I'm trying to design a gambrel roof for my 3 car garage and I was wondering if anyone had any particular thoughts on the correct proportions of gambrel roofs.

What I have so far is below but don't pay too much attention to my trusses internals its a layman's attempt to engineer an overly complicated structure, I'll have BMC sort out those details later.  You'll notice I have a piggyback on top of the truss since I figure a 15 foot tall truss probably won't get delivered.



You can see I went with a perfect octagon in laying out the top chords, somewhere I read that this is the true form of a gambrel roof, but to me its looking a tad boxy.

 All the appeal of a Lowes shed. Grab an engineer and stick frame it. I've heard keep it all inside a compass swing with all corners touching. I think it was an old copy of Audel's that had a good practical treatise on them. I'd go taller sided and narrower with the top pitch. There is a point where that looks pointless too  . Mansard and curb roof would be more to look into.

Look at the trusses at barnplans.com. My barn is built to their plans. The top pitch is 7/12; the side pitch is 12/7, and I think it is a nicely proportioned roof. Their trusses are much simpler, too.

The boxy look of my first attempt and comments below got me thinking more about the different pitch combinations that are possible with a roof like this. Now trying to determine what is the best pitch combination for the classic barn look.  Of course there are an number infinite combinations but I've created this little matrix below to fuel some thought, any ideas or suggestions on what is the best looking barn roof out there?  Pictures would be great too.



Much more legible PDF can be found here:

http://design.medeek.com/resources/truss/PDF/GAMBREL_STUDY.pdf

On our barn, well I took it over, it's another shop  I used the 5/12 over 12/5. I made the sides a bit taller and the top a bit narrower to avoid the cookie cutter look, don't go overboard or it looks tough too though. This is all minor aesthetics, what rocks my world might not do the same for you. One thing I took square, front on shots of a few barns I liked. Import it into something you can pull angles from.

My taste is towards the 6/12 - 12/6, the 5/12 -12/5 is a bit boxy IMO but I can see it would have more space.

I had to actually draw up the right elevation since it is really hard to visualize what the shape will look like without the rest of the building in the picture:



PDF here for those who don't feel like damaging their eyes trying to decipher the microscript:

http://design.medeek.com/resources/truss/PDF/GAMBREL_STUDY2.pdf

Thoughts?

I like the dressed out version. Only thing I see is you might want to check the upstairs window for egress. I like the kickouts at the bottom of the roof, dresses it right up. Now I wonder if my objections to any of the others would fade with a little detailing  .

That looks a lot better than the first one !

Don't get too set on just one yet. 

Now compare the 6/12 12/6 to a 7/12 12/6, my wife actually likes the taller one for more of a residence and the shorter one if it is a garage or barn and secondary to the main house.  I guess that makes sense.



PDF here:

http://design.medeek.com/resources/truss/PDF/GAMBREL_STUDY3.pdf

Kind of interesting how a slight change in pitch can change the look of these gambrel roofs quite dramatically. 

After looking at a bunch of different barns online the kickout and the cupola were a given, also the crow's beak on the main gable ends and dormers adds a certain flair.  The roof is taller than a standard 12/12 pitch so I also added an eyebrow above the single hung 36x40 window at the gable end.  Otherwise the window just didn't look tall enough to fill the space. 

I really haven't developed this plan yet since I'm mostly experimenting with the gambrel shape but it's got me thinking about the dormers.  I've seen both regular dormers and gambrel type dormers (barnplans.com) on these roofs, any preferences either way?

This is developing nicely. Good work.

Compare this roof design/truss to the first attempt:



I decided to go with the more standard 9'-1" ceiling height.  The amount of space available with a gambrel roof is compelling versus the standard 12/12 pitch.

That's essentially the same truss I used in the loft area of my barn. I don't understand the two-part truss for the top- why not just a simple triangular truss? Here's a sketch of what I did (approximately). The top trusses are on top of the conventionally framed lower roof.

Quote from: MushCreek on March 28, 2013, 06:30:35 AM
That's essentially the same truss I used in the loft area of my barn. I don't understand the two-part truss for the top- why not just a simple triangular truss? Here's a sketch of what I did (approximately). The top trusses are on top of the conventionally framed lower roof.

It's whats called a piggyback truss.  Without splitting it into two you end up with a 15.5' heigh truss which is nearly impossible to get down the road.  Making it 12'-6" makes it a lot more manageable for transportation.  That's the only reason to use the piggyback truss, otherwise your right, much easier just to go with one truss.

But Jay's only truss is the top pitch, a piece of cake to transport. Interesting idea. At first glance with it stick framed I'm worried about loading the floor with the verticals but as soon as the floor deflects at all the load is on the steep rafters directly to the wall. You could knock out the verticals IMO... but ask somebody with a stamp first! If you used clearspan joists without the truss's verticals acting in tension though the joist depth probably just went up.

Jay, in your setup I'm assuming the vertical studs are just sitting on the floor and are under the trusses. Good for compression, no tension capacity. They are really just load on the floor after the roof is sheathed. In Medeek's truss the steep rafter is carrying the upper roof load, just as in yours, but the verticals are strapped at their upper end and hang as a chain from that point down to the floor which they are strapped to. (which is why you shouldn't cut those verticals on a truss... Just sayin for anyone reading who might have done that recently ) The verticals in the truss support the joists and so shorten the floor joist span to about 17' instead of 27', letting them get away with a 12" depth. I'll bet the depth goes deeper for a 28' clearspan. That may or may not be a dealbreaker in each situation. Neat option, if you could scab the verticals alongside Jay's trusses and again alongside joists and stick build that lower pitch, that would turn Jays setup into acting like yours without having to mess with a piggyback and it would get the joist depth back down. 18' truss about 6' tall, I joists, it would be a no crane 2 man job. The techs at the truss plant could probably design and run that scenario against the piggyback if its do-able... then try to figure the labor difference.

Mine isn't accurately drawn; everything is tied together with plates and hurricane clips, so it acts like a truss. My floor joists are 2X10 on 12" centers, but I have carrier beams supported by 6X6 columns to support the loft floor. IIRC, my actual trusses are a little over 20' (for a 28' wide barn) and were only $1200 for 25 trusses.

I like the way my loft came out; the ceiling height is over 8', and the side triangles would make great closets if I ever finished the loft. I can just walk through them without bumping.

Nice work Jay. Things appear to be locked down tight and the whole package (truss and stick frame materials) fits into a tidy easily managed load.

Finally got around to documenting my foray into gambrel roof design:

http://design.medeek.com/resources/truss/gambrelroofstudy.html