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I am now making a platform bed for my daughter. The width I have to span with the plywood deck is 69.5 inches. I will have a support piece in the middle so the unsupported widths will be 34.75 inches. Assuming I want to make it to be able to support 500 pounds what do you think the proper thickness of plywood should be. Since I'm asking how about thoughts as to how many support legs for the bed besides the four corners and at least one in the middle of the support beam. There will be no box spring and the king size mattress is a memory foam and I was told it needed solid support not spaced slats.

Thanks for any thoughts and suggestions.

wrmnfzy wrote:I am now making a platform bed for my daughter. The width I have to span with the plywood deck is 69.5 inches. I will have a support piece in the middle so the unsupported widths will be 34.75 inches. Assuming I want to make it to be able to support 500 pounds what do you think the proper thickness of plywood should be. Since I'm asking how about thoughts as to how many support legs for the bed besides the four corners and at least one in the middle of the support beam. There will be no box spring and the king size mattress is a memory foam and I was told it needed solid support not spaced slats.

Thanks for any thoughts and suggestions.

I would use 3/4" plywood with a support beam down the length of the center with with two equally spaced legs on the support beam. That should be more than adequate to support 500 pounds. It is easier to use thicker plywood with less support legs than thin plywood and a bunch of support legs.

Thanks, I planned on using a 2x4 for the support beam and was going back and forth between 1/2 and 3/4 ply for the deck. So you feel the four corners would be enough on the outer frame with the two spaced on the support beam. Thank you for the reply. She plans on painting the unit and I will photo the piece, assuming she doesn't change her mind before I start. I was also fluctuating for the outer frame between 2x6 or doubled 3/4 ply cut at 5-1/2 widths. I planned on 1x3 on the top of the outer frame with a 1" overhang so the plywood would not be a problem.

If I had the choice between construction 2x lumber and sandwiched 3/4" plywood for something that required straightness I would chose the sandwich.

wrmnfzy wrote:Thanks, I planned on using a 2x4 for the support beam and was going back and forth between 1/2 and 3/4 ply for the deck. So you feel the four corners would be enough on the outer frame with the two spaced on the support beam. Thank you for the reply. She plans on painting the unit and I will photo the piece, assuming she doesn't change her mind before I start. I was also fluctuating for the outer frame between 2x6 or doubled 3/4 ply cut at 5-1/2 widths. I planned on 1x3 on the top of the outer frame with a 1" overhang so the plywood would not be a problem.

Yes it should be way more than you need. Again, the 3/4" ply will eliminate the need for more legs which add to the construction time and would be a hassle to install properly.

JPG wrote:If I had the choice between construction 2x lumber and sandwiched 3/4" plywood for something that required straightness I would chose the sandwich.

I totally agree. Laminate two pieces of 3/4" ply 3" or 4" wide for your center beam. It will never move.

Thanks, all I need now is the go ahead from my daughter. I will post.

Are you going to have a box spring ?

If so it will distribute the weight some what.

I like the plywood suggestion , I just completed a bed build and it is solid as a rock , between the wife and I ,,,and the dog ,,,,,we are close to the 500 lbs mark . it is very solid , We doubled the plywood in all the corners as well as the ends where the mattress plywood lays .

No box spring and she wants it to be about 20" high from floor to top of mattress.

As another option pick up two straight kiln dried 2X4’s at HD and laminate them together. That will give you a very stable beam and a little simpler glue up.
Paul