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Roof Ridge Connections

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Don_P:
In the interest of explaining the correct way to frame a ridge board roof for those interested, I thought it might be a good idea to post what the codebook asks and try to explain a little bit about the reasons why.

For those wanting to read along this is in chapter 8, R802.3 Framing Details.
https://www2.iccsafe.org/states/Virginia/Residential/PDFs/Chapter%208_Roof-Ceiling%20Construction.pdf
Rafters shall be framed to ridge board or to each other with a gusset plate as a tie.
The top ends of a rafter need to be attached to a ridge board OR if there is no ridge board they can be connected directly to each other with a plate across both faces of the joint, think about how a truss is built for that connection.
Ridge board shall be at least 1" nominal thickness and not less in depth than the cut end of the rafter
A ridge board is typically 2x material but it is perfectly ok to use 1x (3/4") material. A ridgeboard is not a beam, it is simply something to nail the rafters to. The ridgeboard needs to be the full height of the plumb cut to give full bearing to the rafter. This is to prevent the possibility of splitting of an unsupported end. I have seen a 2x12 rafter split and fail when the split began at a gap at the unsupported bottom edge and followed sloping grain till it ran out at the top edge some feet away. In that case the lumber grader had passed a marginal timber and the carpenter failed to provide a fail safe.

That section goes on to discuss valleys, hips and low slopes.

To continue discussing the top end of the rafter I'm going to bounce to the end of the next section R802.3.1
Collar ties or ridge straps to prevent wind uplift shall be connected in the upper third of the attic space. Collar ties shall be a minimum of 1x4 inch nominal and shall be spaced not more than 4' on center
This is a fairly recent addition to the codes in the wake of high wind roof failures. If you remember the news footage of roofs unzipping at the ridge and both halves flying through the air, this little bit would have prevented that embarrasement. Under the ridge, in the upper third, a 1x4 is connected across from rafter to rafter OR a metal strap is connected over the ridge from rafter to rafter to prevent the top connection from blowing apart if wind either gets inside or a very high wind blows across the roof trying to lift it apart. This locks the ridge connections together. Not required in all areas, sure is easy insurance to install.

Stepping back in the last section it discusses the bottom connection;
Ceiling joists and rafters shall be nailed to each other and the rafter shall be nailed to the top wall plate. Ceiling joists shall be continuous or securely joined where they meet over interior partitions and are nailed to adjacent rafters to provide a continuous tie across the building
I left out the details here and those are important, please go back and read this section before building. The intent of this section is that the bottoms of the rafters need to be well tied to each other across the building to prevent them from spreading.

Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice
If the rafter feet cannot be tied to prevent spreading then the rafters should be hung from the top end. A load bearing wall works or a ridge beam (as opposed to a ridge board). If a beam is used it needs to be sized to support the roof load. Where a ridgeboard carries no load a ridge beam supports half the weight of the roof. This distinction is important, make sure you understand it before omitting ceiling joists or rafter ties.

Hope this helps

jdhen:
Thanks, Don.  Timely information for me.
 As it turns out, I rechecked the height of my temporary poles using another method and realized I'd made a small mistake.  Since I had to get up there and trim it down anyway, I decided to cut it down a little further so that the gap at the ridge board would be at the top as you and Red suggested.  Just to be sure- it's ok to leave the gap at the top or should I fill that in too?

Don_P:
Now we're crossing into the area between the code and physics, I don't mind the gap at the top because it's on the compression edge and won't induce splitting. You can't go wrong filling it and I think that's where the wording in the law comes from.

This is yet another method to check your poles;
http://windyhilllogworks.com/Calcs/ridgehgtclc.htm

I will often set mine a little low and have a couple of shims in my bags to "tune" the height when I bring in the first rafter pair at each end. It beats the heck out of climbing up there with a saw and trimming a high pole down.

Woodswalker:
Thanks Don for the good info about ridge boards, beams, and rafters.  Should be very helpful for those not yet at that stage in their projects.  Good to know that I met the requirements when I built my cabin a couple years back.  Used 2 x 10's as collar ties, far exceeding the 1 x 4 standard, but spaced them 4 ft OC, just meeting that one.  Not sure if they are quite in the upper 1/3 of the "attic" space, but mine is a "vaulted" setup with no ceiling joists or real attic.  Imagine if one were using trusses that were engineered and built off-site they would meet all of the standards as long as they got attached properly to the top plates of the walls.  When I was up on the roof installing shingles and a chimney, the whole thing seemed very solid.  I did use 5/8" sheathing, which also helps.

A little off-topic, I agree completely with your opinions about lofts.  Don't quite understand why so many folks posting here are building cabins with lofts.  I suspect most have not actually climbed a steep ladder leading to one and tried sleeping up there in a cabin heated by a wood stove.  My experience years ago was that you get so hot you throw off all the covers, and maybe open a window up there to get to sleep, and then you wake up in a couple of hours shivering.  Of course, a good ceiling fan would help - if you have electricity.

MountainDon:

--- Quote from: Woodswalker on October 15, 2009, 04:49:16 AM ---Don't quite understand why so many folks posting here are building cabins with lofts... 

--- End quote ---

Those were all reasons we went with a normal flat ceiling. I must admit that I like the outside look of a steeper pitch roof and the open interior appearance. But I also didn't lie the prospect of working on a steep pitch roof.

Ceiling fans would be a help as would opening skylights of good quality.

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