14x24 shed roof

Started by lee5267, January 10, 2008, 12:16:21 PM

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lee5267

I'm considering building a 14x24 with a shed roof similar to John Doane's 16x24 here http://www.countryplans.com/12x18.html .  However on my highest wall I want to go 14ft high (normal 8ft plus an extra 6) so I can include a nice attic space to store things or make into a sleep loft and the short wall will be 10ft to continue the roof out for a 24 wide porch that goes out 7ft.  I plan to make the two lofts the same as in the plans with 2x8's.  Will the foundation be able to support this extra height addition if built to plans?  I also had a question about the cantilever of the floor joists.  In the book, House Framing by Wagner, it says not to cantilever out more than the width of the floor joists so for 2x8 joists this would mean you shouldnt canitlever past the beams more than 8 inches on each end but per the plans it is showing 2 ft.  Obviously many people have done this extra cantilever with success but I wanted to pose the question.

Thanks,

Lee

glenn kangiser

I don't see it being much more load than a cabin with a 12/12 pitch and lofts.  You could increase the size of your footing bases a bit if there are any concerns - soft ground etc.

John uses the cantilever to stiffen the center section of the floor and decrease floor joist size if I recall correctly, so it is considered in the foundation design.  That could be different for a bigger house as a rule of thumb.

Welcome to the forum, Lee.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.


MountainDon

 w* Lee.

I believe John has said the foundation as used in the Little House plans is limited to a 14 ft wide configuration, with a loft being okay. But wider or adding knee wall height for more loft space would require something different. You'll notice the 16 x 24 on that link utilizes perimeter supports.

However, I have concerns about the roof. Six ft on one side and 4 ft on the other, with a 14 ft span calcs out to less than a 2:12 pitch. Seems a bit shallow to me. It could be made to work I suppose. 2x8 rafters (24" OC) would be marginal if there are snow loads involved; 2x10 would be better, and depending on how much and what kind of insulation you plan in that roof, 2x12 could be better yet. (I'm assuming you would insulate the roof, not the ceiling the way you describe the upper space as a possible sleeping loft, as well as storage.

I'm sure John will check in sometime soon and give us his educated slant on this.

Just because something has been done and has not failed, doesn't mean it is good design.

Willy

Quote from: MountainDon on January 10, 2008, 11:12:22 PM
w* Lee.

I believe John has said the foundation as used in the Little House plans is limited to a 14 ft wide configuration, with a loft being okay. But wider or adding knee wall height for more loft space would require something different. You'll notice the 16 x 24 on that link utilizes perimeter supports.

However, I have concerns about the roof. Six ft on one side and 4 ft on the other, with a 14 ft span calcs out to less than a 2:12 pitch. Seems a bit shallow to me. It could be made to work I suppose. 2x8 rafters (24" OC) would be marginal if there are snow loads involved; 2x10 would be better, and depending on how much and what kind of insulation you plan in that roof, 2x12 could be better yet. (I'm assuming you would insulate the roof, not the ceiling the way you describe the upper space as a possible sleeping loft, as well as storage.

I'm sure John will check in sometime soon and give us his educated slant on this.


I just did something like that to my cabin today and got it approved by the building inspector. It has a 12 ft wide area with 2X8 on a 12/5 pitch and a 40 lb snow load rating. I raised the low wall from 7' to 9 ft and the front high wall of 12 ft to 14 ft high. There is a knee wall in the tall wall the whole length but I am only doing 10 ft of the 24 ft long building this way and raise the loft area up 2 more feet by extending the knee wall in that area and just building the rear wall higher. My porch adds strength to the knee wall from tipping since it has a floor and sofet on the area above the decking for storage, access from the loft area. The rafters do not push out on the walls just down since there isn't a ridge between the walls. I also have a 10 ft long wall below the loft to enclose in the bathroom area and this ties into the rafters where they go up 2 more feet with a short wall on top of the loft floor attached to the raised rafters also. The living room area is all open with 12 ft wall on one side and 7 ft tall wall on the other side. Mark


lee5267

Sorry,

I didn't do a very good job describing the changes I plan to make.  The tallest wall will be a total of 14ft high (normal 8ft wall plus an extra 6ft for loft space) and the short wall will be 10ft high total (8 plus 2) to make the roof slope a little more than 3/12 over the 14ft span.  The roof rafters will be 2x10 as the plans call for and the loft floor joists will be 2x8.  The cabin is going to be built in SE Oklahoma so snow loads arent much of a factor and I'll be installing a metal roof as well.  I hope this helps clear things up.  Other than this I plan to build the 14x24 per the plans with 2x4 walls etc. 

Thanks for all the help

Lee


John Raabe

Greetings from Mexico. :D

A floor joist can always cantilever its full depth and the downward forces will be considered to be the same as if the post or beam were directly under it. When you go beyond this you get into bending forces inside the joist (think a very short diving board). You don't want so much load that the joists deflect or bend. That is why I limit the Little House foundation detail to a 14' wide building and light loft loads. We have never had any problems with this foundation, even in heavy snow load areas.

If you going to do a 14' high wall and a 10' wall it would be best to do the high wall with 2x6 full length studs and notch for a ledger. Then either rest or hang joists off this ledger that is secured to the wall. That will stiffen the wall and help hold the shed roof loads wanting to push outward. Note that even where you do not have a loft you will want to tie the two sidewalls together at every 4'.

This modification is a bit beyond the loads and simple structure of the Little House project so I would suggest you sketch out your changes and details and run it by an experienced local builder to make sure you are covered.
None of us are as smart as all of us.

lee5267

ok,

I'm now thinking I will do a shed roof with the tall wall being a continuous 12ft 2x6 wall and the other load bearing wall 8ft 2x6.  After reading the instructions and looking at all the little house plans I find very little about how to actually accomplish the shed roof for a 14x24.  If you were to build the 14x24 with a shed roof at 3in12 pitch how would you do it? 

glenn kangiser

14x24 with an 8 foot back wall at a 3/12 pitch is going to be pretty tight on the low side -- I guess it depends on how much storage or usable loft you want, but I liked your first idea better. 

"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

lee5267

The highest wall will be 12ft tall and the lower wall will be 8ft for a 4ft drop over the 14ft width.  I'm going to make the 12ft wall with continuous 12ft 2x6 studs to deter the outward forces from the roof rafters on the wall like John suggested earlier with the 14ft.  I really wont have much of a loft, just storage really over the bath room/ kitchen from the plans.  I figure I'll still use 2x4 rafter ties every 48" on center and just lag bolt them to the 12ft wall studs since there will be no top plate at 8ft high on it, and sit them as normal on the top plate of the 8ft wall.  I have also been wondering if there is a guide or table to determining how big the beams for the foundation should be if I decided to make the cabin 16ft wide etc.  I had found a table for the floor joist spans but nothing on beam size.

Thanks for all the input.

Lee


John Raabe

When you get into calculating beam sizes on a house of a different size you need to get a local builder or designer to do a load trace and size the beams. This is more custom work than a stock plan kit can cover.

That said, many old builders just upsized things a size or two and usually got away with it. :D

In terms of your shed roof rafters you can do the same details shown in your plans for the low slope roof except the birds mouth cut will be different since your pitch will differ.
None of us are as smart as all of us.