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Author Topic: Gambrel truss - heavy timber  (Read 541 times)

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Offline bmurphy96

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Gambrel truss - heavy timber
« on: July 14, 2017, 11:43:23 am »
I'm going to be building a workshop this fall and would like to use gambrel trusses for possible future expansion. I have my own mill and will be cutting the timbers for the trusses myself. The entire workshop will be a post and beam design using steel plates (ie..not an actual timber frame).

I'm open to changes in size but am planning for a 32' wide by 40' long. Thus I would need a 32' truss. Size of timber isn't an issue..I can cut them up to whatever needed. I just can't find any real plans online for heavy timber trusses like this. I live in NW Florida so there is no snow load. Wind is our enemy here.

thanks!!

Keith

Offline bmurphy96

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Re: Gambrel truss - heavy timber
« Reply #1 on: July 17, 2017, 02:18:35 pm »
anyone have any advice?

thanks,

Keith

Offline Roger Nair

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Re: Gambrel truss - heavy timber
« Reply #2 on: July 17, 2017, 04:37:28 pm »
I would base the solution on a queen post truss with the principle rafters ending at the queen posts.  Context matters purlins or common rafters?  Intended slopes?  Intended use of loft?  Why gambrel profile?
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Offline bmurphy96

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Re: Gambrel truss - heavy timber
« Reply #3 on: July 20, 2017, 06:23:50 pm »
The reasoning for gambrel is that I am looking to maximize future space. What will this space be used for? Not really sure but possibilities include general storage, a "man cave", or even an office space.

I was familiar with Gambrel but I don't really like the look on a a normal barn structure. However just a few days ago I saw a building with a gambrel roof and lean-tos on both sides. With that configuration it looks ok  -- it softens the look of the building if you know what i mean.

Anyways, I am looking to maximize space. I know the queen post setup would be simpler but it doesn't maximize that upstairs space. I have done both standard trusses and king post trusses - I'm sure I could handle a queen post. Just not sure about the sizing really of either queen posts or gambrels.

If i did got with a queen post setup the slope would be pretty moderate - again to maximize space. Maybe a 6/12 or 8/12. I don't really know how you calculate slope for a gambrel though. I thought they where a pretty standard design?

thanks!!

Keith

Offline Roger Nair

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Re: Gambrel truss - heavy timber
« Reply #4 on: July 20, 2017, 11:28:50 pm »
A strict gambrel roof is based on a semicircle, so a 32 ft span yields 16 ft peak height, locate the intersection of upper and lower rafters by projecting 45 degrees left and right to the circles edge from center point of the base.  That should yield rafters of same length.  What you are left with is the engineering in a hurricane prone area.  Try drawing the shape and see if that looks right. 
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell