How much weight can floor joists support?

How Much Weight Can Floor Joists Support?

The first thing to understand is that the amount of weight a floor can support depends upon several factors such as: the type of wood used, its thickness, the number of feet it’s made from, and so forth. If you’re building your own home or remodeling an existing one, you’ll want to consult with a professional before making any major decisions.

In general, floor joists are designed to support between 40% and 60% of their maximum load. That means if you have two 8 foot long joists (which would normally support 80 pounds each), they could theoretically carry up to 160 pounds total. However, most homeowners don’t need to worry about the exact numbers since there’s no way for them to check exactly what kind of wood they use in their house.

If you do decide to measure the weight of your floor joists, here are some helpful tips:

Measure the height of the top joist. This will give you an idea of how many feet tall your ceiling is. For example, if your ceiling is 12 feet high, then measure 12 inches above the top of each joist. You’ll see that these measurements add up to 36 inches which equals 4 feet 6 inches. Divide this figure by four and multiply it by .

So how do you figure out how much weight a floor can support? There are various ways to calculate it, but here’s one method that works well:

1) Take the width of the joists (or whatever length you’re interested in). Then multiply that width times the number of feet. For example, let’s say our joists are 8 feet wide and 12 feet long. So we’d divide our width by 12 to get 4 feet per foot.60 to find the maximum safe load.

If your joists are made from wood, you should expect them to sag in the middle under the weight of your tank. To avoid this, do not place the tank in the center of the room. Instead, either place it against a wall or place a long piece of wood on either side of it to distribute the weight across more than one joist. So that would equal to 4 feet. Then multiply that answer times the number of feet (in this case 12 feet).

So that would equal to 48 square feet per foot (or 48 pounds per square foot).

2) Find out the depth of the joist (in other words, how far it sits into the wall). Some sit deeper than others.

Does the thickness or length of the joists matter? What about the width? The weight a floor can support is directly related to the size and shape of the joists. The wider and shorter they are, the less they can support. If your floor’s joists are much longer than they are wide, try to measure the width of several joists to get an average. Most are about 2 inches in the wall, but some are as little as 1/2 inch. So that would mean we divide the figure we got in step 1 by two.

That would equal to 24 pounds per square foot.

3) Finally, multiply that number by .60 to get the total amount the joist can support. So that would equal around 16 pounds per square foot. This means that you could have up to 16 square feet of floor per foot that’s sitting on top of the joist. For example, if you have a 40 foot by 20 foot room with 10 foot high ceilings, that would equal to 1600 square feet or 160 square feet sitting on your floor at one time.

Now you’re ready to start building your tank! First, place your stand where you want it and measure the area where the bottom of the tank will go. So if our joist is made out of wood and it’s about 4 feet by 8 feet, that would equal to support 128 pounds (this number would be higher if our joists were more narrow or longer than average).

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You wouldn’t want to put any more weight on the floor than that.

Note: If at any time you have a question about what you can or can’t do with your house, consult a local building inspector or contractor for clarification. Then measure out how wide and long you want the tank to be. Next, put down your plastic sheeting and cut out pieces that are the width and length of what will be the tank bottom (be sure to add a few inches on every side so you have something to grip onto when you place it into the tank). Once you have all your pieces cut out, decide how many and what size support columns you need based on the total weight the floor can hold.

Special thanks to J.W. Cels for his help in figuring this out! Then using the lumber you have left, construct the posts. They can be as simple or elaborate as you want them to be, just make sure their sturdy enough to hold up the tank, you, and your equipment (we don’t need any accidents).

Once the posts are constructed, place them under the plastic and make whatever adjustments are necessary for them to sit tightly in place. Once that’s done, you’re ready to move on to the next step (but you still might want to have a few buddies around to help you with this part).

Make sure you and your friends all know which way is up (so the tank doesn’t end up upside down) and very slowly lift up the plastic just enough that you can place wooden 2x4s under it at even intervals. This will be the support for the posts. Now you have yourself a tank bottom!

Now that we’ve got the floor down, let’s get started on the frame for the walls. You can build these any way you want, but it’s best to build them close to the same size as your tank so they blend in with it. Our walls are going to be 4 feet wide and 8 feet high, so that will be 16 square feet (since our wall is going to be 2 feet out from the frame) of wood. Once this is done, slide out the supports and fill in the open spaces with more wood. This step is the most time consuming as it will take a lot of measuring, cutting, and nailing, but it can be done alone if you have to.

You now have a frame, but it’s not quite a tank yet. There are still some things you need to do to turn it into one. You’ll need the following wood pieces:

16 8 foot 2x4s

12 6 foot 2x4s

You may need more than this, but this is what our wall measured out to. Once you have the pieces cut and ready to go, you can begin building the wall around your tank. You’ll want the posts about 5 inches in from the edge of the plastic and extending up to just under 6 feet. The first thing you need to do is add some cleats on the top of the frame. These cleats will support your plywood roof.

So once again, using the numbers you came up with, arrange and cut your boards into the shape of a roof.

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Once your roof is in place, it’ll be a good time to step back and see what your tank looks like so far. It should at least look like a black box at this point. This will mean you can place the boards for the top of the wall on the posts without a problem. We’ve found that it’s best to nail or screw all your vertical pieces first, then fill in around them with 2×4 horizontal pieces. This seems to work the best and will make it very difficult for anyone to get into your wall (especially if you give it a good stucco coating).

Make sure you completely seal up the top of your frame. You don’t want any light coming in if you can help it.

Now that you have a fully enclosed box, it’ll be time to start building your walkway. This is very similar to building the walls, so if you’ve made it this far, it won’t be too difficult for you. You’ll still need to be very mindful of your measurements though.

You can make this as fancy or as simple as you want, but we built ours out of 2x12s and laid them across the top beams of our wall with the assistance of a few 2x4s for additional support. We then added another layer of 2x12s halfway through for good measure.

With your walkway in place, you have created a second floor to your house! You can extend this as much as you want, but we felt that since we just moved in, we wouldn’t need to go all out yet. We should be fine with what we have until the time comes when we really need to expand.

Seeing as how it’s getting late, you and your dad decide to head inside. You both examine your work and are pretty proud of what you’ve managed to accomplish today. You now have a fully functioning, absolutely massive tank and walkway to your second floor (which is pretty big itself!)

You are ready to get started on the inside of the house tomorrow. We’ll see you then.


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