Advantages and Disadvantages of Principal Rafter vs. Common Purlin

[JBW]

 I am designing a 24x40 cabin at the moment and currently have it drawn up with 5 bents. All of the literature I have obtained and read has lead me to designing this structure in such a way. It seems simplest to construct and really seems to fit my design desires. My only hold up is the overhang. Can I just overhang my sip panels to create a 1' eave? I live in southern Arkansas, snow loads are simply not an issue. Half of the house has an 11:12 pitch and the other side is around 11:12. I'll attach some pictures for you fine fellas to look at. These are just some very crude "thinkin" drawings! Unless noted this structure is framed with 8x8 pine timbers. Between bent 3, 4 and 5 will be a loft. Thanks for having me.


  

  

  

  

  

 

[Dakota]

My cabin is the same size as you are proposing.  While I didn't use sips, I did construct 2x4 walls outside the frame.  I just extended my rafter ends out to keep rain and snow away from the structure.

[JBW]

I am working on posting some pictures! That is a great looking cabin! Is that pine? What are the sizes of your post?

[rjwoelk]

I would put 3 ft of overhang on it to keep the sun out and off your walls. I did that on our Cabin and we  just starting to get the sun about mid September. In December it will shine in the south pic window for some warmth. Keeps the rain off as well.

[JBW]

I still don't understand how the framed walls allow for overhang. Thanks

*edit. I see what you were saying, your 2x4 walls are mounted to the outside of your timbers much like sips?

[JBW]

My cabin is the same size as you are proposing.  While I didn't use sips, I did construct 2x4 walls outside the frame.  I just extended my rafter ends out to keep rain and snow away from the structure.

Dakota,
Do you have any more info on this build? Plans etc? What was your timeline on it? How long did it take you to do the joinery then erect? Just curious seeing as how similar it is to what i have in mind! Thanks

[Dakota]

JBW,

The frame is pine, the posts are 8"x8", braces 4"x6", beams are 8"x10", and the purlins are 6"x6".
I built the frame recessed by 4" to allow the walls to sit on the foundation.

As far as info on the build, I made the plans myself with some good advise from @Jim Rogers.  My plans won't help you much as I built a hybred cabin, meaning 24' of it is conventional framing with the last 16' timber frame.  Here's a picture of a model I built.  I shows how the two frames went together.





And here's the finished cabin.



If you have any questions, I'm always happy to help in any way I can.

[Brad_bb]

A 1ft overhang I think will look odd, and not good.  You should be looking at 2-3ft of overhang. 

[JBW]

JBW,

The frame is pine, the posts are 8"x8", braces 4"x6", beams are 8"x10", and the purlins are 6"x6".
I built the frame recessed by 4" to allow the walls to sit on the foundation.

As far as info on the build, I made the plans myself with some good advise from @Jim Rogers.  My plans won't help you much as I built a hybred cabin, meaning 24' of it is conventional framing with the last 16' timber frame.  Here's a picture of a model I built.  I shows how the two frames went together.




And here's the finished cabin.



If you have any questions, I'm always happy to help in any way I can.

Actually, you may be a ton of help! I have really been throwing around the idea of a hybrid almost identical to you model! I have multiple reasons for this. What was your main reasoning for doing a hybrid?

[JBW]

do you worry about the two side pulling apart as the timber frame side settles and shrinks a bit?

[Dakota]

The main reason for building a hybrid, was how long it was taking me to gather logs large enough for the timbers I needed.  I was using trees that were beetle killed instead of cutting healthy trees off my place.  It took about 5 years to gather enough trees that would make good timbers.  While I was waiting, I sawed all the wood I needed for the stick frame.

As far as the frames pulling apart, that won't happen because they sit on the same foundation.  Only movement I worried about was up and down settlement, that's why I have two roof lines.  To allow for up or down movement, I cut slots in the stick frame roof rafters and bolted them to the timber frame rafters.  Its been together six years now with no movement I can see.

[JBW]

Does anybody see a problem with my current bent design? Mainly speaking of the way one side is taller than the other. I did this to gain room for stairs going up to the loft. I have never seen a timber frame house framed in bents with this shape.


  The beam will most likely be one solid piece since i have access to 24' lumber and a mill to handle it.

Thanks for any input!