Queen Platform Bed - what size slats for no center rail?

[Jared Brank]

I have a queen platform bed that I am setting up with larger slats so that I do not need a center support or post. There will be just a mattress laid directly on the slats, no box spring. Together we weigh 400 lbs. The slats will be supported by the side rails only. What size and orientation of lumber do I need to use so that it will not sag (at all!) in the middle with no center rail or legs in the middle of the bed? Are 2x4s laid flat okay for this? Or do they need to stand vertically? Or do I need bigger lumber like 2x6s? How far apart should they be? Wood will be regular yellow southern pine lumber from a lumber yard.

[Ed Aumiller]

Similiar setup... Put 3 or 4 pieces of 1x4's and a either 1/2" or 3/4" plywood then put mattress on top of plywood...
You need something flat and secure to keep mattress from sagging...

[Jamie Buxton]

On various sites around the web, there's a calculator named Sagulator. It computes sag versus load for shelf parameters you input. Structurally, a shelf and a slat are the same thing. For your bed, let's try ten doug fir 2x4 slats laid flat. So one of these slats will be loaded with one tenth of your total load, 400 pounds, which is 40 pounds. Sagulator says the middle of the slat will sag .06". That is, with these ten DF 2x4 slats you get 1/16" sag in the middle of your bed. Is that good enough for you?

Alternatively, you could turn the 2x4s so they're on edge. Say you use five of these slats. Each slat then is supporting 80 pounds. Sagulator says it will sag .02". These slats will be spaced somewhat far apart, so I'd put a layer of plywood on top of the slats to prevent the mattress from falling through. Or maybe some 1x4 slats running the long direction on the bed.

[Jamie Buxton]

One more thought... The calculation I did above uses numbers for dry douglas fir. If you buy construction lumber in some parts of the US, it is likely to be green -- that is, soaking wet. Green lumber is considerably more bendy than dry lumber. So if you use green lumber, my calculations don't apply.

[Andrew Seemann]

Don't forget that the entire purpose of the slats is to give slightly, in other words sag a little bit under load. Putting a mattress on a completely rigid surface like the floor can actually be quite uncomfortable, that is why they typically are set on box springs or wooden slats.

[Bill Dufour]

plywood will block airflow and the mattress may not dry out properly causing mold.
Bill D

[Ed Aumiller]

Dufour,
Unless there is a reason for wetness, there will be no mold.... after 50 years, it is still dry... yes, i am very old...

[Alex Zeller]

I believe box springs are a thing of the past. They are now called platforms and are rock solid. Their sole purpose is to raise the mattress to the height you want it at and provide a flat solid surface. The last queen size frame I made was a pedestal design with a 6" over hang. I did run a center support from head to foot but no center post. I used some red maple that had been in my shop for years that was about 3 3/8 wide and 3/4" thick. The gaps between the boards are just under 3" and it's solid as a rock. The frame is hard maple so it'll handle the weight without issues.

I would think 2x4's would be kind of thick. Normally the sheets and blankets cover the sides and foot of the bed but not always near the head. The 3/4" slats are pretty much invisible but a 1 1/2" board would probably be seen.

[Charlie Jones]

I have built several king beds. I use 3 inch slats and a 2x4 with two center legs. On a queen you can use the same slats and put a 2x4 centered under the slats and attached to the end slat at the headboard and footboard.

[Jim Dwight]

The only way to have essentially no sag is to have significant sized vertical ribs. For instance, the platform bed I gave to my son and daughter in law has the rails pretty low, like for a boxed spring, but I made a platform out of plywood that is as high as a boxed spring. Even though the top is 1/2 plywood, it doesn't sag.

My kids and most of my grandkids and I sleep on platform beds I've made. I've used narrow slats, like 4 inches wide, of 3/4 plywood for double beds. I've used 2x4s laid flat for one queen bed. I've used 1 foot wide slats of 3/4 plywood on several beds. I used slats based upon the theory that the mattress needs to breath. I don't think that is true. The bed I mentioned above has a solid top platform and is several decades old with no mold or other issues. The bed I sleep on has a platform of 3/4 plywood supported by the rails. No holes. Works fine.

My suggestion is to try a platform of 3/4 plywood. It will sag a little in the center but I don't think you will notice it. If it bugs you, you can add some ribs under it. Remember that the stiffness formula places the height of the structural member to the fourth power. A 2x4 vertical is a lot stiffer than laid flat, in other words. If you don't like the idea of no air to the underside, you could use 1 foot wide slats. A 2x4 on edge about every foot near the center would make the platform very stiff. Every 2 foot might be enough.

I think my bed with the solid 3/4 plywood platform is, if anything, a little too stiff.

[John TenEyck]

25 years ago I made my queen size platform bed with a solid 3/4" plywood bottom. I also ran a stiffening rib of plywood to the floor the length of the bed down the centerline. As you might guess, it's rock solid. The mattress is something like 13" thick and is very comfortable. No mold issues, including before I had AC.

John