I have engineered joists that span the ceiling of my garage and support the second floor. I would like to secure storage racks to the ceiling. My intention is to fasten a couple of 2x6s spanning four or five of the joists using construction screws and then mount the ceiling storage to the 2x6s. Will screwing into the bottom flanges weaken the joists?

— Rich Anguish, via email

Contributing editor Andy Engel replies: I spoke with Mark Collins, the New England representative for Weyerhaeuser, the manufacturer of Trus Joists. He pointed me to the company’s document titled Fire-Rated Assemblies and Sprinker Systems, saying that the only published information Weyerhaeuser has for loads from below is for sprinkler piping. However, this type of loading isn’t much different from what you intend to build. The short version is that you can use up to 5⁄16-in. lag bolts in the bottom flanges. For 2-in. flanges, fasteners should be located within ¼ in. of the flange centerline.

For wider flanges, they can be up to ½ in. away from the centerline. Point attachments are limited to 250 lb. for each bolt. You’d have to check with the fastener manufacturer to determine the load each of your bolts can handle. And while the exact specs may vary per manufacturer, for Trus Joists, if the conditions above are met and the weight of your shelving—combined with the existing loads on the joists—does not exceed the overall capacity of the floor/ceiling, you should be fine.

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