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Spliced 38' Ridge Beam Options
davisonh
#1 Posted : Monday, August 24, 2009 1:48:33 AM
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Hey Tao a thought here,since I'm building my own 26 x26 pole barn presently.Basically whats done is you size your ridge board the same thickness of the rafters you intend to install There is a certain procedure thats outlined in the book 'Pole Barn Construction' by Monte Burch that pretty much covers basically how it's done.My father's been in the building business too for 50 or so years and I bought the book to remember how to do it,lol.What you do is this:Buy a small rafter square and figure out the math for you rise and run,for instance I"m doing an 8 in 12 pitch or 8 inches of rise for every foot of run.Cut a scrap piece of lumber the height of your rise,cut out a set of 'pattern rafters'.Nail a piece of scrap up as a temporary ridgeboard the thickness of permanent ridgeboardSet your plumb cut on the ridgeboard,temporarily nail it up,check your birds mouth cut make sure it fits on your top plate squarely.Check all your dimensions,then take the rafters down,setup your real ridge board with two pieces of scrap to hold it in place while you nail up the rafters.Then cut another set of rafters from your pattern rafter.Start with your gable end rafters,then set the other two rafters near the other end of the ridgeboard,making sure the ridgeboard is dead level(very important!)When it is,nail collar ties up against the gable rafter and remove your temp. support boards.Do the same procedure for the other gable end then join(splice)the 2 ridgeboards together by toenailing them.The rafters are what keep the ridgeboard up and in place basically.After that procedures' done then you can cut and nail up the rest of your rafters.Hope that gets you started and good luck.

Pat Miketinac
#2 Posted : Monday, August 24, 2009 4:44:21 AM
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I'm guessing that you are thinking of a heavy ridge beam to rest your rafters on because the straw bales  might not prevent spreading. Do you plan to use collar ties? I used 10x10 green posts and beams from my sawmill to support 4x8 rafters for my earth shelter roof. The 3 beams for the ridge average 11' in length, with posts at the joints that also are in the interior wall floorplan. They rest on a concrete slab thickened to 12", 24"x24"at the posts. This way, no span is more than 12', and there is no outward force to the perimeter walls, so collar ties are not needed.

practicalman45
#3 Posted : Monday, August 24, 2009 5:33:58 PM
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I watched my neighbor put up a nice straw-bale house. Even though some straw bale construction walls "could" be load bearing, to an extent, the local building permit officials do not recognize that as a real strength. (we are in Oregon here and we do get snow loads). What my neighbor did to get approval was essentially build a pole construction building. A space frame of poles. The walls are simply infill in between the pole frame construction. A local builder put up a pole building, then the owner had a "bale stacking party" and put up the walls.

Since you have the poles, this might be a good way for you to go. Just put up a nice long pole for your ridge. It can sit on top of a pole truss at each endwall, and maybe one in the center? Use one with a slight curve and turn the camber up to resist the sagging from the load. Notch your rafter poles or boards to rest on that ridge pole up top, and on the top plate beam (another pole) at the bottom. Use plenty of framing ties and brackets.

I'm not a pole builder, but I am a metal fabricator, and many of the local straw-balers come to me to have me make them their frame brackets. I advise them to use cheap simpson ties and straps where they will not show (inside the walls), and to buy my pretty, black, homemade pole framing straps and tie brackets where they can augment the appearance of the pole frame, where it is visible. Much of the support poles can be hidden, although some like to design it with them showing on the interior. they like the exposed pole frame look. I think it is best to not have your poles exposed to the exterior weather. This is just  a matter of where your bale walls are in relation to your pole frame. I'd never put poles in the ground, set them onto cast concrete piers with good strong brackets cast into them.

Compare prices between store-bought simpson brackets, and the ones your local metal shop can make you from strap steel and plates. Often, the local made brackets can save money over the Simpsons, which are pretty spendy now, too...

One thing I do a lot of is using 5/16" thick steel plate or straps for "splines" . These are the correct thickness to fit into a chainsaw cut kerf. This makes pole framing the major joints, like truss poles, easier. The steel splines have holes pre-drilled, and then the builder drills the poles to match and put through bolts and timber washers through the poles and the splines in the middle.

maxgyver
#4 Posted : Monday, August 24, 2009 5:38:39 PM
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Just go with an engineered beam...LVL would be the cheaper route, lengths up to 48 feet...a gluelam would be pricer but is prettier to look at if you design for that.

 

I would go the gluelam  route and tie the rafters "over the beam" with a pair of triangular plywood gusset plates.  These basically sandwich the rafters between two pieces of 3/4 ply that is bolted through the rafters.  The flat longer portion of the triangle sits on top of the beam.  Ceiling finish is then on the bottom of the rafters and the gluelam is exposed inside.  Obviously some beefy support posts would be needed to hold up the ends of the beam....are you using Infill straw bale with post + beam or are you going the load bearing route?

If load bearing you would need to beef up the box beam for targeted compressive loads, many of the (LVL gluelam) manufacter's websites have data for the load ratings of such beams...check to make sure you get one big enough to handle your roof/ snow loads.

davisonh
#5 Posted : Tuesday, August 25, 2009 1:53:43 AM
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oo,dont forget to tell him max that if he does go with an engineered beam make totally sure you're going to put the roof in soon because if you expose those to the weather for any length of time they will start to delaminate fast.We learned our lesson about those awhile ago when we did a microlam and it rained over the weekend.Nice beams but these started to delaminate just as we doing the floor joists.Had to take it out and replace,big $$$.Just make sure its exterior grade glue that they use.

Tao
#6 Posted : Monday, August 31, 2009 10:37:07 PM
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Thanks everyone for the info and suggestions.  I found that we have a family friend in the area who does construction and he walked me through what I needed and how to go about it.  Basically a lot of the things everyone mentioned.  It's going to be a 6 in 12 pitch and just a single thickness of 2x12 as the ridge beam with 2x12 rafters on 4' centers.  I'm going to use 2x4 purlins on that and put cross-ties on just about all of the rafters.

Anyway, thanks again.

Tao
#7 Posted : Monday, August 31, 2009 10:37:07 PM
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Posts: 134,494

Hi, I'm building a straw bale house which is 32'x23'.  It's going to be a ridge beam roof with 3' overhangs on the ends so I'm looking at needing a 38' ridge beam.  I have access to large trees and have considered cutting down a tree and milling it myself with a chainsaw even though I know it would shrink and check since I'd have to use it green.  However, I'm now looking at splicing together store-bought lumber as I'm running out of time.

First of all, I'm not sure how to find what thickness of a board I would need to cross such a large span, the span would really only be ~30'.  I plan on making the rafters 2x12s so that I can stuff the area in between with cellulose insulation.  My initial idea is to have the beam be made from 4 2x12x20's bolting them together and putting a scab of 2x12 over the joints.  I have no idea if that's enough or too much or what.  I'm having a lot of difficulty finding out information on this so any direction would be really helpful.

I've ordered a roofing book from Amazon, but I'm not sure it's going to be very helpful either.

Thanks ahead of time for any help,
 Tao

 

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