Can the jack rafters in a hip roof, that run perpendicular to the commons, have a different height above plate, than the commons?
The reason I ask: The shed roof I’ve built has 2×10 commons. For the hip roof I’m putting on one end of the shed, I thought I’d use 2×6’s, as the span is quite short. I found that the shortest jack is angled almost 10 degrees more vertically than the longest. When I shimmed both those jacks up to give me the same height above plate as the 2×10’s, they seem to line up just fine.
It’s driving me nuts–and making my brain hurt– that I can’t picture why that should be!
Thanks.
Thon
Replies
If the cuts on your 2X6s are that different, you have a different pitch there. That means your HAP has to be different so your fascia line is the same elevation.
It might help you to draw it full scale on a piece of plywood. Overlay one set of cuts on top of the other to make it obvious what's going on.
I can't picture how a 2x6 could have the same H.A.P. as a 2x10, unless that's a monsterous seat-cut in the 2x10??
Change the pitch or slid the hip off the corner. You can make it work, or just use 2x10's instead of 2x6s :-)
One reason I use the same dimensional lumber for all rafters (in general) is that it takes a few steps out of the roof framing and I don't have to slow down to get it all to work. You may not save enough time to justify the $ saved on materials.
Slide the hip off the corner?? Don't know what that means.Will a hip, by definition, have the same pitch as the main roof, and/or does it have to?Thanks.
Thon
Thon, I think you are confusing some terms in conjuction with their definitions.
When you shimmed up your 2x6's to the correct HAP, you were planing the roof properly. My guess is that you're trying to take the same amount of wood off of the bottom of the 2x10 as you are taking off the 2x6. That is not possible, unless you have raised the top plate in the sections that use 2x6. IF you want the same exact cutout on both rafters, you would have to raise the plates in the 2 x6 section by exactly 3.75". That figure is derived by subtracting 5.5 from 9.25.
Chew on that for a minute and I think you'll understand what you are doing wrong.
blue
Just because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
Guess I didn't explain myself too well--again. <g>My intent (I think!) was to end up with a different pitch on the 1/2 of the hip with the 2x6s. That is, the pitch would end up being whatever 'worked' going from top of hip rafter to top plate. Kind of working backwards, I know, but with so few to do.....
My thinking was: As long as the HAP is the same, all the way across the 2x6s, THAT 1/2 of the hip will be in one plane. (The other 1/2 of the hip IS in plane with the commons.) But apparently that is quite wrong?? <g? And I can't reason out WHY.(Both the 2x10s and the 2x6s have relatively small birds mouths, and I wasn't really trying to make them the same. ) Thanks.
Thon
Picture this: the placement of the hip would work out, if you snapped a line 4" down on the hip and ridge, and dropped the top of the 2x6 rafters to that line, so all the rafters are on the same pitch. The reason the roof-plane on the 2x6 side becomes tweaked is because you're changing the pitch of one side of the hip, without compensating at the hip. When two different-pitched roof planes meet at a hip, it becomes what is known as an "irregular hip" - and the hip is no longer at 45 degrees when viewed from above (Probably what Tim meant by "slide the hip off the corner." If I knew where my Marshall Gross book was, I could show you a picture to illustrate, maybe someone else can - or if I get a little time later, I'll try to draw something with Paint to illustrate). When you drop the rafter depth by 4" (by switching from 2x10 to 2x6), then raise the top to meet at the top of the ridge, you're changing the rise of each 2x6 rafter in your roof by 4". But with descending jack rafters tying into a hip, the run of each jack rafter is shorter than the one above it. Yet the increased rise remains constant at 4". So each jack rafter follows a differing angle (the angle of each jack becomes steeper than the one above it as they descend down the hip). Hence, the roof is no longer in a flat plane.Tim's advice was the most logical solution: stick with 2x10 framing throughout (or Blue's suggestion to raise the wall height by the difference in rafter depth on the side where you have switched to the smaller rafters), and avoid the complicated math required for an irregular hip.
