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How Far Apart Are Roof Trusses

The Spacing Of Trusses For Metal Roof

Spacing Roof Rafters for Plywood

Traditionally, roof trusses are made of timber or wood. It has been done for centuries. Woods are considered the strongest, most resilient materials to hold up the structure of the roof. However, as technology starts to get advanced, metal roof trusses become a thing. Metal is, surely, even stronger than wood.

Down below is the information for spacing for roof trusses.

Can You Change Roof Trusses

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Can you modify roof trusses?

You can modify the trusses, but its an enormous amount of work. If you feel youll be sliding new larger common rafters up inside the attic alongside the existing trusses, youre dreaming. Youll have shingle nails in your way that extend through the roof sheathing.

Can you convert trusses rafters?ConvertingTrussTrusstruss rafterstrusses

Sizing Roof Rafters Example 2

Now lets try another example, but this time a span will be given and you must select the correct size lumber to be used given the following scenario:

Question: When the ceiling is not attached to the rafters and where Hem-fir #3 roof rafters are to be spaced 12 inches on center supporting a snow load of 30 psf and a dead load of 20 psf, what is the minimum allowable rafter size when required to span 14-0 in length?

First step, lets collect all the given information within the question:

  • Ceiling not attached to rafters and a snow load of 30 psf: Use Table R802.4.1
  • Roof Rafter Spacing: 12 inches
  • Species and Grade: Hem-fir #3
  • Roof Rafter Span: 14-0

Now lets find the minimum allowable rafter size given the above scenario:

Therefore given the above example, the minimum allowable rafter size for Hem-fir #3 lumber spanning 14-0 is a 2×10 since it can span 14-5. A 2×8 member for example cannot be used since it can only span 11-9.

To Learn more about the design and construction of wood roof framing, be sure to check out Section R802 of the 2018 International Residential Code .

Fun Tip: To learn how to easily size ceiling joists, be sure to check out this POST.

Hopefully given the above examples you can find it easier to size wood roof rafters per the Tables within the International Residential Code.

In conclusion, lets take a quick second to answer some common frequently asked questions related to roof rafters.

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Roof Rafter Span Tables

As mentioned above, the span tables within the code list the allowable roof rafter spans for common lumber sizes based on what design load scenario is applied.

According to Section R802.4.1, roof rafters are to be sized based on Tables R802.4.1 through R802.4.1. It is very important to select the correct table.

Now in order to select the correct table, we must understand 2 things: Which Live Load is to be use and whether or not the ceiling joists are attached to the roof rafters.

We touched on the loads earlier but let us go over why it is important to know if the ceiling joists are attached to the roof rafters or not.

According to Section R802.5.2 each roof rafter must be tied across the structure via ceiling joists or rafter ties. When the ceiling joists are attached, they act as the tie. When they run in the opposite direction creating a scenario where they are not attached to the rafters, then rafter ties can be used to achieve the tie requirement.

This connection is important because it resists the horizontal thrust from gravity loads and rafter thrust caused by the uplift from wind loads.

Using either a rafter tie or the ceiling joists themselves can vary slightly in the size of the roof rafter used which is why the code creates two types of span tables. One for when ceiling joists are used as the ties and one when they are not used, thus requiring the rafter ties.

Now lets go over what information is found on the tables.

  • Roof Rafter Spacing in inches
  • Sizing Roof Rafters Example 1

    Roof Truss Spacing: How Far Apart Should Trusses Be?

    Question: Where the ceiling is attached to the rafters, what is the maximum allowable span of a 2×6 Douglas fir-larch #2 roof rafter spaced 12 inches on center supporting a roof live load of 20 psf and a dead load of 10 psf?

    First step, lets collect all the given information within the question:

    • Ceiling attached to rafters and a live load of 20 psf: Use Table R802.4.1
    • Roof Rafter Spacing: 12 inches
    • Species and Grade: Douglas fir-larch #2
    • Dead load: 10 psf
    • Lumber Size used: 2×6

    Now lets find the maximum allowable span for a 2×6 member given the above scenario:

    Therefore given the above example, the maximum allowable span for a 2×6 member is 15-6.

