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A friend has decided to put a gambrel roof on a 20×40 barn, and has asked me to help in the framing.
I’ve never framed a roof before, but when I asked for details, I didn’t see collar ties in his drawing. The owner plans on using an engineered ridge beam, and tells me that such a beam will eliminate the need for collar ties.
I’ve followed the debate regarding collar ties on a typical gable roof, but it still seems odd to me considering the gambrel roof.
Does anyone have any tips or advice they can offer?
Thanks,
Michael
Replies
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Michael, with a structural ridge and a building only 20' wide you probably don't need a collar tie. You do need gussets at the intersection of the two rafters, though. If neither of you have built a roof before, a gambrel is a tricky way to start--do you have a book to help you through this?
*Mike,
View Image"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Thanks for the tips.I do have the article on framing gambrel roofs from FHB a couple issues back. The article was helpful, but didn't mention using a ridge beam.Thanks for the info on gussets, Mike. Do the gussets take up the outward stress on the roof? For that matter, how is outward stress determined? I know a gambrel is a tough place to start, but I won't be the head carpenter on this, just hired labor. Nonetheless, it always helps to get all the information I can. I'm comfortable with my tools, and have a good understanding of the way a house works, but haven't worked on a crew before. This could be a good opportunity to leave a good impression, so the more I know walking in, the better the chances of getting more work like this!When I'm not working, I spend most of my free time pouring over old issues of FHB. It seems no matter how many times I pick up an issue, I always learn a bit more.Thanks again,Michael
*Michael,I personally don't like the idea of framing a gambrel with only gussets. I would use a structural ridge or collar ties to take the roof load. I know it's commonly done with gussets, I just don't like the idea unless it has an engineer's stamp on it. The amount of outward thrust at the intersection of roof angles depends on the geometry of the roof and where you live. With a structural ridge there is very little outward thrust, just from the wind trying to suck the roof off. Mostly just gravity trying to pull your roof down. Gussets keep the rafters tied together in this case. For a thorough primer on roof framing, click on Joe's logo above. You'll go into this job knowing your heel cuts from your plumb cuts. Good luck,Mike
*gussets are a new fangled thing with gambrel roofs..as in since plywood...post WWII..traditionally there is a knee wall running the length of the building under each pitch break...the lower rafters and the upper rafters both bear on the knee wall...in some cases the lower rafters extend past the knee wall to cantilever with a plate at their top to bear the upper rafters...the other detail that needs a lot of attention is trimming and flashig the break on the roof... again.. the traditional way is to extend the upper rafter over the kneewall plate and end it with a square cut for a fascia... with or without a crown... this covers the lower roof and becomes the edge of the upper roof... most bad design just wraps the roofing around the break..b but hey, whadda i know ?
*Is the owner-builder seeking tips from internet message boards? Heres one. If he's getting a permit, there will be field inspections, if he's unsure about something, let the inspector answer any questions, be sure and go over this at the footing inspection . He might not want to help,though.
*Thanks again for all the help. I just viewed the property today, and it looks like an interesting job.The owner is still looking for a lead framing carpenter, and if anyone knows someone in Michigan (detroit area), then this is a good lead for them.There IS a structural beam, and an 8 foot wall on either side. At 8 feet, I wouldn't exactly call it a knee wall anymore, but you get the idea.
*MIKE...""and an 8 foot wall on either side. At 8 feet, I wouldn't exactly call it a knee wall anymore, but you get the idea. ""as far as i know... it's still a knee wall... and, as with all gambrels... the knee wall defines the ceiling ht.
*Mike,My current 10-year old shop is a 24-ft x 36-ft two-story with gambrel roof. I built the roof using conventional kneewall framing, and it's held up well. Very straighforward and fun framing project.I'm just now reaching close-in on a bigger gambrel shop at my future retirement place: it's 28-ft x 40-ft and it uses factory scissors trusses made of 2x6 joined with steel nail plates (gussets). In an architect's plan I bought he called for site-built trusses with plywood gussets and glue, but required 1/2" rod collar ties 4-ft on center. The current factory trusses not only support the roof without collar ties, but as long as I sisterd three of them, the engineer said I could hang a one-ton chain hoist from top dead center. That's a 2000-lb dead load at the very center! or is that a live load--guess it depends on what/who I hang, right? Good luck. Isn't it about to snow there?Tom Carter
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A friend has decided to put a gambrel roof on a 20x40 barn, and has asked me to help in the framing.
I've never framed a roof before, but when I asked for details, I didn't see collar ties in his drawing. The owner plans on using an engineered ridge beam, and tells me that such a beam will eliminate the need for collar ties.
I've followed the debate regarding collar ties on a typical gable roof, but it still seems odd to me considering the gambrel roof.
Does anyone have any tips or advice they can offer?
Thanks,
Michael