Timberframe Shed Design

[alpmeadow]

Golden Greetings
Below is a n example timberframe shed design I did using google sketchup.  I thought a simple small design would be better to learn this craft.  Sketchup is relatively simple to learn and the 3D graphic, and the 3D wharehouse is a great bank of already prepared building, furnishings, shop tools etc.
Currently cutting lodgepole pine for the timbers.
Cheers
alpmeadow

[shinnlinger]

I need to mess with this sketchup...those plans look good.

Is your roof system conventional?  It looks "overbuilt" for a TF to me.  I would think 3 rafters sets with purlins would be more "timberframe"

[alpmeadow]

Hi Jim
This particular design and roof system was a traditional timberframe in the notes to a one week course I took several years ago.  Certainly purlins offer an option in the design however I believe a larger timberframe than this is when the purlins come into play.  I'm sure the experienced TF folks in this forum can offer better advice.  I have already cut most of these rafters, so I'll stick with it.
Cheers
alpmeadow

[Clovis]

Hey alpmeadow; where is this 3D wharehouse located at on the web?

[alpmeadow]

Clovis
Goto the following sites for sketchup & 3d wharehouse, when you go to the wharehouse do a search for timberframe shed or cabin and you can see what folks have submitted.  It is an amazing gallery.  Of course you should get the sketchup program if you want to download any models.
Happy Hunting
alpmeadow

http://sketchup.google.com/index.html
http://sketchup.google.com/3dwarehouse

[moonhill]

Common rafters are just as traditional as principal rafters and purlins.  Even more so with a dropped tie beam as in the sketch.  The spacing seems to be quite close, but I don't know what the size of the rafters are.  In my area there are common rafter buildings with spacings of 4'-6', and the rafters are not all that big, 6"x7" or so and most likely tapered.  If those same rafters were sized by an engineer today they would be quite a bit larger, I often wonder what is up with that.  That looks like a nice size shed to get started with.  Tim B.

[Jim_Rogers]

That shed design with all those rafters was planning on having 1" board for the roof decking.
If you're going to use 2" tongue and groove, (which actually finishes at 1 1/2" after planning) you can place the rafters every 4'.
Those rafters are 4"x6":



Here it is in real life:

[alpmeadow]

Thanks for the comments. The rafters in my plan were 4" wide and 6" deep. I will consider Jim's option for wider spacing of the rafter(from 2 to 3 feet, I already have 14 rafters with two not quite up to spec)) with 2" t&g. Here are some views of the corner detail using sketchup 3d mode for viewing and with xray mode on to see the joints.
Cheers
alpmeadow

[alpmeadow]

By the way Jim, I like your picture of the shed.  I was wondering how long it took to build it and when will it be completed?
Cheers
alpmeadow

[Jim_Rogers]

This shed/small barn was from Jack Sobon's first book. With modifications suggested by his teaching partner, Dave Carlon. Dave's suggestions where to not do as many rafters and not as many floor joists. And to change the housing depths from what it said in the book, which was 1" deep to 1/2" deep.

As an experiment I created a jowl post on my sawmill one day:



Not wanting to recut this back to a regular post I decided I'd just use it in the shed. So I cut a second one to frame the side entry doorway with them. If you go inside and look back at the doorway you'll see the jowl posts when it is completed.



This frame was a workshop frame. The students of timber framing who come here to my sawmill yard and shop, cut this frame and erected it here in my yard. It is up for sale.

Once sold I'll push out the pegs and disassemble it and take it to the customer's site and erect it there for them.

How they "fit it out" will be up to them. We do recommend 2" t&g for the first floor, second floor loft, and roof decking. This frame is setup for vertical siding, as it has nailers between the posts.

For fun we decided to again add some live edge collar beams. I took one log and sliced off two sides and then split it down the middle to make two book matched collar beams.

We cut the regular joints in the rafters with a regular sizes collar beam first. Then transferred the collar beam layout to the live edge timbers. Once those tenons were done we modified the standard mortises to make them larger to accept the collar beam tenons.

It was test fit on the bench, or saw horses:



And:



That is John the student who did the collar beams.

