How much weight can my cement-block wall hold?

Answered by Jeffrey Anderson ~ February 27, 2014 ~ No Comments » | Respond to this question

I want to hang a hammock on my lanai/porch, but the walls are cement block covered with stucco. Will cement block hold that much weight (2 people = 300 lbs) safely? Can you recommend the best way to do this if so?

-Dan

Jeffrey Anderson

Dan, there are two issues to consider here: the lateral strength of the block wall and the strength of the block itself. You mention that the wall is part of your lanai/porch so I assume there is some sort of roof system that it supports. By roof system, I mean trusses or rafters of some sort that are anchored with nails or other fasteners at the top of the block wall. If this is the case, there should be a wood plate on the top of the wall that the roof framing sits on.

If what I'm describing sounds like your porch configuration, then there should be enough lateral support for your wall to support a hammock. The roof framing should prevent the wall from leaning or possibly falling when weight is placed in the hammock as the top of the wall is being held in place.

The issue with the strength of the block itself isn't quite as simple. There are numerous types of concrete blocks, but the style most commonly used for residential walls is basically hollow. The block is designed to carry weight placed on it from the top, such as roof or wall framing, but the sides aren't very structurally strong. Most of the time they are only about an inch thick and can easily be broken with the swing of a hammer. Using a block such as this to support 300 pounds in a hammock would be out of the question.

If by chance solid concrete block has been used for the wall, then you may be in luck. The same is true if the block is hollow, but the inner cores have been poured full of concrete. In both of these cases, drilling all the way through the block wall and installing a bracket for the hammock should provide enough support to carry the weight you mentioned. Of course, make sure the bracket itself is rated for that weight. It would also be a good idea to use a large washer under the bolt on the side of the wall opposite the hammock.

If the block is hollow, you may need to get a structural engineer involved. It's possible you might be able to have two large metal plates of equal size made up that would span several blocks. One of the plates would have a bracket to hold the hammock welded on its face. There should be holes in all four corners of both plates so that bolts could extend through the blocks and the plate on the other side of the wall where they would be held in place with nuts. Whether this is possible and what the size of the plates would be wouldneed to be determined by the engineer.

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