24x24 Workshop

[Khaameleon]

Note to the moderator/admin: I'm not sure if this belongs better in this section or the TF plan repository. I posted it here since my plan isn't complete, and this forum receives more traffic which I hope will help with my questions.

This is a long overdue (and just plain long, sorry) introduction for me. I stumbled across this forum about a year and a half ago while researching ideas for my "dream garage", and it was here that I was first introduced to timber frame construction. I immediately fell in love with the beauty of the structures and craftsmanship involved. I knew then that I had to try it for myself.

I've since read over a dozen timber framing books and articles, attended a week long course at Heartwood, and learned to use all sorts of tools that I'd previously known nothing about. I've also spent an (almost) embarrassing amount of time searching and browsing the vast information contained both here and on the tfguild forum. The more I learn, the more I realize how little I know. However, I feel prepared to embark on my first "solo" frame.

Before I go on any further, I'd like to say thank you to Will and Michelle Beemer, Dave Carlon, and Jim Rogers, as well as the countless forum members here who have taken the time to share their experience, advice, and pictures freely with a bunch of strangers on the internet. You're good people.

My dream garage will continue to wait a few more years, but I'm planning to start construction this spring on a "small" 24'x24' workshop. I've attached the current version of my Sketchup plan for review. It is by no means complete.

The design is based on the classic Sobon shed, scaled up to 16'x24', with an 8' shed off the south eave wall. If you recognize it's suspicious similarity to Brian_Weekley's barn, you get a gold star. My thanks go out to him as well, since much of my design was copied from his. I even took into account some of his comments when I redesigned it (taller posts and knee-wall, higher tie beams).

I went with this design because:
a) it's relatively simple and similar to the one we built at Heartwood,
b) it's big enough to store my tools and implements while still affording enough workspace to maneuver materials about,
c) it seemed like the biggest frame I could cut and raise by hand with a bunch of friends (though I think that still remains to be determined), and finally
d) it will fit in better with the design aesthetics of our house than other "beginner" frames I've considered with a similar footprint.

I know it's best to start small, but I really need a workshop that will be large enough to house my tools and still have space to work inside. Winters are bitter cold up here in the North Country. Last February we didn't have a single day above 0F, with most in the -20's & -30s. There's only so much sawing, hammering, and mucking about a man can do inside a house all winter before he begins to draw ire from SWMBO. I doubt I'll be able to make it through another winter without a dedicated workshop. But, I digress...

Even though it's much bigger than the original shed, I think this design maintains a lot of the features that make it beginner friendly without introducing too many more complicating factors. Yes, it will be heavier, and the plates may be unwieldy, but I think we may be able to still use the rope trick to walk it up the side of the frame. I'm not an expert on these things though, so I could be wrong. Your comments are appreciated.

More details to come.

[Khaameleon]

I'm currently in the process of running my load calculations for the roof. I do plan on getting the design approved by a qualified engineer, but I'd like to be confident in what I'm submitting to him/her. The snow load for my area is 65 lbs/sq. ft., and the wind loads are 90mph. The roof will have 2x6 T&G decking, with an as of yet undetermined thickness of polyiso rigid foam, topped with 5/8 OSB or plywood, and finally asphalt shingles. As such, I'd been using a dead load of 15lbs/sq ft, and a live load of 86.15, if I'm using the proper correction for a 12/12 slope (1.41).

I'm considering metal for the obvious advantages of durability and reduced snow duration, but my wife finds it moderately objectionable aesthetically. I agree to an extent.

Right now, my calculations tell me this roof design will only work if I use common rafters 5"x9" or larger. That seems pretty big, and would necessitate a larger plate. I'm not quite sure if a collar tie could help with this. Most of the information is Steve Chappell's book is about truss design, not common rafters and collar ties/collar beams.
I'm also unsure how to figure the additional load incurred by the shed roof on the south plate. do I just figure the roof loads for the shed, and add that on top of the load incurred on the plate from the main roof?

I'm also beginning to realize that the 16' bent span may be too large without adding an additional post. I don't plan on anyone living in the loft or anything, but it would be nice to store some lumber up there as needed. I'd been figuring a live load of 60 lbs/sq ft.

It's also looking pretty likely that I'll need a summer to reduce the span of the 1F floor joists as well, which I haven't sized up yet either. Most buildings I've seen with a 16+foot span are either on slabs or gravel, which makes sense. Since I created this with the ruby extensions, resizing is a breeze, and I'm considering downsizing the width of the main frame to 14' if it's going to take significantly more material than I'd planned.