I asked him when he was done what did he want to work on next? And one of the other students said, "....now he should make a "B"..... as this set of timbers resembled and "A"...... ;D

[alpmeadow]

Jim
I appreciate the character collar tie timber.  What makes timber frames homes so special, is the creative use of timber from both a structural and artistic viewpoint.  Character timbers are out there in our forest, however the forest industry normally rejects these logs as culls and they get chipped up.
Good on you
alpmeadow

[moonhill]

I like the crooks as well.  I try to wiggle some into every project.  I would go so far and use 1" boards on 4' spacing, for a shed.  All the old buildings I have seen are sheathed with rough 1" boards.  I have used 5/4" for boarding.  On my last frame I used 2-1/2" planks.  Tim B.

[alpmeadow]

We have to think of snow load up here in mountain country.  With metal roofing on a 12/12 pitch it is not too much of a problem, but we design for 100 lb/foot load with a minimum acceptable at 66 lb/foot.
We've seen to many car sheds with low slope with owners thinking 2x4 and 2x6 will carry the load.
You may shovel it but out here we play it.(snow).
alpmeadow

[moonhill]

I see, B. C., you get some snow loads than.  I have visited Mt. Rainier in the winter and understand the huge snow loads of the west coast.   I like metal roofing, it's all I use now.  There is nothing wrong with over building or building to the conditions at hand.  Wood is quite flexable.  When we throw drywall at a project and expect it not to crack when the wood bends is where size of timber  often comes into play.  I am still amazed at the size difference of older buildings and what engineers size to today.  Two years ago I worked on a building with an architect, and via him and the engineer the common rafters for a 24' wide building were sized to 7"x 9"'s on a 4'spacing.  In the same area not 3 miles away there was a 225 year old building being taken down, build by a young Scott and his brother, as the story goes.  That building was 24' wide and had roughly a 4' rafters spacing as well.  But the rafters all had wayned edges, and tapered, the tops were 4"x5"ish and the bottoms were 5"x6" if that, a fair bit smaller.  This roof had a layer of wood shingles and 3 layers of asphault shingles applyed over time.   Combine that with a winters snows and a wet coastal rain storm and you have a lot of weight, this roof has stood 225 years of that.  The Roof we built will easily stand as long, guaranteed, which is more than likely where the engineer is coming from, no risk.  Where the young Scott/Irish fellow was using what he had on hand and reason to size his rafters.  This is simular to why Dave Carlon suggested leaving out half the rafters, and Jack Sobon has to CYA in using a 2' spacing with a published book going out to the public.  Even here there are 2x buildings that haven't survived their first winter.  Tim B.

[alpmeadow]

Howdy Moonhill
I guess I'll have to carve my name in the timberframe, just in case 200 years from now someone starts tearing it down, so he knows who done it.  I just got in Steve Chappell book, A Timber Framers Workshop.  I guess he was based in Maine, your area?  I will have to get Sobon's book, is it a recommended addition to the library?
Thanks
alpmeadow   

[Dave Shepard]

I highly recommend Jack's books.


Dave

[shinnlinger]

Jim,

Thanks for sharing that frame...it has the wheels turning...

Alpmeadow,

My feeling is  the less rafters you have to cut the happier you will be, and purlins, in my opinion are easier to cut than rafters, but it is all about the look you want.

On my moms barn and my place too, we ran a 10 or 12/12 pitch with purlins every 32 OC" 

[witterbound]

Interesting thought, using purlins instead of some of the rafters.  Let's say you could leave out one set of rafters out of every three, and you'd replace that set with purlins.  So, you'd be subtracting two timbers with 2 joints on each end.  If you go this route the remaining rafters would have to be upsized to carry a bigger load, I suspect.  It would likely take at least two purlins on each side running between the rafters.  And probably another purlin right at the top so you'd have something to nail to.  That's 5 new timbers, with 2 joints on each end, or 10 new joints.  Plus the 10 pockets you have to cut in the rafters to accept the purlins.  That's a total of 20 new cuts you've got to make, and all you saved was 4 joints.  The rafter joinery is more complicated, but if you've done it a few times it can't be that big a deal to cut two more.  Just thinking out loud.

