Ceiling Beam

[TCR]

I'm getting ready to put walls up on 20 x 30 single story and thinking of using a beam from the bedroom/kitchen wall to the to the 20 ft wall to support 2x8 rafters so later we  might use the space above. looks like 20ft span. any thoughts?

[grover]

No answers???
Google LVL (laminated veneer lumber).  That would be what you should probably use for a ridge beam.  It also has to be well supported on each end because it carries a lot of weight.  I'm no expert but that's what little I've learned.  A lot of the requirements depend on where the cabin is located.  Snow loads, wind,...all that technical stuff.

[flyingvan]

Here's mine, it spans 20'--

It's a 6" x 12".  I guess technically it doesn't span 20' because I supported it at the 8' mark.  It was very heavy.  You can see the big twist in it.  I had to bolt boards to both ends and pull it straight with ratchet straps until the rafters were in.

Come to think of it, my first build had a 20' span.  I used a parallam beam for that, 4" x 12" I think...The parallam beams are very heavy, but don't tend to twist which is nice.  However----the tycos needed to nail in the joist hangars sure don't go in easy like with regular lumber

[UK4X4]

You need to look at the expected loads- ie usage

Then have your local supplier size it, do a sketch of where it will be in the house design and your local lumber yard can size it for you

These days there are many options- from ugly lvl to nice looking glue lams

If you can manage a support then the required size comes down

I have a large beam spaning 36ft but has two posts under it supporting a full upstairs, its a glue lam as its fully in view

You can see it in my build page 2-3

[John Raabe]

TCR:

Also note that if you will have a mid-span support post that the load it carries needs to have solid bearing all the way down to a good sized footer at the ground. Sizing the beam and footer will involve a load trace calculated with your local loads. Your lumber supplier may be able to do this or it would be a small consult with an engineer. The engineer may even have some other ideas that might be less expensive or easier to build.

[TCR]

I have 2 sets of block support in the crawlspace supporting the built up beam, similar to squirl's but with 4 2x8's ,but I may just use 2x12 ceiling joists 24oc with a drop ladder spanning the 20ft way with 2x8 rafters 10/12 pitch.

[MountainDon]

TCR, maybe it is just me but I am having trouble following your word pictures as to what you have already done and what you want to end up with. Drawings with dimensions or photos would help me out.

[TCR]

The ceiling rafters will go the same as floor rafters but 2x12 spanning 20 ft wide. I was trying to figure out a beam so I could use 2x8 instead of 2x12.

[UK4X4]

whats the floor plan beneath where you want the loft ?

as I'm certainly confused !

[John Raabe]

See if this is about what you want to do...



If that is right then the beam needs support at the third point of the house. Looks to be about right for your interior pier.

[TCR]

John the beam is the right direction, only I want it 1st floor to support ceiling joist that maybe later turned to living space. The joist would look like squirl's he used 2x8  I wanted to keep the open living space but not the cathedral ceiling. I may just use 2x12 ceiling joist to span the width, I didn't think 2x8 would support a floor without a center beam .
and I will use a higher pitch than he did
maybe 10/12 or 12/12.  and 2x8 roof rafters.

[John Raabe]

The above image is using attic framing where the rafters and the attic floor joists are connected to each other and spiked to the top of the walls. You may need a beam under the middle of the attic floor joists especially if you raise the pitch and use the space as a loft.

I think the best advice for you at this point is to work with a local builder who can come out to the project and help you figure out where to go next. The communication and mixed terminology is causing confusion here.

[Squirl]

You are right.  2x8 ceiling joists/rafter ties could never support a floor at 24" O/C with a 20 foot span.  There are a whole bunch of handy dandy charts for this.

My own is for a 1 story.  The ceiling will support only the drywall and insulation so I used:
TABLE R802.4(1) CEILING JOIST SPANS FOR COMMON LUMBER SPECIES (Uninhabitable attics without storage, live load = 10 psf, L// = 240) http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_sec002_par023.htm

For a dead load of 5 pounds per square foot and 2x8 spf number 2 ceiling joist can span 18 feet 9 inches.  Because I have 2x10 walls my ceiling joists span 18'-5.5", just under.  They bounced around like crazy while walking up there. 

If you wanted it as a future storage attic you would use chart:
TABLE R802.4(2) CEILING JOIST SPANS FOR COMMON LUMBER SPECIES (Uninhabitable attics with limited storage, live load = 20 psf, L// = 240)
The highest the chart goes is 2x10's, but at 3' per 2" increase a 2x12 would probably span a little over 19 feet for a 20 pound live load.

If you are going to have it as a habitable attic, they are not just rafter ties/ceiling joists, they are floor joists too.

Many people use the lower design value of 30 pounds per square foot for habitable attics vs. the 40 pounds for a full floor.
TABLE R502.3.1(1) FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES
(Residential sleeping areas, live load = 30 psf, L/Δ = 360)a
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_5_sec002_par011.htm

The only 2x12 that would pass at 24" on center for a 20 foot span would be if you could get some Number 1 southern pine or select structural (hard to find and expensive).

If you are doing 2x6 studs you can span 2x10's 12" o/c 19'-0".

If you put in a center beam under the joists, a 2x8 24" would be the right size.

When a beam is supporting a floor above it, it becomes a girder.  There are charts for that too.
http://countryplans.com/smf/index.php?topic=10511.0
You would probably use: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_5_sec002_par015.htm TABLE R502.5(2) GIRDER SPANSa AND HEADER SPANSa FOR INTERIOR BEARING WALLS
The problem is you proposed a girder span of 20 feet without supports.  That is off the code charts and would need engineered lumber such as lvl, gluelam, psl, etc.

From your picture you only have two center posts.  If you put the post for the habitable attic over that, the weight of the two floors would probably overload the footing for that center post.  You would need to do a lot of calculations to make sure.

[TCR]

Thanks squirl, I think you understand, your project is what I looked at when starting mine.

TC

[UK4X4]

Just ran some numbers- spanning 20ft is never easy- really need a support somewhere to bring the loads down

heres with 12 dead and 30 live usable attic

2x10's at 24OC hem fir no 1---fails ---1.5" on its own and if you live load 2" dips in the middle-moment fails too with twice allowed
2x12's at 24OC hem fir no1 ---fails ----0.8" and 1.08" with the live load- moment fails too with twice allowed

Looking at TJI 230 engineered joists

11 7/8" ones fail just with 0.558" deformation at dead load and 3/4" with live

The only ones I could get to pass- and thats with a low feeling score were 11 7/8" TJI 560's on 16" centers


Sure you cant have a beam resting on a wall or post where the edge of the loft is ? then run joists the 10ft to the back wall ?

I have an upstairs loft on my build- its an open ceiling 4x8's spanning 13ft over a central wall 26ft wide building- could have gone 6- but was bigger for looks

[MountainDon]

Sure you cant have a beam resting on a wall or post where the edge of the loft is ? then run joists the 10ft to the back wall ?

I might not be understanding that suggestion/question correctly,   but the joists, if being used to tie side walls together should be running across the width. They won't do that if running perpendicular to the gable end wall.

[UK4X4]

I was concidering only the floor- not the roof !