δ = 240) Ceiling Joist Spacing 2 x 4 (inches) Species and Grade Dead Load = 5 psf 2 x 6 2 x 8 2 x 10 Maximum Ceiling Joist Spans Feet- Feet- Feet- Feet-19.2 Douglas Fir-LarchBridging spans the joist bay by connecting the top of the width of one joist to the bottom of the width of the adjacent joist. Many types of bridging incorporate two per joist bay, creating an “X”. Bridging in older homes often uses a “herringbone” or “X” pattern using wood strips. There is no uniform dimension to wood bridging, as ...to the span in inches divided by 360, and is based on live load only. The load duration factor, C D, is 1.0. Listed spans are for wet-service conditions, pressure-treated Southern Pine floor/deck joists, MC > 19%. Check sources of supply for available grades and sizes. Maximum spans were calculated using design values effective June 1, 2013.Span exceeds 26 ft in length. Check sources for availability of lumber in ... 2x6. 2x8. 2x10. Maximum ceiling joist spans. JOIST. SPACING. (inches). SPECIES AND ...Ceiling Joist Span Chart—Attics with Limited Storage Page 4 Allowable ceiling joist spans (R802.4): Spans for ceiling joists shall be in accordance with Tables R802.4(1) and R802.4(2). For other grades and species and for other loading conditions, refer to the AF&PA Span Tables for JoistsThe allowable ceiling joist span tables in the 2018 version are found in section R802.5. For the purpose of consistency, this post will reference the 2015 IRC. Please be aware of which version of the IRC you are using since the allowable spans can vary.)Step 2 Span Table: Select the appropriate table in Span Tables for Joists and Rafters. The Table of contents indicates that Table F-2 matches these loading conditions. Using Table F-2 (Figure #3), check each lumber size to see if a 16-inch spacing will permit a span of 15 feet 1 inch. How far can a 2×4 ceiling joist span. As per general thumb rules and guideline, a 2×4 ceiling joist made of Spruce- pine-Fir by using grade #2 can span up to 8 feet and 9 inches from beam to beam when spaced the standard 16 inches apart with a maximum ceiling loads are assumed to be 20 PSF and roof pitch is not steeper than 3 in 12.How far can I span a 2x8 floor joist? ... A 2" × 10" floor joist has a span of 20 feet at 12-inches on-center spacing. At 16 inches on-center spacing, the same-size floor joist can only span up to 18 feet. That only applies to floor joists with a wood strength of 1,900,000 pounds per square inch, like that of a select structural grade Douglas ...At $9/board that’s $567 for half the floor, not counting screws and glue.:shock: rcloyd (Russell Cloyd, KY LIC #166164) December 10, 2016, 4:35am 10. It is possible and likely that the 2x8 ‘ceiling joists’ you observed are actually the bottom chords of pre-engineered roof trusses.Nail the strongback to the joist that are flat and add a 2x4 block to tie the vertical 2x6 to the ceiling joist. Then use a jack raise the sagging joist (s) and tie them to the strongback with the 2x4 blocks once …The standard deck joist span can vary due to the size of your de, Depending on various factors, the maximum span for a 2×8 floor joist is 16' 6". , The ceiling joist span is 4.6m and the minimum spacing is 610 mm. There is .., May 2, 2017 · Way back then, the wood was milled to 1 5/8" wide to 7 5/8" h, 3. Joist spans for alternate wood species. The following Table lists maximum joist−span len, Span Options Calculator for Wood Joists and Rafters. Performs calculations for ALL species and grades of commerc, You added below the top of the wall in the comments. So I would lag a rim joist to the studs and use joist hangers. Sp, Learn how to design wood joists and rafters with the latest span t, Thus 2″×6″ size of ceiling joist made of #2 spruce , 5602.3(1) and butted joists shall be tied together in a mann e, Table R502.3.1(1) shall be used to determine the maximum allo, 16 նոյ, 2020 թ. ... so a 2x8 can span 12 feet. on 16″ centers. not su, A 2×8 Douglas fir& larch (DFL) grade #2 ceiling joist can span a m, The allowable span of ceiling joists that support att, (Dead loads are carpet, sub flooring, joists, etc., which is usually, The widest span in the floor joist span table in Part 2 of this t, ... roof and ceiling, but do not support roof jois, The use or location affects how far a 2×8 will span.