Edited 2/21/2005 6:40 pm ET by Huck
No question, 2x10s throughout would have been easiest. But , this old noggin can use the exercise. <g>I've raised all the 2x6s so their HAP is the same as the 2x10s, so that's pretty much solved. I THINK I've just about come to grips with what was happening, but have a couple questions:1. If a hip rafter, viewed from above, is not at 45 degrees, the two roof planes COULD still have the same pitch, yes? In other words, an irregular hip = different pitches? Or, is an irregular hip any that is not at 45 degrees?2. Your second paragraph was exactly what I'm having trouble getting a handle on. I follow what you're saying--and of course, you're exactly right about what happens <g> --but since each jack is at the top of the hip, whether 2x6 or 2x10, it's not intuitively obvious to me why it should work out the way it does. (Would it be different if rafters were thought of as 'lines' instead of having 'depth'?) Apparently I need to play with some 3 dimensional models! LOLMany thanks for helping me understand this!
Thon
1. irregular hip = different pitches? Yes, that's the way I've always used the term, anyway. You could have a hip at other than 45 degrees in plan view, with equal pitched roof sections, if the corner of the building was other than 90 degrees, as, for example, might occur in a gazebo, or an irregular shaped building.
(from Joseph Fusco's Roof Framing website)
"What is an Irregular Hip or Valley Rafter?
"This refers to a hip or valley that does not intersect a 90° outside or inside corner to form two 45° angles on either side of the member. You might have a member intersect the 90° corner forming 30° and 60° angle thus making the hip or valley 'irregular'. This occurs when you join two different roof slopes. The condition that this creates is that the 'general' rules of hip and valley layout and construction do not apply."
2. OK, maybe this will help: Picture the hip that you would normally have cut for a 2x6 roof. It would be at ridge-height at the top, of course, but several inches lower at the plate than the hip you cut for the 2x10 roof. So if you took that hip for the 2x6 roof, nailed all your jack rafters into it, and had everything planing in nicely, and then you jacked it up several inches at the plate, how would that screw things up? The jack rafters at the top of the hip would be little affected, but as you came down, closer to the plate, the more out-of-wack they would be. That, in essence, is what's happening.
Edited 2/22/2005 12:39 am ET by Huck
<This occurs when you join two different roof slopes. The condition that this creates is that the 'general' rules of hip and valley layout and construction do not apply.>Hmmmm...... Armed with my newfound knowledge, I just measured the angle of my hip rafter--about 55 degrees. So apparently I have an irregular hip. Good to know the 'general' rules don't apply! <g> Interesting, to me, that in all the reading I did before starting this hip roof (Ferrer, 15+ years of FHB, etc., I never did see that a regular hip is always 45 degrees. Could have just missed it, I guess).Anyway, with the 2x6 jacks now blocked up, to equal the 2x10 HAP, I understand why the 2 shortest jacks look to still be slightly out of plane with the other 3--though much less than before. My Smart Level says about 1 and 1/2 degrees difference. I'm thinking it may be close enough to make it work as is, but any other suggestions gladly considered.Thanks.
Thon
I'm thinking it may be close enough to make it work as is, but any other suggestions gladly considered.
TAB_A, you've included a lot of info, but you've never given us the facts. Armed with facts, you will get some help.
What pitch is the main? What pitch is the minor? Did you think you were creating a regular hip?
IF you were trying for a regular hip, and accidently ran the ridge long, it would result in an irregular hip and the minor roof would be a different pitch than the major roof.
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
Fun to finally put this Smart Level to some use. <g><What pitch is the main? What pitch is the minor? Did you think you were creating a regular hip?>2 and 7/8.
4 (from the ridge).
Didn't know there were anything but 'regulars'. <g> I was naive enough to think that if my top plates were all level, and my ridge was parallel, I could put the hip rafter where ever on the ridge (a ledger board in this case) that looked like it would work out well, and it would all work out fine! LOL
Must say, I'm learning a lot!At this point, the major roof is decked and felted, so I'm hopeful I'll be able to make any 'corrections' needed, to the minor roof. FYI the major roof is a 'shed' roof with a 12' span. The minor roof's longest span (from the ridge) is about 8'. HTH Thanks again.
