How to Lay Out a Common Rafter

okay hello everybody out there in YouTube land today we're going to learn how to lay out a common rafter in our example right here we're going to lay out a common rafter for a 12-foot white building with a slope of nine twelve you could use this example for any type of common rafter you lay out put in the set of plans they usually give you the width of the building which is a span and the slope on every set of drawings they give you those two pieces of information and that's all you really need to lay out a common rafter so the first step you have to do is select the material you're going to use to lay out your after you have to do uh some rough calculations and make sure you've got a piece of material that's long enough to lay out that calm rafter so we did some calculations previous to this video and we know this piece of material is 2 by 6 9 foot long will be long enough to construct that common rafter step two you want to mark the crown of the board the count of the board is a sweep bow in the board and you kind of got an eyeball down the edge of the board I look down here and I look down this edge and this one's pretty straight but you kind of choose which side has the crown in it you always want to have the Crown's up so through their determination I marked that this side is the crown I put an arrow with a crown facing up the next step you want to do is Mark your plumb cut at the ridge board the plug cut is the cut it's going straight up and down perfectly vertical when the rafter is in position so there's a couple ways you can do it the easiest way is to use the speed square you take your speed square place the flange on the edge of the board the top edge of the board lay it down on your material and you have your pivot point there you pivot it until you read 9 12 on your common cut don't confuse that with your hip and Bailey scale you got to use your common type right there then you mark your plumcot on this edge of the speed square the next step is we want to determine the line length of the rafter there's a couple ways to do it if you buy it speed square from Swanson they usually give you a blue book that goes with it has a set of rafter tails in there but a lot of guys lose those and another way you can do it is use your framing square okay the framing square has a chart here the line length of the common rafter per foot run it's the first line on the framing square and you go down to your 912 you go nine inch mark and it tells you your unit line length is 15 for an 812 and be fourteen point four to seven twelve would be thirteen point eight nine so on and so forth so here we're going to use the nine twelve Sony is fifteen that's our unit line length and that unit line length is the basically the hypotenuse of a right triangle with a run of 12 and a rise of night they'll do that unit line length right there so the next step you have to do is you have to take your unit line links and multiply it by the run the run is half the spin so we know what the span is twelve that's the width of our building the run would be six which is half of twelve so we take fifteen and we multiply it by six so 15 times six equals 90 inches so that gives us our line length of our common rafter it's from the center of the ridge board to the plumb cut of the bird's mouth the bird's mouth is a notch you put in your Raptor than it sits on your double top plate okay so we determined that our line length of our rafter is 90 inches the next step we want to do is measure from the plumb coat of the ridge board or that's the plumb clear to the center of the building nine inches down the edge of the board so we hook our tape right there and we go down and we mark any inches you want to market on the top edge of the board you want to check to make sure our tape is in the correct spot down here all right now we mark our 90 inches right there okay the next step we want to do is Mark our plumb cut for our birds well we can do that the same way we learnt the foam cut its original order we set our pivot point and then 90 inches down here pivot it until we read nine on the common cut and then we mark our plum cut right longer more right there the next step is to run mark our seat cut which is our level cut that our birds model is going to sit on since we're going to have a two by four exterior wall double top plate we want to three inches of bearing on our double top link so we want to cut perpendicular to our plumb cut there where we read three and a half inches since the to wait for the actual width dimension of a to it for this three and a half inches white and then we mark our seat cut that's our seat cut our bird's mouth and the next step we want to mark girl rank in our diagram here it's calling for a one-foot overhang which is including the fascia and we're going to use a 2 by 6 up patient so we're gonna subtract inch and a half from the one inch mark or one foot mark because it's ten and a half inches so we're going to come perpendicular to our plumb cutting our bird's mouth and mark ten and a half inches so we could set it like this go perpendicular go to where we read ten the half inches right there people are mark there and then we do our plumb touch for our overhang you do it the same way rotate it to where you nine alright common cut and draw our plum cutter then the very last step we have to do to mark this rafter is subtract for half the thickness of the ridge board usually if you're using two by six rafters you would use a two eight ridge board so a two by eight is an inch and half thick half of an inch and a half is three quarters of an inch so the next step we would do we would subtract three quarters of an inch off our plum card here so we put mark with clear market 3/4 of an inch back and we have to draw a plumb cut through that mark there so we can take our speed square again and put our nine twelve make sure we come through that mark three quarters of an inch back now all these plum cuts could also be done with your framing square just by using nine on the tongue of the framing square and twelve on the blade it would give you the same same angle as you can see that's our same angle right there nine and twelve nine and twelve and then we would nine to twelve down here and nine twelve there that's a nine and twelve sloped roof and that's the next step we would do we would cut the rafter on this line here we would cut it out about the birds mouth out right here and then we would cut it right here and that would be our rafter and when that Raptor was in position all those plump cuts would be going straight up and down they'd be perfectly vertical and that's it for a common rafter once you cut one out you can mark it as a pattern and if it's a gable roof you can use that for all your rafters throughout the whole building a gable roof is one that just slopes from the double top plate to the ridge board in two different directions so the game world is made up of all common rafters now we're going to go down to the shop and we're gonna cut it out and we're gonna see how it looks okay now we're down here in the shop and we're gonna continue on our lesson right now we're gonna cut out this common rafter so the first thing you have to do is take care of some safety considerations one thing is make sure you have your safety glasses on okay next thing you have to do is you have to set up a saw before you set up the saw make sure it's unplugged and you want to make sure that you're set at a 90 degree angle and then you set your depth of your saw so you check your lower blade guard first of all make sure that it's retracting then you set your depth just below the material you're cutting sixteenth of an inch below your material okay that looks pretty good right about there you want to set the blade too deep the next step is we're gonna plug it in and we're all set ready to cut our rafter so make sure you got your extension cord make sure that it's all Oh show proof okay plug that in and then we're going to start by cutting our plumb cut at our ridge board okay so we're gonna mine are boy out there okay next step is we want to find our bird's mouth all right in order to cut the bird's mouth you want to just go through your seat cut just to that line there and through your plumb cut to that line there and then finish it off either with a handsaw or jigsaw so two hands on the saw you can stop right there and then we'll finish that up with a jigsaw hands on a bit now I'm going to cut by a plumb cut by my rafter tail here okay then the final step is to cut off the rest of the bird's mouth using a jig saw which is easy swing or a handsaw we find or a sawzall either one so then your notch there we go the next step was to check to see what a rafter would look like sitting on a double top plate in position so for a 912 sloped roof we look approximately like that 12 foot wide building you

Channel: CTE TV

Views: 77,930

Keywords: Career and Technical Education, Erie 1 BOCES, building trades, common rafter, roof, rafter, joist, template, gable

Id: TanFSL5omLw

Length: 11min 31sec (691 seconds)

Published: Mon May 21 2018