roof design help!

[sbishop]

Hi all,

I'm debating on what pitch I need for my roof on my log cabin...the cabin is 22X26. I would like to put a half loft and was wondering what options I had.

Exemple: if I made my walls a little taller and drop the loft down a little I wouldn't need a steep roof to get some clearance in the loft.

I would like the loft to be half of the cabin or so. I don't need 8feet below the loft. I would like to get away with a 6/12 pitch if I can. depending on how much headroom will it give me!

THANKS for any help in advance!

[Radar67]

Divide your roof width by half (11 in this case), then figure a six inch rise per foot of run  (66 inches) for 6/12. That is not a very steep roof at all. You would have to have at least a 4 foot knee wall to get any headroom.

Stew

[scsmith42]

If you're planning a loft, you really ought to consider a steeper pitch - say a 10 / 12 or 12/12.  You could probably drop your sidewalls to 3' or so with the increased pitch.

[Raphael]

Like most questions I'd say the answer is it depends...
  The cabin we had access to when I was growing up had a loft under ~6/12 pitch with no knee wall.  Barely enough room for a grown man to stand under the peak.  The loft was stocked with a double row of old steel framed beds (an even dozen IIRC) and functioned perfectly fine as just a sleeping loft.  Trying to organized much storage in the same space could be a pain in the neck (literally) and using it in some sort of social function was right out.

[sbishop]

i'd like to had a bit more info!

the loft upstairs will be a bedroom for me and the misses. not too worried about headroom as long as I can move around the center without hitting my head..if I have lets say 2ft on each side of the peek that is around 6' 1/2 feet..i'd be happy!

the reason i'd like not to have a 12/12 pitch is I will be doing the construction by myself without any help and I can't walk a 12/12 let alone builded it  :D


Can someone explain the term "knee wall" THANKS

Sbishop

[Radar67]

A knee wall is an extension. Most standard walls are 8 feet, then the roof joists and rafters are on top. If you notice in the below picture, the short wall on top of the joists (only on sides) is a knee wall. This one is only 12 inches tall. You might consider this style of roof for more head room. The only help I had raising the trusses was my wife holding them in place at the bottom while I secured them at the top.



Stew

[Raphael]

A knee wall is what you were referring to in your example of having a couple extra rounds of logs above the level of the loft's floor joists.  Essentially a short eve wall roughly knee high to increase usable space under a roof.

The challenge I see in doing this in a log cabin is designing the roof so that rafter thrust doesn't roll those top logs off.  You might have to settle for slightly less than half the cabin minus space for the stairs.

[sbishop]

i've should have added more info at the beginning  ;D

I will be building (as of now) with vertical logs, if I was to cut my logs an extra foot long lets say 9ft. and I ran my loft beams across at 7ft. that should free up some space depending on what pitch I use! below my loft will be bedrooms and a bathroom so 7ft ceilings would be ok..the rest would be open space in the kitchen/living room area!

I should ask Pappy on this forum what pitch he used cause I know he has a loft!

Thanks for the knee wall info....got it now!
Sbishop

[Tony_T]

Gambrel roof (?), steep pitch on the edge, less on the top.  Will give you head room without a knee wall, very structuraly sound. Queen posts are required.  Might be good if you have high snow loads too, snow all falls off steep edges and the stuff blown/melted off the top does not add to the load as it blows away or runs right off.

What I mean about snow load is all the load is supported by the queen trusses (flater part of roof).  Not much force transmitted to your outside plates to induce spread.

[Stephen1]

The Loft,
      I was in the same position as you. The 1st ? is how much head room do you want, that will dictate how much of a pitch you will need based on the width of the building. Which way will the roof be 22 wide or 26 wide. if you go across the 26 you can get away with a 6\12 pitch and still have 6' of head room, but do not forget about the lumber dimensions that you will need to support the roof and the loft floor. If you use the FF tool box down in the left hand corner it will give you some ideas on the dimensions of timbers you will need, to support and build your roof. some more things for you to think about.

[Don P]

We've talked several times about roof thrust recently. I was laying some decking the other day and a good example, hopefully, popped up. Sometimes when we can't get something to force up tight, we make a little pusher like shown in brown. I've got it pushing the red board tight when I step on the "ridge". In order to give much thrust it has to be at a pretty low angle. Imagine if I were to try to use the setup in yellow, it wouldnt give me much force.

I've drawn a couple of triangles, much like the roof pitch triangles on a set of plans.  Look at the vertical leg of the 2 triangles, then at the horizontal leg. The ratio of the legs is the ratio of the forces. Look at the 2/12 low sloped triangle, it has a ratio of 1/6. Or to put it another way, when I step on that board with 200 lbs of vertical force, it shoves outward with 1200 lbs of thrust. Now look at the 12/12 triangle, 1/1. I can climb atop that and it will only thrust out with 200 lbs of force.

Somehow you need to resist that thrust, you can see how going steep makes that easier. Another way is to suspend the rafters from a ridge beam, if they are supported up top they don't thrust.

[beenthere]

Don P
That is a real good illustration. 

[scsmith42]

Don - ditto Beenthere's comment!  Excellent insight and illustration.  Thanks for sharing.

Scott

[Don P]

Thanks guys

After just reading a great post that started with a simple broken bolt, I'll ditto that back at ya  ;D

[Stephen1]

Thanks Don, I also enjoy learning from the masters, I have been reading alot of Jim's. they make great learning also.

[Don P]

Well, I should have adressed this immediately, its working on my mind now  :D.
Stephen I appreciate your comment and understand where it comes from. I am no master though. Like most of us here I'm just a woodworker who enjoys chewing the fat with like minded individuals. This is a unique place to my knowledge where we've been given pretty broad latitude to discuss whatever comes up and try to help one another along. I know a precious few pieces of the puzzle, each of us does. We seem to be getting some new visitors coming through, this is on the front page, and I don't want them to get the wrong impression of us and who is here. I don't want people to feel this is a question and answer forum with some "masters" presiding, we're just boys and girls having fun on the farm 

Now hopefully y'all will post to other threads alot and this will scroll off the page fast  :D

[Jim_Rogers]

I'm no master either.
I just write and post what I've learned........

Jim Rogers

[Stephen1]

Don & Jim, I understand but I still enjoy reading what knowledge you have as it sure is more than me. I enjoy chewing the fat, cause it does help you think towards your goals, and opens your mind to different ideas.