Need Recommendations for Storage Loft Rafter Demensions

[DocHolliday]

I am in the final stages of building my workshop. It is 24 ft x 16 ft, on concrete slab, with a gambrel roof. I have designed and built the entire structure. I finished all of the external trim today. Now I just need to finish caulking and paint it before winter (still have plenty of time in Texas).

My plan is to add 4 ft wide lofts on each end, that span the 16 ft sides. I will use two rafters on each end, that sit on top of the top plates, and attach to the roof trusses. I need recommendations on what size rafters I should use. Should I use 2x8x16, 2x10x16, 2x12x16? It will not be pilled full of junk and probably nothing extremely heavy. I just want to be sure the rafters don't sag (too much), and try to get by without a center column.

Also, for my double doors, do any of you have recommendations on where to get spring loaded floor and ceiling bolts? Or, and better ideas for the pins/cane bolts that secure the left door to the floor and ceiling?

Here are a couple of pictures. I will post more in anyone is interested.

 

[JoeFin]

Use the joist span tables from the building code and design for 50 lbs per sq ft dead load

https://law.resource.org/pub/us/code/bsc.ca.gov/gov.ca.bsc.2010.02.5.pdf

 

[DocHolliday]

Thanks Joe. I appreciate that link.

 

[Cyberbear]

Can't see any in the photo, but if you are going to run electrical in the walls, you should think about fire blocking. This will also help stiffen the walls, especially near any large door openings.

 

[Nowater]

Nice job on the roof.

I suspect most span tables will specify really deep beams for that 16' span. The problem is, deep beams take away from storage space both above and below. You can achieve considerable strength by doubling up your beams around a strip of 1/2" or 3/4" plywood ripped to the same height as your beams. Try making a sandwich of say 2 by 8, plywood and then another 2 by 8 all glued and screwed (nailed) together, for instance.

As long as your beams are very firmly attacked to the side walls, one could stiffen them by dropping a threaded rod down from the ceiling ( roof member) to the beam.

 

[BFBOB]

Wood I-beams. Best strength/weight ratio, shortest depth so takes up least headroom. Do an internet search - load tables are out there. Since you're a DIY type, you could even make your own. 16' 2x4's are easily available. Rout a slot, glue in 1/2" OSB. But, you might find ready made not that expensive - not worth the time/materials to make your own.
It would, however, be an interesting experiment which many of us would love to hear about!

Very nice proportions on the gambrel, by the way. From the inside, the gussets make it look almost like a barrel vault.

 

[DocHolliday]

Ah, good idea. Thanks Nowater. Doubling the beams may be the way to go. But, why the plywood in the middle? I built my headers that way, but only so they would be the same 3 1/2" thickness as the studs.

I'm not overly concerned about giving up storage space to make the beams as strong as they need to be. My walls are 8' tall, and then 6' from the top of the wall to the peak of the roof. So, there should be enough storage for what I have in mind. I will look at the costs of doing it either way.

 

[Throbbin Rods]

Wood I-beams. Best strength/weight ratio, shortest depth so takes up least headroom. Do an internet search - load tables are out there. Since you're a DIY type, you could even make your own. 16' 2x4's are easily available. Rout a slot, glue in 1/2" OSB. But, you might find ready made not that expensive - not worth the time/materials to make your own.
It would, however, be an interesting experiment which many of us would love to hear about!

Very nice proportions on the gambrel, by the way. From the inside, the gussets make it look almost like a barrel vault.

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[theoldwizard1]

Very nice proportions on the gambrel, by the way. From the inside, the gussets make it look almost like a barrel vault.

CONCUR ! What is the width of the upper and lower roof segments ?

The 2x4 interior gussets appear to be "extra". Were they in the original plans ?

I like how the purlins are set into the 2x6 rafters. Lots of work. I assume, the rafter frames were built on the floor and then installed, correct ?

 

[theoldwizard1]

Nice job on the roof.

