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Small Cabin Forum / Cabin Construction / 16X20 Cabin Loft Question (subfloor down, walls next!!)
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mac123
Member
# Posted: 9 Jan 2021 19:38
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Hey everyone, I'm building a 16X20 cabin (off grid), no snow load, code not required, but definitely want everything structurally sound, I have my post and pier foundation and sub floor completed, next are walls (2X4). I'm looking at 8ft or 10ft high walls and a small loft that would span the full 16 feet but only come out 8ft, mainly for a bed and some storage. This will be a 10/12 or 12/12 roof peak ^. I've seen a few examples of connecting the loft floor joists to the walls but would like any examples, pictures or information you all have to offer. The main one that caught my eye was using 2x10s mounted at 8ft height on a 10ft wall, securing into each stud (16OC), adding joists hangers and spanning the 16 ft with 2x10s. This would give me roughly a 1ft knee high wall and 7.5ft to 9ft in the center depending on which wall height I use 8 or 10ft and 10/12 or 12/12. The other wall option is 8ft and sit the loft floor joists directly on the top plate and anchor to rafters but I'm really digging the knee high wall.

I'm a novice so my question is can anyone elaborate anymore on this setup or offer an alternative, or maybe someone sees a flaw with the plan, any and all info is much appreciated.


Big Thanks
Mac

mac123
Member
# Posted: 9 Jan 2021 19:40
Reply 


Again I',m just trying to get my bearings on the loft set up, I'm trying to avoid a center beam under the center of the loft floor but its not out of the question.

gcrank1
Member
# Posted: 9 Jan 2021 20:43 - Edited by: gcrank1
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You can tie into the ridge beam downward to the outer loft joist; no post below, to a support beam center of the joist span. Think bridge building.

Nobadays
Member
# Posted: 9 Jan 2021 22:03
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This calculator might help... HERE.

mac123
Member
# Posted: 10 Jan 2021 00:25
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Quoting: gcrank1
You can tie into the ridge beam downward to the outer loft joist; no post below, to a support beam center of the joist span. Think bridge building.


I'm not sure I know what you mean... I understand ridge beam and loft joists but "to a support beam center of the joists span" is throwing me off. Can you post a pic from google?

mac123
Member
# Posted: 10 Jan 2021 00:27
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Something like this setup would be ideal....
Knee_High_Wall_3.jpg
Knee_High_Wall_3.jpg
Knee_High_Wall.jpg
Knee_High_Wall.jpg


mac123
Member
# Posted: 10 Jan 2021 00:28
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Quoting: Nobadays
This calculator might help... HERE.


Thanks!!

mac123
Member
# Posted: 10 Jan 2021 00:33
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Found another example.
Knee_high_Wall_4.jpg
Knee_high_Wall_4.jpg


Brettny
Member
# Posted: 10 Jan 2021 07:05 - Edited by: Brettny
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Looks like they used a ledger style board with joist hangers. Unless your going to close in under the loft floor joists your going to see hangers.

To span 16ft with no center support your going to need some serious lumber.

Have you thought about doing a gambrel roof? It gives u way more head room and you can put the loft floor ontop of the wall plate...the strongest place for it. I'm not sure how good joist hangers are at holding your walls from spreading out. You don't need snow to have your walls spread out, gravity is always trying to do that.

mac123
Member
# Posted: 10 Jan 2021 13:20
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Quoting: Brettny
Unless your going to close in under the loft floor joists your going to see hangers.


I think that would be okay.

Quoting: Brettny
To span 16ft with no center support your going to need some serious lumber.


I had two construction friends reference 2X12 or 2X10, theres not much weight going in the loft besides a bed and some light storage, since this is a project/vacation home I was trying to go light where I can, 2x10, what do you think Brettny?

Quoting: Brettny
Have you thought about doing a gambrel roof?


I have but the style isn't what I'm interested in, but I agree with you about resting the loft floor on the top plate, seems like the most structural sound location. I've considered scraping the knee high wall just to do that. What about 8ft walls, loft floor joists sitting on top and then building a short 2 ft wall, resting rafters on short wall? I think I've seen images of this but not very familiar with the style and how everything connects. I'll see if I can find an image.

