|
| Author |
Message |
WILL1E
Moderator
|
# Posted: 5 Aug 2021 08:31
Reply
16x30 cabin with 10' deep by 16' wide loft on either ends. Lofts will be for sleeping only and will only have a bed and maybe a small dresser. The WI construction standard calls for 40/10 live and dead loads and L/360 deflection for FLOOR joist. Since this is a loft, i think the specs for "ceiling joist w/ attic storage" would be sufficient. The specs for that are 20/10 L/240.
Using the span calc. using SPF lumber it calls for a 2x8 w/ 16"OC to make that 16' span. Original thought was to run all the loft joist in the 16' direction. But then i saw North Rick's method where he ran one loft joist across the width of the cabin and the rest perpendicular to it since that distance was shorter. So if i followed his concept where the 1 joist at the open end of the loft ran the 16' direction and then the rest ran the 10' direction, how do i calculate what i need for that 16' board since it will now carry the load of all those 10' joist? Is there a span calculator that works for sistering of joist or for doing built up beams?
I like this option because i feel like it would save on how much lumber i need. However, i do not want a support pole going to the 1st floor and i'd prefer not to have to go up in lumber size from a 2x8.
|
|
ICC
Member
|
# Posted: 5 Aug 2021 09:07
Reply
The possible issue is that the joist as you called, at the open end of the loft floor is actually a beam if you connect short joists from it to the end wall. Needs to be bigger than a joist. Plus that places loads on the end wall that it would not get with joists across width. That may mean header adjust to doors or windows in end walls. And then you don't have the joists across the width trying to act as rafter ties, even though that may not be at the actual wall tops.
|
|
WILL1E
Moderator
|
# Posted: 5 Aug 2021 10:12
Reply
Quoting: ICC And then you don't have the joists across the width trying to act as rafter ties,
I knew I was missing something!
|
|
Brettny
Member
|
# Posted: 5 Aug 2021 11:03
Reply
I dont think your really going to save anything by making the joists go the other way. If you do your left with how are you going to tie the walls together with the joists running parallel to the top plates.
For 16' wide with no center support I wouldn't use anything but 2x12x16 and 16"oc.
|
|
Grizzlyman
Member
|
# Posted: 5 Aug 2021 22:47
Reply
I am skeptical about 2x8s for 16’ joists…
|
|
WILL1E
Moderator
|
# Posted: 6 Aug 2021 07:50
Reply
If i use 40/10 L-360 floor joist specs, the span calc says 2x10 joist can span 15'5" which would be enough for 16' wide building stick framed with 2x6's.
The floor joist will be 2x8's but there will be a built up beam in dead center below the joist.
|
|
travellerw
Member
|
# Posted: 6 Aug 2021 14:02
Reply
Quoting: Grizzlyman I am skeptical about 2x8s for 16’ joists…
I'm with Grizzlyman.. All the Span tables I looked at say 2x10 for that span span using SPF. Also 16" on center.
|
|
Brettny
Member
|
# Posted: 6 Aug 2021 15:12
Reply
Quoting: WILL1E The floor joist will be 2x8's but there will be a built up beam in dead center below the joist.
So the actual un supported span will be 8'?
A way around useing 2x10 and gaining headroom in the loft would be to put your 2x8x16' loft joists in like normal then in the center (at the 8' mark) put a carry beam in below them. Frame it into the wall on one side and it would have to have a post carry the other side.
|
|
|
WILL1E
Moderator
|
# Posted: 6 Aug 2021 15:43
Reply
Quoting: Brettny So the actual un supported span will be 8'?
For the floor joist on the main floor, yes...actually less than 8' when you subtract the widths of the 3 built up beams that will support the cabin. I think the span calc. said 12' something using the 40/10 L360 and 16"oc specs.
|
|
Brettny
Member
|
# Posted: 7 Aug 2021 06:07
Reply
Quoting: WILL1E For the floor joist on the main floor, yes...actually less than 8' when you subtract the widths of the 3 built up beams that will support the cabin. I think the span calc. said 12' something using the 40/10 L360 and 16"oc specs.
That's good but dosnt help the loft floor.
|
|
WILL1E
Moderator
|
# Posted: 9 Aug 2021 08:17
Reply
Brettny I guess i don't understand your original question then...i know the joist on the first floor won't affect the loft floor, but that's what you asked.
My comment about the 2x8 floor joist was to explain that 2x8's would suffice as there would be a center beam so they weren't spanning the full building width.
|
|
|
