loft bed design questions

[Matt Hunstiger]

I am making a loft bed for each of my kids. They each have full-sized beds, so the mattresses are 54"x75", and that's what I'm building the frame around. The verticals for the corners and ladder (part of one corner, so 5 vertical posts in total) will be 4x4s, and I'm planning on making this out of Southern Yellow Pine. The support structure underneath the mattress will be: a perimeter of horizontal cleats attached to the bottom/inside of the 1x6 rails, 1x4s across the width of the rectangle, and 3/4" plywood atop that.

So here are my questions:

Does the support for the mattress need a central piece down the middle halfway between the side rails, since it's a full-size mattress (dashed brown line in top view sketch below)? If yes, what size and best way to attach it to the middle short ends of the box?
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What size should the supporting horizontal cleats be around the perimeter? Below I made a sketch with the cleats in green, as seen from above and then as a cross section.
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Thanks for any suggestions. Apologies for my artistic skills. I hope my questions make sense.

Matt

[Scott Winners]

Your 4x4 post strength is magnificent overkill, no worries there - but look for FOHC end grain. Free of heart center cut. No pith, and no face grain. You want the ones with all edge grain on all four sides. Also, beware moisture content. I can't buy SYP up here, but Doug Fir 4x4 I can get are almost never dry all the way through. Look also for run out. If you are looking at a stick that is pretty straight most of the way and you can cut off the wonky bit, you got a keeper. Platform height/ 4x4 length is not specified in your post, I imagine probably around 6 feet for an 8 foot ceiling.

If you can overlook the Fellowship of Huntsville Church FOHC is internet searchable. When you cut a bit off your 4x4s, do rip or split one open to check the MC inside the board to have realistic expectations. I will be ecstatic for you if you find 6-8%, but I will not hold my breath. What you do want is for this thing to not come apart as the 4x4 finish seasoning.

If freestanding and tall enough to put a desk under you are going to want diagonal bracing of the 4x4 on two adjacent sides, three would be better. You will have more than adequate post strength to use SYP 2x4 as the fifth leg supporting the ladder rungs, most likely.

There should be some consideration to how much the children are expected to weigh when they graduate HS and move away to college, and how active they are in their sleep. If they are going to move out in their late teens at or under about 200# and they aren't wresting the fitted sheet loose from the mattress every night, 2x4 for the 5th leg.

I would probably go with riven or split hardwood rungs. You could do shallow dados and SYP 2x4 rungs, but I would not hang the rungs on screws alone.

Can you cut shallow dados in the post tops so the load is transferred from the mattress frame directly to the posts with the fasteners just holding the pieces in alignment? As drawn you are counting on the fasteners to hold the kids up in the air.

For the cleats, bigger is better. It comes back to how much they toss and turn in their sleep. Half inch plywood will probably be fine on the slats. I had a queen sized bed with half inch ply to lay the mattress on after I moved out of my parents home (if you know what I mean) and half inch was plenty.

So cleats. I just realized today I can buy pretty nice DougFir 1x6 for about the same price as junky furring strips, with the caveat I need to rip the DF down to furring strip size.

My concern at this step is to get it glued and screwed (or nailed) together without the cleat splitting. If you can make your cleats and slats 3/4 x 1 1/2 actual out of nicely grained SYP or DougFir you are probably going to be fine on splitting during glue up if you predrill and counter sink your screws. I would glue full length and have enough screws in there to take the clamps off and get busy on squeeze out as soon as I was done driving screws. You really really want to turn the face plates and cleats into one piece of wood. Think of the finished plate/cleat subassembly as a 2x2 with a permanently affixed 1x4 stiffener. You could start with a 2x6 and router out a 1x4...

So 1x6 frame around the perimeter, with a cleat 1.5 inches tall and 0.75 all around, I would want to shoulder the 4x4 posts to accept both the cleat and the facing on the shoulder at the top of the post. I would no want the post tops sticking up over the cleat. Maybe 1/8 to 1/4 shy. I do want slats at both the head and the foot end resting right on the cleat so the plywood is fully supported full perimeter.

I would put in another cleat wherever the seam in the plywood falls. For your 54" width x 2 assemblies you are going to need three sheets of plywood. I personally would cut a 16x96 inch scrap off the first two sheets, and then 2 pieces 22 inches plus one kerf width out of the third sheet. That would give me a puny scrap to send to the dump, 2 scraps at 16 x 96 and the center seam in the finished item as close to on center as I could make it easily without buying a fourth sheet of plywood.

