Hot Topics: Roof Rafter Construction

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Original Post: Roof (rafter) Construct

Dixie2012 - Forum Topic Moderator

I am in the planning stages of my 24 X 36 wood frame shop.

First, I have called two places nearby that build truss's & gotten prices on what I need. However, I have always built my own rafters but... I have never built any to span the 24 ft across not including my eves. They wanted a little over $2,100 for the trusses, delivered. While its reasonable, they are using 2X4's. Again, I prefer to build my own & I want 2X6 rafters & ceiling joists. (Because... that's what I want).

So, should I decide in the end to build my roof, my question is, is the proper way to do this:

Join two 2X6X12' end to end (24') for ceiling joists & "sandwich" the joint with a 2X6 on each side, bolted together? If so, what length of "sandwich" should I be making this? At this point, I'm asking about ceiling joists only. The rafters wont be an issue since I can get 2X6's long enough to build my rafters.

XSleeper - Group Moderator

Not that you need more opinions that steer you toward just buying the trusses... but another factor is that generally, truss mfg's use "structural grade" lumber, not just the stuff you buy at the box store. It is critical that the lumber used in truss mfg has no knots or defects. Trusses are engineered and once the parts are assembled, they act as a single component- but they are only as strong as their weakest link.

If you think you can somehow make a truss that is better than the mfgs, you should put your engineering degree on the wall and start your own factory.

marksr - Forum Topic Moderator

A truss has an engineered design and IMO is the best way to go. It's generally stouter than anything you can site build even using heavier lumber. How do you intend to support the roof rafters.

Dixie2012 voted this post useful.

Pilot Dane - Group Moderator

I would pick a truss almost anytime over stick building on site. If you want to stick build there are many websites with "span tables" for what size rafters are needed.

cwbuff - Member

When I built my garage I used 2X6 rafters. Were I to do it again I would use trusses. They are just quicker and easier to install. I used I joists for the ceiling for the full 24' span. You could also hang the joists from an engineered beam.

The contractor replacing my roof is doing away with the traditional rafter framing and using trusses. He tells me that he can have the trusses installed and sheathed in two days.

Dixie2012 - Thread Starter

Mark, since there wont be any interior walls to support weight, I was going to run a horizontal brace from one side to the other. Kinda form an "A". Then use at least two vertical braces on an angle on each rafter board (like "V") from the rafters to the ceiling joist, then one from the horizontal brace to the ceiling joist. Also, I was going to cut a triangle out of plyboard to put at the ridge of the rafters. Then I was going to put horizontal braces between each rafter & joist for support between the rafters & joists.

The engineered truss's are only about 100 lb each using 2X4's so that was also a plus. I can easily put those up from the ground except for bracing & nailing. I haven't figured my lumber pricing vs the $2,100 for truss's but, I'm pretty sure there wont be much difference. While I know from experience the truss's are most probably the best way for me to go without a doubt on this specific project, I like to build my own. One of the issues is, I just cant get my mind trained on 2X4's for roof material on this big of area.

marksr - Forum Topic Moderator

Drive by a house under construction, 2x4 trusses are used successfully everyday.

You can have trusses made out of 2x6s but both the price and weight will increase.

Dixie2012 - Thread Starter

Mark, Understood & agree, but it's kinda like the other side of this story which my wife & I discussed heartedly before getting tpo far into this project. "My mind says I can but my body says I cant."

So, I know that "engineered" truss's are designed by people who have a LOT more experience & education than I do about this... Without a Doubt.

I'm just a guy who has this attitude about being "sure"... being thorough. Doing it the way "I" know how to do it. My mind says "be sure". So I tend to want to over do, to make sure I don't have to go back & do it again. "If a little does a little good... a lot will do a lot of good." (I know that's not always true but that's just me. I prefer to over do, rather than take chances).

In the end, I know my best bet is just call the man & buy the trusses. I just need to get all the advice I can from every angle & make the best decision I can with that information. I appreciate y'all's input.

Wirepuller38 - Member

If you decide to go with trusses (my choice also), be sure to mention to your truss supplier if you have any plans for storage in the shop attic. This will affect the design of the trusses in shape and size of lumber used.

XSleeper - Group Moderator

Not that you need more opinions that steer you toward just buying the trusses... but another factor is that generally, truss mfg's use "structural grade" lumber, not just the stuff you buy at the box store. It is critical that the lumber used in truss mfg has no knots or defects. Trusses are engineered and once the parts are assembled, they act as a single component- but they are only as strong as their weakest link.

If you think you can somehow make a truss that is better than the mfgs, you should put your engineering degree on the wall and start your own factory.

Pilot Dane - Group Moderator

I like trusses for the ease of installation. I am usually working alone and a shop like yours I'd build three walls and leave one end open. I've built an arm for the loader of a tractor so I can pick up a truss and place it up on the walls, all from the tractor seat. Then I can climb up and nail it in position. I'd pick up a truss from the yard drive into the building and start placing them at the back and work forward.

Stick building a roof usually means it's built in place. You'll somehow have to set a ridge beam or you'll need helpers to simultaneously set a rafter from each side to meet in the middle. That's after you've worked out the angles and cut the rafters to size. It can add more variability and uncertainty to the cost and schedule of your project.

If you are concerned about the roof not being overbuilt all you have to do is spec higher rated trusses. Spec for a higher snow loading or spec for storage on the bottom chord (floor of attic). Just because it's a truss doesn't mean it can't be overbuilt. I overspec'd the floor trusses in my house. They are long spans and I didn't want any bounce so I picked a lower deflection ratio. Instead of 16" high trusses I have 20" high and the floors are rock solid.

Dixie2012 - Thread Starter

Thank you PD. Good post for my info.

You are correct on building rafters. I usually get my pitch, set a ridge pole & build the rafters, then set them up one at a time. One on this side then one to match on the other side... all the way to the end.

Its just the way I have always done it. Its the way I know how, so trusses are a new venture for me. I am always a little cautious of the unknown. I'm comfortable with what I have previously done... and a little uneasy when I attempt something like this having never done it. However, I have pretty much decided to go back to the idea of trusses on this shop.