Finding roof rafters

[fcfcfc]

Without punching holes, measuring not acurate, how do you find the wooden roof rafters accuratly. Stud finders don't work that great on roof shingles etc..

.....Bill

[maker of toys]

look for the nails that hold the soffit and /or facia boards up. A good magnet might be helpful here. . .

if you have confidence that your builder was good with the level-square-plumb aspect of his/her trade, you can estimate the location of the rest of the rafter based on that data.  (here in california, with a plethora of fly-by-night developers,  earthquakes and houses built on loose fill, that might be misplaced confidence. . .)

Use a square (or measured 3-4-5 triangle), plumb bobs, a straight edge  and a tight string (chalk line) to transfer the location of the facia/soffet nail locations to the top of the roof. . .  a couple of tripods might be useful, too.

basically, thus:  if you can locate 2 points on a line, you can use those to project the line off into space.  

get a good helper and a ladder.

find row of nails on the soffit/facia. you may want to verify with the studfinder or a couple of small nails that you are on the center of the rafter. set one plumb-bob so that the bob settles on the center of said row. we'll call this one the datum, for lack of creativity.

align the square or triangle with the (presumeably reasonably square) edge of the roof, with one arm out across the first coupla rows of shingles. line the edge of that arm with the datum plum-bob tip. the other end/tip of that arm/triangle forms the second point on the line . . .so cheat however you have to to make sure it agrees with the best information you have on the subject rafter.

 take (or have the helper take) another plumb-bob to the ridgeline, and use it as the new endpoint of your projected line, or 'target'.  move the target until the tip of the arm of the square, the datum plumb-bob and the target plumb-bob all line up.  Use the straight edge as a sighting aid if you must look from the ground. take your time, and do it right.

mark the places that the points of the plumb-bobs settle at.  stretch your chalk line between those points, and off to the next rafter. slow, tedious, exacting, and probably at least partially inaccurate, but if the alternative is  tearing up the shingles and decking. . .

the above advice is free, and is, of course, worth exactly what you paid for it. . .

good luck-

-Dan

[zap]

Barring punching holes, every way I can think of, this late at night, involves accurate measurement.  If you can't measure accurately then you might have no business trying to mount anything on a roof... having said that:  If you're in a colder climate, wait for a heavy frost.  Even a well insulated roof will usually start to thaw the frost unevenly and the rafters will appear like magic.

Another idea, but one that once again involves measuring... Take 2 big neo magnets, set one on the roof in some area where you "think" you might be able to find it on the underside of the roof and take the other magnet and run it on the underside of the roof decking till the magnets mate up then measure to the rafter.  Practice having the magnets mate on a piece of plywood or such so you know how they mate up and where to measure from.

If you have no attic access and you can't measure accurately then I'd say your stuck with punching holes, otherwise measure from a plumbing vent or other roof penetration, if any.

P.S. Maybe you can beg, borrow, rent(?) a different stud finder.  Mine was one of the first "electronic" versions and can find rafters 2 inches deep when set correctly.

Good luck!

[pepa]

tap along the roof litely with a hammer, you will hear the difference in sound when you reach a rafter, pepa.

[Darren73]

your other option is to drill through from the inside, that way you know your hole will be where you want it in relation to the rafter.

regards

Darren

[Titantornado]

A cheap electronic stud finder.  Available at any hardware store for $10

[fcfcfc]

Hi All:

Thanks for all the comments. Underside is not accessable. Stud finders have a hard time because of all the shingle nails which have big heads. I am sinking 3/8" lags down and you really have to be OC on the rafters. Boy, what an app for UWB!! But I don't know of anyone who has that tech avail for that purpose. The elaboate measuring is fine, but it still a leap of faith, and the slightest angle error can put you off allot. I need to be within 1/8" of OC. I bought a Zircon i700 which is suppose to have deep scan 1.5". But between the sheathing and the shingles your left with only 1/2". I need one that does about 3" or 4" for wood. No such animal I guess.

I guess I have a problem without a simple but accurate solution.

.....Bill

[Gary D]

If you have metal ridge vents, simply remove one or several. You can project down from there. Then replace them, of course. Reroofed my mom's house this past weekend,oh the pain! Was only 13 squares tho.  ;-)   Gary D.

[craig110]

I agree that one measurement with a stud finder through shingles isn't valid due to the nails.  In putting up my panels, what I did was search for each stud in three or four (and sometimes five depending upon what I was seeing) different places.  I only accepted that I actually found a stud when a set of the stud finder's "hits" all lined up nicely and if the proposed stud location was approximately 16" from where I thought the next stud was at.  (This isn't as much of a which-came-first problem as it may seem.)  I put about 50 bolts into 10 studs and the bolt missed the stud only around 3 times in the whole process, and those were just due to being too close to the edge.

So, bottom line, a cheap stud finder can work through shingles, but you can't just go with one measurement.

Craig

[Titantornado]

Yea, if the roof was installed correctly, the only place you should have roofing nails is under each shingle tab, near the bottom edge, at dead center.  Try scanning in the middle or upper portion of the tab. (the sensor is near the top of the scanner)

Also, another trick I've used if the scanner isn't giving you a real clear point of center or broad indication, is to perform a "stepped" scan.  To do this, I scan across until the first light comes on.  I don't move the unit, but turn it off and on to reset it's sensitivity, and move it a little closer to the rafter and repeat the proceedure.  I may do that two to four times to reduce the sensitivity, and ends up giving me a clear point of center, or at the very least, two indications of edge close together.

Your scanner should easily be able to perform your required task.

[Slingshot]

Locate one rafter by any means necessary.  There have been some creative suggestions, but one hole from the inside will also do it.  Once you have one reference point, you can measure rafter spacings (uneven or otherwise) on the inside of the roof and then mark off these same spacings on the outside.

[vawtman]

Why would you want to sink a 3/8 lag into a support and weaken it.Why not widen the base and support it to the deck?

[jmk]

Iwouldn't go by the nailing in the soffit. It's made from 2 by 4 blocking and only will be the same if the soffit is running on the same pitch as the roof and nailed directly to the bottom of the rafter. This hardly ever happens. I would step side to side  and watch the way the roof bends. Then tap with hammer. Pepa is right you will hear a thud sound. Pick a tab up and drive a nail till you find both sides of the rafter. Put a dab of tar on the holes and let the tab back down. Its as easy as that.  

[Catch66]

A tip if you need to drill along rafter to find on exterior.

Take a steel clothes hanger use a pair of dic's pliers and cut a 45 degree angle your bit then after cutting other-end place along inside of rafter and will smoothly drill with minimal hole.

Catch 66

[thirteen]

most roofs need better vents installed or maybe you could replace one open the roof and install one and measure the studs or look into one of the vents.

[icicle]

If they did it by code, The rafters should be on 16" centers




measure under your over hang to the side of your house then mark it on top then add a 1/2" to find center. I think in not mistaken they measure from the outside edge it 16" to the outside edge.




Some places require 12" center on rafters. check on the building codes.

[framistan]

Another method instead of hammering and listening for the difference in sound

it makes, is to bring your cordless electric shaver up on the roof.  Hold it against the roof in various spots and listen to the tone change.  As you move

the razor over the rafter area, the tone will change and you should be able to

tell where the rafter is pretty accurately, and easier than the "hammer" method. I was surprised nobody else suggested this.