first time jumping in to this group. My question is related to putting a gambrel roof on a 21 x 21 addition we are adding to our house in NC. The addition will be 90 degrees out the back of the house. I have been told by the local truss building company that I have to use vertical braces where the upper pitch and lower pitch meets. The difficulty that I am running into is that I have also read that you can stick build the rafter system using plywood/OSB gussets and thereby increase the amount of living space under the roof. Any assistance in what direction to go would be appreciated.
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Replies
I'm surprised that your truss guy can't find a way of increasing usable space under the gambrel trusses. Stickbuilt can me done, but don't know that a building inspector would be that keen on it. Truss manufactutrers give you an engineered product and I think a BI would like that better than something you cook up with 2x's and plywood.
Mybe BossHog who designs trusses for a living will see this and offer advice.
Welcome to Breaktime and good luck with your addition!
Thanks for the welcome. I just went over the truss plan and if I go that direction, the livable space will shrink from 21' x 21' to 21' x 14. I suppose that I could utilize the knee wall space for storage, but pretty sure the wife wants the maximum floor space (the space under the gambrel is going to be her art studio). The attached article seems to make sense to me, but don't want to go down the road that irritates the BI.
How can you get a 21' room if the building is only 21' wide?
I busted a mirror and got seven years bad luck, but my lawyer thinks he can get me five.
Typical truss designer, trying to verify dimension right out of the gate. ;-)
They can't get your Goat if you don't tell them where it is hidden.
I'm just trying to figure out what the guy is trying to do...
I used to have a handle on life, but it broke
I knew that , just poking fun. I think his aim is to not have any vertical support under the intersection of the two roof pitches.
Might be done using parallel chord gambrel roof trusses? But he isn't going to get the inside dimensions of that room to match the outside dimension no matter what he does.
They can't get your Goat if you don't tell them where it is hidden.
I'm not sure exactly what he's thinking, since he didn't answer my question.
I'm guessing he wants something like this?
View Image
There are two problems I see with that. The structure is indeterminate, and could not be done with trusses.
The second is that he would need something at least 14' deep for his floor system. He may not have thought of that.
He may be able to stick frame it if he uses beams at the pitch breaks. Assuming I understand what he wants, that's the only option that I see.
Bumpersticker: Stupidity is not a crime, so you're free to go
My impression is that he wants something along these lines:
View Image
Edited 6/16/2008 1:07 pm ET by DonNH
Your idea would certainly work.Maybe the OP will come back and tell us what he's after for sure.Or maybe we're just talking to ourselves.(-:
Man cannot discover new oceans unless he has courage to lose sight of the shore.
don
your photograph appears to float above the page.
how do it do dat ?
carpenter in transition
You forgot to take off your 3D glasses.
Yeah! That's cool!
Forrest
open the file he attached and there you can see it's a kind of boarder effect that was added in some photo editing software.
It is kind of cool.
Like John said, it's just a border effect that was on the photo.
I just did a quick search to find a photo of what I was picturing. Should have included the link (it was an ad for some outfit which makes garage/barn kits or plans, I think).
I've also seen plans which just put a plywood gusset at the corner, rather than the truss arrangement, but doubt that would handle significant loads.
Don
A little A.D.D. are we?:>)
how would that look as my title Tim Kline, AdD. ?
do you think anyone would ask ?
carpenter in transition
Like you didn't stay focused long enough to capitalize all the D's. ;-)
They can't get your Goat if you don't tell them where it is hidden.
heck, do you know how hard it is for me to respond to a post i made 10 days ago ?
carpenter in transition
I like it.
Late getting back to this issue, dealing with some substantial flooding. Here is the background, we have placed a 27' x 21' deck on the rear of our house. The deck is supported by 36" concrete footers and 12" concrete posts set 7' on center. The posts are set below the proposed 21' by 21' 2" x 6" load bearing walls of the addition. I will be be using double 20' 9 3/4" TJI 230 floor joists (14") on 16" center and 1 1/8 Timberstrand rim board. The area under the gambrel will be my wife's art studio and therefore I am trying to determine the best approach to maximize the amount of space that she has. The truss guys have proposed a design that requires vertical supports at the slope break that rest 3' 8" in from the load bearing wall thereby reducing my overall floor space by about 7' 4". Your design achieves what I want to do. May I assume that 3/4" OSB Gussets would be used to achieve the necessary structural integrety? Thanks for all the good guidance.
