Murphy Bunkbeds

[Dennis Putnam]

I am in the process of customizing a trailer and want to include Murphy style bunk beds mounted horizontally. I have found several plans but I am concerned with how they mount the sleeping surface to the frame. After creating the rectangular frame, the recommended platform is 3/4" plywood attached with pocket screws every 16". I know pocket screws result in strong joints but I just can't see this being strong enough to support a 250# person tossing and turning during the night. Am I being paranoid or rightly concerned? Is this really going to be strong enough to work or should I be looking a some other form of construction? Total weight of the finished trailer is also a concern. TIA.

[Adam Herman]

do you have a link to the plans? could you dado the frame to accept the plywood, like a drawer bottom and then use some pocket screws? With glue, this would make for a very stiff frame and platform.

[Dennis Putnam]

Thanks for the reply. Here is one set of plans although I plan to use alder for the frame rather than plywood. I thought about the dado solution but then I will need to use wider boards for the frame. I want to keep the thickness as close to that of the mattress as possible (6") and keep the weight down as well.

http://www.diynetwork.com/how-to/skills-and-know-how/carpentry-and-woodworking/how-to-build-a-side-fold-murphy-bunk-bed

[Adam Herman]

i see, i was thinking the screws were the other way for some reason. I do not see any issue with strength on this, glued and screwed. I would consider strap hinges or something else to increase the number of screws on that joint though.

[Dennis Putnam]

Thanks. I guess I'm just underestimating the strength of pocket screws and glue.

[Lee Schierer]

Gluing to a plywood surface is still not a dependable joint in my mind knowing the quality of plywood these days. I would opt for good quality # 8 or #10 x 1-1/2" or 2" flat head screws (not dry wall screws) every 6-8" around the perimeter of the plywood bottom up into your Alder. I would also glue the joint before assembly.

[Jerry Miner]

Thanks. I guess I'm just underestimating the strength of pocket screws and glue.

Probably so. The sheer strength of a pocket screw is on the order of 200 lbs. per screw. Use a few more if you're nervous. Glue will help, too.

[Robby Tacheny]

The majority of the strength is at the corners anyway. If you are worried, you could make the wood less tall so that there is less force being applied when someone presses against it. Those sides are not there to hold the person in the mattress, its there to keep the mattress from shifting anyway.

If this is for kids and you see it taking a lot of abuse, just add 1.5" and use 2x lumber for the vertical sides and maybe a few lags and washers from the bottom up.

That's a cool idea. No matter what you do, ease/round the top edges of the wood so someone doesn't a sharp corner in the side or on the bottom of their legs. ;)

Robby

[Mike Schuch]

YES, YOU ARE BEING PARANOID!!!!

Like you I always over build everything and make it much stronger than it has to be. Go look at any brand new $50K trailer and look at the construction techniques used and you will realize pockets screws every 16" is way over kill by every trailer manufactures standards. Every trailer I have looked at it is top quality building if your bunk is held together by a half dozen staples.

Add some construction adhesive, dado a groove or add a small strip under the sleeping surface to further hold the 3/4" plywood if you must... but you really don't need to. I have never seen a commercial trailer with 3/4" ply for a sleeping surface... you will be lucky to get a 1/2" ply sleeping surface and most likely be sleeping on 3/8" ply in most trailers.

[Lee Schierer]

Probably so. The sheer strength of a pocket screw is on the order of 200 lbs. per screw. Use a few more if you're nervous. Glue will help, too.

Except in this design does not place the screws in shear. They are in tension and it is unlikely the screws would break before the threads pull out of the plywood bottom.