Joists Vs Rafters

When it comes to building a roof, there are two common types of structural elements used: joists and rafters. Both of these elements have their unique benefits and drawbacks, and choosing the right one for your project can have a significant impact on the final outcome of your construction.

In this article, we will discuss the differences between joists and rafters and compare them so that you can make a well-informed decision about which one is best suited for your specific needs.


Joists are horizontal structural elements that support the ceiling of a room or the floor of an attic. They are typically made from wood or steel and are spaced at regular intervals to provide adequate support for the ceiling or floor above.

Types of Joists:

1. Solid Joists: They are most often used in smaller projects such as home construction or renovations.

2. Engineered Joists: They are created using a mix of natural and processed materials like laminated veneer lumber (LVL) or I-joists. They are more expensive than solid joists but are specifically designed to provide better sound insulation and support over greater spans.

Benefits of Joists

1. Lightweight: Joists are relatively lightweight, which makes them suitable for ceiling or floor supports in most homes.

2. Cost-Effective: Joists are less expensive than rafters, which is ideal if you are working on a tight budget.

3. Easy to Install: They are easy to install, making them a great option for DIY projects.

Drawbacks of Joists

1. Limited Span: Joists have a limited span since they cannot bear concentrated loads over long spans.

2. Less Support: They are not as strong as rafters, which means they cannot support the weight of the roof on their own.


Rafters, on the other hand, are inclined structural elements that form the shape of a roof. They are typically made from wood or steel and are spaced at regular intervals to support the weight of the roofing material above.

Types of Rafters:

There are mainly two types of rafters – Common Rafters and Hip Rafters.

1. Common Rafters: They are inclined roof framing members that run from the ridge to the plates, perpendicular to the ridge.

2. Hip Rafters: They form the angle where two sides of a roof meet.

Benefits of Rafters

1. Span Capabilities: Rafters have a much larger span capability than joists and can bear much heavier loads.

2. Structural Soundness: Rafters are designed specifically to withstand heavy loads, which means they are structurally sound and reliable.

3. Can Span Longer Distances: Since rafters can support more weight, they can span longer distances than joists.

Drawbacks of Rafters

1. More Expensive: Rafters are more expensive than joists, which can make them less appealing for those working on a tight budget.

2. Difficult to Install: They can be more challenging to install than joists, especially if you are not experienced with this type of construction.

Joists Vs Rafters – Comparison

1. Support Capability: Rafters are capable of supporting much heavier loads than joists, which means they are better suited for larger projects where structural support is essential.

2. Stability: Rafters are designed to be more structurally sound than joists, which means they are less likely to warp or bend over time.

3. Span Capabilities: Rafters can span longer distances than joists, making them an ideal choice for large structures such as commercial buildings.

4. Cost: Joists are less expensive than rafters, which makes them a more budget-friendly option for those who are looking to cut costs.


1. Are joists or rafters better for roofing?

The answer to this question depends on your specific needs. If you are working on a small project or have limited space, joists may be a better option. However, if you have a larger structure or need more structural support, rafters may be the better choice.

2. Can you use joists instead of rafters?

No, joists cannot be used instead of rafters as they are not designed to support the weight of a roof.

3. How far apart should joists be for a roof?

The standard spacing for joists in a roof is 16 to 24 inches apart.

4. How far apart should rafters be for a roof?

The spacing for rafters in a roof depends on the roofing material and the slope of the roof. The standard spacing for rafters is 16 to 24 inches apart.


Choosing between joists and rafters ultimately depends on the size, scope, and intended use of your building project. Careful consideration of your structural needs, budget, and the span capabilities of each option will help you make the right choice. Whether you choose joists or rafters, remember to have an experienced contractor or builder assist you with your project for optimal results.