For the slats I would use more slats at 3/4 tall by 1.5 inches wide rather than fewer 1x4 slats. One each at the head and foot end for sure. If you have one slat every foot or less it will support a 200 pounder no problem.

If one of your kids is playing football and bulking out, for the center cleat you could use a 2x4 instead of 1x2. Perfectly fine to taper the ends down to the 1.5 actual to match the frame at each end, but thicker in the middle where the cleat (beam) needs more strength. Like a floor joist in timber framed buildings.

Then half inch plywood on top. Your 1x6 is probably going to be 5.5 inches wide, minus 1.5 actual for the cleat, minus 3/4 actual for the slat, minus probably 7/16 for the plywood, your rim for the mattress should be around 2 and 13/16, should be fine.

The two main things I see not drawn are shouldering the post tops so the weight of the kid goes directly into the mattress into the top frame into the posts with your (non weight bearing) fasteners just holding stuff in alignment, and diagonal bracing on the legs.

I would not expect to find all eight 4x4 with one trip to all the home stores in town, local. One thing you could do, for practice, is use your 4x4 offcuts at maybe 24" or so and start with a 'loft bed' only two feet off the floor. That will give you a practice run at the joinery, it will give your remaining 4x4 posts at 72" nominal more time to season, and if your build falls apart with a kid on it they probably won't get hurt and you can inspect and upgrade before you build taller ones.

[Maurice Mcmurry]

Our twin bed size bunk bed mattress holders were (are) a box made from 1" x 7" hardwood with a 2 X 4 laid flat for a cleat around the inside. The deck is 5 ply 1/2 inch Fir plywood. I did not use a center support. Your Kids are going to have the coolest rooms.

[Matt Hunstiger]

I really appreciate the replies. One frustration is that the SYP 4x4s I can only special order from Menards, so I don't get to pick it, but it is kiln dried. If I use Douglas Fir 4x4s, kiln dried, I can pick it because it's at the store. The 8 footer Fir are about 3 dollars more than the SYP, which isn't such a huge deal.

The design I'm using is supposed to look like this
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and ultimately comes from here http://blog.afloat.ca/p/loft-bed-plans.html

Compared to the plans from that website, my version would be taller, so that an actual functioning desk for eventual teenagers could fit underneath, as well as a custom bookshelf. The plan I found has the posts at 68", which I think is way to short for a desk underneath. Looking at the image above, the 3 1x6s are 16.5" tall, plus the 2 3.5" gaps gives 23.5" total for mattress height and containing rails. The full sized mattresses are about 10" tall. So about a foot of rail containment when factoring in the plywood, cleats, and transverse supports. But that only gives (68-23.5) 44" of space below, so I was thinking the 4x4s should be 84" tall. That way you'd have about 24" between the top of the mattress and the 8' ceiling, and about 60" of space underneath the bed, which is enough for someone to actually sit at a desk.

I'm also interested in using bed frame hardware, so that the 1x6s would abut rather than overlap the vertical posts, which is what I drew the blue and purple 1x6s not overlapping the orange posts. I didn't have enough detail in the original post, but perhaps with all of those 1x6 horizontals racking won't be a problem? Maybe using hardware like seen below (fairly inexpensive but well-reviewed, from Rockler) is a bad idea in terms of racking and I should be using fasteners (the plans call for through bolts)? It's no problem adding some diagonals to stop racking. I was initially thinking of bracket hardware for the two short end rails above the mattress on the side opposite whichever short wall is against the wall, to aid in getting the mattress up and changing sheets (those two could just be popped off), but then I got enamored with having all brackets. I could still have some diagonal supports, even with brackets, or maybe just drop the brackets, except for the two I just mentioned for changing sheets and putting up the mattress.
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Thank you. I have more to mull over and probably have more questions!

[Gary Ragatz]

Matt,

I have no first-hand experience with loft beds, but 24" of clearance between mattress and ceiling seems awfully tight. Probably fine for little kids, but if, when they're teens, they're approaching 6' tall, getting in and out of that bed is going to be a chore. Even when the kids are small, that's not much clearance for changing linens. I'm 6' tall, and I would need clearance of almost 36" to be able to sit up in the bed, even allowing for sinking into the mattress a couple of inches.

