1

I've got a 16' (length) x 10' (width) saltbox-style shed that I'd like to convert into an office. The roof is supported by simple triangle trusses of 2 x 4's. Each of the trusses is cantilevered out beyond the framing about 12". This is a simple 2d drawing of the framing, shown from the side of the shed, with the chord laying on the top plates:

Shed side angle

I'd like to know what my best options are for how to get more headroom in the space. I've thought about adding a 4 x 4 in the walls on each end of the shed and installing a ridge beam, but that wouldn't solve the cantilever problem. Collar ties would probably be sufficient for the size of this shed, if it weren't again for the cantilevers.

Could I use some sort of slider and wedge combo with plywood gussets to shore up the roof support? Or is there something else I could do?

11
  • 2
    Keep the same design but just increase the height of the walls.
    – Solar Mike
    Feb 19 at 8:38
  • Another option is to lower the floor.
    – Solar Mike
    Feb 19 at 8:40
  • How much more headroom are you looking for?
    – Armand
    Feb 19 at 8:42
  • The chords sit at about 6' 3", and I'd like to get it up to 8 feet. Ideally, I'd open up the structure so I could vault the ceiling. Lowering the floor is not a possible option, and increasing the height of the walls is complicated based on the shed placement. Feb 19 at 9:12
  • Does your area have snow?
    – Jack
    Feb 19 at 22:56

2 Answers 2

4

Option 1

As a variant on increasing the height of the walls, you could create a mini truss for the front and rear cantilever portions. The vertical truss pieces should typically be 2/3 in for 1/3 cantilever. See the annotated photo. Add the ridge beam (roughly sized as two structural 2x12's nailed together from New Zealand residential codes) and add the green vertical truss piece and then remove the bottom chord. The bottom cord keeps the walls from moving out under a roof load, so with the new design, the orange metal will be needed so the rafters can now take that force. I would normally use 1/8" or 1/4" steel on both sides bolted on, but nail-on plates may be strong enough.

Lookup standard span tables for your country to figure out the ridge beam sizing and if you have any concerns, check with an engineer.

Annotated changes

Option 2

Use a plywood box-beam inspired by the solution from @Jack. This avoids having to add a ridge beam and would be what I would do personally. See https://img.bretts.com.au/long_span_beams_span_tables.pdf for more details on box beams and span tables (in metric) to get familiar with this. Add structural adhesive as well as the nails for extra strength. The nails are critical, do not use screws unless they are specifically for structural applications and follow the nailing pattern.

You can try to do some truss calculations on your own using https://skyciv.com/free-truss-calculator/

Plywood Box Beam

12
  • Can you clarify the "orange metal" comment? It's not clear how the modified framing prevents the walls from tilting outward at the top. Feb 19 at 16:03
  • @AloysiusDefenestrate It (the orange hardware) means to make a moment connection to restrict the outward movement. I don't think 2x4s can handle the task.
    – r13
    Feb 19 at 18:48
  • This is a really interesting idea. How would I put these mini trusses together? Would I need to sister the studs and break through the top plate? And re: the structural ply, are you thinking gussets for that space? If you’ve got any articles or resources I’d love to see them. Feb 19 at 19:20
  • @r13 is correct, the orange metal bracing (I should have said plates) take the moment that would cause the walls to spread outwards or fall inwards. You would need some bolt-on plates for this as timber probably wouldn't be strong enough. I based this upon designs from AS/NZS3604 which is the standard timber design handbook for New Zealand and Australia.
    – Eric
    Feb 20 at 11:13
  • @JoshWinskill - for the studs above the wall, you either need to break through the top plate to install them or you can install them above the wall and add steel strapping down the front and back to ensure that it is as strong as a stud that has the 2/3 backspan.
    – Eric
    Feb 20 at 11:17
1

This is a slightly different take on another answer.

enter image description here

enter image description here

9
  • That may work, but I think the forces on the front box beam at the ridge are likely to exceed the capabilities of plywood. Bolting on some steel brackets would fix that and make this viable.
    – Eric
    Feb 20 at 11:19
  • @Eric ,both sides of the roof are essentially "hung" off of the ridge beam. The rafter tails of either roof only need to bear on the outside walls. There should only little if any splaying of the roof rafters in this configuration. The plywood and the associated 2X4s are to transfer the cantilevered roof load directly to the wall plate. The plywood is essentially a replacement for metal truss plates, nailed well enough so the shear forces are kept in check
    – Jack
    Feb 20 at 17:44
  • as long as the gable ends have enough bracing and the building isn't too long, that should hold, then.
    – Eric
    Feb 21 at 8:35
  • @Eric , Yes, that is the remark about the posts in the end walls. It looks like your answer is doing pretty good!
    – Jack
    Feb 22 at 2:51
  • appreciate your inputs as well. You may want to commented on North American sizing of timber and structural grades since you are the expert there.
    – Eric
    Feb 22 at 9:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.