Loft bed design

Question

So I am very much new to woodworking and I stupidly proclaimed to my housemates that I was going to build myself a loft bed. Obviously this ambition was met with a lot of ridicule and doubt so now my stubborn ass has no choice but to make this bed for better or for worse. I've researched as best I can and come up with a very messy preliminary design which I've had to make on ms paint as I don't really have the money to be paying for any actually good software, I was hoping you might be able to provide me with any tips/hints/improvements that could be made.

The wood I'm currently planning on using is 100mmx100mm 5th grade Scandinavian redwood for the 4 legs and then 50mmx100mm white fir for everything else (side note: could I get away with using the white fir for everything? The 100x100 legs are a significant expense which I figured is probably necessary but I'd love for someone to tell me I'm wrong hahaha) The length of the bed will be 190cm, width will be 135cm and height will be 136cm. The stupidly colourful diagrams below represent the corner joints - 1 is a birds eye view of the joint where the yellow is the leg, red is the rail and blue is the stretcher. 2 shows the view of the joint from the front and 3 is from the left (both with screws/bolts). For the middle stretchers I thought I'd just do a lap joint. I wasn't sure whether I should be using screws or bolts for this, is there generally a better or more appropriate choice of those two? I'm also still unsure on how best to join the horizontal and diagonal supports.

I know adding another horizontal support on the left side would increase stability as would adding a diagonal on the back - these are things I'm open to doing but would prefer to not as I have a wardrobe/chest of drawers on the left so a horizontal beam would be slightly inconvenient, and there's a window at the back which I'd prefer not to block with another diagonal if at all possible. Do you think these things are necessary or can I get away without them?

A few notes

1. I can't drill into the walls as I'm renting

2. If possible I'd like to avoid using glue so I can take it apart when I have to move out and take it with me

3. My current plan is to use plywood on top then put the mattress on that, does this make sense??

4. I haven't bought any of the wood or screws etc yet so open to change on anything really

5. Please be nice/constructive I am aware I'm in way over my head lol but I'm going to attempt this even if it is going to be a disaster I'd just really like it to not be

Thanks in advance for your help!

Answer 1

A few points:

• 100x100mm for the legs is massive. 75x100 should be plenty and 75x75 or 50x100 would probably be my choice if you build it right. I built an awning for my house a while ago using 100x100 legs and thought afterwards that I should have used something much smaller. Smaller sections will want better bracing though.

• Also consider that if it turns out too flimsy you could double up afterwards. For example, if you used 50x100 for the legs and they didn't feel sturdy enough you could come along after with another 50x100 and screw it to the first to reinforce. This might even be cheaper than a single larger piece of 100x100. It won't look as good though obviously.

• My gut feeling is that your design will rack badly from left to right. Extra horizontal supports are not a good way to solve this unless they are very wide. Use diagonals or ply gussets as suggested. Diagonals don't need to go the whole way corner to corner; even small ones will greatly increase the rigidity of the structure and won't get in the way so much.

• Similarly, I'd consider something like 25x150 rather than 50x100 for the rails. It'd be stiffer in the appropriate direction and would help reduce racking a bit.

• There is really no replacement for screwing something to the wall to make it really rigid, really cheaply. If you haven't done so already I'd ask your landlord if they would mind you drilling a couple of holes. IME they might not mind if you promise to thumb a bit of filler into the hole when you leave.

• In your diagram your screws coming at different directions will run into each other. You'll need to stagger them slightly. Also keep in mind that screwing end-on into the grain is weaker than screwing across the grain. You can compensate by using long screws - just make sure your drill/driver has a decent amount of torque.

• I have a feeling that if you lay a mattress onto ply you might get perspiration trapped there, leading to mould. I think this is one reason why beds traditionally use slats.

The dimensions I've suggested are just my gut feeling. If possible, go and have a look at what you are considering and lean your weight onto it to get a feel for how beefy your pieces really need to be. It's normal to overestimate how thick things need to be so I think you might be surprised.