Thursday, August 28, 2008

Moving libraries

The family move is finally complete, or at least the major furniture moving is complete. Currently, the house is loaded with stacks of boxes awaiting their distribution to cabinets and shelves. By the way, if you're ever looking for software to organize your furniture in a floor plan and don't want to spend major dollars or learning time on some overspecialized home planning application, I heartily recommend the Open Source program Sweet Home 3D. While not perfect, it was big help. Since we were moving to a radically different floor plan, we needed a way to test our furniture in the new home layout and Sweet Home 3D worked well for us. We were able to decide which pieces of furniture would fit in each floor and room well before the actual move, making things easier for the movers and ourselves.

My office moved from a basement den in a townhouse, to an upstairs bedroom in a single-family home. There was some sacrifice of total floor space in the move. During the moving process, even the movers expressed concern that the amount of weight in boxes of my books was getting excessive for the room. My main library consists of four sets of shelf wall units, 37"w x 12"d x 72"h, with five shelves each. (Sorry for the English units, but those are the common values of my furniture measurements.)

I've traditionally heard the claim that because modern homes must be able to support the weight of a waterbed, the weight of my books couldn't possibly exceed this. This is a simple physical claim to test and I decided to do a few simple calculations.

With a few searches on Google, I found that the weight of a water bed can be up to 1800 lbs.

I also discovered that modern homes are built to handle an average "live load" of 40 pounds per square foot. This is a theoretical average load. Your home may vary, but if it is built to many local codes, this should be a safe number to use. To compute the theoretical average load for the room, you must multiply the load average per area by the area of the floor. In my case, this comes out to 10ft x 12ft = 120 square feet. From this we compute a load limit of 40 lbs per square foot x 120 square feet = 4800 lbs. Clearly, my new office would not have a problem with a water bed, but would it have a problem with my library?

I didn't have easy access to a simple scale that could accurately measure the weight of some of my actual books from which I could compute a density. Another search on Google suggests the average density of paper is about 0.03 lbs per cubic inch. If the cabinet were completely full of paper, the weight of each shelf wall unit would be (37" x 12" x 72") x 0.03 lbs per cubic inch = 960 lbs. But the books do not uniformly fill the shelf space. There are small books, medium books, and a few large books and the shelves are spaced to accommodate the largest book on that shelf. There is a lot of empty space in each shelf. I'll approximate the effect of these size differences with the estimate that only about half the volume of each shelf is filled with actual book matter, reducing the total weight of each shelf to 480 lbs.

This gives a total estimated weight for my library of about 1900 lbs. Even here, it exceeds the weight of a water bed. This estimate is also well below the 4800 lbs theoretical design limit of the floor, but my estimated "live load" does not include the weight of a desk, a file cabinet, the computers, and other miscellaneous components (such as myself) in the office. If the shelves were fully packed with books, the total estimated weight comes to over 3800 lbs, which is much closer to the design limit.

I feel a little safer now about loading my shelves, but plans for any additional shelf units in this room will certainly be re-examined. It also may be time to start paring down my collection, perhaps discarding that collection of Scientific American that is (almost) complete back to around 1975. :^(

For more information on these topics, I found sites supporting aquarium hobbyists to be very useful. The most useful resource I found is Residential Wood Framed Floors and Aquarium Weights.

Ardent book collectors and home librarians might want to consider some of the potential limits in their passions. I've not heard of a home collapse due to the weight of a personal library, but I wonder if it has actually ever occurred.

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