Skip to Content

Joist Vs Rafter, How Are These Different? When To Use Each

Joist Vs Rafter, How Are These Different? When To Use Each

Suppose you are interested in the architecture and construction sector. In that case, beams are going to be a fundamental part of your knowledge. Understanding what they are, what they are used for, and what differentiates joists from rafters is essential for their proper use.

The joist and the rafter are technically the same: both are linear structures that serve to support a load. They are necessary for the backing of constructions. The difference is that the joist is horizontal support crossed in the design. However, the rafter is an element of architecture itself.

This article will explain the definitions of "joist" and "rafters," their differences, and examples of using both words correctly, among others. If you are interested, keep reading below.

joist word in the dictionary

Definition Of The Word "Joist"

The joist is a semi-resistant element that makes up the slab's reinforcement. Its concrete section is constant regardless of its length. The only thing that varies is the steel section that goes inside. Its characteristics, together with its inverted T shape, should be light and easy to manipulate.

The difference between the beam and the joist is that the design of the beam supports a load by itself; therefore, it is more resistant.

The most common type of joist is built of a concrete material subjected to precompression pressures applied through its steel reinforcement. It is a self-resistant joist, meaning that it resists the weight by itself and all the efforts to which it will have to be subjected to, without the need for extra concrete. Also, it is semi-resistant because it is made with highly resistant concretes, dosed by weight, and controlled in laboratories, using steel inside them for more support.

How Can I Use "Joist" In A Sentence?

Some examples of sentences with the word "joist" are:

  • We assume that the joists are three meters away from the wall. If we drove ten nails into the ground three meters from the wall, only three would sink into them.
  • I went on a trip to an island with my family, and we decided to explore. We found a park that, to get there, we had to cross a bridge. It seemed easy to pass from the shore, but once on the bridge, the joists turned out to be old and squeaky when trying to put weight on them, so we had to turn around.
  • This week I had to submit my first architectural plan at work. After reviewing it, I realized that I had to add a section of joists. I had to postpone the meeting for two days and spent all that time redoing the plans. It was a nightmare!
  • The house I bought is too old, and the joists that support the attic are falling apart. I had to disassemble them all and start the project from scratch. The house had a low price, but with the remodeling, its value will double.
  • In summer my house is too hot. Our air conditioning was damaged a year ago. We cannot add a fan because whoever installed the joists in the room ceiling did not add the cables that pass the electricity. So now we have to live with portable fans everywhere, but they are hideous and take up too much space!
  • Yesterday I was assembling my closet, and I dropped the hammer on the deck. The blow cracked the floor and also a joist supporting the area. Now I have to call a construction company and my savings to travel I will have to spend on that.

Definition Of The Word "Rafter"

A rafter is a sloped structural beam that extends upward from the top of the wall, creating a slope. It is designed to support the roof deck and its associated loads. The rafters are typically made of wood in house construction. Some traditional roof styles are distinctive for having exposed rafters.

In many modern constructions, they replace the rafters with prefabricated roof trusses. Roof trusses are triangular structures that, due to their shape, are very resistant. In construction, they combine joists with rafters. They are typically designed and manufactured outside of the construction site, which helps speed up the process.

Roof trusses are less fiddly to use and may offer more support, but you can't create an attic with this type of structure. Raffled ceilings are perfect for creating storage spaces or attics in homes. If you don't have this space, your house is most likely made up of roof trusses.

How Can I Use "Rafter" In A Sentence?

The following examples illustrate "rafters" in sentences:

  1. I want to learn to do aerial dance. That's why I nailed several fabrics to one of the rafters in my living room. My mother is unhappy that I drilled the beams, but I don't think it affects their structure much.
  2. I gave exact instructions to my architect on how I wanted my rafters to look. Yesterday he showed me the map, and it is not at all as I had told him. It turns out my husband met up with him after me and changed all plans. There are no rafters, and he filled the place with roof trusses!
  3. I want a country house with wooden rafters to bring nature from the outside to the inside. My husband does not like the idea. He says that the only thing transported from the outside to the interior will be the bugs.
  4. I asked the architect who is designing my house yesterday if it is possible to omit the rafters. The problem is, I want a flat roof, and all the rafters I've seen are shaped like a triangle.
  5. One of the main reasons for deforestation in my city is the construction of houses. Apart from the space, they cut down the trees to make wood and use it in construction, such as rafters, window frames, doors, and even stairs and pot holders!
  6. The company that installed the rafters in my house did a lousy job: some are out of level and are causing water leaks every time it rains. I called to get it fixed, and they want to charge me for the new labor. They should give me a refund, not ask me for more money!
  7. I am building a guest house next to my home. It will be a single story, but I'll take advantage of the rafters and make an attic. I have yet to choose if I will make it an extra room or a storage area.

rafter word sign in neon

Does Every Rafter Need a Joist?

Ceiling joists serve to prevent rafters from pushing the walls outward, and this means that the joists do not support the rafters but the walls themselves. Because of this, it is not mandatory to add the joists as support for the ceiling. Still, it is recommended so that the structure of the construction is stable and safe.

Can I Use Joists As Rafters?

It is not common to use joists as rafters, but if the joist meets the length, weight, and height requirements, they can be considered substitutes. However, it is best to keep the rafters or roof trusses to support the ceiling structure.


Both joists and rafters fall into the category of the support structure. The difference is in their function: joists can be more versatile, while rafters are used solely to support the ceiling. However, both are important to the durability and quality of the build. If earthquakes are frequent where you plan to build your project, add as many beams as possible to maintain a safe construction structure.