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    Roof Shapes Suitable For The Truss

    Trusses are suitable for a number of roof shapes

    Roof type

    Two categories of loads on trusses can be distinguished: deadload and life load.

    Dead load

    Dead loads for roof structures are basically the own weight ofthe materials used. These forces act vertically.

    own weight of truss:

    · for timbertypically 0.25 kN/m2

    · for steel: use thefollowing formula:

    where L = span inmetre

    typical weight of steel truss: 0.10kN/m2

    weight of purlins / battens

    · for timber trusseswith battens: negligible · for steel trusses with steelpurlins: 0.09 kN/m2

    weight of roof cover

    0.27 kN/m2 for MCR tiles

    0.12 kN/m2 for steel roofing

    0.47 kN/m2 for clay tiles

    weight of under-roof, timber 24 mm thick, 0.14kN/m2

    Note: Dead load per horizontal surface area of roof covermaterials increases with the slope of the roof: multiply with 1/cosa where a is the roofpitch or slope. For a typical slope of 30°, the increase in load perhorizontal surface area is 15% hence, an MCR roof would weigh 0.31kN/m2 of area covered.

    Life load

    Wind load: the magnitude of the wind load depends on theroof shape, wind direction and location of the building . Forlightweight roof structures and cover materials, the wind load is the mostimportant load. Wind can also create suction forces and whole roof sections canbe blown off. Appropriate fasteners and holding down bolts or anchors must beused .

    Snow load

    Wind loads increase with the elevation above ground level andthe degree of exposure . Thefollowing assumptions have been used:

    Post Frame Roofs In Severe Weather Conditions

    Many post frame or pole barn construction use 8-foot spacing between trusses. Since the weather is a critical factor, how well do these hold up in the severest of weather conditions?

    Investigators have found that post frame structures fare surprisingly well in the tornado-prone areas of the Central United States. The design allows the buildings to minimize damage caused by the deadly forces of these storms. The deeply embedded vertical posts when sunk to a level of at least four feet and on concrete piers provide a substantial grounding that holds the structure in place. Traditional stick-built structures attach to a foundation at ground level and are vulnerable to ripping loose. Thus resulting in destruction due to the shear point above grade level.

    The trusses of post frame buildings are firmly attached to those deeply embedded vertical columns with rather than traditional roof structures that are connected with light steel connectors.

    When high winds strike a properly built post frame structure, the forces redirect downward and evenly into the ground beneath. Thereby minimizing the potential for total destruction.

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    Wind Force Against The Roof

    When designing your roof, you should also consider the wind pressure exerted on it daily, especially if you reside in a hurricane-prone area or a region with strong winds.

    The wind force against the roof will influence whether youll need a typical roof truss spacing or something more powerful and well-reinforced to resist strong winds.

    If your local area experiences a lot of winds, consider adding smaller spacing between the roof trusses. That will make the roof more robust.

    How To Calculate Truss Spacing And Cost

    Framing A Roof With I-Joists Pt. 2 (Framing and Sheathing a BCI Roof)

    Calculating your truss spacing is an exercise in economics. When it comes time to plan your building, contact your building supply store to get quotes for your truss: slope, span, and spacing. Ask for a quote for trusses at 16 and 24 on center. Once you get that, you can do some math.

    Before we do some math, keep in mind that youll always need one extra truss than youve calculated to account for the very first truss that will sit on your sidewall and serve as the first truss.

    Lets say the supplier will sell you trusses spaced at 24 on center for $4 a linear foot. If your trusses are 30 long, you will simply multiply 30×4, which is $120 per unit. If you have a 40 long house, then youll need 20 trusses plus one more for 21 total. 21×120 is $2520 for your trusses.