I suspect most span tables will specify really deep beams for that 16' span. The problem is, deep beams take away from storage space both above and below. You can achieve considerable strength by doubling up your beams around a strip of 1/2" or 3/4" plywood ripped to the same height as your beams. Try making a sandwich of say 2 by 8, plywood and then another 2 by 8 all glued and screwed (nailed) together, for instance.

As long as your beams are very firmly attacked to the side walls, one could stiffen them by dropping a threaded rod down from the ceiling ( roof member) to the beam.

CONCUR !

Skip the plywood spacer. Nail a ledger to the end wall studs that is level with the doubled joist. If you are only doing light storage you only need to double the joist furthest from the wall, if you are spacing the joists 24" O.C. If you go 16" O.C. you probably don't need to double the last one.

If it is "light" storage, you probably only need 1/2" plywood if you add blocking (use joist hangers) between each joist, every 4'. The blocking will also prevent the joists for rolling/twisting.

 

[Nowater]

My understanding of using the plywood in the middle of the beams, is not that it is a "spacer." Rather, I have been told that the plywood in the middle like that adds a tremendous amount of strength, almost equal to an additional full size beam. It is all a moot point, as the OP says he has plenty of vertical height.

Incidentally, additional strength can be had by adding some full depth blocking between his beams. As the beam is loaded, it will deflect down, and also try to twist out of position. The more it twists, the more it loses strength in the vertical direction. The blocking resists that twisting action.

 

[DocHolliday]

CONCUR ! What is the width of the upper and lower roof segments ?

The 2x4 interior gussets appear to be "extra". Were they in the original plans ?

I like how the purlins are set into the 2x6 rafters. Lots of work. I assume, the rafter frames were built on the floor and then installed, correct ?

I certainly appreciate the compliments. on the roof design. I actually built the first side wall, and stood it up, and I just didn't like the shape of the roof line. So, I laid it back down and spent a couple of hours with a ruler and several pieces of paper coming up with a design I was happy with. For a common gambrel the upper section would be half the height of the building's width, and each roof section would be 45* angles. I didn't really need, or want, and 8' upper section, so I did my best to make each section and angle symmetrical. I would have to look back at my drawings to give exact measurements, but the sections are somewhere around 67" with 37* angles.

I've never built a structure like this, so I've spent countless hours researching each step and design. Yes, I built and assembled each truss on the floor and then installed them (by myself, using a jig I made to hold one side in position while I nailed the other). I just didn't feel like the gussets alone would be enough support given the 16' span. I read about several different methods, but the one I felt was best was the 2x4 bracing that triangulated each joint. I originally added the purlins as a way to stabilize the trusses until I added the roof decking. I staggered them so I could nail them through the trusses, rather than toe-nailing.

 

[DocHolliday]

CONCUR !

Skip the plywood spacer. Nail a ledger to the end wall studs that is level with the doubled joist. If you are only doing light storage you only need to double the joist furthest from the wall, if you are spacing the joists 24" O.C. If you go 16" O.C. you probably don't need to double the last one.

If it is "light" storage, you probably only need 1/2" plywood if you add blocking (use joist hangers) between each joist, every 4'. The blocking will also prevent the joists for rolling/twisting.

My understanding of using the plywood in the middle of the beams, is not that it is a "spacer." Rather, I have been told that the plywood in the middle like that adds a tremendous amount of strength, almost equal to an additional full size beam. It is all a moot point, as the OP says he has plenty of vertical height.

Incidentally, additional strength can be had by adding some full depth blocking between his beams. As the beam is loaded, it will deflect down, and also try to twist out of position. The more it twists, the more it loses strength in the vertical direction. The blocking resists that twisting action.

I like both of these ideas. I did plan on using a rafter against the end walls and attaching them to each stud. I will probably double the beam furthest from the wall and add blocking between the rafters (with joist hangers).

I appreciate everyone's input and suggestions. I will post a few more pics shortly.