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I am planning to apply tongue and groove ash to my attic ceiling in order to create a cathedral ceiling. The house is about 85 years old; the existing roof rafters are 2×4 (true dimension by the way) 16 inches on center 17′-0″ in length top plate to ridge. There are 10 existing collar ties (also 2x4s) at ~32″ on center that are 6′-8″ above the floor height. There is a dormer that interrupts the ceiling at about the mid point forcing an 8′-0″ wide gap in the collar tie system.
Being too tall, I would like to move the collar ties up to 7′-8″. The underside of the ridge is at 10′-4″ and the roof pitch is 9:12. At the new height of 7′-8″, the collar ties would be 8′-0″ in length. My plan is to use 2×6 Ash for the new collar ties. The length of the attic is 30′-4″ and the width of the attic space is 27′-0″. Now for the questions:
1. Can any one direct me to the necessary information / tables to estimate if rising the collar ties is structurally sound?
2. Does 2×6 sound reasonable or should I go up to 2×8’s?
3. I think it would look nicer if I went to a 4′-0″ spacing on the collar ties; could this be accomplished if I doubled the 2×8’s on either side of the existing rafters and inserting a 2x filler piece to brace the paired collar ties?
4. Can anyone recommend other solutions?
Thanks for any help you can offer!!!
Replies
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There are a lot of variables to consider, what is the roof loading? do you get snow in your area? huricanes? Since your house has been standing for 85 years it must be strong enough, but for that span, 2x4 rafters sound too small to me. Moving the collar ties up will only increase the stress on the rafters. The rafters are what you need to worry about, a rafter will probably fail before even a single 2x6, doubled 2x8s would be redundant. Really the best advice would be to contact a local enginer who can personaly inspect the structure.
Jay
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A nice alternative to collar ties is to use a scissors truss. The collar ties do less and less good at keeping the rafters from pushing the walls apart as you move them up.
*I'm with Fred on this one. The rafter size is way, way too small by today's standards. I would seriously consider re-doing the roof structure before you dump a bunch of money into the house. As far as I'm concerned, collar ties are useless in most situations.
*Most people have very little understanding of what ties in rafters can and can't do...That said if the rafters can't spread at their lower end due to attic floor joists then what I do is bolt ties as high as necessary and rely on them shortening the effective load carrying length of the existing rafters...If you have low or now snowloads and all is well now then go ahead and bolt ties in place out of 2x4 as high as you like.Have done your exact project before with great success, near the stream,J
*Your roof sounds very much like mine - same pitch, similar lengths, true 2X4's - but mine is hip with a 6' ridge with hip roof dormers all four sides. Top plate on ballon fram is 10" above attic floor joists. I know the collar ties have never seen tension. They have probably seen compression in the winter - but until recently snow never built up - it melted! I removed the ties. I'm now sistering the long spans with 2X6's, (offset for approximately 7" depth from sheathing) sheathing several bays with 1/2" ply applied following the principals of APA stressed skin panels, covering with polyiso, and blowing cells behind before 1X4 t&g finish.
*if you have joists keeping the walls from spreading-ridge from dropping, what function do collar ties serve?
*If the rafters are undersized for the loads, the collar ties amt keep the rafters from deflecting. At least thats what I have observed in many old houses.
*YB,As I stated above the ties can be in compression and still be usefully allowing the rafters to be less in strength than if no ties existed. the engineers want them bolted though instead of nailed...Have you ever gone in an attic and observed all the ties peeling loose? I have.Near the stream,J
*Bill, Jack (happy Easter) Istarted to write my inability to understand but I held my hands tentlike and I guess I do get it - I sure wouldn't try to explain it though. thanks.Great day to be breathin', isn't it?
*Great Day to have no nail holes that's for sure,Near the stream,J
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I am planning to apply tongue and groove ash to my attic ceiling in order to create a cathedral ceiling. The house is about 85 years old; the existing roof rafters are 2x4 (true dimension by the way) 16 inches on center 17'-0" in length top plate to ridge. There are 10 existing collar ties (also 2x4s) at ~32" on center that are 6'-8" above the floor height. There is a dormer that interrupts the ceiling at about the mid point forcing an 8'-0" wide gap in the collar tie system.
Being too tall, I would like to move the collar ties up to 7'-8". The underside of the ridge is at 10'-4" and the roof pitch is 9:12. At the new height of 7'-8", the collar ties would be 8'-0" in length. My plan is to use 2x6 Ash for the new collar ties. The length of the attic is 30'-4" and the width of the attic space is 27'-0". Now for the questions:
1. Can any one direct me to the necessary information / tables to estimate if rising the collar ties is structurally sound?
2. Does 2x6 sound reasonable or should I go up to 2x8's?
3. I think it would look nicer if I went to a 4'-0" spacing on the collar ties; could this be accomplished if I doubled the 2x8's on either side of the existing rafters and inserting a 2x filler piece to brace the paired collar ties?
4. Can anyone recommend other solutions?
Thanks for any help you can offer!!!