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Roof sheathing tolerance

b128's picture

Getting ready to install roof sheathing over rafters.  Problem is that this was our first attempt at installing rafters and for a variety of reasons (mostly my fault) the rafters are not flush - some are off by as much as 3/16. 


Do I need to shim the rafters to get them closer?  How flush do they need to be to avoid having a wavy roof?


Details: It is a 5/12 shed roof, 12x18 and we are going to put on asphalt shingles. 

(post #108792, reply #1 of 11)

Don't lose too much sleep over it. You probably don't have much of a site line on at 5/12 roof. If you do, you might want to adjust them. Just shave off the big humps.

Is anybody out there? 

(post #108792, reply #2 of 11)

"How flush do they need to be to avoid having a wavy roof?"

They would need to be PERFECTLY flush to avoid a wavy roof.

"some are off by as much as 3/16."

3/16 difference is very good. Trusses are usually off by more than that. If you are rough framing by the 16th you are doing better than most.

"...going to put on asphalt shingles. "

Standard 3-tab shingles will show waves much more than dimensional/architectural shingles. But, even if you are installing 3-tabs you probably wouldn't notice wave until differences that neared 3/8" in 24 o.c.

DC

(post #108792, reply #3 of 11)

You can buy a new tool! A power planer will shave off any high one very nicely.


You take a straight edge and find the high ones and have at it.


When you set rafters it is a good idea to crown them with the hump up.


That way they are more consistant and the really high ones you shave down.


"There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."
Will Rogers
______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #108792, reply #4 of 11)

would you really worry about 3/16" though?

I know I wouldn't.

Usually, if it's so bad it would need to be planed, it wouldn't make it into my cut pile. You are already sighting the board for crown before you cut... why would you allow it onto the roof if it is so bad that you know it will need planing?

I have taken back lots of unusable lumber and i have planed, repaired, and replaced existing lumber, but have never planed framing lumber I installed.

DC

(post #108792, reply #8 of 11)

I agree with you. If i had a rafter that needed strightnening I would do it on the ground. And 3/16" is well within tolerances


I thought the poster was doing this as a DIY project and might want to buy a new tool.


I didn't mean to misinform them. Sometimes I like to go above industry standards because I just want to. I see something and have the time so I do it.


"There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."
Will Rogers
______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #108792, reply #5 of 11)

Getting ready to install roof sheathing over rafters.  Problem is that this was our first attempt at installing rafters and for a variety of reasons (mostly my fault) the rafters are not flush - some are off by as much as 3/16. 


Do I need to shim the rafters to get them closer?  How flush do they need to be to avoid having a wavy roof?


Are you saying that they are not flush with the top of the ridge?


Are they not flush at the birdsmouth at the top of the outside plate?


Did you use one rafter as a patteren and scribe all the rafters with that pattern?


If so, did you crown all the rafters to the top and keep the top of the pattern flush to the top of the rafters?


 


Joe Carola
Joe Carola

(post #108792, reply #6 of 11)

Just getting ready to go put the sheathing on - it is a 4 hour drive from home.


Yes, the crowns are up.


Yes, I used the first rafter as a template for all the others.


They are not flush at the birdsmouth.  They are pretty good at the ridge. 


There were two problems. 1) I did not cut the birdsmouths consistently.  I tried using 3 or 4 different tools - thus some of the difference.  2) The lumber ranged in width from 7 1/8 to 7 3/8.  I didn't catch that until too late.


I do have a power planer, and I just cut some 1/4 shims.  Between the two I will get it close enough.


Thanks for the comments.

(post #108792, reply #9 of 11)

They are not flush at the birdsmouth.  They are pretty good at the ridge. 


They are not flush at the top? That means your overhang will be in and out when you put the fascia on. You always nail the birdsmouth first so that the overhangs stay the same. Any adjustment is at the rdige. 


There were two problems. 1) I did not cut the birdsmouths consistently.  I tried using 3 or 4 different tools - thus some of the difference. 


If you do it again, just use a circular saw and over-cut the birdsmouth and every one will be the same.


 2) The lumber ranged in width from 7 1/8 to 7 3/8.  I didn't catch that until too late.


The lumber difference won't matter at all when keeping the top of the pattern flush because the HAP cut and birdsmouths will all be the same height. Just the bottom will show the difference and that doesn't matter.


You can plane if you want, or just do as Joe and Blue said. Or, wait for Joe, Blue and myself and we'll come up and help you..;-)


 


Joe Carola
Joe Carola

(post #108792, reply #10 of 11)

Don't ask ol' blue because blue has a different theory and approach to rafters and planes etc.


Yall place undue importance on the birdsmouth and cut it perfectly as if it's important.


Blue (that's me) puts the utmost importance on two parallel planes: the ridge and the fascia. Everyting in between those two lines is negotiable...including the birdsmouth.

Is anybody out there? 

(post #108792, reply #11 of 11)

Yall place undue importance on the birdsmouth and cut it perfectly as if it's important.


I'll take that from where it's coming from. Meaning,you cut rafters different than I do. I have a pattern and use that. Every single rafter is the same size flush at the top. The HAP cuts and overhangs are all the same size. Doesn't matter what the difference is in the width of a rafter.


You can use a 2x8 that's 7-1/2" and the one next to it can be 7", the tops, HAP cuts and overhangs will always be the same. String your walls and nail the birdsmouths tight first and your overhangs will be nice and straight. Any variation at the ridge can be easily adjusted to fit flush at the top of the ridge.


If you don't nail the birdsmouth tight first and try to fit the ridge first and push the birdsmouth out, you obviously screw up the overhang and fascia height and the height of the HAP cut at the plateline.


Your way works because I think you put your overhangs on first and you don't even cut a birdsmouth or something when stick framing. Maybe you make the birdsmouth bigger, who knows, it works for you and my way works for me. My way is simple and easy. Slide the rafter and birdsmouth until it hits the top plate and nail away resulting in a nice straight fascia line.


 


Joe Carola


Edited 8/22/2009 12:41 pm ET by Framer

Joe Carola

(post #108792, reply #7 of 11)

I'm with Blue. . .

Get a box of doughnuts and some coffee and start nailing ;-)