Thon
So - Do you call your Wife "Slot B" ???....(Sorry - Couldn't resist)(-:
Carelessly planned projects take three times longer to complete than expected.
Carefully planned projects take four times longer to complete than expected, mostly because the planners expect their planning to reduce the time it takes.
Not usually. <g>When she stopped laughing, she said, "As long as it's not slut B".
Thon, I think you're finally figuring out what is happening.
Just run with it. It's fine.
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
Cool.
If the 2-3 inches of snow doesn't show up today, I'll give it a go.
Thanks!
Regardless of the angle your hip makes with the ridge, looking from above, the hip rafter will determine the pitch of the roofs. Since it must be the same hap as the commons in order for that portion of the roof to plane out, the hap will be a predetermined number.
The difference between the hip and the commons will be the greater length of the hip and the lesser depth of the notch in the hip. This is because the hip will be longer and the angle between horizontal and the top edge of the hip will be smaller.
If the hap remains the same around the perimeter, no matter what the pitch, you will still have one problem. The end of the rafters will be lower on the steeper roof plane. This requires a shortening of the steeper plane and a resulting shorter overhang.
edited because I forgot to mention...
As Blue said, your hip will not go out directly over the outside corner of the room if your hip angle as viewed in plan view, or from above, is not 45 degrees to the ridge. Be sure to compensate for this when you pick the location of where the hip will cross the plate.
If the 2X6 jacks are in a steeper plane, as I think you are describing, the hip will be set back just a bit on the wall.
Edited 2/23/2005 10:57 am ET by Ziggy
<If the hap remains the same around the perimeter, no matter what the pitch, you will still have one problem. The end of the rafters will be lower on the steeper roof plane. This requires a shortening of the steeper plane and a resulting shorter overhang.>Yep, that's what I've got. Not a problem on the back side of the shop, though.<As Blue said, your hip will not go out directly over the outside corner of the room if your hip angle as viewed in plan view, or from above, is not 45 degrees to the ridge. Be sure to compensate for this when you pick the location of where the hip will cross the plate.>As I understand it, because my hip rafter is at about 56 degrees, and I put it directly over the outside corner of the building, I ended up with the problems described. Too late to change it now, but I'll know better next time! <g>Thanks.
Tab,You have a 12' run with a 2-7/8/12 pitch on one side and a 8' run with a 4-5/16/12 pitch on the other side. What is your overhang?Is your roof like my drawing?Joe Carola
<Is your roof like my drawing?>Sort of. <g>The major roof has an overhang of about 20".
The pitch on the minor roof is 4/12. I may have led you astray on its 'run' though. The actual rafter length of the end king common is ABOUT 8'. This, and the jacks for the minor roof, are terminating on what will essentially be an interior wall, so there will be no overhang here. From this wall, in order to stay under the gable end roof overhang of the barn I'm attaching the shop to, I'll run a very short, more steeply pitched roof, to the end of the shop (top plate is 6' 8" high). Probably clear as mud. <g>In any case, weather today looks good and I have high hopes of seeing how it all works out. Very much appreciate all the assistance!Thon
Hoo-boy...Tab_A, you're going to give me fits here trying to interpret you....lol!
I think I'm understanding you and I'll re-phrase it in the way we would discuss it onsite.
You are willing to have two different pitches. The "main" roof will use 2x10's. The "minor" roof, is the hip end, and will use 2x6's. Since you have two different pitches, you should understand that sometimes, the hip will not run directly over the corner....but sometimes it will.
Confused yet? I'll explain.
If you insist on running the hip over the exact corner of the building, then you are dictating that the HAP will be equal on both the Main roof, as well as the Minor roof. What you did, was to try to change the pitches, while creating two other fixed variables....Variable 1)the hap must be equal 2) the hap must land over the corner of the building. Essentially, you are fixing too many variables, some of which conflict. You quickly found out that by rasing the pitch, it worked with the first two varialbles....you created three sets of compatible variables.
I hope I didn't complicate that too much...I'm just explaining what/why/when.
