Curious about the right beam size for spanning 18 feet? Building or renovating involves key decisions, and your choice here can impact structural integrity.
In order to ensure safety and stability, you will need to know what size beam to use for your project.
What Size Beam To Span 18 Ft?
For an 18-foot span, a standard SPF #2 grade 2×10 dimensional lumber beam (1-1/2” x 9-1/4”) is sufficient for lightweight residential floor and ceiling loads up to around 30 pounds per square foot when spacing joists 16” on center. LVL beams allow longer spans, but 2x10s are an economical choice for basic 18-foot residential projects.
Beam size chart for 18 ft span:
| Beam Type | Size |
|---|---|
| SPF Dimensional Lumber | 2×10 |
| LVL | 1-3/4″ x 9-1/2″ |
| Glulam | 3-1/8″ x 6″ |
Different Types of Beams for an 18-Foot Span
Here are some of the most common types of beams:
Wooden Beams
The most economical and available choice for residential settings is using dimensional lumber such as 2×10 or 2×12 SPF boards for an 18-foot span.
These can be doubled up for added strength if needed. Just ensure the grade and wood species meet structural requirements.
Steel Beams
Steel I-beams provide an excellent strength-to-weight ratio for longer spans while avoiding wood shrinkage issues.
But steel is more vulnerable to rust if exposed to moisture and can have higher material costs. Proper corrosion-resistant coating helps avoid rust pitting.
Glulam Beams
Glulam or “glued laminated timber” offers better strength than dimensional lumber by laminating wood layers together in a more compact size.
Glulams resist cupping or twisting better. Their manufactured process also allows large custom beam lengths.
Concrete Beams
Concrete beams can be precast or formed and poured on-site. Their rigid compressed strength resists deflection well over long spans like 18 feet.
But concrete adds considerable weight. Reinforcing the rebar gives tensile strength.
Calculating Beam Size
Understanding the Basics
Calculating the right beam size may seem daunting, but it’s crucial for safety. First, think about all the weight your beam will bear.
This includes not only the permanent stuff, like walls and roofs (known as dead loads), but also what comes and goes, like people and furniture (live loads).
Building codes set limits to ensure everything stays sturdy.
The Role of Bending Stress
Bending stress is a critical factor. When your beam supports a load, it bends slightly. Too much bending can lead to sagging or even failure.
We need to figure out how much stress your beam can handle without bending too far.
Span Length Matters
The length of your span matters. An 18-foot span needs a sturdier beam than a shorter one. Longer spans require more support to prevent sagging in the middle.
Material Matters
The type of material you use makes a big difference. Wood and steel have different properties.
Engineers use these properties to calculate the minimum beam size needed.
Complex Calculations for Commercial Use
For big projects like commercial buildings or heavy loads, engineers turn to complex structural analysis software.
This software crunches all the numbers, considering every detail to ensure safety and strength.
Simplicity for Residential Projects
Thankfully, for everyday projects like decks or porches, you can rely on simplified span charts.
These charts provide guidelines for choosing the right beam size based on the span length and expected loads. It simplifies the process for residential applications.
Factors to Consider
Material Type
The choice of construction material plays a critical role in determining the size of the beam needed.
Each material, whether it’s wood, steel, or something else, has its own unique properties.
These properties include strength, elasticity (how much it can flex without breaking), shear values (how it resists forces that try to make it slide), and allowable stresses (how much load it can safely carry).
Depending on the material you choose, these characteristics will influence the size of the beam necessary to support your specific span and load.
Load Considerations
The loads that the beam will bear are of utmost importance. There are two main types of loads to consider: dead loads and live loads.
Dead loads are permanent, unchanging loads like the weight of the building itself, including walls and roofs.
Live loads, on the other hand, are temporary and can change over time, like the weight of furniture or people moving around inside the building.
Higher floor loads (for multi-story buildings) or snow loads (for regions with heavy snowfall) will require a larger and stronger beam.
Concentrated loads, which are heavy objects placed in specific areas, can also affect the sizing of the beam.
Design Codes and Standards
Construction has rules, and these rules are outlined in design codes and standards.
These standards provide guidelines for how much stress a beam can handle and how much it’s allowed to bend (deflect).
The specific standards to follow depend on the type of application and the occupancy of the building.
Following these guidelines is crucial in determining the minimum size of the beam.
Structural System and Support Conditions
How the beam is supported and connected at its ends is another factor to consider.
Beams can be supported in different ways, such as simply supported (supported at both ends) or cantilevered (supported at one end).
The way a beam is supported impacts its sizing requirements. Simply supported beams generally require less capacity compared to cantilevered ones.
Deflection Criteria
Deflection refers to how much a beam bends or sags under a load. It’s important to control deflection to prevent excessive bending and sagging under expected loads.
To do this, engineers set allowable deflection limits, which help determine the minimum beam depth and stiffness required for the specific application.
Durability and Environmental Considerations
Consider the environment where the beam will be used. Factors like moisture levels, temperature variations, and the potential for decay can influence material selection.
It’s important to choose a material that can withstand the conditions it will be exposed to and how long it will last in those conditions.
Economic Factors
The cost of the beam materials and fabrication can vary significantly.
Larger beam sizes may require heavier supporting elements like posts, footings, and hangers, impacting the overall cost of the project.
It’s essential to strike a balance between strength and cost-effectiveness.
Construction Methods and Equipment Availability
Accessibility for delivery and installation are practical considerations.
Some beams come prefabricated, which means they are manufactured off-site and then delivered and assembled on-site.
This can simplify the installation process compared to constructing beams on-site.
You need to ensure that you have the necessary equipment for lifting and placing the beam safely.
Local Regulations and Zoning Requirements
Local regulations can significantly impact the design and size of your beam.
These regulations may include requirements for handling snow loads, wind loads, and seismic (earthquake) loads.
In historical districts, there might be restrictions on the type of materials you can use.
To navigate these regulations, you may need to submit stamped engineered plans for approval before proceeding with your project.
FAQs about what size beam to span 18 ft:
What Are The Methods For Determining Beam Size?
There are two methods, e.g., the S 456:2000 method and the thumb rule method.
Can A 2×12 Span 16 Feet?
Yes, it can easily span 16 feet. In fact, according to some estimations, it has gone up to 22 or 23 feet.
Is LVL Beam Good To Span 18 Ft?
Yes, it is as good as any other beam. You will need 9-10″ GLULAM or LVL here.
Final Words:
Determining the appropriate beam size for an 18-foot span is a crucial step in any construction project.
By considering factors like material type, load considerations, and local regulations, you can ensure the structural integrity and safety of your building or renovation.
Making the right choice will provide the support needed for a sturdy and long-lasting structure.