[Jim_Rogers]

Other considerations:
If you run the regular common rafters, not purlins, then the roof decking runs gable to gable. In this position it is easy to run the decking out a little to make some overhang without using another rafter for support. Maybe only 6" or so.

If you do use purlins then the roof decking runs ridge to eave. So you may have a chance to over hang the eave a little more, if you have some support out there. But you won't have any way to over hang the gable ends. And as mentioned you have to up-size the rafters and put in a purlin for the ridge, then called a ridge beam.

Taking away wood from the rafters at the ridge can again cause some concern; if it's not done right.....

Then it's a matter of assembly.

With common rafters, no purlins, you just put together a pair, horizontally on top of the plates and stand them up. Secure them at the plate with two large long screws, and at the ridge with a piece of strapping, as a temporary brace.

With rafters and purlins you have to stand up one gable end of rafters and then insert the purlins into these rafters, hold them up in place as you tip up the next set of rafters, aligning all of them with these purlins. Which maybe difficult to do. This of course is if you're using a tusk tenon. If you're using some drop in tenons on the purlins, such as dove tails, then you have to deal with the problem of what happens when the dove tails shrink and the purlins can pull out of the rafters. If this were the case you'll be relying on the roof decking to hold the purlin to the rafter.
Or if you're using rafters and purlins with tusk tenons you could stand up two pairs of rafters, with one secured, and lean out the other pair as you fly in the purlins one by one. Again this can be done but it requires more raising hardware such as straps and come-a-longs, and maybe a crane.

Personally, in my opinion, the common rafters system is easier to cut and raise.

Jim Rogers

[alpmeadow]

Thanks for your comments.  I take this as a welcome learning experience.  I believe that I have to apply the "Kiss formula" (too late stick building a shed would have been much easier).  I will stay with rafters for now.  One issue that has me concerned is that the rafters notched into the side beams may need to be secured? I plan to have a 2x2 temporary nailer at the inside peak to stabilize and space the rafters as they are installed.  Long screws(lag bolts) the rafters to the beam at the notch joints, but I think it needs some form of tiedown?  (Thanks Jim you posted the answers just as I was writing this)

For other designs for this size of timberframe, please visit this blog that "has purlins" and a well documented small TF cabin work-in-progress.
http://timbercabin.blogspot.com/2007_01_01_archive.html
Cheers
alpmeadow

[Don P]

Don't forget a diagonal sway brace as well as the spacing nailer to keep the group of rafters from toppling.
The lag in your case will almost certainly be enough to prevent uplift, that is one check that should be done on a house though.

Moonhill, I've removed rafters that tapered to as little as 3x4 and bowed almost 3" in span. He was within bending strength, he was certainly over my limits in deflection. I've seen what must have been the same guy's kid a generation or two later using a 2x4 under almost the same span and overall load with equal results. These were both in old virgin red oak that was weaker, less dense, and structurally inferior to the faster grown modern stuff. We do tend to dumb down grading to where the wood is twice as strong as the weakest 5% of the supply, so a careful builder nowadays is making things many times stronger than required. I guess when I look at that its the two extremes of the pendulum's swing.

[sheneman]

Hello all, the blog that alpmeadow mentioned above is mine (http://timbercabin.blogspot.com).

As far as purlin vs. all-rafter design, I chose larger (7x7) common-rafters with (4x7) purlins.  I am sure that an all-rafter design would have worked fine, but I simply wanted to try out purlins.  In my design, the purlins joined the common rafters with dovetails.  The raising was simple:  once two rafter pairs were raised and connected with purlins, there was no need for additional temporary bracing during the raising.  As a result, the roof went up quickly.

It helped that I was able to test-fit and make adjustments to the entire roof frame on the floor of my workshop.  That turned out to be critical to a speedy raising.

I designed my timber-frame roof to have no overhangs whatsoever.  Instead, I stick-framed the roof on top of the timber frame using 2x6 rafters.  This was effective in creating substantial overhangs on both the eaves and gables, and supplied large cavities for insulation above the ceiling.

