I’m about to frame a hip roof that has a common rafter length of about 28′ including tails.
I know this has been discussed before but I hate reading through threads at length. The roof will be stick framed (not trussed) what’s my best option for a rafter of this length?
overlap on top of purlin? If so can I set all the rafters and then build supports or do I need temp. support while framing?
Arrow splice over purlin?
All ideas are welcome RTC
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Replies
I dunno, but . . . . nice hat !
Greg
Took me a while but I found it!
Where are you that you can't get 28' rafter stock? Here in MA we can get up to 28' hem-fir in 2x6,8,10, & 12. You could also use I-joists as well. I guess the layout and bearing points in the house would really be what would ultimately determined the solution. My first choice would be to get long enough stock to not have to piece it in. So my first choice would be dimensional lumber, my second choice would actually be the purlin wall with broken span and dimensional lumber and my third choice would be I-joists.... just because I don't really enjoy working with them even though we do all the time (not for roofs, yet, anyway).
When I do frame using a segmented rafter to complete a span, I like to have the lower rafter have a seat cut at both the top and the bottom to bear on the walls. The upper rafter would have a seat cut at the bottom and ridge/plumb cut at the top. Raftera would be cut to lap each other at the purlin wall approx 24" or so and nailed together then I'd use hurricane ties to secure them to the plates.
I can't get 28' board and that's why I was wondering about splicing and purlins.
I always thought that purlins had to be at about a 45 angle is this correct or are the purlins you're refering to actuall walls?
RTC
I wasn't talking about 'purlins', but a purlin wall. A purlin wall is a detail I see on drawings from time to time. It's basically just a load-bearing wall, usually somewhere in an attic, but not necessarily, whose main purpose is to pick up roof load.
Purlins are something that I'm not sure how I feel about... but then I'm no engineer. I think they're a nice looking 'belt'.... but you better have matching suspenders. That's my two cents anyway. I'd never try to engineer purlins myself to pick up that sort of load you're talking about.View Image
Manhandle it! Or put a handle on it man.
you should follow the plans
Yeah right! my plans didn't even give me proper wall layout.I have engineered all the framing myself.With the approval of my engineer and wind storm but that's usually after the fact.
RTC
Perhaps you should look at a span table before you buy 28' rafters.
We can get up to 36' - 2 x 6 / 2 x 8 structural grade finger joint rafters here in TX.
I used to have the website of the manufacturer, but can not find it. Our builder friendly main lumber supplier stocks the product.
In your case, I would recommend a lap over a purlin.
Edited 7/21/2006 7:12 pm ET by txlandlord
Thank you. where can you get that long stock?
I get most materials from Zarsky local to Corpus or McCoy's all they carry is 24'.
just finished some box beams like you've been talking about I post the framing pictures soon soon so many confused people may come to understand the simplicty.
I'll problably lap the rafters over purlin that are at an angle , right? Rafters in first and then supports? Thanks again RTC
OK, checked your profile and your in my area.
Home Lumber (BMC) / Rosenberg, TX / Rick Rangel sales rep / 281-342-4282
Tell him John Luther / Brothers Custom Works told you to call
Rtc,
I don't understand why this isn't on your plans, especially with a rafter that long. I've used 2x10's and 2x12's that long before and we can get those all the time with doug fir.
Are you designing this yourself?
There are many ways to frame this. You can frame this with a 28' rafter or a microlam beam to break the span. Can you give more information?
I can't seem to get anything but southern yellow pine @ 24'.thinkig of using two piece rafter over purlins installed after rafters.
RTC
We used 28' green doug fir 2x12 a few times in the last six months. Heavy heavy heavy, but they worked. If I had a frame that had more than 10 of those, I'd find them kiln dried and have them shipped in. Here in WA that is a little easier since there are quite a few mills within 3-4 hours.
The frame we are finishing up right now, we used I-joists as the main rafters (31 and 32' long) and they were a breeze to install.
http://pic9.picturetrail.com/VOL293/2163851/11350387/164188144.jpg
http://pic9.picturetrail.com/VOL293/2163851/11350387/164188134.jpg
http://pic9.picturetrail.com/VOL293/2163851/11350387/164188126.jpg
http://pic9.picturetrail.com/VOL293/2163851/11350387/164188803.jpg
http://pic9.picturetrail.com/VOL293/2163851/11350387/164184887.jpg
http://pic9.picturetrail.com/VOL293/2163851/11350387/164183331.jpg
We have walls underneath the rafters to break the span.
In your case, can you frame walls under the rafters? What we've done in the past is to run a string on the underside of the rafters (after they were sheathed) and frame the walls so that the rafters were pretty close, all within 1/4" of the measurement taken at each end from the rafter to the string.
If you use walls below the rafters to break the span, or purlins braced to a wall, make sure it is a wall with a footing.
edited to add: excellent pics, btw, as always!
"he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
Edited 7/22/2006 10:57 am by Huck
Ya, I almost said that, but I saw he had concrete slab as his floor. For us on a crawl, then definitely we need support.
Thanks for the comments. I'm riding high, pun intended because Floyd Landis just took the yellow jersey and looks to win Le Tour de France.
