Firstly, the reason I am here is that there is no local code or inspection requirements for my building (I live in the Caribbean) - but, I would ideally like it to meet US code (or similar) as closely as possible to give me some peace of mind! And so I’m keen for any input or suggestions.
I am happy with most aspects of the building, and I believe I have given correct attention to downward forces, outward thrusts, and bending moments. However, I am not happy with my mitigation of upward forces (uplift due to wind) and this is obviously especially important in the Caribbean where we are prone to hurricanes.
Here is the basic sketchup design (with some rafters etc removed for clarity) and photographs below. Dimensions of the box section are 27ft x 17ft. Eaves overhand a further 18". Ridge height is 12ft from ground. Posts are 8ft tall. Rafters are 3x6. Ridge is 3x12. Pitch is 26 degs (6 in 12). Perimeter wall beams & central rafter tie all 3x10. Posts 6x6. Diagonal braces 3x6 & 3x3 respectively. Roofing 1x6 v-joint covered in stone slates. Wall beams / rafter tie connected to posts with 1/2" s.s. through bolts, posts structurally tied to adequate concrete sub base (7" 4000psi, BRC + 1/2" rebar). Everything else screwed with 10 x 3 1/2" deck screws (6 screws per rafter, 3 at each end)
Sketchup Image: IMAGES COPIED IN REPLY BELOW
Overview Image:
Roof Image Image:
IMAGES COPIED IN REPLY BELOW
Through bolting of wall beam / rafter ties Image:
IMAGES COPIED IN REPLY BELOW
Post bases Image:
IMAGES COPIED IN REPLY BELOW
I’m fairly confident with my structural tie down of the posts, and the wall beams / rafter ties. My concept of the structure was for the ridge timber to essentially just be a ridge board, however since there are only 3 rafter ties (3x10, one at each end plus one in the middle, so they are 13’6" apart) I decided to go for 3x12 ridge timber as I considered it to be a ridge beam (rather than board) between the the rafter ties, so I didn’t want it to sag and create outward thrust pushing out the wall beams. Anyway, that all works fine, I fitted a stone roof (aprox 7,000 lbs roof tiles) with zero deflection to wall beams and zero issues. And we don’t get snow here!
But I am concerned about uplift forces, which (for the life of me, I can’t understand why given that I live in the Caribbean) I haven’t given any consideration to…and we are entering hurricane season. I am fitting simpson strong ties x 4 to each rafter (2 at the wall beams, and 2 at the ridge, so both sides at both ends). Shown here:
Hurricane ties at ridge (Simpson H4 left & right pairs) Image:
IMAGES COPIED IN REPLY BELOW
Hurricane ties at wall beams Image:
IMAGES COPIED IN REPLY BELOW
That satisfies me at the wall beam end, but I keep looking at ridge and am worried that nothing is holding the ridge beam/board from potentially rising up in a hurricane…
Are the simpson ties at the ridge good enough? If the ridge tries to rise up, the 3 rafter ties will go into compression and prevent this? Or do I need to add collar ties? I’m hoping to avoid collar ties as not to ruin the aesthetics, but if so needed was planning to have some fabricated out of 1/2" steel bar and placing 4 across the building (so just under 8ft apart each) around 1/3 down between ridge and wall beams.
Please let me know your thoughts. And yes, I know…I really should have thought about this and asked BEFORE picking up my tools…but the original project was a lot smaller, I did the whole thing myself, and I probably ended up biting off more than I could chew.
