Building Guidelines | Floors | Joists (2023)


Introduction & Regulations

I.S. EN 1995-1 2005: Design of timber structures – Part 1 or simply Eurocode 5 outlines guidelines that should be followed when designing timber structures and elements. A series of harmonised structural design codes for building and civil engineering exists across the European Union, I.S. EN 1995 being just one. In Ireland, Eurocodes are published and made available by the National Standards Authority of Ireland (NSAI).

With the introduction of I.S. EN 1995, all conflicting national standards have been withdrawn. The NSAI are currently revising Irish Standard I.S. 444: The use of structural timber in buildings. The span table for floor joist spans referred to in this section and other guidance are reproduced from findings of the NSAI Timber Standards Consultative Committee and reflect the requirements set out in Eurocode 5 and the Irish National Annex. NSAI have available a full set of span tables.

Species Of Timber

In Ireland, softwood timber is used as structural timber in domestic builds. The typical species, which are sourced either domestically or from overseas, include spruce, fir, pine, redwood, whitewood, and larch. In order to aid users in identifying timber, a system was created in which the species and source code as well as other information about the timber is stamped onto the timber.

Examples of abbreviations include:

  • WE/SG1 = Western European (including Britain) Sitka/Norway spruce, pine and Douglas fir – Species group 1. Source – Ireland

  • WE/SG2 = Larch, Scotch Pine – Species group 2. Source – Ireland

  • EW = Whitewood – Source North and North Eastern Europe (includes Scandinavian countries and Russia).

  • ER = Redwood – Source North and North Eastern Europe (includes Scandinavian countries and Russia).

  • EW/ER = Whitewood and redwood combined – Source North and North Eastern Europe (includes Scandinavian countries and Russia).

Timber Strength Classes/Grades

When dividing timber into strength classes, an abbreviated strength class divided in ascending order based on both the species and the grade of the timber is used, i.e. C14, C16, C18, C22, C24, C27. Two examples of strength grades are GS and SS, where GS stands for general structural grade and SS stands for special structural grade. Both are visually graded.

Identification markings that indicate the strength class and strength grade of timber should be stamped onto the timber in order to comply with the requirements of I.S. EN 1995.

Identification Marking Stamps

The following material is required by I.S. EN 1995:

  • Strength class

  • Species/Species combination of timber

  • Strength grade

  • Reference to the timber standard to which the timber was graded

Examples Of Grading Stamps

Examples of markings that are compliant with I.S. 14801-1 are:

  • A waterproof inkpad should be used for stamp.

  • The minimum stamp size is 25 mm x 140 mm.

  • All stamps to have heavy duty facings and handles are to be heavy duty.

  • The reg. no, field is the company’s NSAI registration/grader’s number.

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Moisture Content

The moisture content of timber should not exceed 20% at the time of construction and while in service. Individual moisture contents are allowed to be up to 24% at the time of construction but the average should be less than 20%. If the area of the timber is being used has high moisture content, this should be accounted for in the design.

Joist Span

Building Guidelines | Floors | Joists (1)

Table C13 - Joist span table - Domestic


External walls supporting floor joists provides further detail with respect to bearing and joist hanger type


Using the table provided above it can be determined which is the most appropriate and cost effect section to be used. For example assume the floor in question has a span of 4.5m. From the table above we can see that a joist 47mm x 225m of strength class C18 fixed at 400mm centres is permitted to have a span of 4.55m and is therefore suitable for use. A C18 joist of 44mm x 225mm fixed at 350mm centres ie permitted to span 4.62m and would also be suitable.

It should be noted that all spans in excess of 2.7m require bridging to be provided at 1.35m centres. using the table above the most cost effective section can be selected based on the required span.

Joining Floor Joists To External Walls

Walls and floors are tied to aid stability to external walls. Recommendations for strapping to be used are outlined in Technical Guidance Document A of the building regulations. Galvanised or austenitic stainless steel straps 30 mm x 5 mm in cross section should be used when strapping floor joists to external walls.

