Make the mattress platform as high as possible while providing adequate headroom in order to provide maximum living space. Three feet of headroom should be adequate. When someone is startled from sleep, they may sit up quickly without thinking about headroom—thud!
A mattress on a rigid piece of plywood is much firmer than when it is on top of box springs. Put your son’s current mattress on the floor and let him try it for a couple of nights before you go to the trouble of building the loft bed.
Assuming the person tried out the floor and liked it, let’s get started on the loft bed. The simplest design is a plywood-covered frame suspended between four-by-four posts. If you would like to get a little fancier, consider building the mattress frame so that the mattress is recessed down in it.
A standard twin-size mattress is about 38 inches wide by 76 inches long, but measure the mattress to be safe. Make the frame a half-inch bigger all around than the mattress to allow for just a little wiggle room. Do not make it too big, or your son will surely bruise his shins on the hard edge that extends out.
First, make the mattress frame using standard two-by-six lumber. Assuming that your son has a normal mattress, the size of the finished frame will be 39 by 77 inches. Use nails or screws to assemble the two-by-six frame pieces. The plywood cover will provide plenty of rigidity for it.
Make the plywood cover with three-quarter-inch-thick A/C plywood. To make this simple without measuring, line up a four-by-eight-foot sheet of plywood on one corner of the frame. Nail or screw it to the frame. A fastener every eight to 10 inches should be adequate. Saw the plywood along the other two sides so they are flush with the frame.
Now, get out the calculator. Measure the thickness of the mattress and the height of the ceiling over the bed. Subtract 36 inches (headroom) plus the thickness of the mattress from the height of the room. This will give you the proper distance from the floor to the top of the bed frame.
For an eight-foot ceiling and a nine-inch-thick mattress, this will be 51 inches. Lay four four-by-four-inch by eight-foot posts side by side on the floor. Push them up against a wall so that they are all even. Measure 51 inches from the wall and mark each one with a square.
Measure up two more feet and cut off the excess. This allows about two feet of post to stick up above the bed. It is attractive and provides a place to hold when getting in and out of the bed. Bevel off the sides of the top ends for a more decorative look. Adding a headboard later also helps.
Lay out the four-by-four posts on the floor. Set the frame up on its edge on top of the posts at the 41-inch mark that you made. Drill holes and assemble it with 3/8 lag bolts. Attach the other two posts and have your son help you to tilt it up. Attach a small ladder at one end.
