paper thin bunk plywood

[Doug33]

Yesterday I winterized the TT. In the process I had to access the hot water heater and the bypass valve. The water heater is located under the lower bunk. My particular TT model has the double bunks, which are very comfortable and easily accessable for even adults. I've actually slept in the lower bunk a couple times.

In order to get to the water heater I have to remove the mattress and then unscrew the "plywood" sheets and lift it out of the way. I was shocked at how thin the wood is. I knew I was in trouble, because when I crawled towards the back of the bunk to unscrew the far end, my knee started to go right through the wood, making a huge crack in it.

I know manufacturers are trying to save every almighty single pound from a TT, but this is absurd. I can't believe this wood supported anyone without collapsing.

After finishing winterizing, I didn't bother putting the wood back in place or screwing it down. If there is a warm spell, I will remove the thin wood, and replace it with something else that is stronger. I was thinking using a pressboard, but I know they are pretty heavy.

Has anyone else replaced their bunk plywood, and if so, what did you use to replace it with. I'm not too worried about adding a few pounds, but I would still like to keep it as light (and cheap) as possible.

Are their synthetic (plastic composite) alternatives to plywood or pressboard?

[Doug33]

dtzackus wrote:

I replaced it with a 1/2" plywood, I added two finger holes to make it easier to lift up on it when I had to put the bypass on the water heater.

I'm going to do the same exact thing to make it easier to access the water heater.

[dtzackus]

Our lower bunk had the same cheap wood. Actually ours was simply the paneling, two pieces. We used it to make shelves in the cabinets for the kids.

I replaced it with a 1/2" plywood, I added two finger holes to make it easier to lift up on it when I had to put the bypass on the water heater.

[oughtsix]

3/8" Baltic birch plywood would be plenty strong. 1/2" will give you plenty of over kill factor. 3/4" is just nuts! When I was a young college kid the bottom of my water bed was only 3/8" thick and it supported me and the weight of all the water. I love overkill but 3/4" plywood is way way way to much overkill.

Hardboard is not very strong. I wouldn't use it. It is barely stronger than particle board.

You could look at chip board but I still think 3/8" Baltic birch is the way to go!

[majorgator]

The panels beneath my bunks, master bed, and dinette are all the same thin luan-type stuff. The weight distribution properties of the mattress/cushion and the positioning of the supports beneath are good enough that the rigidity of the panels don't come into play. I think that it's an interesting concern, but not a valid worrying point. Just my opinion.

[handye9]

Doug33 wrote:

handye9 wrote:
On my last TT, I didn't need to replace plywood, I did need to add some. The 200 lb weight rating, was not enough for my plan to use the TT at deer camp. I have two boys who are over six feet and 250 lbs.

I added a layer of 1/8" plywood and installed some moldings for additional support under the upper bunks.

After the mod, the boys said the the bunks were FKA (fat kid approved).

For replacement, I would replace that 1/8" playwood, with 1/4" plywood. You'll only add a couple pounds and the bunk will be much stronger. If it is an upper bunk, consider adding some vertical support.

Thanks for the reply. Can you be more specific as to the mouldings you added?

The existing bunk plywood is actually two sheets side by side, so there is no issue removing them or having to bend them. However, I like the idea of just adding another layer instead of removing the existing. Although one now has a big crack in it where my knee went through....:o

I didn't need additional support for lower bunk. it was built on 2 X 2's.

The upper bunks were supported on 3 1/2 sides, by walls and cabinets. Probably just 2 X 2' stapled to the studs. I added some wood moldings (like a thick door casing) that matched the finish on the cabinets. Fastened them to the studs, using 1 1/4 inch screws. Maybe, I didn't need to do that, but, we never had the upper bunk slide down on top of the lower one.

[wmoses]

beemerphile1 wrote:
If RVs were built as sturdily as some people think they should be, they would weigh twice as much and you would need a bigger truck. Everything is a compromise.

Hahaha ... thanks. You saved me the trouble of making this point. 🙂

OP - Your experience is the same as mine with the dinette on all my trailers. The thickness of the plywood is to make the RV as light as it can be while at the same time resisting the load of a design human backside - wider area than a knee means that it would not fail under butt load but will crack under knee (point) load. Can't get away from using the knee in some cases, e.g. on our U-shaped dinette when moving the day-night shades.

Adding another layer on top is not the best solution since shear between the planes could still result in failure. We I you, I would replace the panel with a thicker piece of plywood after I did a knee test on it.If satisfactory then it would be fine of any other distributed load that a reasonable body can put on it. 😉

[2012Coleman]

Have you considered installing slats instead of using a solid piece of wood? My son has a bunk bed with slats and is supported very well.

[bhh]

+1 on the Sagulator http://www.woodbin.com/calcs/sagulator.htm In general, "engineered wood" products (press board, OSB, plywood) are less stiff than solid woods.

One thing to note is that deflection is proportional to the cube (^3) of thickness. So double the thickness, you increase stiffness by a factor of 8.

If you want a good compromise of weight vs. stiffness, consider a shop-built torsion box. http://www.core77.com/blog/furniture_design/a_look_at_torsion_boxes_26334.asp Or adapt one from a "hollow core" door.

[Doug33]

WyoTraveler wrote:
I had the same problem with lower cupboard floors.1/8" or less. Had to be bent to be removed. However, useless with such thin plywood. I used 1/2" plywood and installed in sections. May want to do that with your bunks. I reinforced framing also. If you take a drawer into a paint store you can get stain mixed to match just like paint. I took a sample of plywood I planned on using and they matched it very well. I went to Sherman Williams paint store but I'm sure they can all do it.

No appearance issues, since the lower bunk wood is under a mattress and not visible.

I might not even worry about the upper bunk, since I doubt that it will be used much.

[PAThwacker]

colliehauler wrote:

PAThwacker wrote:
I see double bunk beds at 300lb, 600lb, and 1,000lb ratings. I would not buy light weight double bunk trailer with horrid 300lb double bunks.

Most bunk beds have a 125lb or 150lb rating, (for kids).

I am talking about double/full Over double Full Bunks.


Kids bunks aka coffin bunks are 150 to 300lbs

[coolmom42]

Check this out:

SAG CALCULATOR

I ran across it when figuring out what I needed for some storage shelve. Your bunk is basically a big shelf.

The main thing I learned is that even a small reinforcement strip can make a lightweight material support a lot of weight.

[beemerphile1]

If RVs were built as sturdily as some people think they should be, they would weigh twice as much and you would need a bigger truck. Everything is a compromise.

[dadmomh]

Is it possible to just add some vertical supports under the luan? Maybe 3 or 4. It would still allow the flexing of the luan and you could get it out as needed. For an upper bunk, how about adding 1x3 material, maybe 3 or 4 crosswise for the length of the bunk. Back in the day of my boy's bunkbeds, the upper bed had the cross supports and it worked fine. You may have to make a "lip" for the 1x3s to sit on, much like what is probably under your dinette seats. Fast, cheap and easy.

[WyoTraveler]

I had the same problem with lower cupboard floors.1/8" or less. Had to be bent to be removed. However, useless with such thin plywood. I used 1/2" plywood and installed in sections. May want to do that with your bunks. I reinforced framing also. If you take a drawer into a paint store you can get stain mixed to match just like paint. I took a sample of plywood I planned on using and they matched it very well. I went to Sherman Williams paint store but I'm sure they can all do it.