Comments, questions, and laughter at my mistakes; all welcome.

[GAB]

First off welcome to the forum.
24 x 24 is a nice size but I suggest you build such that you can grow the building in the not too distant future.  There is never enough storage space.
As to your questions I have ZERO qualifications to answer them.  Hopefully someone will be able to.
Gerald

[peterpaul]

Hello Khaameleon,

First off, I have little experience with timber framing, however, I am a licensed construction supervisor.  I would like to make one suggestion for your roof construction which is; on top of your poly iso, (approximately R 6.5/in) I suggest that you run 1x4's from eave to ridge, nailed with ring shank nails through the foam into your 2x roof decking and then nail your 5/8 sheathing to the 1x4's.  Add soffit and ridge vents so you end up with a vented, cold roof.  This is particularly beneficial if you end up using asphalt shingles as your roof assembly will remain cooler in summer aiding in the shingles longevity.  Also with asphalt shingles, a vented roof will help prevent ice dams as heat does not build up and melt the snow from the bottom up as the top side of the roof is the same temp as the outside air.  FYI, Ice dams form as the melt water runs down the roof, under the snow (which is a great insulator) then hits the cold roof overhang and freezes.  This continued process adds layer upon layer of ice build up at the eave creating the ice dam.  I have built houses with and without this method of venting and based upon my experience, the vented roofs have zero problems with ice dams.  This is less critical on a steep pitch metal roof as the snow load duration is much less.

The picture below is a photo of my house, from last winter, (I feel your pain regarding snow and temps last year).  As you can see in the photo, I have no ice dams yet there is estimated 4-5 feet of snow in the valley.   


Also soffit venting can be concealed so that it is ascetically pleasing and does not detract from the appearance of the house.  Below is a house I recently built with this type of concealed venting.

[tule peak timber]

Wow, what a gorgeous house you built ! How did you handle shear with all that glass on the visible wall ?  Rob

[Khaameleon]

I would like to make one suggestion for your roof construction which is; on top of your poly iso, (approximately R 6.5/in) I suggest that you run 1x4's from eave to ridge, nailed with ring shank nails through the foam into your 2x roof decking and then nail your 5/8 sheathing to the 1x4's.  Add soffit and ridge vents so you end up with a vented, cold roof.

Thanks peterpaul, you're absolutely correct and I'm actually planning to do just that. In my haste to post, I neglected to mention the 1x4s as well as the vapor and ice barriers. I was mostly thinking about the dead load at the time. While I don't think that adds an appreciable amount of weight, I'll refigure the load to be sure.

My last home was built in 1858 and had an unvented, hot roof. The ice dams were horrendous. I won't inflict that pain upon myself or anyone else.

The house in your second picture is indeed beautiful. I'll have to look into techniques for handling/concealing soffit vents when I get to that stage of my plan.

I also realized that I forgot to mention the wood species I'm using for my timbers, EWP. I'll have some more time to work on my plans and figures this weekend, and will update as I go.

[Brian_Weekley]

it's suspicious similarity to Brian_Weekley's barn, I even took into account some of his comments when I redesigned it (taller posts and knee-wall, higher tie beams).

The Sobon Shed design is a nice project to build.  That's a good size and the extended plates and rafters will make a nice overhang.  You might want to add additional girts to the taller walls.  Would you like to trade?

[Khaameleon]

Anyone out there with common rafter experience care to comment on my roof load question? Specifically, I'm trying to size my rafters to handle the snow load for my area (65psf), and wondering how a collar tie/beam is figured into the equation, if at all. From my novice viewpoint, it would seem that even though the collar "tie" is in compression it would have some effect to reduce the span of the rafter as a beam when calculating load.

I've gone through all of my TF books and can't find anything regarding how a collar tie would impact rafter span for load calculations with common rafters. I did find a TFEC article that spoke to collar tie placement a bit (http://www.timberframeengineeringcouncil.org/images/pdf/TFG%20Article%20December%202007.pdf) but beyond general terms about the transfer of load stresses it didn't really address what I was looking for.  Perhaps I'll just save this question for my engineer. I just thought I'd ask some of the more experienced members around here first.

Thanks,
-K.