    Now, lets say the supplier will sell you trusses for 16 inches spacing at 3.75 per linear foot. First, well multiply 3.50×30, which is $105 per truss. Now well need more trusses for this spacing, so 40×12 is 480. Divide that by 16 and you get 30 trusses, plus one more. Now, well multiply our price per unit, $105×31 which is $3255.

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    How Far Apart Should 2×6 Rafters Be


    Max. Live Load 20 lbs/ft2

    Maximum Span
    Rafter Spacing, Center to Center Lumber Grade
    24 13′

    Subsequently, question is, how far should roof joists be apart? A roof joist is always spaced no more than 16-inches apart from another roof joist. If the roof is not completely square, you can decrease the space between joists but never increase the space. In other words, you would space a roof joist 15-inches apart from another roof joist but never 17-inches apart.

    Furthermore, what is the standard spacing for roof trusses?

    These standards are as follows: typical roof truss spacing means that they are usually about 24 inches from centre which means at the centre of one truss, there will be a two-foot gap, or twenty-four-inch gap, until the centre of the next truss.

    How far can a 2×6 Rafter span without support?

    The table states that 2 X 6 rafters spaced 16 inches on center can span a maximum distance of 13 feet 5 inches. Another option are 2 X 8 rafters spaced 24 inches o.c.

    Building A Roof For A Large Shed

    Building a roof for a large shed

    Building a roof for a large shed is a straight forward job, especially if you plans everything from the very beginning. If you want to get the job done quickly or you dont have a large expertise in the field, we recommend you to build a gable roof for your storage construction.

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    How Do You Calculate Roof Trusses

    How do you calculate trusses?

    How much weight can roof trusses support?

    What is the difference between a truss and a joist?

    Is it safe to hang punching bag in garage?

    Can you span 12 feet with a 2×6?

    How much weight can a 2×6 Rafter support?

    How far can you cantilever a 2×6 roof?

    Are two 2×4 as strong as a 2×8?

    Are two 2×4 stronger than one 4×4?

    Can a 2×6 span 14 feet?

    How far can a 2×6 Rafter span?

    How far can a 2×6 span for a metal roof?

    What is stronger 4×4 or 2×6?

    Why is a truss better than a beam?

    What is the weakest bridge?

    What truss design holds the most weight?

    Can you turn rafters into trusses?

    Are ceiling joists load bearing?

    Can you modify roof trusses?

    How do you support roof trusses?

    What wood is used for roof trusses?

    What materials are typically used to build roof trusses?

    How is purlin spacing calculated?

    Which is stronger Z purlin or C purlin?

    What is the difference between purlin and rafter?

    roof trussesspacingtrussesbetweentrussesspacing

    What is the standard spacing for roof trusses?

    How far apart should roof joists be?

    Roof Truss Spacing: How Far Apart Should Trusses Be

    How Far Apart Do I Set Rafters for a Tin Roof?

    I was doing some work in my attic last year and crawling around between the trusses. As I moved between them, I noticed that they seemed further apart than other framing members in my house. I wondered if roof truss spacing was different and if so, I wanted to know how far apart trusses should be?

    Roof trusses should be 24 apart, on center. Trusses are allowed to be closer together, at either 12 or 16 on center, but building codes allow for 24 on center spacing without using heavier duty fasteners for truss to wall connections. If you live in a hurricane-prone area, you might consider moving your trusses to 16 on center.

    Trusses are engineered to the specifications of each specific house. That means the style and size of wood on a truss varies from house to house. In this article, well go over the reasons for spacing your roof trusses 24.

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    Truss Spacing For Shingled Roofs

    Roof truss spacing seems to be a topic with no consensus. Most Americans live in traditional stick framed houses, apartments or condominiums, where roof trusses are most typically spaced every two feet.

    Reader CHARLIE writes:

    Dear Hansen Pole Buildings, May I ask how far apart was the Truss placement in your Re-roofing with Shingles article?

