Replies

1. 
   Guest_ | Oct 04, 1999 07:12am | #16

   *
   I've got a single story home, 29'w x 39'l. 2x4 wall construction, 2x6 ceiling joists, 2x8 roof rafters, 16"o.c. sheathed with 1 x 6 boards. The roof is a 6" to 12" pitch. Here's my question. I want to remove some interior wall, creating a large great room. I also want to remove the ceiling rafters back around 16' from the gable end, creating a cathedral ceiling in half the house. Any suggestions on the most cost effective way to hold the walls in? I've thought of using collar ties, every 4 feet, right above the wall plate, with perhaps a scissors truss arraingement. Any ideas would be appreciated.

   Ray

1. 
   Guest_ | Sep 29, 1999 06:52am | #1

   *There is another post about collar beams that may enlighten you a little bit. You can add a structural ridge beam, or go with the new collar ties, or add scissor trusses. It's an economics question (as all are). The project I am currently working on (mentioned in the other post) Turned out to be cheaper to tear off the second floor and re-frame with trusses.-Rob

1. 
   Guest_ | Sep 30, 1999 04:27am | #2

   * drvnputt

   Removing some of the interior walls is not so much a problem because in most cases their not bearing. Removing the floor joist are. Depending on how many you remove will dictate the proper course of action. I would recommend that getting a P.E. to look at it is always a good idea in any case.

   The major problem in removing ceiling joists is that the weight of the roof (the actually structure) is "always" applying force to the exterior walls at an angle equal to the roof slope, this cause them to spread. This is also why most flat roofs have walls that move in as opposed to out.

   How you proceed depends in part on the "look" you are trying to achieve with the ceiling. Whether a "cathedral" (two sloped vertical planes that intersect to form a peek), a "tray" (a sloped vertical plane that intersects a flat horizontal plane) or a "vault" (something with some other form of geometry).

   By far the simplest of them is the tray ceiling, usually installing collar ties that are bolted through the rafters will suffice. In most cases these collar ties can also be used for the ceiling rafters. In a vaulted ceiling the use of ties can also be used. Installing these about a foot above the project/proposed high of the vault will usually work fine. You then need to construct whatever and however your members to create the vault.

   The most complex one is the cathedral ceiling. Most would be tempted to just remove the joists and use the "existing" rafters up to the ridge. It's a given you shouldn't do this. You could remove the whole existing roof that will become the "cathedral" and install a scissor truss system but, this would add a great deal to the cost of the project for the obvious reasons. A good solution to this problem is to install ties in the fashion of a scissor. Bolting them down about 2 feet down along the rafter and at the wall/rafter plate. This will create the cathedral. Again, whatever you do, you should consult with a P.E. Good luck.

   Joseph Fusco View Image

1. 
   Guest_ | Sep 30, 1999 07:09am | #3

   *Joe, thanks for the reply. The project in question is on a lake property, very country looking. As a result, lots of wood showing in the application would not be bad. What I was thinking of was putting a 2 - 2 x 6 collar ties on either side of every third rafter. These would go the full width of the house that will have cathedral. (29') I was then thinking of installing a 4 x 4 from the ridge pole vertically to the center of the collar ties, and fastening it to the ties. Then installing a 2 x 8 from the intersection of the 4x and the collar tie to the midway point on each side of the roof, attached there with gussets. All told, I'd be removing 12 ceiling rafters, and replacing them with 4 of these assemblies. I'd be interested in what you think of this. Thanks in advance.Ray

1. 
   Guest_ | Sep 30, 1999 08:01am | #4

   * Ray,

   Ok, lets see if I got this right. . .

   Something like this? This would be a nice looking detail, I would do it in fir. You could make it resemble a "post and beam" structure. I would still have the numbers done by a P.E. to make sure everything was ok.

   Here are some pictures of one such ceiling I did awhile back. You might get some ideas or "inspiration" from them.

   Joseph Fusco View Image

2. 
   Guest_ | Sep 30, 1999 05:28pm | #5

   *Joe,Nice room. The stick drawing you show is what I had in mind, although I was thinking of having the collars lower, like right over the wall plate. There is another posting in this section talking about collar ties, and it's a bit confusing. One thought seems to be that the collars should be as low as possible, another is that they should be higher. I prefer the scale in your stick drawing, and will probably go with something like that if it works from an engineering perspective. I'd feel alot more comfortable if the pitch of my roof were steeper than it is, with the snow loads and all.Ray

3. 
   Guest_ | Oct 01, 1999 12:35am | #6

   *Joe - nice use of graphics, and sound advice.Ray - there is one thing I would like to see. That is the same type of drawing for your 6:12 pitch. The illustration Joe used is much steeper than that so the problem I envision is not as apparent.I think that gravity is pulling down on that whole structure and on a shallower pitch, could exert the force needed to make the rafters sag (or even break) at the intersection with the horizontal ties. Maybe Joe can illustrate what I'm tryin' to "show with words". I have GOT to learn to use CAD! - jb

4. 
   Guest_ | Oct 01, 1999 03:03am | #7

   *I'm with you Jim. Love the graphics capability used by Joe. As far as my 6:12 pitch, I'm not as concerned with the rafters sagging as I am with the outward force on the walls. At the present time, there are no collar ties, not knee walls in the roof system, and it's been fine since 1955. Just the ceiling joists tying in the walls.