[peterpaul]

Hello 
I don't know if this helps answer your question or not, regarding Common Rafter sizing, the International Building Code, IBC books, include many tables to allow the user to determine the rafter size based upon the roof assembly for a specific application (span, load, material, fasteners, etc).  The tables use 2x lumber on x centers with various snow loads.   The books I have, (which are on a job site so I cannot copy and paste) include a "commentary" on each code.  I have found this very helpful in understanding the intent of a specific code.  Regarding collar ties, in a conventional roof system, i.e., rafters tied at ridge and wall plate,and the CT is connected to the rafter,  I believe the CT is in tension as it is design to counteract the outward force of the roof assembly against the outer walls as the roof tries to flatten under load.  In a roof assembly with a structural ridge, where the ridge is designed to support the roof load, the CT's would be in compression as the roof rafters deflect inward under load as they are supported at each end.  The IBC also specifies the fasteners and hardware required to prevent uplift as well.  For those framing members not covered by the IBC, a design professional should be consulted.  Disclaimer, I'm not an engineer, just a hack.

[tule peak timber]

How did you handle shear ?

[tule peak timber]

I'm sitting here with my architect looking at the glass reveal on this home and he suggested that the sheer is handled by the floor and ceiling diaphragm. Rob

[peterpaul]

I'm sitting here with my architect looking at the glass reveal on this home and he suggested that the sheer is handled by the floor and ceiling diaphragm. Rob

Hi Rob
I apologize for the late reply, your architect is correct, the engineer designed a large "A frame" truss for the gable ends supported by interior and exterior walls/posts to basement.  The shed roof rafters are supported by the A frame and  outer wall.  There are a total of 5 gable ends such as this on the house.  There are also beams running the length of the main floor on the outer wall under the windows as well.   
Peter

[samandothers]

Khaameleon
Welcome to the FF.  I do not have the knowledge to help you but am enjoying your thread.  Hopefully someone will be along to help shed some insight on your design.

[BAP]

I too cannot offer much for help, but am following this to learn as much as I can because I want to build a 26x28 foot Sugarhouse. As far as your wife not liking metal roof, there is a lot of nice colors available nowadays that look really or can blend right in with the surroundings. Makes for a really long term, maintenance free roof.

[tule peak timber]

Peterpaul, Thanks for the response. We are building right now ourselves and have a 60' wall that has a large amount of glass. My architect advised me to incorporate some special sheer construction to handle the lateral loads and I'm always curious how others are dealing with like issues.
Cheers and keep on building.
Rob

[Khaameleon]

I was able to figure the rafter sizes required for my roof load (5x8) with a little nudge in the right direction. I've got a better handle on roof load calculations now.

Unfortunately, after reviewing my design and considering the time investment in the joinery, I realized I could get a larger and more space efficient structure for a similar time investment. At the risk of getting in over my head, I've decided to go ahead with building my 28x36 garage instead. I spent some time this weekend on the design and hope to have it in a place I feel comfortable sharing soon.

Thanks to all those who have welcomed me and given their input.

[Brian_Weekley]

At the risk of getting in over my head, I've decided to go ahead with building my 28x36 garage instead.

Go big or go home.   

[Khaameleon]

Quick update. I haven't had much time to spend drawing out the joinery for my garage design in sketchup, but this should give a general idea of where I'm going.

The longest timbers I can get around here are 20', so I tried to design around that. I really like common rafters and want a nice big overhang on the eaves, which meant I had to find a way to join two timbers to make a rafter long enough to cover the run of the roof. It seemed like the best place to do this would be over the principal purlin of the queen posts. I'm pretty sure the joint I've used in the model would be acceptable at this location, though it seems most commonly used at rafter foot/post connections in contemporary frame design. The only name I've seen given to this joint is "rafter foot/post joint" in Steve Chappell's book A Timber Framer's Workshop. I should note that I'm planning on step-lapping the lower rafter member into the principal purlin and top plate, but I haven't had a chance to draw that in yet.

Anyone familiar with other ways of accomplishing this? I know most scarf joints wouldn't be suited for such a task given all of the bending forces a rafter is subjected to. I wouldn't feel comfortable using a stop-splayed undersquinted scarf in my roof, though I know they've been used on rafters before (at least in restoration work).


-K

[Brian_Weekley]

Just a suggestion...You might want to export a jpg from your Sketchup drawing and post it in your thread also.  This gives everyone a chance to see your design and comment--especially if they don't have Sketchup on their computer.  In addition, if you have an older version of Sketchup loaded, it won't let you open a newer version file.

[witterbound]

I've got common rafters, but they end at my wall.  My roof overhang "structure" comes from 2x4s that are a part of my insulated roof.  I didn't want any part of my timbers exposed to the elements.  I suppose I wouldn't feel that way if I were building a barn or a workshop.....