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bobbotron
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# Posted: 14 May 2012 02:28pm
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I recently bought some small cabin plans off the internet. It's a small cabin with a loft, cathedral ceiling and a ridge beam for the cathedral part.
The ridge part seems under built to me. 12/12 roof, the ridge is 14' long, 8' wide on each side (16' total.) 2x8" for the ridge beam, seems pretty undersized to me, even with 45 degree roof slope. Also, the way it's attached to the structure seems a little less than secure.
Any recommendations on structural engineers in the Ottawa, ON/Gatineau area? I'd like to get a stamp on the (modified if necessary) plans, but money is somewhat a concern; I want to do it right but not pay for services I don't need, you know?
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toyota_mdt_tech
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# Posted: 14 May 2012 03:55pm - Edited by: toyota_mdt_tech
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There is really no load on the ridge beam once rafters are in place. Just use collar and rafter ties.
Mine showed a 1X8 for my ridge, it was signed off. When I submitted the plans, they actually looked it over, was included in the permit price. They just made notes in red where they wanted changed. No change to my ridge. It was 20 feet long. I did end up using a 2X8X20, only because finding a 1X8X20 was not easy to find.
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soundandfurycabin
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# Posted: 14 May 2012 04:32pm
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Go to your library and have a look at "The Span Book" by the Canadian Wood Council. There will be several tables for ridge beams, for different snow loads and wood species. You'll have to know your snow load....ask the building dept if you don't know it. Then look at the line for a supported width of 8'.
The values from The Span Book are accepted by Canadian building codes, so you likely won't need an engineer's stamp, unless Ottawa requires it for all buildings regardless.
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bobbotron
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# Posted: 14 May 2012 04:32pm
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Thing is, I want that section to not have rafter ties, to get a cathedral (ie, wide open) ceiling. I believe this is called a structural ridge? Perhaps I'll run rafter and collar ties by the "design committee", with the rafters moved up 1/3 of the way...
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bobbotron
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# Posted: 14 May 2012 04:34pm
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Thanks soundandfurycabin, I'll take a look at that!
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toyota_mdt_tech
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# Posted: 14 May 2012 05:24pm - Edited by: toyota_mdt_tech
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A collar tie near the top 1/3, would give you an open look, you could sheet over it, so it would be flat. As for rafter ties, leave nice exposed beams for looks (rafter ties) otherwise, just have some engineered "scissor" trusses made, you can avoid the collar/rafter ties.
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razmichael
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# Posted: 14 May 2012 05:30pm
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You may the best solution for a structural ridge is a LVL beam(s). Take a look at LVL Spans on page 5 for examples of beams for a ridge. Just about truss manufacturer or even a big box store should be able to give you the requirements for your needs. These are not nearly as expensive as I originally thought and will span much further with less wood than regular lumber. I'm looking at them because I can more easily transport them to my site and then build them up on location (I'm looking at 16 ft and then 8 ft sections) with a support at the split. Keep in mind that for a structural ridge you must ensure that the weight at the supports has a clear run to the foundation as this is supporting a great deal of the roof.
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bobbotron
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# Posted: 15 May 2012 10:03am
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I really need to get down to a lumber yard and discuss this with one of their people. I have thought about doing a structural ridge along the length of the building - 22', to keep things simpler.
"Keep in mind that for a structural ridge you must ensure that the weight at the supports has a clear run to the foundation as this is supporting a great deal of the roof." - does this mean there has to be a solid post going all the way down, or does it still count if there's a sill plate from the wall below? Do you have a photo of what this would look like framed?
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MtnDon
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# Posted: 15 May 2012 10:11am
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The columns do not need to be one piece as long as they are connected properly, braced by the rest of the wall structure so they will not bow and rest on a foundation that can support the load. The lumberyard can provide the correct LVL for the job when you tell them the bldg size. They or the engoneer or the engineered tables will take snow, wind etc loads into account for the LVL. They usually can not or will not provide much help as to sizing the support columns or the foundation, though.
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bobbotron
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# Posted: 15 May 2012 12:53pm
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Thanks MtnDon. Hopefully I'll get to a lumber yard this weekend and see what they say.
Since everyone likes photos, here's a photo of the place where the cabin will go, you can just barely see the lines in this photo.
Line levels for the cabin are UP by bobbotron1, on Flickr
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bobbotron
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# Posted: 25 May 2012 12:03pm
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Haven't got out to the lumber yard yet, but hopefully soon... The two I've emailed haven't returned my emails, not a great sign.
MtnDon, could you give an example of proper wall bracing for the ends? I think I know what you mean, but want to make sure I'm not overlooking something.
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bobbotron
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# Posted: 25 May 2012 02:05pm
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Also, I'm becoming confused when people discuss "span" with relation to structural ridge boards. Does this usually refer to the length of the ridge, or the width of the building the ridge is supporting, or something else? (Or do people sort of inner mingle this?)
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toyota_mdt_tech
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# Posted: 25 May 2012 03:38pm
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How long a board is between supports is what the "span" refers to.
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bobbotron
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# Posted: 28 May 2012 09:59am
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Another option I just thought of would be to keep the framing as normal, but
1) use a LVL ridge beam for the 12' span
2) run a 6x6 (8x8?) post down from the ridge/loft to the floor (with a sonotube underneath supporting) and modify the end of the other external wall so the beam is resting on the wall, and not end nailed.
Thoughts?
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bobbotron
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# Posted: 30 May 2012 03:02pm
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Well, I've been brushed off in email by one of the local lumber yards.
Got a hold of the span book at the library, it looks like for the 12' span, 3 2x10's (ish, I don't have the #'s in front of me) will work for a structural ridge, if I use a post to support it near the loft.
I don't think I'll do it, but it would be fun to use one of the many ironwood (Ostrya virginiana) trees on our lot as this post. There are a ton growing on the property, I think I could find one that was easily 8" to 10" (or more) in diameter and 16' long. A carpenter friend suggested I use some of these as the basis for the loft ladder, I think I'm going to try that when the time comes.
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bobbotron
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# Posted: 21 Jun 2012 12:09pm
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So, I'm starting to like the idea of rafter ties more and more. I believe they can be spaced out about 48" apart, and we could triple them up for a nice beam look. And then there's no fooling around with the ridge beam or support columns, which sounds a lot of fooling around compared to putting some rafter ties up!
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