Small Cabin

Small Cabin Forum
 - Forums - Register/Sign Up - Reply - Search - Statistics -

Small Cabin Forum / Cabin Construction / 16X24 Post Frame Cabin with Loft
Author Message
Backcountrylife80
Member
# Posted: 16 Jan 2023 21:56 - Edited by: Backcountrylife80
Reply 


Fellow cabin builders,

I am in the beginning stages of planning and building a small cabin. I have searched for a design similar to what I want to do, but have not been able to find much information.

I have seen a lot of designs for a 16x24 cabin but none that are a true post frame design that have a loft. I realize that traditional stick framing lends itself more to what I am trying to do, but because I am building to a degree on uncompacted soil I have chosen to go with a post frame design.

I used a 24" auger bit and dug 10 holes around 68" - 70" deep. This depth allowed me to have my footers in undisturbed earth and still have four feet of the posts buried below grade. I poured around two feet of concrete in the bottom of each and used a laser level to set rebar stakes in the bottom of each to mark the tops of the forms. Each footer should be within 0.5" - 1" of being on the same level. I plan to use Post Protectors and run rebar through the bottoms of the posts for uplift protection, and then pour a collar up around the post.

The hole configuration for the 10 posts is 8' on center all the way around accounting for the three inches my girts add to the finished outside dimension of 16X24 feet.

I ordered (8) 3 ply 2x6x16 and (2) 3 ply 2x8x24 nail lam posts from Menards that have the trimmable bearing block in the top. My eight side posts will be the 16 footers and the two end poles in the middle are the 24 footers. I plan to bolt a 2x6 to the bottom of each side post oriented against the face of of it on the inside that will rest on the top of the concrete collar before I back fill my holes and trim all of them to the same height so that I can rest a rim joist on it and have a crawl space underneath to run my plumbing as well as raise the cabin up to increase my view.

I plan to have a 12/12 roof pitch and use a glulam beam for a structural ridge beam that will run the 24' from end to end and support it in the middle with another column of some sort.

The part of the design that I am struggling with is how to tie the rafter ends to the top of the poles. The loft will require 2x12s at least 16" on center to span the 16' feet across the cabin (narrow way). I know that traditionally in post frame design, a header of some sort, usually a double header is nailed to the top of the posts for the trusses (Or in my case, loft floor joists) to rest on.

In my particular case, if I was using engineered trusses, it would be a simple matter of setting the truss ends in the notch after trimming the block to the appropriate height and running carriage bolts through the post and truss end to secure them. However, as I am wanting a loft, obviously second story floor joists (or rafter ties) need to be closer together than 8 feet.

Naturally I would like to utilize the trimmable bearing block/notch system for the rafters/rafter ties that line up with the notches on my poles, but for the four rafter ties/floor joists that sit between each pole, I'm not sure how to fasten them to the header so that they are on the same plane as the ones in the notches. If I was just sitting homemade rafters on a traditional top plate, I would just run the rafter ties or floor joists across and nail them into the sides of the rafters and trim them at the correct angle. If I set the 2x12 floor joists in the available notches in the posts, the rafter would have to come down directly on top of it and be attached with a truss plate of some sort, whereas the others would normally be set with a birds mouth cut and have the floor joist nailed in from the side. I have also considered making gussets with OSB or plywood and gluing and screwing them to the floor joists and to make my rafters.

If I understand load distribution properly, a load bearing ridge beam supports half of your roof load and the long walls on each side will each carry a fourth of the roof load. If this part is executed properly, and with my girts tying all of the posts together does this mean that I don't have an outward thrust issue at that point? This isn't even factoring in the 2x12 floor joists that will be running across the 16' span for the loft. (I have't decided yet if the loft will run more than half the length of the cabin, but it will be at least half.

Perhaps I am way overthinking and overcomplicating this, but I wanted to get some other opinions on the best way to do this and was curious to see other true post frame cabin designs (with a crawl space and not on a poured slab) and with a loft.

Should I just forget about putting the floor joists in the two poles with notches and run a double header that can hold a top plate, and then rest all of my floor joists/rafters on that? I have also seen designs where 2x6 uprights are installed between the headers in each spot where a truss does not line up with a pole and fastening them that way, but this is for a truss that has the bottom and top chords attached with a thin plate, thus allowing it to be nailed to the upright running in the same plane, instead of with a rafter tie nailed to the side of the rafter.

I am not interested in cutting corners or saving money at the expense of structural soundness. I am building this in Oklahoma where we do not have snow loads, but we do have high winds, and it goes without saying that in addition to the points discussed, I would be incorporating all the appropriate metal ties and hardware normally used to ensure a safe structure in completing the roof framing.

I have located some very reasonably priced engineered trusses that are a 12/12 pitch and designed for a loft, but would only leave me 8 feet of usable space in the middle of the loft and I really want the entire open space available. It would also not allow me to have an open ceiling that I really want in the end of the cabin that does not have a loft. If I went this route obviously I wouldn't need a load bearing ridge beam.

Any input/advice based off of solid engineering principles or real-life experience would be appreciated.

Thank you!

Your reply
Bold Style  Italic Style  Underlined Style  Thumbnail Image Link  Large Image Link  URL Link           :) ;) :-( :confused: More smilies...

» Username  » Password 
Only registered users can post here. Please enter your login/password details before posting a message, or register here first.