2x4 Attic Floor Joists

Strengthening attic joists for live loads by sistering.

2x4 attic floor joists.

If you want to put down flooring in your attic and want more insulation underneath that floor then you need to increase your joist size. That s a big size and strength difference between the two types of attic joists even if the joist spacing is the same. This is not a load bearing wall. If your attic joists won t bear the weight necessary to finish out a living space but the engineer cleared them to support floor decking for light storage you can install inch plywood or.

Common sense tells you that large floor joists can carry more load and spacing joists closer together also increases the load bearing capacity of a floor. Sistering installing new larger joists next to the existing ones is one way to bring your attic floor up to code. Sistering is the process of adding a new joist next to each existing joist. I can t imagine a garage layout that would have a span short enough to make with 2x4 s even sistered.

Often existing joist bays are filled with electrical and heating ducts that will need to be relocated. Most spans are typically 10 to 12 feet so we typically use 2x8 or 2x10. If one end of the span is supported by a beam up the middle of the garage that probably wasn t sized to support a floor either. The studs in question span 16.

But you can still double the capacity of the existing 2x6s in the attic floor so first let s make sure that s enough for your situation. There is a wall under part of the attic which helps support the studs at approximately midspan. The extra two inches of vertical distance when a floor is framed with 2 x 10 joists rather than 2 x 12s can be quite important for example. Is an attic with only 2x4 joists holding up the ceiling strong enough to use for storage.

If the attic were designed as living space those ceiling joists would become floor joists and be much bigger. Positioning the new joist adjacent to the existing preserves precious ceiling but it does come with some potential complications. My calculations tell me assuming 2 southern yellow pine joists which are common in my area that 2x6s 16 inches on center will span 9 feet 9 inches with allowable deflection being the governing factor. The depth or height of your floor joists depends on how far they can span without sagging.

There are online span calculators available that tell you the maximum span for. If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists. But larger is not always better when builders are constructing a home or adding a room addition. Sistering 2x6 joists next to your current 2x4 joists will simply give you a new floor height of 5 1 2 inches as opposed to the current 3 1 2 inches.