If you don't mind the hip landing somewhere besides the corner, you can drop the 2x6's down and simply reframe the entire hip and all the jacks. This will effectively allow you to create the two different pitches. In this case, the hip will need to slide towards the main roof...now the two HAPS are different and the exact point at where they meet is somewhere off the corner of the building.
One more thing you should know: if you choose to leave the hip over the corner and raise the hip end, you will have created a "regular" hip, where both sides of the roof are equally pitched.
blue
Just because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
<Confused yet? I'll explain.>Much less confused, than when I started! Looks like you did understand what I tried to explain. Many thanks for taking the time--very helpful.Thon
Your welcome Tab
you said: "If a hip rafter, viewed from above, is not at 45 degrees, the two roof planes COULD still have the same pitch, yes? In other words, an irregular hip = different pitches?"
I haven't thought this out to any great degree, but I can't think of how a regular pitched roof could have anythig but a 45 degree hip.
So, you are correct. The irregular pitched roof will always have something other than a 45 and all regular roofs will be equal pitched and have a 45.
I think you got it now.
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
I guess it's a little too late to ask if you adjusted the depth of the bird's mouth on your hip rafter, usually a half inch or so deeper (?) than the commons? I put the question mark since it's been a long time since I cut in a hip roof.
Allen in Santa Cruz
Had a few minutes to kill, drew a plan of a 12 x 18 building with hipped roof, and 12" overhang.
Swung the hip an extra 11 degrees past 45 because you said so.
The pic attached shows where the hips go if across the building corners, yielding a shorter soffit, and away from the corner, to yeild the same soffit size.
Interesting that it it doesn't appear to move very far off the corner, for the same size soffit.
Tab, the differences in the pitch aren't that great. That's why it doesn't move far off the corner.
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
Tab,If you sat the hip on the corner and had a 12" overhang on the 2-7/8/12 pitched side you would have a 8" overhang on the 4-5/16/12 pitched side keeping all the H.A.P. cuts the same height at the plate line. If you wanted the same overhangs at 12" your hip would sit off the corner towards the high pitched side 6" and that would give you equal overhangs.Joe Carola
Joe, that just does't seem right to me. I've never calculated "how far off the corner", but 6" just sounds like an awful lot for these two low pitched roofs. Mybe were thinking of two separate issues.
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
Blue,Like you I figure everything from the overhang because there's less confusion and you can't go wrong. If you snap out Tab's dimensions on a deck using the inside corner of a 90° wall come in 12" on both walls which would be your overhang and snap the two lines now come back from those snapped lines 12' one side and 8' the other side and snap those lines and at the top where they meet snap the line from that point to the inside corner of the shoe which would represent the back of your fascia.That line is the angle your hip runs and when it crosses over the 12" line which is your plate line on the 8' run side (Steeper Pitch Side) you will see that it's 6" off the corner like I have in my drawing.There's several ways to figure the hip offset using math but if you snap it out on the floor it's right there no mistake.One way with no fancy Calculator for the Hip offset is to do this:(High Pitch - Low Pitch) x Overhang ÷ Low Pitch = Hip OffsetTab's Pitches were 2-7/8/12 and 4-5/16/124-5/16 - 2-7/8" = 1-7/16" x 12 = 17-1/4"/2-7/8" = 6" (Hip Offset)There's a lot of ways with the Construction Master if you want to know also without snapping it on the floor or just snap it out on the deck like my drawing.One way with the Construction Master is this:2-7/8 [Inch] [Run]4-5/16 [Inch [Rise]Press [Pitch) Returns 56.31° (Angle of Hip running off wall)12 [Inch] [Run]Press [Rise] Returns 18"18 - 12 = 6" (Hip Offset)Joe Carola
Edited 2/24/2005 8:39 am ET by Framer
Joe, the math don't lie, and the picture looks true too.
I guess I've never really given it any thought. I cannot remember one instance of me measuring the offset. I can't think of a reason why I would want to know that dimension. Well, now I know...if I ever run into a roof like this, and I don't already have my overhangs done, I'll know where to aim the hip!
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
And, as we know from seeing your precision bevel cuts done without lines, your aim is true!
True Blue. How 'bout dat? ;-)