Unusual bed sag with new mattress

HI all-

I just recently purchased a new latex mattress, the details of which can be seen in the following thread:

The mattress is situated on a platform bed and seems generally to be OK, but we’ve noticed that one side of the bed sags a bit under weight. At first we suspected it was the mattress, but after rotating the mattress 180-degrees on the frame, the sag seems to be situated on the same side of the bed. It should have moved to he other side if the mattress were the culprit, so the problem must be with the bed, although we never noticed anything like this with the previous mattress. We’ve inspected the bed with weight on the problematic side and have not noticed any unusual flex in either the slats or the frame, and we’ve tried two sets of slats with the same result.

Attached below is a crude diagram of the bed minus the slats:

It’s a 5-leg design with a center support rail. one side of the rail feels softer and floppier than the other side. I don’t think this is an issue of weight differential because the lighter person sleeps on the problem side. I suppose my question is this: should I just summarily dispose of the bed frame, or should I expect something like a bunkie board or similar to help with the situation? Any insight into the matter would be appreciated.


Hi LilFonky,

I think your testing has confirmed that the issue is somehow with the platform (and it would greatly surprise me if an issue like this was with a new mattress) but it’s unclear to me exactly where the source of the problem may be.

On principle and based on curiosity alone … I personally would try to track down the problem but this is because I just don’t like spending money on something when it isn’t necessary and I also like to track down a problem before I “fix” it.

What type of slats do you have on top of the mattress? Are they a double set where the ends of each side rests on the center support and are they solid on the mattress without any shifting? Are they connected with a fabric strip or just loose slats? If you put the slats on and walk on them … are they secure and can you notice any flexing or shifting that may account for the issue? Can you notice the issue more on the top part (by the head) or lower part of the frame or both? Is there any obvious flexing of the frame itself without the slats (wobbly, going out of square, or the center support seeming to be loose where it is connected)?

Also … can you explain a bit more about what you mean by “one side feels softer and floppier” because the frame should be very solid and not floppy at all.

My tendency with a wood frame would be to try and identify the cause and “fix” it if I could before I replaced it.


The slats are one solid, not split into halves, and they are connected by a strip of fabric. We tried a different set of slats constructed in more-or-less the same fashion but more closely spaced, and got the same results. The “one side feels softer and floppier” comment was in reference to the feel of the mattress when laying on it, not to the frame itself. The frame looks and feels solid when the mattress is removed. I’ve not walked on the slats, but that’s a good idea. The issue seems to run the length of the mattress, and if I roll my body from from port to starboard, the problem becomes evident as soon as I cross the center of the mattress, past where the center support rail runs. There must be some kind of asymmetrical flexing going on but it doesn’t seem visible in any obvious way.

To be clear, it’s not a dramatic effect and I didn’t notice it on the first two evenings of sleeping on the mattress. There’s no corresponding noise. It’s not the sort of thing that interferes with our sleep, it’s just a perplexing, somewhat-annoying-to-think-about curiosity. I’m leaning towards a bunkie board purchase to see if that helps.

Question: how are bunkie boards typically constructed? Are they a solid plane covered in fabric or are they like a box frame with cross members?

Hi LilFonky,

Asymmetrical flexing of some type in the platform bed itself would be my guess or somehow the side of the bed is bowing out or the wood that the slats are resting on on that side is somehow loose or flexing.

I think a bunkie board would probably help because it would be more solid and less affected by any flexing of the frame than just the slats.

There are quite a few types of bunkie board just like there are different types of foundation and some are better (and stronger and more supportive) than others. They were first used as a thin base for a bunk bed mattress meant mainly for kids so were made fairly cheaply with a wood frame with a few slats across it covered in cardboard and fabric. Great for kids but not really for adults. Since the advent of platform beds … they started to make them in all sizes and a little stronger with more cross slats and hardboard or MDF on top as a legitimate thin replacement for foundations. Some are made with more closely spaced slats like a slatted foundation instead of a solid surface over fewer cross slats. Even just slats by themselves with fabric strips to join them are used as a bunkie board without a frame with edge pieces for the slats to sit on. Plywood covered with fabric is also used although this is not as good an idea because plywood is more prone to flexing and warping over time and can contain glues that offgass.

A standard bunkie board would have a frame with various cross slats with a hardboard solid surface on top and this should work to solve the issue. A slatted slatted bunkie board on a frame like this should also work well and provide more ventilation for the mattress.

It’s a mystery though and I’m curious what the cause ends up being. Walking or crawling carefully on the slats on the affected side should show something flexing or moving that wasn’t supposed to.


Seems like the bunkie board is the way to go. A couple of other questions, just to make sure I understand what I’m getting into.

1)The idea is that the bunkie board goes on top of my current bed slats, yes?

  1. Do you know if the bunkie boards linked above are structurally similar to the Crate and Barrel bunkie boards you’ve linked up in other threads, or else to these Poundex bunkie boards?

Based on price and your recommendation I’m leaning towards the FOA piece you linked up, but I want to be sure I’m considering all the angles. Anything else I should be thinking about before I decide?

Hi LilFonky,


If you click “details and dimensions” … the Crate and barrel says that they use cardboard which is not as strong and would flex more than hardboard (or closely spaced slats). The poundex description only says “solid wood” so its probably fine (although it’s more expensive).

I know that haverty’s has one that according to the questions and answers has a solid wood surface (not cardboard). There are probably many more but I haven’t done much research into the best bunkie board sources.


I’m wondering if your bed is level, if the center foot sits level and/or completely rests on the floor. Another thought is whether the slats are properly supported by the center bar. Do they rest on a ledge and if so is that ledge sufficiently deep enough or at least equal to the depth of the ones at the edges. I suppose it could be possible that the “ledges” could be insufficient at the edges too but less noticeable since one doesn’t sleep at the edge?

Oh and have you tried adding more support to the center in the form of two additional makeshift feet?