What if, rather than thinking about someone sitting under the bed, you used that space to store a desk on wheels? Kids pull it out when they need a desk and push it back when they need the floor space. Seems like there would be plenty of space for a good-sized desk and chair under the bed.

A note on Menards SYP. I special ordered some 2x SYP lumber a couple of years ago. Quality of the wood was fine, but moisture content was nearly 20% in most of it. Took a few months of air drying in my basement to get it dry enough to use for a bench project.

[Matt Hunstiger]

I don't know what happened to my other reply, so I'll try it again.

That's a good point, Gary. Sitting at the table I can look directly at ~51" using a tape measure touching the ground. So I think maybe I'll cut the posts 84" and start with a lower bed setup, then move up the frame as the kids get bigger. Putting a desk on wheels could work too. Thanks for the reply.

Matt

[Scott Winners]

When I was in college the kids with loft beds were able to sit at their desks under the beds, but they couldn't stand up under there.

[Scott Winners]

If your Doug Fir has on the mill mark or mill stamp the characters "s-GRN" is was surfaced green. Western Wood Products Association (WWPA) specifies such a label can only be applied to Doug Fir "under 20% moisture content." My experience with s-GRN DF suggests the moisture content when my sticks are surfaced is typically somewhere between 19.9 and 19.99 percent.

There are multiple agencies providing mill stamp certifications for SYP. To interpret the mill mark you would need a picture of the entire mill mark to figure out which agency issued the stamp, and then look up the spec for whatever else is in the mill mark on that agency's website. The SEMA (South East lumber Manufacturers Association) grading guide is/was available online as a .pdf, so I didn't buy a paper copy. I have zero hands on experience with SYP, but on paper it is very much like Doug Fir, the best of the regional softwoods for strength and so on. Neither one of SYP or DF are hickory or white oak, but they are both plenty stout, plentiful and inexpensive.

4x4 posts from either will be more than adequate post strength for a loft bed. Bracing against wracking and eventual failure is the more important problem.

[Matt Hunstiger]

So I've been thinking about the feedback and taught myself some sketchup to make a mock up. Right now the top of the posts and the top rails are at 84", which may change as I talk to my kids about what they want (lower). Note that although I'm talking nominal board sizes, in sketchup I did use 0.75" x 1.5" for a 1x2, 0.75" x 5.5" for a 1x6, 1.5" x 3.5" for a 2x4, and the 4x4 posts are 3.5" x 3.5". Other than the plywood, the only thing I'm using is 1x2s, 1x6s, 2x4s, and 4x4s. I found a lumber dealer (Bliffert) where I can get SYP 4x4s without having to buy them sight unseen, unlike Menards. Everything will be SYP except for the plywood, and the ladder rungs, which I will use a hardwood.

Image 001.jpg

I included a 10" tall mattress in white for reference. The lower stabilizing boards are 1x6s that are diagonals to prevent racking. They will be overlapping the posts and double-bolted to them. I just arbitrarily chose 2' and 3' heights for where the diagonals would intersect the posts, but if flatter or steeper diagonals is better, let me know.

The interior box which the mattress sits in is 76.5" x 55", and the plywood pieces are 76 3/8" x 32" and 76 3/8" x 22 7/8", which I can get from 3 pieces of 1/2 plywood (for two beds).

Image 002.jpg

Under the plywood I have eight 1x2 slats, four on either side of a central 2x4, which will have a rabbet cut out of each end so it rests on top of the cleats and is flush with the other 1x2s. Under the seam between the plywood sheets along the long axis will be another 2x4, which will overlap the shorter 2x4 through a 0.75x3.5" dado cut through the shorter 2x4.

Image 003.jpg

Image 004.jpg

As can be seen, the but end of the longer 2x4 abuts the end cleats. I was thinking of joining them with Kreg pocket screws, placing the pocket holes on the top side of the longer 2x4's ends. I am open to other suggestions if this is a bad idea.

For strength I have changed the original idea of the cleats just hanging off the interior/bottom of the 1x6s with glue/fasteners to having recesses/shoulders cut into the 4x4 posts, so that the cleats have something to sit on over the posts (in addition to being fastened to the 1x6s with glue/screws).

