Question about roof trusses

[zoominomad]

I'm planning to build a shed/wood shop on a concrete slab, and am wondering at what width do you guys recommend switching from home-made trusses to pre-built trusses.

I was originally going to go with a 12x16 footprint, and home-made gambrel trusses. I'm torn between going with this, and going bigger. I would really like to go up to somewhere close to 16x20, but was unsure if my 2x6 trusses with plywood gussets would be viable option at this width. At this size a regular gable roof around 4/12 pitch would work fine for me as well.

I'm trying to put together some fairly accurate cost estimates for the different size buildings since the cost will be the main factor is determining size. I've come up with about $2500-3000 for the 12x16, but don't know how much the cost will change on the 16x20 due to not really knowing what route I need to go with roof trusses.

 

[Stuart in MN]

Depending on what you want the shed to look like, you may want to consider buying commercially built studs. For an example, this is a link to the Menards website: https://www.menards.com/main/c-5658.htm They sell 12' 4/12 trusses for $34/ea and 16' 4/12 trusses for $43/ea - at those prices it would be hard to justify all the time and effort to build them yourself.

 

[zoominomad]

Thanks Stuart, yeah I found that same page after posting this. Like you said, it's looking pretty hard to justify building them myself. We don't have Menard's anywhere close, but I'm assuming I can find similar pricing around here.

I also looked at square tubing steel trusses, but I'm thinking those are probably more geared toward pole built applications. For 16' I'd be looking at about $115 each, but would only need 2 or 3 to span the whole building. I sent one of the local manufactures a message to see if something like that would fit my needs. It would cost around the same as wood trusses, but I don't know how it will work for what I'm wanting to do.

 

[theoldwizard1]

I would really like to go up to somewhere close to 16x20, but was unsure if my 2x6 trusses with plywood gussets would be viable option at this width.

Are you talking a "true truss" ? If so, the truss webbing will pick up and distribute the load. They can be designed to have an attic space.

Or are you thing of a completely open grambrel roof with a full second floor for storage ? You are correct, the plywood gussets would not be adequate, but you could use 2x6 as a collar tie under the ridge between the left and right roof rafters and tie across the "knee" between the upper roof deck and lower roof deck.

 

[zoominomad]

Are you talking a "true truss" with a bottom chord ? If so, the truss webbing will pick up and distribute the load. They can be designed to have an attic space.

Or are you thing of a completely open grambrel roof with a full second floor for storage ? You are correct, the plywood gussets would not be adequate, but you could use another 2x6 as a collar tie under the ridge between the left and right roof rafters and tie across the "knee" between the upper roof deck and lower roof deck.

Thanks Wizard, I'm talking about a true truss. If I go up to something larger than 12X16 it will eliminate my need for more overhead storage. I'd like to find the trusses that allow for some storage down the center, but I don't need much height. I wouldn't need to get in the "attic", I would just want to be able to use it to store stuff I don't regularly use, like outdoor furniture cushions, etc.

 

[theoldwizard1]

This is a gambrel roof truss.

The benefit is that it can span a MUCH wider area (30 - ?? ft) and still use common dimension lumber (typically 2x4 or 2x6). You loose most of the benefits of a gambrel roof (large attic) but you keep the "look" on the outside.

Just guessing, but I would say this gambrel roof is spanning about 20'. Plywood gussets. The only additional bracing is the collar tie. Note the blocking on the side for proper spacing.

 

[kbs2244]

DIY truss designs and such.
Stamped drawing avaible if needed.

http://www.ag.ndsu.edu/extension-aben/buildingplans/construction

 

[zoominomad]

Thanks guys! I really appreciate that picture. Helps me visualize what can be done with an open gambrel truss. I just have a hard time visualizing it being strong enough, but this type stuff helps cure that. lol. That link is freaking awesome by the way kbs! Thanks!

 

[theoldwizard1]

Thanks guys! I really appreciate that picture. Helps me visualize what can be done with an open gambrel truss.

You are still mixing your terminology. A "truss" has boards running between the rafters and the bottom "chord" (floor/ceiling joist). These boards are called the "web". The web can be designed for an attic space, but it is not fully "open". (See previous image.)

The advantage of a truss is that smaller lumber can be used (typically 2x4) because the load of the roof is more evenly spread.

Another benefit of using trusses for a gable roof is that it can be pre-fabbed in a factory and quickly installed.

 

[Scott r c]

Around here I don't think you can hardly buy the lumber for what a truss company will build them for.

 

[James-W]

Around here I don't think you can hardly buy the lumber for what a truss company will build them for.

I agree, I don't see how it could be cost affective to make them yourself. You need to build a jig so you get the trusses all the same size, then you need to buy all the materials and the wood needs to be straight, not like some of the **** you get at the local lumber yard. Then too, you will most likely need to have some help in building them. I don't mean to be pessimistic, but I just don't see how you can come out ahead by building them yourself.

 

[brass89]

not sure whether you're looking toward gambrel or gable style roof, but if gable style (a frame) roof trusses i would say bare min 2x6 (bottom cord) for a 12ft span and if looking to up it to 16' span then at least a 2x8 bottom cord. going by memory from my days working in a truss plant. i didn't engineer them, just built them. standard gable style trusses with top/bottom cords and webs pretty much negate any loft/attic space. they're also engineered with the webs landing in the proper locations based on load specs. not sure i'd trust osb/ply gussets and a 'homemade' truss for larger spans - at least not in a gable style, gambrel may very well be different. it's only so strong and true trusses use steel plates of varying size (spec'd by the engineer/architect) which are pressed into the wood on both sides with a hydraulic press. not glued/hammered together.

i'm only trying to err on the side of caution, not scare you away from building bigger. however, the bigger the span, the bigger the risk and potential for things to go severely south - i'd rather someone not risk their safety. just sharing my experiences even if they're mostly limited to gable trusses. best of luck.