How Did This Get Started

My kinds wanted bunk beds. My wife thought they should be full size. I looked at commercially available options and they seemed too flimsey.

Planning

I wanted to build this out of wood, and figured construction lumber would be strong enough. Most of the commercial solutions used 1x3s or 1x4s with maybe one center support. The posts weren’t much bigger,

Structural Choices

I decided to use Simpson Joist Hangers and Structural Screws for this project. Many people use lag bolts or pocket screws. I am sure that works fine, but I wanted

Poor Calculations

Structural supports are actually 2x4s, and I am using the AWC calculator for floor joists. Inputs: 2x4’s, L/360 deflection, 19.2” spacing, 30 psf live load, 20 psf dead load Outputs: Max Span: 77”, Minimum Bearing: 5/16”

My spacing is 17.5”, so slightly stronger than the calculator gives credit for. The length of a full bed is 75 inches, and my length ended up being slightly higher than that, but less than 77 inches. Much more than 5/16 of an inch rest on the Simpson joist hangers, so I assume this is a minimum

Total weight capacity: 54”74=28 1/8 sqft. Dead load over 28 sqft = 1254 inch wide 1x4s (0.5 lbs / ft) = 124.5*0.5= 27 + 70 lb mattress ~ 100 lbs dead load ~ 4psf dead load Live load max = 28 1/4 * 30 = 843.75 lbs. The 2x4 joist hangers are rated for 690 lbs, 2x8 at 1,040 lbs. Subtract the wood and mattress from690 and you get 600 lbs.

So with all that said, the lowest value is 690 lbs, so I figure each bunk is rated for 600 lbs.

This is enough for a few kids, I’ll take it.

Preparing and Finishing the Wood.

First step was to route a 1/4 inch roundover on every edge. Sand each side - 80, 150, 200 grit Stain Three coats of poly

Stain that was given to us by… It is a combination 2 parts X 1 part Y. Then I put three Final coats was PolyWhey from Vermont Natural Coatings. This was about twice the price of traditional polyurethane, but I have been trying to go for more natural options. Three coats on every surface used up 2 quarts.

Spacing

There were four spacings to consider

  • Under the Bed for storage
  • Wanted 7 inches from the bottom of the post to the top
  • Height from top of bottom bed to bottom of upper
  • 8 foot ceilings - 13 1/4(platform plus bed) * 2 - 7”(under bed storage) = 62.5 inches. I put 30” above the bottom since the beams give an illusion of an extra 3.5 inches.
  • Height from top of upper bed to ceiling
  • The above calculation left 32.5 inches from the top of the upper bed to the ceiling.
  • Spacing from top of upper mattress to bottom and top of the guard rails
  • Guard rails ended up being 2x8’s. The standard is to have guard rails 5 inches above the top of the mattress. The 2x8’s were positioned so that half an inch was below the mattress, leaving 7 above. This should have been lowered by an inch or so.

Adding Screw Caps

After assembling everything, I realized the scew heads were sort of sharp and would rip up bedding, mattresses and kids. So I went about finding a way to cover them. Ended up putting Pro-Dec Snap-Caps on every screw to protect whatever they may come into contact wth.

Costs

Lumber: $ 310 Hardware: $ 240 Finishing: $ 140

What I Would Change

If I did this again, I might go for a different type of post and beam connector. The Simpson connectors were fine, but expensive and difficult to get perfectly square. I could use hidden T connectors, but would need to change the beams to 4x6 and the hidden connectors are $45 per connection instead of $6. Outside of Simpson, there are some Concealed post brackets for $7 each, likely $10 including screws.