8X12 Cabin/Shed

[JC1001]

Hello everyone  - Lurking for a few months now and recently purchased the Big Enchilada plans.
I have no experience in construction and have learned a ton for all of you already - thanks! All your stories are very inspiring!

I have a few acres in Texas that I am planning to build on in 2 phases:

   1. Build small 8x12 cabin/shed --- to learn construction principles before doing anything larger
   2. Build a larger cabin after the small one  --- some version of John's plans
   
I do not have plans for the 8x12, but have been dabbling in Sketchup as you see here.
   - Roof will be 10/12
   - 8 foot walls
   - I want one half of the 8x12 to have a loft

I am not confident on how to structurally accommodate the vaulted / open ceiling  necessary for the loft. I've read a lot about how it is  necessary to keep the walls from spreading. Being inexperienced, I do not desire to use a ridge beam and it may be overkill for this size structure. My plan was to use 2x6 trusses (with 2x4 bottom chord) tied together with gussets on the side that does not have the loft. On the side that does have the loft, to use 2x8 rafters (no bottom chord) with 2x6 floor joist about 1' 9" below the top plate for the loft. Collar joist on the rafters on this side would be easy to accommodate.

My sketchup shows this approach - sorry could not get a real clear angle of it all - but you can see the 2x6 trusses on the left side, and the 2x8 rafters on the right (actually, as the sketchup is a work in progress, all rafters on the right but 1 are depicted as 2x6 - I will update to 2x8). I also used a 2x6 truss on the gable end on the loft side.  (My Sketchup does not show the collar joist I could put on the rafters). I went with 2x8 rafters so that the rafters would be deep enough to accommodate a deep birds mouth cut necessary to make the exterior of the roof align in a single plane.

Am I completely off track with this? I'm thinking that I am.

Is the following a better approach:

Due to the size of the cabin...could I use a ridge board, 2x6 rafters throughout, bottom chords only on the side without the loft, collar joist throughout and, on the loft side have 2x6 floor joist about 6' 5" up on the wall for the loft. As I write this - this I've almost convinced myself that this is a better idea.

Thanks everyone.
JC

[Don_P]

Yes, a 2x10 would work as a ridgebeam. You don't need the 2x4 bottom chords structurally with a ridgebeam and the poor tie created by the dropped floor joists isn't then a problem since the ridgebeam removes horizontal thrust... if the ridge doesn't sag the rafters can't push the walls outward. If the ridge were to be flexible then the rafters need to form triangles.

The cathedral end wall should be balloon framed. the loft end wall should either run from floor to floor and then from loft floor to roof, or be balloon framed.

Studs shall be continuous from support at the sole plate to a support at the top plate to resist loads perpendicular to the wall. The support shall be a foundation or floor, ceiling or roof diaphragm or shall be designed in accordance with accepted engineering practice.

Double check your rough openings, the door width looks odd.

[JC1001]

Thanks Don - I will have to read up on balloon framing. In my reading I always note the distinction between ridge board vs ridge beam...and I wrote it wrong in my on post 

Without knowing any more than I do now, I think I would rather contend with a ridge board and not a ridge beam but will do more study on roof framing with a beam. Would you consider a ridge beam the only correct way to build what I've described?

Your right about the door dimensions - it is odd. I am planning on building a narrow batten door approx 30" wide or so. With such a small cabin, thought I could save some wall space and perhaps it may even be visually appealing....maybe.
JC

[flyingvan]

Have you considered adding eaves to the gable ends?  You have really nice sloping eaves on two walls then nothing on the gable ends.  It'll help protect the windows and foundation too

[JC1001]

Thanks Flyingvan - I will be putting eves over the gable ends. My Sketchup is really a work in progress.
JC

[Don_P]

In this case the ridgebeam can be a simple 2x10, what is often used as a ridgeboard in a larger building. What makes it act as a beam though is the supports at each end. A continuous column or load path of support to rigidly support the beam is needed. A header around the window carried by full height studs will work. Balloon framing is simply the lingo for full height studs. Flyingvan's drawing shows the same error in gable end framing that your first drawing had, those studs should run unbroken from floor to underside of roof framing, no horizontal top plate in that wall unless there is a floor to laterally support the break.

[JC1001]

Thanks Don for your thoughtful post. You have made it much more clear to me. I think I'm getting it and will redo my Sketchup drawing based on your comments.

Excited to get started on my build I completed the solid concrete block pier foundation and sub-floor last week. I should have waited as I only have a half baked cabin plan on what I'm doing. I will not do any more work on my build until I have a solid plan for the remainder of the cabin...especially the roof structure, gable walls and ridge beam. Once I have my plan baselined and I can move on to the framing I will start a new thread for my build - but this is what I have done so far.

