Roofing, Rafter and Ridge Beam Help Needed.

[canada340]

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[jproffer]

1) You can't overlap the 2 boards to make the ridge because, as you said you would have to adjust the rafter length, but in doing so, you also adjust the rafter pitch, even if only slightly. The plywood wouldn't lay right, the shingles wouldn't lay right...it just wouldn't be right. Get 4 - 16 ft. boards and cut them to 14 ft., then cut one of these in half (7 ft. each). Lay 2 14 footers end to end, then place a 7 footer on one end, then the last 14 footer, then the last 7 footer, effectively making a 28 ft. long, double beam. Make sure when you put the bolts in, that they won't be in the way of a rafter coming up.

2) If you insist on stick building the roof (which I wouldn't), you can leave out the spanning 2x4 if you cut the birdsmouths. Price trusses to span the 18 feet, you may be surprised. BTW, 2x4 rafters?????? NO...2x8 minimum.

3) The pitch of the roof is a number of feet of rise, compared to 12 feet of run. 4/12 is fairly typical and easily walkable. To establish the pitch, measure out 12 feet from the top of the wall, at that point nail a board that is 4 feet tall (assuming you want a 4/12). The line between the top of your board to the top of the wall will be the roofline. You can adjust according to what you want without having the whole roof built and then saying "I wish that was a little lower (or higher)"

[Joe Bartok]

Copy and paste this url in Google:
http: //www.tfguild.org/confs/confeast2002/eastprogram02.pdf
Remove the space between the : and /, and click on Google Search. (I'm uncertain regarding the legalities of "hotlinking" to a discrete file, so I broke the link). There's some good info on ridge beams on Pages 37 and 38; one of the best articles I've ever read, explained in layman's terms.
Check out this Ridge Beam (http://constructionforumsonline.com/viewtopic.php?t=520) discussion, links and the attached images.

While others show it the same way but they have an extra 2x4 running Horizontally to the opposite wall to form a triangle.
This perfoms the same function as the "tie beams". A properly sized ridge beam and purlins eliminate the necessity of tying the walls together, but it's extra work, material and $$$.

[canada340]

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[Sweep]

A "ridge beam" spans the full length of a building or to intermediate columns and no horizontal "ties" are necessary between the tops of the walls. A bird-mouth in the rafter at the wall top plate is necessary for proper load transfer and should be required by code. However, such a beam for a 28 ft span would be a minimum of 5" x 18" of laminated veneer lumber with no splices.

A "ridge board" carries no load. Rafters are nailed to each side in alignment with one another and the board acts as a nailer and also stablizes the rafters laterally, etc. A ridge board only needs to be as big as the height of the cut end of the rafter. Tie members are required between the tops of the walls. A bird-mouth in the rafter at the wall top plate is necessary for proper load transfer and should be required by code. A truss is a prefabricated form of this design with intermediate chords added to allow the rafter parts of the truss to be smaller.

The minumum rafter would be 2x6 but if you are in Canada you would probably need 2x8's @ 16" o.c. for snow load.

Asphalt self-seal shingles can be used on a 3" in 12" roof slope if two layers of underlayment are used. Roll roofing will work too but I wouldn't go lower than 4 in 12 in a northern climate. Use self-stick rubberized-asphalt membrane (ice & water shield) at the eaves.

You should be required to have a structural engineer's stamp for a ridge beam design or for trusses but probably not for a ridge board, rafter, and tie design if those elements are sized and their connections described in the building code.