The ledger board seemed the easiest but I also know its the least supportive.

mac123
Member
# Posted: 10 Jan 2021 13:30
Reply 


Something like this... Not necessary my favorite idea but figured I'd throw it out.
Stick_Frame_2.png
Stick_Frame_2.png
Stick_Frame_1.jpg
Stick_Frame_1.jpg


gcrank1
Member
# Posted: 10 Jan 2021 14:38
Reply 


If you come down to center from the ridge to a support beam going to the end wall the joists on top of said beam only have an 8' span each side; way smaller joist lumber required.
Its the same idea as a post from underneath to a center beam with the joists on top except it is tied to the ridge or even trussed to the rafters to the sides.

rpe
Member
# Posted: 10 Jan 2021 16:00
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So your loft joists will intersect the side walls, rather than sitting on top of the plate? If that's the case, then why not put jack studs at an appropriate height nailed to the existing studs, and set the loft joists into the wall, on top of the jack, and against the normal (king) stud. That would eliminate the need for hangers.

Brettny
Member
# Posted: 10 Jan 2021 16:14
Reply 


If you use the knee wall method how do you support the walls from bowing out? Even a 12in beam onto of the top plate..something will need to support the walls from bowing out.

Brettny
Member
# Posted: 10 Jan 2021 16:21 - Edited by: Brettny
Reply 


Also some have referenced useing a ridge beam and not a ridge board. A ridge beam would support the peak of the roof mostly from the ends. Unless you have foundation supports in the correct spot you shouldn't use this method.

As to what dimention lumber to use I would go with Gcrank suggestion and put a beam in the center and have the joists center hit them. Again you will need foundation supports in the right spots.

mac123
Member
# Posted: 10 Jan 2021 19:14
Reply 


Quoting: gcrank1
If you come down to center from the ridge to a support beam going to the end wall the joists on top of said beam only have an 8' span each side; way smaller joist lumber required.
Its the same idea as a post from underneath to a center beam with the joists on top except it is tied to the ridge or even trussed to the rafters to the sides.


🤔.... Okay, I think I understand, makes sense and definitely another way to handle the loft. Thanks!

mac123
Member
# Posted: 10 Jan 2021 19:18
Reply 


Quoting: rpe
If that's the case, then why not put jack studs at an appropriate height nailed to the existing studs, and set the loft joists into the wall, on top of the jack, and against the normal (king) stud. That would eliminate the need for hangers.


Okay.. Doesn't seem like a bad idea, and that way the loft joists aren't hanging off of a face plate nailed into each stud, seems way more supportive.

mac123
Member
# Posted: 10 Jan 2021 19:47
Reply 


Quoting: Brettny
Also some have referenced useing a ridge beam and not a ridge board. A ridge beam would support the peak of the roof mostly from the ends. Unless you have foundation supports in the correct spot you shouldn't use this method.

As to what dimention lumber to use I would go with Gcrank suggestion and put a beam in the center and have the joists center hit them. Again you will need foundation supports in the right spots.


Sorry, terminology trips me up, I planned on a ridge board, not beam. Yea I don't believe I have the proper supports for a ridge beam, post and pier foundation, no extensive poured footers to support such a large load.

gcrank1
Member
# Posted: 10 Jan 2021 21:12
Reply 


The jack studs on the sides will give you joist end support from beneath so no shear load.
If they are then well nailed or even bolted to the studs to the sides it will tie the two wall sides together preventing wall bow-out.
On that loft.... if you treat the outer joist (hanging over the room) like a truss up to the ridge and/or with diagonals to the rafters they all become a truss rafter and imo can well support the reduced size loft joist, deck and bit of stuff loads you describe.
Fwiw, my 1st build 37ish years ago had 2x8 on 16"ctr's fir loft joists for the 12x12 'bedroom'. It never sagged. Given the loading I could have used 2x6's even though it exceeded the 9' span the 6's would normally be rated for. It was a cabin sleeping loft not a house upstairs room or storage for bowling balls. Had I salvaged 2x6's I would have used them, as was, I had 8's and wasnt going to buy lumber. It was overkill, practically speaking.

snobdds
Member
# Posted: 11 Jan 2021 00:26
Reply 


I did 12 foot walls with TGIs at 8 foot supported next to a stud. They are on the two eve walls. This gives me a three foot knee wall in the loft with 8 foot ceilings, a very usable space all the way to the wall. Now special engineering allowed me to accomplish this with relocating the refter ties, so understand it can be done, but it needs to be thought through.
2666.jpeg
2666.jpeg
20180901_085605.jpg
20180901_085605.jpg
20190714_100058.jpg
20190714_100058.jpg


WILL1E
Moderator
# Posted: 11 Jan 2021 08:22
Reply 


I've been contemplating a similar loft construction @mac123. If you are trying to minimize how much lumber you are using, the ledger board/joist hanger option saves 10+ 2bys in the walls for jackstuds...however, as others have said i would agree going into the walls and using jackstuds would be the most robust option.

If your not going by code you don't have to worry about fire blocking in the walls either which i've heard can be a pain.

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