couple more roofing questions

[dug]

In midst of roofing process and have a few questions.

I am notching the gable end rafters to support the fly rafters, 2 ft. on center. I want to make sure the fly rafter supports line up with roof sheathing.
Do you usually trim the bottom sheet (first course), or start with a full sheet and trim on the top. I would rather trim the first course on the ground unless there is a reason not to.

Do you run the sheathing clear to the peak, or leave a small gap at the top?

Thanks!       -Dug

[dug]

Oops! Posted in wrong section. Sorry, don't know how to move it.

[MountainDon]

You can not move it.        Not a big deal, but I shifted it here.

What sort of venting? With a ridge vent leave a slot at the ridge to vent through. Otherwise I butt the sheets up pretty close.

As for trimming I don't think it makes any difference. You want to stagger the sheets as you go up the slope, and have the sheets oriented with the long side parallel to the eve and ridge.

[dug]

There will be a ridge vent so I'll leave a gap.

2 by 6's O.K for fly rafter supports? I know it may be overkill but I have a lot and no 2 by 4's handy.

I'll try to pay more attention where I'm at next time before posting.

[Redoverfarm]

Dug 2X6 will work.  Like Don stated you need to stagger the joints and that includes over the fly rafter.  Hopefully it will not hit on that rafter that the fly is attached to.  Unless you build this exact you will probably have to trim the eve end of the sheeting as well.  I always work from bottom to top and from one end to the other. Leaving the cuts on one end and the top.  Make sense.

[MountainDon]

One more thing on sheathing the roof.

Sometimes the dimensions of the roof surface work out to the last row being rather narrow. If I remember correctly, even if it means some waste, sheathing strips should not be any narrower than 16" for 7/16 material. This is to prevent break through when walking on the roof. It may not be you who steps on an 8 inch narrow strip right now, but maybe some other (250#) person in the future.

[davidj]

Around our way ("left coast"), the fly rafter supports are called "lookouts" (if they're set flat).

If you're cutting the notches for the lookouts in-place, then it's a fair bit of work to cut them (and a fair bit of inhaled sawdust, depending on your scaffolding setup).  Personally, in this situation, I'd rip the 2x6s down to 2x4s, saving 1/3 of the work.
If you're notching at ground level then it's probably less of an issue, but if you've a table saw sitting there it'd probably still be quicker to rip them.

Also, as the complement Mt Don's reminder, don't forget to cross at least 3 rafters in the horizontal dimension with the plywood.  E.g. if the roof is 10ft long and rafters are 2' oc, then you need to do 4ft and 6ft lengths (wasting 1/8 of the plywood) rather than 2ft and 8ft (when you might not waste anything).

I hope your roof isn't 16'4" x 33' like mine was!

[dug]

I hope your roof isn't 16'4" x 33' like mine was!

Not quite- 16' 6" by 33'! Yeah, there will be some waste.

As always, great advice. Thanks everyone!

[Jens]

Peg and Don_P probably won't like this advice.  The way we used to notch the gable rafters for the lookouts in West coast time, was

1. Measure up from end of rafter tail 24", subtract 1.75", then put the next mark at 3.5" up. 

2. From the first mark, hook the tape on a nail, pull the tape out to 24" and go (make edge mark, X on far side from where you started, 24 and go), and proceed until all marks are made.

3. Once you have all of your 3.5" mark outs, set your saw blade slightly more than 1.5" deep, and crosscut the top of rafter at each mark

4. Set your blade to full depth, and with the short side of saw shoe against the top of the rafter, plunge the cut in until the piece is severed.

This method ends up with over cuts, and isn't the neatest way, but when you need to get it done quickly...the rafter is sheathed, and has studs attached to it, so the over cut won't hurt its performance.

[dug]

interesting method Jens- would have never thought that. I already did mine the more conventional way (eating lot's of sawdust).

So I would like to build my roof with an 'open' soffit if possible. Nothing real fancy, I was thinking t-11 or something similar under the eaves. from what I gather now, this won't be so easy because I need to run sheets to the edge which makes sense for more strength. I guess I thought I could sheath to the edge of house and cut whatever size pieces I needed for the eaves that would show from underneath.

Any suggestions for doing this another way?

[Redoverfarm]

Dug I take it that you are referring to just visually seeing the rafter tails rather than covering them up with the soffit.  You should have a facia board at the rafter tail ends.  I am a little confused when you say "open" but later you indicate cutting T111 to cover. 

Here is what I did for an "open rafter".  The gable ends and eves of the cabin is all soffit with the exception of the porch.

[dug]

Redoverfarm-

Sorry, sometimes it's hard to get the terminology right. For my front porch, I want to do it exactly as you have pictured. I also want the gable ends to be open from underneath, but I don't want exposed (painted) osb. Basically I want it to look like the roof was sheathed with planks.

Hope this makes sense.

[Redoverfarm]

So you are saying that you want to inset your T111 up into the rafter bay against the OSB or sheeting turned to represent planks between the rafters that are exposed.  I think in this situation I would undercut the demensions of the T111 and being careful not to penetrate your roof attach to your sheeting or OSB.  Then follow-up with a piece of 3/4" X 3/4" square stock against your rafter edge where your T111 butts up against your rafter.  I may be off base in understanding what you are doing but if this is what you are doing then that is what I would do.

You will need to protect the wood in some fashion though whether it be stain, sealent or paint. I like stain.

[dug]

I like it!

I was thinking of using pieces of t-111 instead of osb, turned upside-down, for sheathing at gable ends. Think I'll use your idea instead.

Thanks!

[John Raabe]

I sheathed my open rafter porch with 1x4 lap cedar siding - smooth side down. It looks great from below and is thick enough to not show the roofing staples.

You don't want to use OSB in that exposed installation. ACX Plywood and exterior rated panels should be fine.