Strapping should be carried over at least 2 joists, with bridging directly underneath, secured with at least 4 fixings with at least one of the 4 in the second joist. Build the strapping at 2 m centres into the external wall as the courses are built; include packing between joists and wall.

External Walls Supporting Floor Joists

If floor joists are supported by external walls, straps are not required in the longitudinal direction of joists in houses containing not more than two storeys where the joists are at centres of not more than 800mm and;

  • Have at least 90mm bearing on the supported walls or a 75mm bearing on timber wall plate at each end.


  • Joists are carried by joist hangers as outlined in I.S. EN 845-1:2013 + A1: 2016 Specification for ancillary components for masonry – Part 1: Ties, tension straps, hangers and brackets.

Joists should be notched for straps to ensure a level finish for flooring.

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Diagram C123 - Typical strapping detail of floor joists to cavity wall

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Diagram C124 - Typical strapping detail of floor joists to hollow blocks

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Diagram C125 - Alternative strapping detail of floor joists to hollow blocks

Strapping & Packing

Straps are not required at party walls when:

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  • Packing is placed between the last joist and the wall at no more than 2m centres.

  • The floors are approximately the same level.

  • Packing is as close as possible to in line across the wall.

  • Where the strapping/packing is interrupted by an opening such as a stairwell, ensure that the opening is less than 3 m parallel to the wall and also that extra strapping and packing is provided to compensate for the strapping and packing that will not be provided due to the opening i.e distance between packing pieces is reduced.

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Diagram C126 - Typical packing detail to provide stability at a party wall

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Diagram C127 - Typical packing detail around opes

Trimming Joists Around Openings

Stair Openings

Specialist design may be required for trimmer and trimming joists. Ensure the engineer employed is qualified by examination, in private practice, and possesses professional indemnity insurance.

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Diagram C128 -Typical trimming detail around stair opening

Supporting Floor Joists With A Steel Beam

An issue with using steel members to support floor joists in the case of dormer or storey-and-a-half roofs is that, when joists are notched into the web, there may be a loss of continuity of position. This can be overcome by installing straps across the bottom of the beam. The minimum cross-section allowed for the straps is 30 mm x 2.5 mm and they must be nailed to the joists securely.

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Diagram C129 - Typical fixing detail of floor joists to steel beams - from underside

Beam and fixing detail are to be the designer’s specification. The engineer appointed must be qualified by examination, in private practice, and possess professional indemnity insurance.

Ensuring Floors Are Rigid

Adequate bridging ensures that joists do not twist and that the floor is stiff. Bridging should comprise of solid timber with a depth at least ¾ the depth of the floor joists. I.S. EN 1995 states that bridging is required in all floor joists where the span is greater than 2.7 m at centres less than 1350 mm.

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Diagram C130 - Typical detail to ensure rigid floors

When building joists into walls, ensure that bearing of 90 mm is provided and that the void left between the joist and blockwork is packed tightly with mortar. Alternatives to building the joist into the wall comprise end bridging between joints or using appropriate hangers built into the masonry.

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Diagram C130 (a) - Minimum bearing detail for floor joists built into walls

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Diagram C131 - Typical packing and bridging to ensure rigid floors

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Diagram C132 - Typical herring bone strutting and packing detail

Notching & Drilling

I.S. EN 1995 outlines notching and drilling requirements. Take extra care when notching and drilling joists. Notching and drilling should only be located in the positions and to the appropriate depth.

Only notch the top of joists, unless the joist being notched has been specially designed by an engineer who is qualified by examination, in private practice, and possesses professional indemnity insurance.

Ensure that the depth of saw cut is not greater than the depth of the notch itself. Inappropriate notching that weakens joists should be avoided and plumbers and electricians should be informed and made aware. Excessive notching is not permitted.

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The horizontal distance between hole and notch should always be greater than the depth of the joist.

