An owner asked the shed designer for as much storage as a sub-100 sq ft shed can give. With trusses, there is one obvious place to look: the triangle over the bottom chords. So the designer now has an attic storage option for truss roofs.
What the option does:
- Checks the attic for storage. The bottom chords are checked for 20 psf of storage (IRC Table R301.5, "uninhabitable attics with limited storage") instead of 10.
- Lays a deck. Panels of the floor's material go across the inside trusses' chords, wherever a 12" tote fits under the top chords. Panel ends land on a chord.
- Adds king posts. At 20 psf a 2x4 chord no longer spans 8 ft on its own, so every truss gets one. The deck goes either side of it.
- Leaves the end bays open. That is how you reach the deck.
How much you get. It depends almost entirely on pitch, because the 12" clear-height line moves in from each wall as the roof flattens. At starting prices, before tax:
| Design | Deck | Added cost |
|---|---|---|
| 8x12, 4/12 | 10.8 sq ft | $101.39 |
| 8x12, 6/12 | 28.1 sq ft | $134.94 |
| 8x8, 6/12 | 14.3 sq ft | $58.56 |
| 10x12, 6/12 | 44.3 sq ft | $148.59 |
| 12x16, 5/12 | 80.1 sq ft | $229.85 |
On the default 8x12 at 4/12 the deck is two 8" strips, about $9 a square foot of shelf. That is a poor buy next to a $40 shelf unit. At 6/12 the same shed gets 28 sq ft. Wider sheds do better because the triangle grows with the width. The cost is the deck panels, the king posts and their gussets, and a few more nails.
Pitch is the lever. A steeper roof costs a little more roof and pushes the peak up. If you have a height limit, the designer still says when it can't be met. If storage matters, 6/12 is where an 8 ft wide shed starts to have an attic worth decking.
The checks are screening checks against published values, not an engineer's design. The chords are checked for boxes and seasonal things, not for people or heavy tools.