Thanks for all the excellent input and advice!
JC

[Don_P]

yup, kinda jumped the gun. Right now there is no foundation support for the ridgebeam support posts, a section of pier under the window king studs and at the opposite gable under the ridge support studs. You should add them for another reason as well. Look at the alignment of your current piers, they will do a pretty good job of resisting winds that hit the narrow gable ends but present much less overturning resistance if the wind hits the much larger eaves sides of the building. Having piers or wall sections oriented along the gable ends will help with resisting thoes winds as well as completing the load path from the ridgebeam.

[JC1001]

Don:
My 1st error of many to come
I would rather not add the additional pier if not absolutely necessary just due to the pain it will be to do so at this point. But, If I am going to do it, I'm thinking of using a floor jack to raise one gable end at a time an inch or so to slide the last concrete block into place as I build the new piers up and level.

Prior to adding the additional pier on each end, I thought I would ask if you think there is any hope without it - given the information below. What do you think?

As it is now,without additional pier support, the maximum unsupported length between the joist is 6' 9 1/4".
The joist are 2x6 sitting on top of a 2x8 mudsill at each end.

The cabin does have protection from wind in that it is located in a deep in our property surrounded by trees and not exposed on a hill side.

I took this 8x12 concrete block pier layout from the book 'Build Like a Pro' by Joe Truini. The structure represented in the book, however, with this pier layout is not using a ridge beam. The book itself has excellent reviews and is often recommended to novices like me.



After a little more study today I came across this thread (http://countryplans.com/smf/index.php?topic=7250.25 ) from someone with a similar challenge and used a modification to Don's 'plant shelf' design to resolve. Using this as inspiration - here is my crude sketchup. It shows: On both ends of the 2x10 ridge beam bring down the load using vertical 2x4s. The 2x4 is supported by a laminated 2x6 header that spans the top plates to bring the load down to the walls and thus directly on top of the piers.

In feedback appreciated.
JC

[UK4X4]

Being that your only in TX and probably the closest to snow you'd get would be a good frost, roof weight is not so high

If you want a ridge beam , could you persuade another couple of 2X6's in behind the end joist ?

Or make the door header a triple full width and enlarge the supports above the the foundation, your really only building a shed !

[Don_P]

you're really only building a shed !

"It's only X" doesn't have any design values, learn to build that way and you will find the limits. Structural design is really just a rational process.

Build small 8x12 cabin/shed --- to learn construction principles before doing anything larger

Explore your options rationally. Quantify loads and provide resistance. If it survives that process you have found one viable option.
Including gable end overhang, the design load on each end of the ridgebeam is 7' of length X 4' of width. The "tributary area" supported by each end column is 28 square feet. Design load is 10 pounds per square foot dead load (material self weight) and 20psf Live load (wind)... 28 square feet X 30 pounds per square foot =840 lbs.
If there is a door header the 840 lb load is split in half with each door king stud carrying 420 lbs down to bear on the rim joist. The rim joist then has a span of 81.25" and 2 point loads of 420 lbs each bearing at about 1/3 points along the rim.
http://www.timbertoolbox.com/Calcs/2ptbeam.html
Use 900 for Fb, E=1.6 and Fv = 175psi... when it fails, double the rim joist to 3"x5.5"

Doubling the rim is a viable option on that end.

At the other end of the ridgebeam, a single post at midspan delivering 840 lbs down to the center of span of the rim joist at that end.
http://www.timbertoolbox.com/Calcs/beamclc_ctrptld.htm
then try a triple, 4.5x5.5"

So there is the way to think about a problem using construction principles 

Another real world observation that varies from one inspector to another, my inspector doesn't care what DIY book I read it in, his codebook is the one that matters. These foundations aren't in there, an engineer would be required on a habitable structure.

[JC1001]

Thanks for the valuable comments. I will at least double and triple the 2x6 rim joist on each end. It had not occurred to me to do this.
JC

[JC1001]

Going out to build this morning - supposed to finally have a nice sunny weekend with almost 70 degree weather (gotta love Texas winters).

Goal this morning is to double up the floor joist on each end as I am going to attempt a ridge beam.

Going to use a 2X10 for the ridge beam. Question - are 2x4 on each end adequate for the ridge beam support post?

Thanks for input.
JC

[Don_P]

yes a single 2x4 is sufficient. I like to build them with 2 side studs that run alongside the ridge, forming a "yoke" that the ridge sets in. For this a couple of scabbed on blocks 2-3' long would do the same thing though.

[JC1001]

Hi everyone.
I purchased 'The Visual Handbook of Building and Remodeling' that was recommended to me and I've looked all over the Internet, but cannot find what I'm looking for so thought I would ask the experts.

I'm trying to learn how best to frame up my balloon framed gable ends, ridge beam, beam support post and rafters. I know there can be various approaches, but I would like to employ a proven method.

Some examples I have seen do not seem to have a top plate and have studs (cut at the top end the same angle as the rafters)attached directly to the gable end rafter. Other approaches seem to have a top plate that the rafter sits on in addition to a 'nailer' attached to the top plate as well, I presume to provide additional attachment points for the gable rafter. Plus how to frame up the ridge beam and support post into the overall framing approach.