[Jim_Rogers]

That method works......

[shinnlinger]

Good thoughts on the rafter vs purlin debate.

I just want to say I dont think you pro rafter people are wrong or anything, I might have to try an all rafter design myself next time.

WHen I did mine, I used a crane (which I happpen to have very easy & cheap access too) and that does make it easy!

On my last frame thought the purlins weren't ready so I raised the rafter sets and braced them with 1 and 2x stock as you would any rafter set or truss and called it good until I could go up and drop my purlins in with rope and 1 guy on each rafter set pulling them up.  Went pretty smooth.

[moonhill]

One of the things I like about a purlin roof system is the boarding is easier.  One board from peak to eve, for the most part.  You don't have to square the ends just snap lines when your done and cut on the line.  I cut one end of the boards, the peak end, right in the stack of lumber, with a chain saw,  the eve is the snap line.  With rafters you have multiple cuts and variable widths to deal with.  I love having the option of either roof system, each one has its place. It would be hard to pick a favorite method, I'm split 50/50. 

As for screws I have been using GRK fasteners with the t-30 bits.  I have wondered about strength of the GRK's compared to the black panel screws, I'm assuming they are stronger.  Also, In 75-150 years are they going to be so rusty the bit won't  work in the head.  The other part will they even have bits to fit that fastener.   It' bad enough using 5-6 different bits on a job.  Maybe I should go back to nails.   I think there will be some grumbling.   Tim B.

[alpmeadow]

The timberframe shed is taking shape.  Thanks shenneman for your input and welcome to the forum.  Please see below the wider spaced rafter system(going 2 ft to 3 ft+ does complicate spacing for roof buildup?).  If I rough cut long timber 6"x2"x16' plus for T&G and air dry(long time) it should work for the roof deck.
Please see below the updated frame image and an image showing detail layout for post IA.  It shows dimensioning from square rule edge for two sides of the timber for joint layout.  It is in xray mode to show joints in sketchup.
Comments welcome. 
Cheers
Irv Graham

[Dave Shepard]

And here is what it looks like from the outside:



This is the original shed at Hancock Shaker Village, not a very good picture though. Last time I saw Jack, he was trying to get me to put a new roof on it. :D Those are nice drawings Alpmeadow, I still do mine on paper.


Dave

[moonhill]

Alpmeadow, I always place/base my brace measurement from the top of the post or from the bottom of the tie, to the bottom of the brace pocket.  Here I see that measurement based from the bottom of the post.  Is that just the way Sketchup calculates the numbers?  You have 6'-9" from the bottom of the post to the bottom of the tie, which I'm assuming is an 8" timber and reduced to 7" at the joint.  Than a number, 3'-9-7/16" from the bottom of the post to the bottom of the brace pocket.  That leaves you with a brace leg length of 2'-11-9/16".  Again, assuming you are housing the brace to 7" on the post and the tie, that measurement should be 36" and giving you a brace length of 50-15/16" from point to point.  (36/.7071=50.912176)  Why 7/16" short?  Also the brace peg is showing a 1-9/16" peg hole placement.  I think you want that at an even 1-1/2" and draw on the brace tenon by 1/8+" in 2 directions.  I see a 1/8" draw on the tenon on top of the post which is correct, and the peg hole on the top plate should be 1-1/2" off the seat.   Does this compute or am I missing something.  Maybe it is just the way Sketchup works?  It seems like a lot of fractions and I like whole numbers for the most part.  Tim B.

[alpmeadow]

Well darned if you caught me with my pants down Moonhill.  Yes my braces have shrunk and should be 50.91" as in my timberframe notes.  Early in my sketchup design I used a tool called scaling and it slightly shrunk my 36" brace. I am rattling through my design to shift every brace into its proper location and size.  I guess I couldn't see the forest for the trees, and extra experienced eyes on the plan sure helps to catch simple errors.  Much appreciated.