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Diagram C133 - Simply supported joists - notching and drilling

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Diagram C134 -Typical notching limitations

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Diagram C135 - Typical drilling limitations

Proprietary Floor Joists

The following section provides guidance for construction as well as general information regarding the use of proprietary engineered timber joists such as I-Joists and open steel web joists in masonry construction. Any additional requirements or instructions outlined by the manufacturer should be followed also.

A timber I-Joist is a structural member engineered from wood and is primarily designed to be used in floor construction. Usually, a timber I-Joist consists of a solid timber or Laminated Veneered Lumber (LVL) flanges separated by a vertical web that connects the top and bottom flanges. The web is usually formed from OSB or plywood and glued into grooves in the top and bottom flanges.

An open steel web joist typically comprises of timber flanges that are similar to those used in the timber I-Joists but are generally formed from solid timber. The flanges are connected using Open Steel “V” shaped metal webs that are fixed using integral nail plate connectors.

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Diagram C136 - Typical proprietary timber I-joist and steel web joist

Third party certification, which outlines compliance with the Building Regulations namely, Irish Agreement Board (IAB) certification, British Board of Agreement (BBA) certification and, occasionally, European Technical Approval (ETA) certification, must be provided where proprietary timber I-Joists and open steel web joists are used. The company or some 3rd party must show how the product complies with the Irish Building Regulations where a product has ETA certification. Usually, open steel web joists are manufactured under license and under the supervision of the accrediting body. The technical literature provided by the manufacturer will include important information about the design and use of the joists. This literature should be read in conjunction with this section.

Please Note It is important to ensure the correct information for the correct product is being used and that the recommendations in the information and this section are adhered to due to the large number of I-Joist and open steel web joist systems and manufacturers to choose from.

Construction Guidance

With all the following topics, the manufacturer will provide in-depth specific information. The following merely lists general guidance for the topics.

Design Of Joists

Although the relevant approval certification contains some design information, most engineered joist systems provide a design service. The design service and the manufacturer’s technical literature contains any requirements such as joist sizes and layouts, bearing, drilling, and lateral restraint.

Cantilevered Joists

In the case of cantilevered joists, due to the special design and construction requirements, care should be taken. Ensure preservative treatment is added where they extend over an external wall. Be sure to seek advice from both the joist and preservative manufacturers as there may be additional requirements such as blocking and vapour control layers.

Moisture uptake is a problem to which this kind of cantilevered joist is quite susceptible. To avoid this problem, ensure good construction details are designed and that on-site workmanship is of a good standard. During construction, joists must be sheltered from excessive moisture and weather. I-Joists and steel web joists are not appropriate for use where the joist is exposed to external conditions.

Moisture Content

The approval certification outlines advice regarding moisture content of joists. It is important to protect joists from exposure to moisture and protect them from weather on site during construction.

Drilling & Notching

Ensure that the webs and flanges in both I-Joists and steel web joists are never drilled, notched, or altered at all without the manufacturer giving approval in writing. Knockout holes are pre-punched holes provided by the manufacturer in order to accommodate services like plumbing, heating pipes, and electrical cables. In the event that extra holes are required, seek the manufacturer’s guidance regarding location so as not to affect the shear capacity. Services may be passed through the open web of joists in steel web joists.


Minimum bearing requirements will be specified by manufacturers. When using hangers, the instructions of both the joist and hanger manufacturer should be followed when fixing the joist to the hanger. Typical end bearing details have been provided below.

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Diagram C137 (a) - Various end bearing typical details

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Diagram C137 (b) - Various end bearing typical details

Handling & Storage

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Joists should be stored vertically and evenly stacked with bearers in line off the ground, and protected from weather when being stored. In the case of timber I-Joists and open steel web joists, the manufacturer’s instructions should be followed during handling and installation as they are lightweight and have unique characteristics. Take care to make sure that the I-Joists are braced horizontally during construction and avoid damage to the steel webs throughout construction.

Where heavy loads such as blocks must be supported by proprietary floor joists, ensure the manufacturer’s recommendations regarding propping are followed.

