What are double floor joists?
Double floor joists are two joists side by side that are usually nailed or screwed together along the length.
Why would you use a double floor joist?
The main reason for doubling up floor joists is to double the strength of a single floor joist. This allows you to install a supporting post off the double floor joist to hold a second storey or a roof beam. So instead of having a post run all the way from the roof to the ground, it can stop at the double floor joist. If the post continued to the ground it could end up on top of buried sewer and drainage pipes, for example. Another benefit of this method is if you are aiming to keep the area under the deck as open as possible.
When you are building your deck, double floor joists can give you that extra strength required to support your roof or to free up some of that valuable space under your deck.
For further reading on calculations for floor joists check out some of our other articles on floor joists.