The picture I posted was only to ask if that was what you were after.No, I do NOT think that putting plywood gussets on rafters will make something like that work. Not even closeWhat I suggested was using structural beams at the pitch break joints. Then you could get what you wanted easily enough..You didn't specifically ask for advice on the floor system. But no way in hell should 9 1/2" I' joists be spanning that distance. I did a thread on floor vibration that will explain why I feel that way:http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=21010.1.Where are you at that you're dealing with flooding?
Abandon all hope, ye who believe the government
The TJI Joist are 14" not 9 1/2". The folks over at Stock Building Supply provided me with the nomencalture and therefore didn't think to questions their recommendation. I have looked at the literature on TJI Joists and didn't see anything larger than 16", in your opinion would a double TJI 560 joists set on 12 inch centers work? As far as flooding, I work for DHS and that's what we do.
If the I-joists are 14" deep, I don't know why they would have to be doubled. They would likely work fine at 16" O.C.Make danged sure they're not trying to pass off 9 1/2" I-joists to span that distance. I'm pretty sure you would not be happy with the feel of the floor..BTW - I have no idea what "DHS" stands for. I was just wondering if yu were involved in the flooding along the Mississippi river...
The soundtrack to Indecent Exposure is a romantic mix of music that I know most women love to hear, so I never keep it far from me when women are nearby. [Fabio]
sorry, DHS is Department of Homeland Security. Specifically, I work for Federal Emergency Management Agency (FEMA). Could you elaborate on your recommendations on using "structural beams at the pitch break joints". I am pretty much a harry homeowner with enough knowledge to be dangerous.
The attached file shows roughly what I was thinking. The red boxes indicate where you would need structural beams. .You might get some flack for working for FEMA. As I'm sure you know, not everyone is a fan of the organization.(-:I don't live too far from the Mississippi in Illinois. Don't know if you have any info about the flooding that you can or would want to share. I did a lot of sand bagging back in 1993, but have not had the opportunity so far this year.
When a man tells you he got rich through hard work, ask him whose? [Don Marquis]
I came to FEMA in mid 06 and it seems that the new Administrator (Paulison) is doing the right things to turn the agency in the right directions. I didn't see the attachment you referenced.
I hope you're right about FEMA. Us "commoners" don't know much except what we hear in the media. Sorry about the attachment - I got it hooked up this time.
My husband was just OK looking. I was in labor and I said to him, "What if she's ugly? You're ugly." [Beverly Johnson]
Can you explain what the beams at the pitch change point will accomplish? It seems to me that the loads from the upper trusses still are transmitted to the first floor top plate through the lower pitch rafters, so what exactly does a beam do?BruceT
The beams carry the load for the upper roof section.
They can't get your Goat if you don't tell them where it is hidden.
"The beams carry the load for the upper roof section."I don't understand. My cabin has no beams at the juncture of upper roof rafters and and lower roof rafters and it has stood for 68 years in an area of 20 foot annual snowfall.The drawing in the earlier post showed upper roof trusses joined to lower roof rafters, clearly transferring the load directly through that path. How does a beam improve on the load path?
BruceT
I do not know what the load path is in your cabin . I would assume from what you say that it has no beams therefore the loads must be transferred down the rafters. the key is what does the connection between upper and lower rafters look like.
I do know that if you put a beam at the juncture between th etwo roof planes that the beam will carry the load down though the use of posts. I have worked on and been in far too many old gambrel roofed barns to even question that. I am pretty certain that is what boss was getting at.
They can't get your Goat if you don't tell them where it is hidden.
"My cabin has no beams at the juncture of upper roof rafters and and lower roof rafters and it has stood for 68 years in an area of 20 foot annual snowfall."
Hard to say. It could be well built, or you could just be lucky.
Standards for building have changed a lot over the past 68 years. Just because something from the past has held up doesn't mean that it's acceptable now.
You don't have to deserve your mother's love. You have to deserve your father's. He's more particular. [Robert Frost]
Hijack Alert Boss do you have any experience with hinged top chords on trusses? This current job of mine normally would have required "piggy back" trusses because of transport limitations. (truss is 53'6" span, 8/12 pitch with a 22'6' wide attic room)
3 quotes from different suppliers , one of whom is proposing the hinged system and I am unfamiliar with it. Cost difference between the hinged supplier and the other two is substantial, they are 40% less expensive.
Supplier is telling me it will also save considerable time/labor during erection of the roof.
They can't get your Goat if you don't tell them where it is hidden.
I've heard of hinged top chords, but have never used them. We looked at trying some for some trusses for modular homes once. I've definitely never heard of hinged top chords on something that big. I wonder if the hinge plates would get damaged in transit.