RTC,
My lumberyard here in Austin delivers all over the place. We just finished an house with all engineered lumber. Rafters were all 2x8 LVL. They delivered 48' sticks and we had some rafters as long as 30'. All perfectly straight and the 1 3/4" nailing surface is a joy to deck. At the 48' lengths we had almost no waste. Their price is great for that product (but that maybe because we did the whole house out of engineered wood).
Texas Redwood 512-385-5334 (Jim Donovan), Tell him Bruce Haikola sent you.
Bruce
using LVL's do you have to use purlins or bearing walls?......RTC
"using LVL's do you have to use purlins or bearing walls?.."Rtc,No, you don't need purlins (what I think they are) or bearing walls for 28' rafters. You don't even need them with 2x10 or 2x12 rafters at 28'. You just make sure you put the collar ties in at the right spot. Since your designing this stuff you can do whatever you want but it has to be done right as you know.I've never used the term "Purlins" but I've used microlams before mid-span or whatever span to break up the rafter length. This way you don't need any bearing walls, but you need to post down under the microlams.Since this is a hip roof, you would have to have a purlin/microlam beam the length of the ridge or a little longer to get close enough to the nearest jack rafters so that you can post down to a wall somewhere underneath because it's not like it's a gable wall and you can go from one end to the next.I would get microlams since you can't buy 28' 2x10's or 12's and do them in one shotHere's a drawing I did a while back with microlams and you cut birdsmouths on both rafters to sit on top.Joe Carola
Edited 7/22/2006 3:32 pm ET by Framer
Joe.... I didn't say he 'needed' purlin walls or bearing walls. Just that it is one option he has to make it work if he decides to piece the rafters in. Your LVL diagram accomplishes the same thing, with the beam replacing the wall. I was under the impression that we were all just throwing options out there for him. I think we've all agreed the using one continuous rafter, regardless of species or type of stock, is still his best option.View Image
Your LVL diagram accomplishes the same thing, with the beam replacing the wall.
Yeah, and again, those builit up beams made of microlams need to be supported below by a footing. If they run from exterior wall to exterior wall, then it should be no problem. But on a cut-up roof, that's often not the case."he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
That's what I mean. It'll be tough to run them exterior wall to exterior wall on a hip roof though, won't it?View Image
Yeah, you gotta have an interior bearing wall or shear wall to run 'em to."he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
Brian,I wasn't directing that at you at all. I thought that a purlin was the same thing as my microlam.If I can make it to the fest, your not going to beat me up now are you?....;-)Joe Carola
You'd kick my azz anyway. No sense talking tough to a tough guy. Even I know better than that. :)View Image
Hopefully if we meet, I'm just a happy, physical, hugging, annoying kind of guy amongst friends. Although, my wife says that I'm annoying no matter what I do........;-)Joe Carola
You gotta get there Joe... if I can make it from MA......View Image
so your'e sayinig I could have about a 26.5' rafter run using 8" deep lvl with no support but collar tie?
Where would they be placed ? up against the ridge or 1/3 down?
Would this work the same for TJI?
...................RTC
please answer my question.bump................RTC
I have framed a roof with all LVL material the only down side was the cost if your in a budget situation and the wieght of the LVL's. But you can span a long distance and it made for a really clean frame and solid.
Howie
As mentioned in all these other posts, the use of the midpoint support needs to be answered by your architect or engineer. The midpoint support can be eliminated, but you need to size the rafter correctly.
Unfortunately, my engineer does not travel as far as my lumber company.
Bruce
I have plenty of walls below that can be used as bearing walls or purlin.
A purlin is basically 2x4 run from load bearing wall , to a plate nailed to the rafters horizontallywith a stiff back along the plate.
The use of purlin has alwaty been used around here.
...............RTC
TJI
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I got the purlins set up wher I need them, now given the choice would you
A. over lap the 2x8's 4' each way on top of the purlin
or...........
B. cut 2' into each board for an arrow splice.
LVL's and TJI's are not an option to me.
RTC
bump
If you've got some solid purlins going on, with adequate bracing down to a wall with a footing, I'd say you're good to go on the overlap. 4' overlap seems like overkill to me, but I'm not an engineer. I used to do the arrow splice on hips that I had to break, then plywood either side glued with construction adhesive and peppered with 8d's, then a brace from the break down to a bearing wall. But not on individual rafters."he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
I'm not an engineer either, what overlap do you think would be adequate?
It comes down to buying 2x8x16 or 2x8x18. I will be using one of each for each rafter. If I used only 16's then I would have that 2' overlap.
2' over lap on a 28' run doesn't seem to safe. especially down here. Thanks................RTC
Get an engineers opinion. There, now that I got that out of the way, I'd say go for what feels right to you - I'm a notorious overbuilder myself (at least, that's what I've been accused of!).
"he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
Edited 7/25/2006 1:36 am by Huck
I need a new engineer .Thanks......RTC
RTC.... I gotta ask.... what do the plans say to do? Or is this something you're building in your backyard by the seat of your pants? I'd need an engineers stamp on something like that here... unless it was already dealt with on the plans. View Image
we're not required to have an engineer stamp the framing plan, or even have one for that matter. He does have to inspect the framing for windstorm and the city for code cmpliance. no woories.
and yes I am I flying by the seat of my pants.
I got it figured out though now .I'll post pics soon............................RTC
Edited 7/26/2006 1:17 am ET by RTC