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How to beef up 2x6 ceiling joist to use attic for storage

BELLDENTAL's picture

I have a rancher style home with 2x6 ceiling joist rafters and 2x6 roof joists rafters.  I would like to use my attic for storage of normal house hold goods such as seasonal decorations, clothing, books, files, paperwork, etc., not sure of exact weight of items to be stored.  I have purchased 3/4 inch plywood to apply to top of the ceiling joist rafters to use for the attic flooring, but I am concerned about the span of the 2x6 rafters as they span 12 foot in one section and 16 foot in another section, all ceiling rafters are on 16 inch centers.  My concern is that once I install the 3/4 inch plywood flooring and start using the attic for normal household storage I may start to see the ceiling plaster start to crack due to the weight of the flooring and storage.  I am wondering if I can get away with either sistering a ripped down piece of 5 inch x 8 foot plywood to the center of each joist to prevent sagging, or a 2x6 sistered along the entire length, or a 2x8 along the entire lenght would be enough.  My budget is tight so I want to use the least expensive method to beef up the ceiling rafters. If someone could please advise me what they think would be the best and least expensive way to go I would greatly appreciated it.

As long as you are not (post #207173, reply #1 of 5)

As long as you are not dancing nor storing reams and reams of paper records weighing thousands of pounds in your attic, a simple 3/4" plywood floor over your rafters should be fine.  No beefing up needed.

If you have something heavier, simply place it close to the wall instead of in the center of the ceiling joists.


How do you intend to get the sheets of plywood up there?

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But remember -- People who (post #207173, reply #2 of 5)

But remember -- People who live in grass houses shouldn't store thrones.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

No way are joists that size (post #207173, reply #3 of 5)

No way are joists that size adequate for an attic floor.  Especially the ones spanning 16'. You need to sister them with joists deep enough to span that distance.

I've heard the arguement before that you're not going to store that much up there. But how much is "that much"?  How much will the stuff that's stored up there increase over time.  (The old rule oif thumb: Stuff expands to fill the available space)  How much will the next homeowner store up there?

I strongly suggest doing it right, and not cutting corners.

I agree with BossHog.  The (post #207173, reply #4 of 5)

I agree with BossHog.  The 16' span can tolerate about 15-20 lb/ft (depends on the species of wood you have) before you'll see cracking in the plaster and run a very good risk of cracking the beam (extremely bad news for the room below).  That's not much when the beam itself and the plywood will weigh about  7-8 lb/ft all by itself.  The 12' span can tolerate 25-35 lb/ft (also depends on the species of wood) which at least begins to be marginally functional for storage but is really easy to overload unintentionally. 

If you do decide to go the unreinforced route, make sure you glue and screw the plywood to the joists and use tongue and groove plywood.  This will maximize the ability of the joists to 'help each other' in the case that one joist gets overloaded and the others are lightly loaded.  Even this is prone to accidental corner cutting during installation, however.

Best is to just spend the effort to sister these beams up and still do the glue and screw with tongue and groove plywood.

You can save money and effort (post #207173, reply #5 of 5)

You can save money and effort by using 1/2" ply instead of that 3/4". There is no need for the thicker material and it weighs more.