Image 005.png

So the long-side 1x6s abut the posts on the ends, but the long-side cleats rest on shoulders cut into all the posts. The short-side 1x6s will sit on the shoulders just on the very ends. The short-side cleats do not sit on top of the posts, as I wasn't sure of the utility of 0.75" of the ends having something to rest on. Happy to be informed I'm wrong.

Here is a view with the 1x6 removed on the short side.

Image 006.png

The left side post of the ladder is a little funky because I have the 1x6 going through to the far right post, and room for the cleat to sit on a shoulder, and on the front side of the post there are recesses for the 2x4 ladder rungs. Here is a close-up with the 1x6 removed.

Image 007.png

The horizontal 1x6s will be attached to the posts with hardware from Rockler. The diagonal 1x6s will be bolted. I was just going to put the hardware on the outside on the long-side 1x6s so that the interior of the post and 1x6 surfaces are flush.

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Comments, suggestions welcome.

Matt

[Jamie Buxton]

Kids won't mind climbing up into bed. But who's going to be changing the sheets? How does that person feel about this bed?

[Matt Hunstiger]

That's a good question. That would mostly be me. The lofts will be in a corner of each room, so my plan is to use the top two end rails that come off to slide the mattress out a few inches to aid in changing linens. Right now the under-head clearance is about 5'. The goal is to be able to sit under there with a desk. So right now my 10yo is about 4'7" tall, which of course gives plenty of clearance for standing and sitting. I'm about 5'9", and sitting at the dining room table my head would still have room at about 4'6". He might of course be taller than I am. Anyway, I could bump the setup down 6"s. I can also build it with lower posts now, and redo it when they are older with taller posts. I should set up something to see what changing the sheets would be like for this bed. "oh, what fresh hell is this?"

[Gary Ragatz]

Matt,

I hate to be a naysayer, but I don't think you can achieve what you're trying to, when you're working with an 8' ceiling. 24" mattress-to-ceiling clearance is probably okay for your 10yo. It's going to be a PITA for you changing linens. And your plan seems to be to make that clearance tighter as the kids get bigger.

My suggestion is to size the loft for a 36" mattress-to-ceiling clearance. This should give you comfortable sleeping space as the boys grow and reasonable clearance for you to change linens. This isn't going to allow enough space to sit at a desk under the bed, so you need to rethink how to use that space. If you don't like the idea of a roll-out desk, here are some other possibilities:

(1) If you really want the kids to spend time under the bed, put in a couple of beanbag-type chairs so they can lounge there. Also good enough if they're using a laptop or Chromebook for school work. Get them each a lap desk, in case they need a writing surface. Build in some shelves or cubbies for storage, some decent lighting, and they have a nice lounging/workspace. With a 50" clearance under the bed, this might work for them through high school.

(2) If you really think they need a desk, build a fixed worktop into the loft frame. Kid sits outside the footprint of the bed, so head clearance is not an issue. Chair slides under the worktop when not in use, so it uses up almost no floor space. You could put in some task-lighting under the bed frame.

(3) If the boys use a chest of drawers for clothing storage, maybe that could go under the loft, and the freed-up space could be used for a desk.

So, I've beaten this drum twice now, and I'll shut up.

[Matt Hunstiger]

Gary,

I do not regret these comments at all. Nothing has been purchased, and nothing written in stone. Since my longer update with Sketchup the other day I have bumped the height down half a foot in my model, which puts the post tops at 78", leaves ~28" between the ceiling an the mattress top, and has ~4' 6" under the frame clearance. My son is sleeping so I will measure his dresser tomorrow to see how tall it is. I know my daughter's dresser would fit under a shorter setup. Actually now that I think about it I kind of like the idea of a desk that is attached to the frame, but swings up out of the way. I just rewatched a bit from Ask this Old House where Tom Silva helped a woodworker build a wood shop in her 1 car garage, and they made a bench that hangs from the wall on a hinge with legs that fold out ("How to Set Up a Garage Workshop | Ask This Old House"). So here's just a quick rectangle in sketchup without any real frame showing a desk surface that could be attached to the short end. I like this idea.

Image 008.jpg

[Gary Ragatz]

Matt,

I think the fold-down desk idea has a lot of potential. Wouldn't be practical to put drawers in the desk, but if you wanted some storage, you could attach some shelves/cubbies/whatever to the posts, so they're hidden when the desk is folded up, but accessible when it's folded down - kind of like what you might see at the back of a roll-top desk.