5. 
   Guest_ | Oct 01, 1999 03:58am | #8

   *jb & Ray,

   This should pretty much cover the "concept" here. This is done to full scale so it is an accurate portrayal of the project.

   Joseph FuscoView Image"The price of apathy towards public affairs is to be ruled by evil men." -- Plato

6. 
   Guest_ | Oct 01, 1999 04:35am | #9

   *Thanks Joe

7. 
   Guest_ | Oct 01, 1999 04:45am | #10

   *Ray,

   Anytime. . . .

   Joseph FuscoView Image

8. 
   Guest_ | Oct 01, 1999 08:07am | #11

   *Yeah, that looks like it might be OK. Do you see what I was getting at though? The higher you go with the collar ties, the greater the chance of gravity overtaking the rafters, especially as the pitch gets flatter. Joe, I like the diagonal webs (?) too. I think lots of folks would try to get by with just the horizontal member, and be askin' for trouble. - jb

9. 
   Joe_Zegar | Oct 02, 1999 02:43am | #12

   *RayDo you envision your 4x4 posts being in compression or in tension?In normal post and beam construction, a post like this (a king post) would be in tension, and is designed to prevent the beam (the collar tie in your case) from drooping, which would result in the tops of the walls pulling inwards. For it to be in tension, both ends must be adequately fastened so that they cannot slip. Also, the ridge beam must be capable of supporting the weight. It's unlikely that your beam is.If the intent is to support the roof with the post (the post is in compression) then the beam (collar tie) must be strong enough to support the roof load in addition to its own weight, without drooping. I cannot imagine that doubled 2x6s, with a span of 29', can accomplish this.While the diagonals, if properly fastened at both ends, will help, they will put an additional stress on the rafters.This scheme may keep a roof over your head, at least until the middle of winter, but you will probably not be satisfied with the results. I believe you should take Joe Fusco's advice and talk to an engineer. Regardless of what you decide to do, at least you'll know.Best of luckJoe

10. 
    Guest_ | Oct 02, 1999 03:24am | #13

    *JimbobHere's one where I guess I got away with i justa horizontal memberThe collari beamsare 3pc, 2x6 white pine, glued and bolted with the middle lamination showing a reveal of 3/4". One member of each beam is attached to a set of rafters and the top plate. The pitch is 6/12. The room is 12'w X 16'L X 16'h . Ceiling is 1x4 v groove t&g white pine onto 2x10 rafters @24"oc. Guess I dodged a bullett eh???? Not!!!-pm

11. 
    Guest_ | Oct 02, 1999 03:30am | #14

    *nope. That looks great. That isn't what I was tryin' to say. I was talkin' about the situation Joe's photo showed with the horizontal member part way up the slope, not right at the plate line. I think that if the collar tie (or whatever nomenclature) is above the plate, it is trying to pull the rafter into a reverse crown situation. I in no way meant a tie right at the plate like you have there. - jb

12. 
    Guest_ | Oct 02, 1999 07:09am | #15

    *Drvnputt:As a backup to Joe's advice to get a PE before embarking on this roof modification, let me tell you about the house that my sister lives in. It is a ~ 7:12 roof similar to the trey ceiling that Joe depicted. I would guesstimate that the collar ties are at the upper third of the rafter spans. The house is at least 50 years old and built with rough sawn lumber. Granted, it lasted 50 or more years, but the rafters have sagged noticeably, the ridge board has become "sway backed" and the center sections of the walls have bowed out about 8"! The house is actually owned by the university that she and her husband work for, and recently a PE was brought in for a structural analysis since an addition was being discussed. The PE basically condemned the house in it's current state. It was pronounced as unsafe with snow load. Another PE was brought in, who essentially came up with the same thing. Know anybody with a spare 953 Cat?

13. 
    Guest_ | Oct 04, 1999 07:12am | #17

    *I was planning the post to be in tension, that is, supporting the ties from drooping. I'm interested in why the diagonals would put stress on the rafters. I figured they would act somewhat like a truss, that is transferring downward load from one side of the roof to the other. Am I wrong? Also, why do you feel I would not be satisfied with the results? By the way, I will definetly see an engineer prior to the deed being done. Just looking for alternatives in the meantime. Thanks for the info.Ray