Restraining Walls Laterally

Technical Guidance Document A of the Building regulations states that external walls must be restrained by the floor; the same as with conventional floor joists. Some typical restraint strapping have been shown below. Also, the manufacturers will provide supplementary guidance if restraint is required in the longitudinal direction of joists.

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Diagram C138 -Typical lateral restraint strapping detail to external walls

Web & Joist Stiffeners

To avoid joists buckling, it may be necessary to include web stiffeners at critical load points, such as at heavy point loads, cantilever supports, or where load bearing partitions are located. For open steel web joists, stiffen using solid timber braced laterally; for I-Joists, include plywood or OSB fixed to each side of the joist. Illustrated below are details of both types of web stiffener. Manufacturers will provide information regarding location and fixing of stiffeners.

In addition to the situations outlined, it may be necessary to include web stiffeners at the ends of joists being supported. Generally blocking pieces are sufficient for this purpose.

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Diagram C139 -Typical details for web and joist stiffeners

Joist Hangers

Ensure joist hangers used are appropriate for the specific joist being used. Manufacturers will generally outline the appropriate hanger along with guidelines for the particular joist as the hanger will most likely be unique to the joist.

In order to fix an I-Joist to the hanger, blocking pieces or possibly web stiffeners may need to be fixed to either side of the web. Where I-Joists are supported by other I-Joists, backing timber needs to be included to fix the hanger to.

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Diagram C140 - Typical joist hanger details


Generally, the manufacturers will provide site drawings that provide specific guidance on bridging /strutting requirements.

Timber Preservation

When treatment of the timber is necessary, the manufacturer’s advice should be sought regarding which treatment is compatible with the particular type of joist.


How far can you span 4x2? ›

Depending on various factors, a 2×4 floor or deck joist can span a maximum of 6' 7” at 16” spacing or 7'11” at 12” spacing. A 2×4 ceiling joist with 16” spacing has a max span of 7' 3” and with 24” spacing, the max span is 6” 4”.

What span can a 2x6 support? ›

A 2×6 can support up to 50 pounds per square foot of weight without sagging with a maximum span of about 12 feet when spanning a distance horizontally, with the 2×6 standing in a vertical position. This number includes both live and dead weight.

What thickness should floor joists be? ›

When choosing a joist spacing, check that your floorboards (or sheets) are strong enough to span over the width chosen. As a general rule - floorboards should be a minimum 16mm thick for joist centres up to 500mm and 19mm minimum for centres up to 600mm.

How far apart should joists be? ›

Deck joist spacing should never exceed 16″ on center (with the exception of MAX deck boards, which allow for maximum 24″ on center). For a more rigid feel, 12″ or less may be preferred. If adding additional framing, be sure to keep all boards level and in plane across the tops.

How far can you span without a beam? ›

A rule of thumb is 1.5 times a joist's depth but in feet when spaced at 16” centers. In 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”, and a rafter 6'-7” and 23'-9”.

Are 2x4 OK for rafters? ›

You can use either 2×6 or 2×4 rafters for roofs with a 3/12 pitch or greater, but it depends on the overall size of your shed. For roofs that won't experience heavy snow loads, a gable roof can span up to 22' with 2×4 rafters.

Which is stronger 2 2x4 or 1 2x6? ›

So if a double 2x4 has bending strength of (3")*(3.5")^3 = 128.6, then a single 2x6 has (1.5")*(5.5")^3 = 249.6. This means a single 2x6 is almost twice as strong in bending as a double 2x4.

Does double joists increase span? ›

Size of Lumber

For example, if you double the thickness or number of joists in a floor, the distance the boards can span will increase by approximately 25%. But if you double the width of the boards, the distance the joists can span increases between 80% to 100%, even though you're using the same board feet of lumber.

Are joist hangers load bearing? ›

Joist hangers can be used anywhere you need to strengthen a load bearing connection. Joist hangers use face mount attachments to fasten joists to ledger boards and beams. You can buy joist hangers for different sized lumber.

Does it matter what direction floor joists run? ›

An important thing to know about joists is that they usually run in the same direction throughout a house. If the visible joists in a basement or attic run east to west, for example, you can be fairly certain the invisible joists under the bedroom floor also run east to west.