    Im considering a 24x 36 pole barn for a recording studio build but would need asphalt shingle type roof. Im concerned that a suitable design would need additional rafters to meet the 7 lb/sq ft load requirement.

    Most designs I have seen are showing the trusses 4 OC.

    Respectfully, Charlie

    Mike the Pole Barn Guru writes:In this particular article roof trusses were actually spaced with a pair every 12 feet directly aligned with sidewall columns. This style of post frame construction affords several advantages:

    In order to be within spanning capabilities of common sheathing, dimensional lumber roof purlins, on edge, were joist hung between truss pairs, every two feet.

    When you order a post frame kit from Hansen Pole Buildings with asphalt shingles, we automatically have our engineers design for this added load, as well as reducing deflection criteria so you end up with a nice, smooth roof. We also take into consideration Building Code requirements to account for a future overlaid reroof .

    How Far Apart Are Trusses In A House


    . Keeping this in view, how much space should be between trusses?

    Standard roof Truss SpacingThese standards are as follows: typical roof truss spacing means that they are usually about 24 inches from centre which means at the centre of one truss, there will be a two-foot gap, or twenty-four-inch gap, until the centre of the next truss.

    Additionally, how far apart should rafters be? Builders do, however, tend to space rafters in one of several industry-standard increments, typically either 12, 16 or 24 inches apart. These spacing intervals are measured “on center,” meaning that the measurement is taken from the center of one rafter’s horizontal surface to the center of the next rafter.

    Similarly one may ask, how far apart can metal trusses be?

    The bay is the space within the truss and the longitudinal joining members are purlins. A 10′, 8′, 6′ and 4′ spacing between trusses has been the standard for most types of construction for years.

    How far can trusses span without support?

    Trusses can easily span 10-15 metres or more without the need for internal supports.

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    When To Use A Roof Truss

    Roof trusses are characterised by an economic use ofconstruction materials . Composed of individual lightweightpieces, a truss can also provide considerable advantage in transport andassembly as compared to conventional roof structures. On the other hand, trussesare more labour-intensive and require connection devices. However, if a greaternumber of identical trusses can be manufactured, then considerableeconomies of scale can be achieved.

    The structural height of a truss is usually larger than theheight of similar structures using solid beams. For roofs, however, this isusually no disadvantage as roofs must often – depending on roof cover materialused – be higher at the ridge and lower at the eaves to facilitate roof drainageand ensure water tightness.

    Competitors of the Truss

    While the use of steel for roof structures almost invariablycalls for a truss, it is with timber structures where the truss has strongcompetitors. These are the purlin and the rafter roofs.

    The purlin roof

    The purlin roof consists of both rafters and purlins. The ridgepurlin is supported by posts. The rafters act as simple supported beams betweenthe purlins, either with or without cantilever.


    The rafter roof


    The following table presents the main features, and the pros andcons of the three basic design options for roof structures. It can assistdesigners in selecting the most appropriate roof structure for a specificapplication.

    Note, large hangars and halls are not considered.


    What Is The Run Of A Rafter

    Long Span Trusses

    The length of the rafter is given from the long point of the ridge cut at the top down along the top edge the board to the same plumb cut on the rafters notch. The next result is the run. This is the horizontal measurement from the outside of the wall to the inside of the ridge.

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    What Is Span Length

    The span length is the measure taken from the inside of the shed framing to the interior apex of the rafter. Another way to look at it is from the beginning of the birdsmouth cut to the opposite, interior facing edge.

    Understanding this is key to knowing how far your rafters can span. For instance, 2×4 SPF shed rafters can span up to 11 when placed at 12 O.C. If you have a gable roof on your shed, youll have two sets of rafters, with a ridge beam in the center uniting the rafters on each side.

    Therefore, for gable roofed sheds, the rafter span table is indicating how far a rafter can span half of your sheds width.

    If you have a single sloped roof, then the 11 span distance for 2×4 rafters O.C. means that your shed should be no wider or longer depending on how you orientate your single sloped roof than 11.


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