Hi,
I recently purchased a house in Leakey, TX which is a 23 year old two-story house approx. 30’x30′. The house currently has 8′ ceilings on the second floor. The roof is a standard gable with a 4/12 pitch. The ridge board is 2×10, 2×8 rafters 16″oc. the ceilng joist are 2×6 and 2×8, 16″oc which connect on top of an interior wall.
My plan is to attempt to vault the ceilings with rafter ties on every third rafter (so I can remove the ceiling joists).. I understand the rule which no rafter ties beyond 1/3 length of the rafter. Even less with a roof pitch of 4/12.
Part of the second story will remain at the original 8′ ceiling (for venting and hvac) and the rest of the room will be vaulted (approx 18′).
I would like to use the whole 1/3 of that rafter span to run my ties. Is there anything I can do to run that span safely? Can I double rafters on the connections with the rafter ties?
Thanks in advance for any help given…
Mark
Replies
Off the top of my head I'd say that's nowhere near being structurally adequate. Not even if you put rafter ties on every rafter. But I don't know what you loading requirements are down there.
Your best bet may be to put in a ridge beam. Then the forces you have to deal with are a heck of a lot lower.
Thanks for the reply.
The requirements are for a 10psf roof dead load and 20psf live load.I did run it by an engineer who told me I could raise it 1.5 ft off the top plate. I was looking to see if their were anyway I could safely stretch it a bit more.
I agree totally about running the beams, but because of the footprint of the house, I would need to install two extra lvl's which would be a huge pain to put in out there.
Your best bet would be to turn the rafters into a scissors truss by adding some 2x4s or 2x6s and a threaded rod for the vertical center member. Your eng friend could tell you how to do this and if you need to do it every rafter or not.
Thanks, I will run it by him, but do you think scissor truss'es would not work for that existing 4/12 pitch?
I've vaulted a number of ceilings such as in your situation. The biggest cost if you aren't using a ridge beam is the reduction factor per building code on rafter spans requiring a lot of new lumber to be added. For example in an area that would require single 2x8 rafters with a ridge beam, I had to use doubled 2x10s - a huge difference.
The multiplication factor for allowable span is the distance from ridge to the bottom of the new rafter tie divided by the distance from the ridge to the top plate so with the rafter tie in a normal location atop the wall plate the rafter span is multiplied by "1" and it doesn't affect the span table. As the rafter tie goes up the allowable rafter span drops rapidly. Halfway to the ridge you've already cut rafter spans in half. This is in a rather small footnote in the load tables so many remodelers overlook it, but it makes a huge difference in the cost of reframing the area.
It's also not insignificant adding the required number and size of rafter ties. You will most likely be adding two new rafters sistered onto each existing and code is a new rafter tie for each rafter with something like 12 true 16d nails at each connection. Your framing inspector may require the new rafters to be placed 12" oc so the new rafter ties match the cute clean picture in the book unless an engineer stamps something else.
A young engineer might allow any existing rafters to be considered in the rafter calculations, but in reality, the new rafters have to fight the sagging existing ones while bringing the roof back into a straight condition so they don't contribute to the strength of the framing, but rather take away from it. In the worst situations I've had bowed rafters crack in half when forced straight by the new rafters.
I'll bet this situation is the number two place homeowners and inexperienced remodelers get in trouble when opening up rooms (the first being a misunderstanding of load bearing walls and headers).
Best of luck!
Thanks for that option Don. This is such a remote area that permits, codes, or whatever is not required. However, this will be our retirement home and I want something that will be safe and stand the test of time. Fortunately, I have a custom home builder and a retired master carpenter who live in the area and hope to get their input soon also. I was also thinking about sistering some new rafters on to increase the rafter span. What I was concerned with is the span of the rafter ties in itself which would be approx. 22+-'. I was thinking about 2x8 or 2x10's and running a strongback on top of these ties. Do you think I would have any problems with these spans? and the connection between the rafter ties and rafters? 1/2 bolts? plates? what do you think? Thanks.
Everything you need to know about how to build it correctly is in the code book. If you are governed by building codes or not, they are the best way to know what size of lumber to use, and how to make the connections for safe long-lasting structures. Imagine that.
Rafter ties are normally the same size as the rafters when vaulting a ceiling - no need for a strong back of any kind. The connection is detailed in the code book - don't make up something that you don't know will work when the specifications for a solid joint are already written down just waiting for you to read. Simply use the correct number of heavy 16d nails on each connection (12?) - these are NOT gun nails.
I just caught your reply Don, appreciate the advice. Fixing to order my 2006 IRC book.
A couple of questions:
Are you using a half-Windsor or a full-Windsor on these ties?
If it's a Leakey house anyway, why not just tear off the roof and replace it?
Unfortunatly, even after beeing fully rebuilt, the will still be Leakey.
you could always install a structural ridge beam. this would be an option to rafter ties located in the lower 1/3 of the attic space. this would allow you to raise your ceiling height.