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Double 2x6 span

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Forum topic by Clourenco posted 10-27-2017 01:36 PM 570 views 0 times favorited 10 replies Add to Favorites Watch
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Clourenco

4 posts in 54 days


10-27-2017 01:36 PM

Topic tags/keywords: double 2x6

Hi everyone,
I was hoping someone could shed some light on some stuff for me. I have a room thats 18×21. There is 2×6 for rafters and 2×6 for ceiling joists (18ft span). I want to get rid of the ceiling joists and make it a cathederal ceiling. I want to know if doubling up on the rafters is enough to support the 18 ft span.


10 replies so far

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smitdog

310 posts in 1943 days


#1 posted 10-27-2017 03:51 PM

Watch this video for why you can't just remove joists.

With nothing tying the tops of the walls together the load will force the tops of the walls apart. The video explains how a ridge beam is needed to carry the roof load.

-- Jarrett - Mount Vernon, Ohio

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Clourenco

4 posts in 54 days


#2 posted 10-27-2017 04:31 PM

This is for an intersecting roof with a 2/12 pitch. Its not an A frame roof

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Clourenco

4 posts in 54 days


#3 posted 10-27-2017 04:45 PM

Sorry, I should have explained this better. it’s a three season portch that has slow slope roof comes off the garage. in 3/4 of the room there are ceiling joist and I want to make that part catherdal so it’s all the same. Again,
The rafers are 2X6 and the ceiling joists are 2×6. I want to know if double up on the rafters will be good for a 18ft span. What do you think?

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smitdog

310 posts in 1943 days


#4 posted 10-27-2017 04:59 PM

It’s really not a simple yes or no question unfortunately. I would get a structural engineer to figure it out. That’s too major of a modification to just start changing things without really knowing where the loads are being transferred. If the joists are just there to hold up the drywall then yes, you can pull them out without a problem. But if they carry any other kind of load then no, you’ll have to figure out what is going to carry that load when the joists are out of the picture.

-- Jarrett - Mount Vernon, Ohio

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Clourenco

4 posts in 54 days


#5 posted 10-27-2017 06:32 PM

I believe it was only there to hold up the drywall as there was only some 1×2 tied into the rafters from the ceiling
joists. Would a picture help?

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jonah

1467 posts in 3136 days


#6 posted 10-27-2017 08:42 PM

One of the functions of ceiling joists is to keep the outside walls from bowing outwards. They’re not just to support things resting on them. They also add rigidity to the building, as any cross-bracing does.

I really wouldn’t recommend removing framing unless you know exactly what load is being carried by what and what exactly is needed to maintain structural integrity.

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Dark_Lightning

2920 posts in 2946 days


#7 posted 10-27-2017 09:35 PM

The new Uniform Building Code will require more than 2 X 6s. I don’t have the book in front of me, but you’re probably going to have to go to 2 X 10s. It isn’t a matter of it being strong enough like it is. The new code takes the ‘94 Northridge quake into account, for a higher margin of safety in a major quake.

I built an addition on my previous house, and was allowed to span 18 feet with 2 X 6s at 12” O.C. That doesn’t fly with the newer seismic requirements, in spite of the fact that I sustained no damage in that quake, at 5 miles from the epicenter, and in the bad direction.

-- Random Orbital Nailer

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runswithscissors

2563 posts in 1863 days


#8 posted 10-28-2017 02:34 AM

To prevent the walls from being forced out by the downward thrust of the roof, you could do as they did in the middle ages—use flying buttresses. Check out photos of Notre Dame cathedral, for example.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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JADobson

921 posts in 1948 days


#9 posted 10-28-2017 02:50 AM

you could do as they did in the middle ages

:). I studied Medieval history in school. This makes me happy.

-- No craft is very far from the line beyond which is magic. -- Lord Dunsany

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tomsteve

667 posts in 1057 days


#10 posted 10-28-2017 01:37 PM

if i read this correctly, you have a shed roof that is attached to the garage similar to this:

18’ span is quite a bit for a 2 by 6 rafter. i dont think it would even be good at 12 OC. around here, max span for a 2 by 6 rafter is 16’ using 12” spacing and SYP.
however, there are times doubling up rafters helps, but may not fly by code, which i assume youre flyin under the radar.
however, some pictures would help us help you determine the course of action to take

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