Do floor joists have to sit on a beam? ›

Floor joists spread the loads bearing from above, and must be framed adequately to complete the load paths. Ideally, if a load-bearing wall runs parallel to floor joists, then it should sit directly over a beam or a joist supported by a load-bearing wall below.

What is acceptable floor sagging? ›

The degree to which your floor slopes or sags indicates whether or not you have reason for concern. Typically, floors that slope 1-1/2 inches or less in 20 feet is not a problem. Floors that sag 2 inches or more in 20 feet, though, are a cause for concern.

What is the difference between a rafter and joist? ›

The main difference between joists and rafters is that joists are usually more horizontal to the ground while rafters are used for steeply sloped roofs.

How do I calculate how many joists I need? ›

How do I calculate the floor joist that I need?
  1. Subtract the width of your floor joist from your floor's length: 120" − 1.5" = 118.5"
  2. Divide that difference by the sum of the on-center spacing of the floor joists: 118.5" / 16" = 7.40625.
  3. Add 1 to this value and round up the answer to the next whole number:
24 Oct 2022

How long can joists be without support? ›

With 16” spacing, a floor joist can span up to 14' as long as it is not cantilevered and terminates with support on either end. If the joists are 24” apart, then one 2×10 joist can span up to 11' 5”.

How long can steel beams go without support? ›

steel beams only support the weight of the masonry partition and self weight, and. steel beams span no more than 4.0m, and. the masonry partition is built centrally on the steelwork beam, and.

Can I place beam without column? ›

1 Answer. Yes they can intersect without a column at the intersection, 1 of the beam will be known as the primary beam and the other as secondary beam. The secondary beam will pass through the primary beam which will act as the support. You will 1st design the secondary beam before the primary beam.

Why are trusses stronger than rafters? ›

Rafters Require More Load-Bearing Walls

Because manufactured trusses are designed to correctly distribute a roof's weight to the house's outer walls, they don't need as many load-bearing walls inside to keep the structure standing.

Why is a 2x4 not accurate? ›

Now, most timber is milled and planed to give it a little more of a finished look, and a little more of a consistent size and profile. Because of this extra milling, a 2x4 no longer measures a full 2 inches by four inches. Instead, a 2x4 is really only 1 1/2" by 3 1/2".

What are 3 types of rafters? ›

Types of rafters
  • Auxiliary rafters. These are sometimes used to support a principal rafter.
  • Hip rafters. These span from the building's outside corners to the ridge board at a 45-degree angle.
  • Valley rafters. These rafters are located at the building's inside corners at a 45-degree angle.
  • Compass rafters.
22 Dec 2021

Can you use 2x4 for load bearing wall? ›

When bearing wall heights do not exceed 10 ft. 2 x 4 framing is generally code compliant. Here at Medeek Design we typically only specify 2 x 4 studs @ 16" o.c. spacing, for small sheds and garages with a building widths less than 16 feet.

Can 2x4 be used for load bearing? ›

A 2×4 can hold up to 40 pounds or 300 pounds when laying on its edge without sagging when laying horizontally. Several factors can lower or increase a 2x4s strength, including wood species, lumber grade, and moisture content.

Are 2x4 ever load bearing? ›

If it's a solid 2x6 or greater turned vertically going from the jack stud on one side to the other, there's a good chance the wall is load bearing. If there are only cripple studs on a flat 2x4 to give you something to attach the drywall, it likely isn't load bearing.

How far can joists overhang? ›

The American Wood Council states that cantilevers are limited to 1/4 the span of the joists. Joist Spacing (o.c.) Maximum allowable overhang cannot exceed 1/4 of the actual main span.

What if joists are too far apart? ›

The Downfalls of Improperly Spanned Joists

If the floor joists are too far apart and you leave the problem for too long, you might end up with the floor caving in on itself. It can also have a negative impact on the foundation of the home and the overarching structure.