I wish my butt did not go sideways, but I guess I have to face that. [Christie Brinkley]
Thanks Boss, I have asked the company to send me a pdf of just what the configuration of these trusses will be. I can see some advantages besides the simple cost savings to purchase if they are as easy to erect as this company makes it sound.
One whole "pick and place" less to have to deal with for starters. Back to the subject of the thread.
They can't get your Goat if you don't tell them where it is hidden.
I'd sure like to see the detail if you don't mind posting it. This old dog is definitely still learning new tricks..BTW - You probably already know this, but - Bracing is always required on the flat tops of piggyback trusses. the truss manufacturer should call out the bracing. Most of the time it's 2X4s at 2' O.C. But every once in a while on really big trusses I've seen them call for plywood.
I can do anything you want me to do so long as I don't have to speak. [Linda Evangelista]
I will send you the stuff I have. it isn't much but you can look at it.
They can't get your Goat if you don't tell them where it is hidden.
Can you shoot me an email address and I will reply with a forward .
They can't get your Goat if you don't tell them where it is hidden.
Boss,I tend to be a little slow in learning stuff. Is the attached what you were talking about when we were discussing using a beam at the pitch change?
I don't have a power point viewer here at home. I'll try to looking at that on Monday at work - May have one there.
You know you're getting old when you get the same sensation from a rocking chair that you once got from a roller coaster.
Boss ,
His drawing shows the beam in plane with the roof rafters at the intersection between pitches ,rather than being beneath the intersection as I would normally envision it.
They can't get your Goat if you don't tell them where it is hidden.
YOu can get a free PPT program at openoffice.org Bob's next test date: 12/10/07
picture format
View Image
Joe H
That's exactly what I was thinking, except that the beams should be oriented in a vertical position.
How much does it cost to entice a dope-smoking UNIX system guru to Dayton?
-- Brian Boyle, UNIX/WORLD's First Annual Salary Survey
Then wouldn't they be columns? (Just yankin' your chain.)
I can't say what boss was thinking for certain but I think what he meant was the beam is below the intersection of the rafters not in plane with them.
They can't get your Goat if you don't tell them where it is hidden.
I don't really think it would matter if the beam was under the rafters or in plane with them. As long as it supported the rafters - That's the important thing.
The fact is that government cannot produce equality, and any serious effort to do so can destroy liberty and other public goods. [Jeane Kirkpatrick]
The other thing is that the original poster was concerned with usable space. A gambrel roof without beams going parallel to the ridge (or no other supports, such as ties to prevent the rafters from pivoting), will tend to push against the walls at the eves and spread them. The roof my be okay (for a while), but eventually the walls will bow out, the ridge will sag and then bad things can happen.
"Can you explain what the beams at the pitch change point will accomplish?"
Stability. All the loads are handled through the beams. that way you don't have a bunch of unbalanced loads puting wierd stresses on the different members.
People spend money they don't have, to buy things they don't need, to impress people they don't like.
Don't want to put words in Bosshog's mouth, but what I think he means is the structural beams would run parallel to the ridge, each side of the ridge, down right where the slope changes from shallow (running down from ridge) to steep (running up from eves). In such a case, your gable ends would be load bearing--or at least there would need to be support down to ground from the point where the beams bear on the gable ends.
Yup - You got it.
Bosses are like legs. When they get to the top they become asses.
Here are a couple links.
http://www.countryplans.com/redic.html
http://www.coastalcontractor.net/cgi-bin/article.pl?id=163Joe Carola
My thoughts exactly.
View Image
Don't worry about your BI..please yourself first...then figure out a way to prove that your design will work.You might give up the idea for the entire space to be clear and opt for a couple of places to put in some "pilaster type" abutments. Between the abutments, you could use some structural beams instead of the normal "purlin". Bob's next test date: 12/10/07
I built a vacation home with gambrel roof. Had iron brackets made. House is 30'x40' on top level.
Sorry about the size of "living room" picture
If you can be content with a conventional ceiling with attic space, you can easily stick frame the thing with no perpendicular members.
This cabin at Lake Tahoe was built by my father in 1940. Rafters are 2x6 on 24" centers; ceiling joists at the pitch change are also 2x6. Current codes require closer spacing, but after 68 winters with no sagging, I don't know why.
Incidentally, upper pitch roof sheathing is 1x12's spaced 4" apart; lower pitch was sheathed with 2x6 T&G.
That's a good-looking, welcoming kind of house.
Forrest