One of the questions we're often asked is, "My dorm requires us to use the existing bed or bed springs, how do I use existing dorm room springs with an OP Loftbed" Our usual answer is:
Instead of using plywood for a mattress platform, you will use the existing springs instead. You will need something to support the springs, so build two more center mattress supports and install them near the head and foot of the bed. This will give you three supports for the existing springs. Be sure to measure your springs before fabricating the pieces of your loft bed to make sure that they will fit inside the mattress supports. For a twin OP Loftbed, the springs must measure less than 74"x37". For a twin extra long OP Loftbed, the springs must measure less than 79"x37". It's also possible to make your loft bed a little bigger to accommodate springs that measure more than this.
Another option would be to just set the springs from the bed in your room on top of the mattress platform. You could possibly use a router and create slots in the mattress platform for the legs of the existing bed to go through as well to decrease the amount of unused space between the springs and the mattress platform.
These are just a couple ideas. Brian in Ohio decided to replace the mattress platform entirely with the existing bed springs and bolt the springs to the legs of the OP Loftbed. He sent a number of pictures to show us how he did it. You'll find them below, just click on a picture to enlarge it.
If you are going to use this method (or even the previously mentioned methods) you will want to carefully measure the bed springs before you begin fabricating the parts of your loft bed. With this method, you want the bed springs to fit snug inside the legs of your OP Loftbed--a good tight fit is important to reduce shaking of the bed.