Gambrel Roof Question - 36 foot span

[jeff216410]

I am working on getting zoning approval to build a 36x40 barn/garage. The unit will be for storing and working on cars and other projects. My question is how can I get a 36 foot span with a gambrel style roof with as much usable space upstairs?

I currently have a gambrel style garage with a 2x10 floor 12 on center with 3/4 plywood. The span is about 20 feet. The roof trusses are 2x6 with 2x4 collar ties and nice heavy 3/4 plywood gussets. The steeper angle of the truss is 2x6 all the way down to the floor deck. Knowing that this style roof will try to spread under loading, the builder used joist hangers attached to a 2x10 laying flat on the floor with the trusses nailed in so the truss cannot spread under load. I don't know if it meets code but it looks clever and that roof is very very solid.

Can I just make a larger version of the same thing? It's nice not having knee walls but I can live with them if I need to. I know the floor will have to carry the knee wall weight plus roof truss load if I go that route.

I was planning on using I joists or floor trusses for the 36 foot span with 3/4 plywood glued and nailed. I'm working very hard to have no posts or walls downstairs. Any suggestions would be appreciated!

 

[Gary Fowler]

I have a standard 4/12 roof that spans 30 feet with engineered wooden trusses. I have a small attic storage area right in the middle about 12 feet wide. I would think it would be no problem at all with a gambrel roof for 36 or even 40 feet. Just go to a truss manufacturer and have them design and get them to design and build them for you. I havent got a lot of weight per sq. foot loading on mine but it is solid when I walk around up there.
The laminated I beams should span the 40 foot width if you wanted. Just get them engineered for the load and you should be OK.

 

[davedj1]

You are going to need two carrier beams to support the floor, a truss (especialy home built) cannot support that kind of span without beams below. There is an involved array of bracing that needs to go onto engineered truss's. the proper framing procedure without a truss system would require a king beam and queen beams. In order to have any kind of usable storage or weight bearing upstairs.
Gambrel Style Wood Barn Kit - Post and Beam Barn Kit - Barn Building Kits - Timber Frame Plans
Gambrel Roof Joinery - Timber Frame Forums
Hope these help.

 

[scgargoyle]

I'm building a 28' wide barn with plans from barnplans.com. They do have plans up to 36' wide, and I believe you could possibly get floor joists that will span that. In my case, I'm going to have some posts and beams to cut costs on really big engineered joists. The way their plans work, you build your four walls and the loft on top. Then you lay out the truss full size up on the loft floor, and build the first one over the pattern. After that, you nail down temporary blocks as a fixture to build the rest of the trusses. Finally, get some (big) friends and stand them up. The trusses are self-supporting, so the loft is wide open.

 

[SPIKER]

mine is 38 feet inside with about 11 foot height on 2nd floor to the bottom of the straight span that ties the top of the gambrel roof together. the side walls are rather steep for a better floor usable space as it was going to be living qtrs upstairs. I didnt go the I beam & had to have a center posts down the 50 foot side. They used 2x6 for the fab on site trusses and they used more on the floor to nail the trusses too.
I like the idea that someone used the joist hangers on the floor board to help keep them from schotching towards the outside & bowing the walls.
Mark

 

[dex3361]

When I built my garage I had the same goals, I wanted no posts downstairs and I wanted 8 foot ceilings upstairs. The dimensions are 28x36 and I have a 24" support beam down the center. That is where you will need to get the engineering right in the beam sizing. I agree that you may have to have 2 main support beams to handle that length. I made my roof slopes to be 4/12 on the top section and 12/4 on the side walls to keep the spreading effect down to a minimum. I went overkill on the collar beams and used a collar on every wall and roof rafter. I also used rough sawn oak for the trusses. Not the prettiest build but it hasn't sagged a bit in 20 years. As you can see in the pic I just recently got around to adding the loft doors before I stained it again.

 

[crazyal]

Here's my garage. The span is 28' and the trusses were engineered for a 80lb snow load.

The cement walls are 2' and the wood walls are 12'. The second floor is 2' lower than the sides of the wall giving 8' under the cord. You can see it well but I used a steel I-beam to support the second floor so both floors have no posts in the center.

 

[jdmar]

I echo the comment "talk to your truss manufacturer." Tell them what you want. Also give them options so you can see a cost differrence. I have a 36' wide gambrell barn with engineered trusses. My first floor is clear spanned. My second has an 8' high by 16' wide space with 8 foot "knee walls. i.e the upstairs is rectangular in cross section and 8' high, 16' wide.

Here is a link to my old thread so you can see what they looked like:
http://www.tractorbynet.com/forums/projects/121279-barn-building-tractor-help-4.html

...I guess I ought to update my old post someday to showed the more "finished" project!


Good luck
Peter

 

[Aguanga]

It sounds like this website should answer your question. Of course, yours may need to be designed different depending on the loading and any seismic requirements for your location. I'm looking to do something very similar myself.

http://www.apmbuildings.com/Gambrel-Attic-Trusses.pdf

 

[schmism]

There is going to be a balancing act you need to do between a number of things

1) max height for a single truss (generally 12 but sometimes 14')
2) max span for the storage room in a clear span truss (interior space)
3) architectural look

and

That is the "classic" timber framed gambrel roof barn on the property im closing on in 2 weeks.

But note, the height of the siding till the first break in the roof is 10' length to the peak is another 6'+.

the width of that barn is infact 36'

So if you use a single truss, you wind up with a squashed look to the roof.

NOTE the timber framed barn above uses about a 4' deep truss to support second floor load (aka all the hay stacked on the second floor)