I can figure out all the angles, etc...just really looking for a solid framing approach/design for the gable ends

Can anyone please point me to a book, Internet site or posting that I could reference?

Thanks

[Don_P]

I think I've posted some pics here but couldn't tell you where 
Rob Thallon's "Graphic Guide to Frame Construction" shows several ways to frame the roof at the gable end.

[JC1001]

On advise from the forum I have changed my framing strategy. Images show my new model (and my poor sketchup skills). Gable ends are balloon framed and I have used a 2x10 ridge beam. I will also triple up the 2x6 floor joist on the gable ends since I did not provide a pier in the middle of the gable ends. Was not sure if I needed 2 top plates on the gable ends, but that is what I see most often posted, so I did the same. I have 2x4 bringing the load down from the ridge beam down through the rest of the gable walls. The framing is 2x4, rafters are 2x6.

Before getting to work on it, I wanted to ask if anyone see any issues with this design? Did I get the balloon framing right, with the ridge beam?

Also - I'm still considering how I am going to add the covered deck. it be a shed style roof coming off the front of the cabin. I was considering building the deck on its own piers (similar to how I did the shed), with no attachment of the deck itself to the cabin. The deck's roof, on the other hand, would attach to the cabin via a 2x4 ledger that I place under the rafters. I plan on cutting the rafter tails some, to give more room for the decks roof.

[Don_P]

This is something to remember when you build larger. Adding load part way through the build can give you problems with beam sizes. The porch floor and roof add load to the front girder and footings. You need to go back and check these.

The loft floor joists need to rest on a ledger that is let into the studs, the joists should be nailed to the studs. Or the joists can rest on the headers, nailed to the studs with jack studs under the few that don't have a header to rest on... I'd go with the tops of all headers at door header height and run the joists from that elevation.

At 8' wide the gable end framing should be centered in those walls, the ridge support should centerline on a layout at 48". I usually run the support post and another 2x up each side of the ridge to form a "yoke" that the ridge drops into. You can raise the ridge to be flush with the rafter tops.

[JC1001]

 Lots of rain (finally) but that has slowed my progress. I did manage to get the walls up this weekend.

Question on the bottom plate / door threshold --- I am going to build the door, but not sure if I should cut the bottom plate out of the threshold or to leave in place. I was intending to leave it in place permanently, but with more rain coming - if I remove it, water could at least drain from the deck.

Thanks for any input.

[John Raabe]

You can cut out the threshold for drainage (in my opinion). The final threshold and flashing will be part of the door install.

[John Raabe]

test post to watch title

[JC1001]

A little more progress.
I will have exposed rafter tails and not clear on a few details:
- is a facia board (such as a 1x6) attached to the tails necessary? Is a function of such a board to keep tails from warping?
- I was planning to cut the rafter seat wide enough to lay over the top plate and 1/2" sheathing. I am now thinking seat should be wider so that I can slide the board siding (board and batten) underneath the tails. If I do not do this - how to handle the intersection of where the board siding meets the rafter tail?
Thanks for input.

[Don_P]

The fascia is a protection board for the tails and something to hang a gutter from. The subfascia which attaches to the tails is a piece of 2x framing that helps support and brace the tails, it also provides a nailer for the soffit. The fascia, being a bit wider, then covers the sub and soffit and then hangs down a bit more to provide a drip edge below the soffit.

The seat can go out to overlap the siding, or it can be tight to the sheathing and then the siding is notched around the tails, or, if there is soffit boxing in the tails the siding dies into the soffit along a straight clean line. I prefer a level soffit on the eaves if at all possible. Current code is calling the birdsmouth a notch and so limiting the seatcut notch to 1/4 of the rafter depth max... I'm still shaking my head on that one.

[JC1001]

A little more progress. I will be notching the gable rafters soon and putting in the fly/bridge rafters (not sure what they are called) to support the roof over hang.

As I'm getting close to sheathing the roof...I've been considering what to do about venting the roof or if I even need to.

Rafters are 6" and will be a 'cathederal' type ceiling. Metal roof. My plan was to lay batts between the rafters...leaving about 2" space between the batts and the roof decking, put blocking between each rafter down at the eave end and cut notches in the top of the blocking for air flow. Unfortunately, I ran the rafters to the top and even with the ridge beam...so I do not have a space up top for a ridge vent.

Looking for suggestions on the venting. How about if I install small 4" solar powered vents like you would find on sail boat cabin up top on each side of the roof? Other ideas? Although not a full time cabin by any means...I think I should be venting in case moisture gets in between the roof decking and finished ceiling inside.

[John Raabe]

Looks like you have air intakes at the bottom of each rafter bay but you need to vent the tops as well. Your metal roofing system probably has a venting cap. Ask about that. If not, this is a flexible system for venting roofs and sidings.

http://www.cor-a-vent.com/