Wow, I like the image of the shed.  My course notes confirms, "the 12x16 foot shed garden tool shed featured in this book was was designed and built for the Hancock Shaker Village, a museum of old Shaker buildings in Hancock, Massachusetts."  It nice to acknowledge the historical values of what is being created.
Cheers
alpmeadow

[witterbound]

Shinnlinger,

I don't think you pro-purlin people are wrong either.  Just wanted to point out some of the factors in using purlins vs rafters.

In fact, I'm pretty sure that principal rafter/purlins are now the dominate type of roof system used in timber frames.  I think this began because it's easier to put the bents together on the deck and raise them with a crane, then drop in the purlins, than it is to put up each post, then put a plate on top, then fly in the rafters.  A lot more raising time is typically needed for a post and plate (common rafter) design, I think.

Back before the reinvigoration of the timber frame industry in the US, I think the common rafter system was the primary roof design.  I've never seen an old barn with principal rafter/purlins.  Anyone else seen one?

One advantage of the purlin system is that you don't have to have as many long timbers.

[moonhill]

Yes I have seen them all over the place, principal rafters and com. purlins, old and hewn.  What you are talking about is the Bensonite method, it is not traditional.  Tim B.

[routestep]

On small sheds, I don't think wall plates and rafters are very hard to set up if made out of softwood. A plate can be lifted in place by parbuckling with two men per bent. With 4" by 6" rafter pairs one man can push them in place if the rafters are fairly short.

[alpmeadow]

Golden Greetings
Attached is the Post IA plan drawings of front and side corrected for the brace joints with dimensions added.  This replaces the previous post drawing reply 25 dated March 5, 2008.

This should work for cutting.
Thanks again for input
alpmeadow

[alpmeadow]

To the PM
A question was raised how to setup Sketchup to get a planview of the timber in my previous posting.  I responded as follows:
Thanks for your comments.  In sketchup if you go to camera, standard view, front and this view has the timber shown properly, or select the standard view(top, side etc) that works for you.  Next go to camera view, parallel projection it will remove the 3d perspective that messes up your drawing.  You can still change the standard view  to top or other views as it is still a 3d drawing.
Try it out.
Cheers
alpmeadow

[alpmeadow]

PM received as below.

I like your model of your 12 x 16 timber frame shed. I notice you use 8" x 8" posts. Do you think 6" x 6" would work? Thanks

I responded
6x6 posts can be used however a different design and sizing for mortise and tenons is recommended, and I am not qualified to recommend such alterations from that published in Sobon's book.
This comment will be added to this thread.  Good Luck
alpmeadow

[moonhill]

6x6's could be used, but the joinery will have to shrink as well.  I bump my timber up to 9x9 just for the convienence of the joinery.  Tim

[Jim_Rogers]

PM received as below.

I like your model of your 12 x 16 timber frame shed. I notice you use 8" x 8" posts. Do you think 6" x 6" would work? Thanks

I responded
6x6 posts can be used however a different design and sizing for mortise and tenons is recommended, and I am not qualified to recommend such alterations from that published in Sobon's book.
This comment will be added to this thread.  Good Luck
alpmeadow

Statements like: "6x6 post can be used...." maybe true but you shouldn't be making them without careful review of the intended loads to be put on the frame.
The person who is asking this question should review the frame loads and/or have it reviewed to insure that the 6x6 post can handle the load.

We don't know where the new sized frame will be constructed so we shouldn't just assume it will be ok. Nor do we know what loads he'll place upon the loft area if any.

There are lots of facts to take into consideration, and we don't have any of them here and now to consider.

The frame from the book was sized so that the author could be covered if anyone from just about anywhere built this frame. What that means is that the posts are oversized to handle just about any load. But we can't just assume that building the same size shed that we can reduce the size of the posts to fit our stock on hand or our wallet.

Each frame has to be reviewed for the location conditions and the intended loads for the current use.

Jim Rogers

[alpmeadow]

Hey Jim
Yes, we better say "could" rather than "can".  That's why I bought it into this thread so, wannabe's, just like me, can digest the great content and almost, wise members of this forum.
Sounds like you had a great time at the southern workshop.  What do you do with timbers that the missed layout or cutting marks?  Toothpick timberframes?
Cheers
alpmeadow