What are the best floor joists? ›

Steel Floor Joists

These days, steel floor joists have become very popular since they are more long-lasting and durable than wood joist options. They are created to provide a better load-bearing system for the support of home structures.

Should you use screws or nails for joist hangers? ›

For outdoors use hot-dipped galvanised nails. Never use deck screws or drywall screws to install joist hangers. Dont reuse joist hangers. Dont modify them by cutting them shorter.

Why can't you use screws in joist hangers? ›

While structural nails are typically used to fasten joist hangers, you may be wondering if screws can be used instead. You can use screws explicitly made for joist hangers. However, avoid using any other types of screws as they cannot support joist loads and are not designed to withstand shear force.

Do you need to use all holes in joist hangers? ›

Standard joist hanger connection

Nails placed in all holes guarantee full load capacity. Unless specified otherwise by the designer, always use full nailing.

Do load bearing wall run parallel to the joists? ›

Any exterior wall that stands on the foundation sill can be considered load bearing. Walls that run perpendicular to the joists are load-bearing walls. Walls that are parallel to the joists rarely are, but sometimes a bearing wall will be aligned directly under a single joist.

Should floors run vertical or horizontal? ›

The most common way to lay hardwood flooring is by aligning the planks parallel to the longest wall. Apart from a few exceptions like sagging joists, this is the preferred direction to lay wood floors because it aesthetically provides the best result.

How far should joists be from the wall? ›

2 inches/50mm the norm, air can circulate, services can be run, and traditionally (and properly) a 50mm thickness block would be fixed between the first joist and the wall to solidify the entire floor construction and prevent any whip or slight movement. So yeah, 50mm.

Where should you not drill holes in joists? ›

You can put holes in floor joists anywhere along the length of the joist, but you can't put them any closer than 2″ from the top or bottom edge of a joist. The maximum size of a hole is 1/3 the depth of the floor joist.

Whats the difference between a joist and a beam? ›

Joists are small, numerous, and supported by a beam. Beams are large, few in number, and supported by a foundation, posts, or a wall. Beams are meant carry and distribute the main structural loads of a flooring system down to the posts, walls, or columns below. Joists on, the other hand, provide secondary support.

What is the difference between a stud and a joist? ›

Joists – are supportive timbers which the flooring is fixed to. You can see the joists here on this image – they run horizontally at floor level. Studs – are a vertical framing usually made of timber or steel which forms part of a wall or partition.

Should I worry about uneven floors? ›

If differential settlement isn't fixed, it could lead to structural damage. So, if your home has uneven floors, you should contact a foundation repair professional and request an inspection. Problems caught early can be less expensive to repair.

What makes a floor weak? ›

Poor structural design

A damaged foundation is often the leading cause of uneven floors. Foundation damage can come from age or poor design or craftsmanship that results in a foundation too weak to hold up your house's weight. A weak foundation results in warping, cracking, uneven floors, and hordes of other problems.

Is it normal for old houses to have uneven floors? ›

Uneven floors are normal in old houses.

This can be for several reasons, such as rotting floor joists, ground settling or simply poor construction.

What is meant by purlins? ›

purlin in British English

or purline (ˈpɜːlɪn ) noun. a horizontal beam that provides intermediate support for the common rafters of a roof construction.

What is the overhang of a roof called? ›

What Is a Soffit? Your roof by necessity, will often times extend over the walls of your home. This overhang can go by a few names, such as the house eaves or the rafters of your roof. The underside of this overhang, when given a finished appearance, is known as the soffit, which means “something fixed underneath”.

Which is stronger trusses or rafters? ›

Trussed roofs hold many advantages over rafters, including: The strength of trusses over rafters is unquestioned. In many cases, trusses are several times stronger than rafters, even when built with less material. The secret in truss strength is in its construction.

How far apart should holes be in joists? ›

Adjacent holes must be at least three times their diameter apart and no hole may be within 100mm (4”) of a notch. Measure the clear span between supports and the joist height.

