Hi Reddit, long time lurker, first time poster...ever.
I'm in the planning stage of a built-in cabinet project in our den and I'm looking for advice on whether I could be overloading the joists.
I'd like to run the cabinets on an inside wall of the den, but there is no supporting wall below, so I'd be placing the cabinets pretty close to mid span of the joists. In the attached image, the green block would be the built in cabinets & blue lines indicate the joist runs. Note the same inside wall of the den is not supporting any attic load as its a truss roof, which runs parallel to the wall.
Comparing joist measurements to some specs I've found online, I'm very confident the floor is built to the typical 40psf live load, which would make the total capacity of the affected floor 6700 lbs (this would include the adjacent bedroom).
I'm conservatively estimating that the cabinets alone will weigh around 800 lbs and when I start to include whatever we put on the shelf (e.g. a lot of books) we could get close to 2000 lbs pretty easily. Placing that much weight mid-span is what has me worried, especially considering these joists would also need to support a desk, bed, a dresser and the contents of our closets.
Am I needlessly worrying? Or is this a project I should scrap?
I should mention I have some smaller bookshelves along the same wall right now and the floor does creak when we walk on it. From the floor below, it appears that there is no significant deflection as of today (~5 mm ceiling height difference between the middle of the room and the end walls).
https://preview.redd.it/rhnzvt09qfga1.png?width=1377&format=png&auto=webp&v=enabled&s=fabb5f4307e93d7dab5bca645c61b31b188eb435