# How many joists do I need for a 12 foot deck?

Table of Contents

## How many joists do I need for a 12 foot deck?

For example, if the joists are spaced 16 inches apart and are 12 feet long, the logical choice is a 2-by-8 joist which can span up to 12 feet 10 inches at this spacing. If the joists were 15 feet long, then 2-by-10 joists are required, which can span up to 16 feet 5 inches.

## How do I calculate how many joists I need?

To estimate them 12 inches from centers add 1 to the number of feet in length of one wall on which the joists are placed. For example, suppose a building is 32 feet long, and the joists are placed 12 inches from centers. We simply add 1 to 32, which makes 33 the number of joists required for one span.

## What size joist do I need for a 20 foot span?

In that case, you need something like a 12-16″ GLULAM or LVL to span the 20′ and can use simple 2×8-10 dimensional lumber 16″OC as floor joists.

## How far apart do joists need to be for a deck?

16″

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.

## What size joist do I need for a 12 foot span?

How do I keep them even? In general terms, joists spaced 16 inches on center can span 1.5 times in feet their depth in inches. A 2×8 up to 12 feet; 2×10 to 15 feet and 2×12 to 18 feet.

## How far can you span a 2×6 deck joist?

Decking made of 2x4s or 2x6s can span up to 24 inches. If you will run decking at an angle, you might need to put the joists closer together.

## How big should the joists be on a deck?

As a rule, the larger the deck, the larger the joists. For example, joists spaced 16 inches from the center of the joist next to it can span 1.5 times in feet the depth of their inches. To learn more about deck joist sizing, spacing, and allowable span, reference this chart.

## How big of a floor do you need for a deck?

When laying out the joists, you may plan for placing them on 12” or 16” centers. Although 16” centers are common in residential construction, it’s usually best to place joists on 12” centers. The flooring above will support more weight and be less likely to sag over time.

## What should the spacing be on a floor joist table?

The floor joist spacing is the distance between the centers of any two installed joists. See the image below for an example of joists spaced 16″ on center (16″ o.c.). Since the example house we are designing for is 12 feet wide, we need to find, in the floor joist span table, a joist size and centering that can span 12′ or wider.

## How does the floor joist count system work?

The Floor Joist Count calculator computes the number of joists (joists and end plates) required for a floor or deck based on the dimension of the room or deck and the on-center joist separation. Floor Joist Board Count (Jc): The Floor Joist Count calculator computes the total number of boards needed for the joists and end-plates combined.

As a rule, the larger the deck, the larger the joists. For example, joists spaced 16 inches from the center of the joist next to it can span 1.5 times in feet the depth of their inches. To learn more about deck joist sizing, spacing, and allowable span, reference this chart.

The floor joist spacing is the distance between the centers of any two installed joists. See the image below for an example of joists spaced 16″ on center (16″ o.c.). Since the example house we are designing for is 12 feet wide, we need to find, in the floor joist span table, a joist size and centering that can span 12′ or wider.

When laying out the joists, you may plan for placing them on 12” or 16” centers. Although 16” centers are common in residential construction, it’s usually best to place joists on 12” centers. The flooring above will support more weight and be less likely to sag over time.

The Floor Joist Count calculator computes the number of joists (joists and end plates) required for a floor or deck based on the dimension of the room or deck and the on-center joist separation. Floor Joist Board Count (Jc): The Floor Joist Count calculator computes the total number of boards needed for the joists and end-plates combined.