How thick do floor joists need to be? ›

Floor joists shall have a bearing support length of not less than 11/2 inches (38 mm) for exterior wall supports and 31/2 inches (89 mm) for interior wall supports. Tracks shall be not less than 33 mils (0.84 mm) thick except where used as part of a floor header or trimmer in accordance with Section R505.

Are floor joists considered structural? ›

A floor joist is a horizontal structural component that spans an open space between beams that transmit the load to vertical structural components. These joists, a component of the floor system, support the weight of the walls, furnishings, appliances, and even humans inside a room.

Are trusses stronger than joists? ›

Floor trusses offer better strength and stability than floor joists in larger spans.

Is joist tape required? ›

Joist Tape: Why It's Essential & When to Use It

In order to protect your deck's substructure from weathering and moisture, protective tape for your joists is a must.

How far can you cantilever a 2x4 joist? ›

The American Wood Council states that cantilevers are limited to 1/4 the span of the joists. Joist Spacing (o.c.) Maximum allowable overhang cannot exceed 1/4 of the actual main span.

Can I use 4x2 for decking joists? ›

4 x 2 Timber Rail / Joist. Pressure treated timber joists. These decking joists are the most common sized framing timber for decking. They provide a solid structure for fixing your decking boards too.

Can I build a shed floor with 2x4? ›

If building on a foundation other than a treated wood frame, you will need to acquire 6 units of 8ft long pressure-treated 2x4s to put under the shed for floor joists, and shorten them to 7' 6.5”.

What size beam do I need to span 16 feet? ›

For a 16-foot spans, the wood beam has to be at least 14 inches in depth and 6″ in width (3-2×14) used for residential building, wood frame structure or projects.

What is the cantilever rule? ›

The general rule of thumb is that the back-span (the portion of beam supported below) should be twice the distance of the cantilever. The cantilevered beams then extend out to catch a W10x77 steel beam at the perimeter of the cantilever.

Do trusses need load bearing walls? ›

Since the truss contains its own internal support structures and will rest on the exterior walls of the building, no internal load-bearing walls are necessary.

Should you nail or screw deck joists? ›

Screws are superior for laying down the decking. They hold things flush better and have a better fastener/tensile strength, which keeps boards from popping up over time. However, unless you use more expensive structural screws you need to use nails for structural elements and joists.

What is the maximum distance between deck posts? ›

The two most common sizes used for deck posts are 4×4 and 6×6. When using 4×4 posts, place them no more than 6 feet apart, and when using 6×6 posts, no more than 8 feet apart. The reason for these standards is that the railing system won't have proper support if the posts are too far apart.

How far apart should joists be for wood decking? ›

How wide apart should decking joists be? In North America, joist spacing for residential decks is 12″ to 16″ apart, or according to local building code. Most decks require 16″ spacing for the deck itself, with 12″ spacing used for special applications, such as stairs or commercial structures.

Is OSB or plywood better for shed floor? ›

OSB has twice the horizontal shear strength of plywood. It's a better option than plywood for subflooring in attics and sheds. Also, OSB panels can be an advantage when flooring a big or odd-size shed, reducing the number of joints on a floor.

Can you use pallets under a shed? ›

Wooden pallets can be a great choice as a shed foundation because they have a high load capacity. Each pallet can withstand an average of 3,000 pounds in weight.

Do you need cement under a shed? ›

Do you need a foundation for your shed? Typically, small sheds in the size range of 6×8 or smaller do not require a foundation. However, we suggest placing all sheds on a foundation for structure and ventilation purposes.

How much does a 20 foot LVL beam cost? ›

The LVL beam thickness is usually between 1.75 and 7 inches. The price for beams that fit 10 feet of space will range from $3 to $5 per linear foot, while a 20-feet span will need a beam that costs $6 to $11 per linear foot.

How far can a 2x12 beam span? ›

A 2×12 with an E of 800,000 psi and Fb of 790 psi also works, since it can span 15 feet and 10 inches. Given a design span of 15 feet 1 inch and a 16 inch joist spacing, first determine which size lumber will work.


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