Building a workshop - stick frame roof vs. truss?

[lonestar]

Hi, I'm a novice builder and I'm bulding myself a 24' x 24' workshop. I'm considering stick framing the roof vs. trusses roof for greater attic space / storage/ possible office etc.

My first question is should I use 2x6 or 2x8 for the ceiling/floor joists (24' span)?

After the walls are up should I then place the ceiling/floor joists then lay 3/4" ply before I start on the roof?

What size should my ridge Beam be to span the 24'

I am unsure as to the process of installing the ridge beam. I have seen 4x4's at each end with the ridge beam set on top but how are the 4x4s attached?

Doesn't the ridge beam support prevent a window going in the middle of the gable end?

Are / can the 4x4's be removed after the ridge beam is set and the rafters are in place/

Any alternative suggestions are appreciated.

I received an estimate of $1500 for trusses 24" O.C. with an attic built in but this also requires an 8/12 pitch vs a 6/12 if I stick frame it.


Am I killing myself here or should I just go with the trusses?

Thanks

Regan

[Richard A Hetzel]

You're not killing yourself, but you are kidding yourself. Neither 2x6 nor 2x8 can possibly span 24 feet as ceiling joists, much less as floor joists supporting storage or office. I do not think a 24-foot span can be achieved with sawn lumber. Deeper composite joists may do it, and the lumber yard can possibly get the joist manufacturers to design them for you.

A ridge in a normal roof is not a structural member, and does not require support at the ends, except for temporary supports during construction. A ridge is essentially nothing but a nailer for the rafters.

A ridge beam is different. It is structural, and requires support at the ends. A ridge beam which spans 24 feet will be a chunky pair of LVL's at least. If the rafters will not be tied at the bottom by ceiling joists, or when the rafter spans are too great for a normal ridge, then a ridge beam is necessary, but one shouldn't be necessary spanning 24 feet.

Since you seem to have little aptitude for structural design, perhaps a better choice would be trusses, where the design is done by the truss manufacturer.

[lonestar]

Thanks for your answer Richard,

So, If a ridge beam is not necessary for the 24' span, what should the ridge board size be? I'm assuming the rafters can be 2x6.

Also what would should the ceiling joist size be?


I may end up going with the trusses but I'm looking to optimize the space in the attic.

Thanks again
Regan

[Richard A Hetzel]

A ridge is typically one size larger than the rafters. The rafter size can be obtained from tables in the building code. They will depend on the species and grade of lumber used, and the snow load you must design for, but 2x6 will probably be inadequate.

The ceiling joists for a 24-foot span are beyond 2x12. You'll have to get into composite joists, and then there will be some choices.

[lonestar]

Thanks again Richard,

Can I attach a 2x4 brace approx 6' in from the wall and tie in the ceiling joist to the rafter? Would this in effect decrease my "span" to 12' and allow me to use a 2x8 ceiling joist with 40 psf live load limit?

[Richard A Hetzel]

No. It just transfers floor load to the rafter, which would then probably have to be increased in size.

[concretemasonry]

lonestar-Based on your replies, it appears you are looking for an excuse to use the members you have already determined without providing any information on location (codes, snow, wind, seismic), without paying for a complete design (aka DIY anyway possible).

Dick

[lonestar]

concretemasonry

I don't really have anything predetermined other than I want a usable attic space. I live in San Antonio so there is no snow and winds are rarely above 10 mph. The truss mfg guy said he could build trusses out of 2x4s with a 40psf live load suitable for storage with a 12' wide by 8' high room with 8/12 pitch for $1500.
I'm just considering stick framing it to avoid such a steep pitch and save some $

[Don_P]

The trusses in this case are going to be far and away cheaper and stronger due to the 24' clear span desired. If there was a load bearing wall down the middle that equation might change but for longer than about 16' clear span its hard to beat a truss. I think he'll be 8' just down the center and about 4' at the sidewall of his attic room.

[Richard A Hetzel]

So, use 16" deep composite joists of the right strength, 2x8 rafters, a 2x10 ridge, and good luck building it so that the tops of the floor joists don't protrude above the rafters...and you can't cut them. I doubt that will be cheaper than trusses, and there is still that one problem to solve. The trusses are the way to go. Dimension lumber can't span 24 feet no way.

[Joe Carola]

So, use 16" deep composite joists of the right strength, 2x8 rafters, a 2x10 ridge, and good luck building it so that the tops of the floor joists don't protrude above the rafters...and you can't cut them.

Richard,

He can nail a box on the joists, a plate on top of the joists and nail the rafters on the plate with hurricane ties, angled braces or a kneewall under the rafters.

[Richard A Hetzel]

Yes, and he will need squash blocks in each joist, also, and probably web stiffeners. There is a lot of stuff that has to be done just right, and I doubt it would be cheaper than trusses.

[Joe Carola]

Yes, and he will need squash blocks in each joist, also, and probably web stiffeners. There is a lot of stuff that has to be done just right, and I doubt it would be cheaper than trusses.

Richard,

When I frame on top of the joists we have decking down and then add the plate, so you don't need any squash blocks or web stiffeners because it's just like framing the first and second floor floor joists.

[lonestar]

So Joe, Are you saying that after running the joists (2X?) I can lay the decking on the joists then add a plate on top of the decking then tie into the rafters?

If so, what size would I use for the joists and rafters?

[Richard A Hetzel]

When I frame on top of the joists we have decking down and then add the plate, so you don't need any squash blocks or web stiffeners because it's just like framing the first and second floor floor joists.
I'd like to see that in writing from the joist manufacturer.

And once and for all, 2x joists will NEVER span 24 feet. Never.

[Joe Carola]

I'd like to see that in writing from the joist manufacturer.

Scroll down to 2b. When using I-joists with a rimboard, you don't need any squash blocks or web stiffeners. Every house and addition I frame, I've never used them once. Just solid block under point loads in 2e.

http://www.norbord.com/images/ijoist_guide.pdf

And once and for all, 2x joists will NEVER span 24 feet. Never.

We're talking about I-joists not 2x's. 2x's WILL span 24' if used as ceiling joists in a garage. I've framed many 24' garages with 2x's and double rows of strongback for ceiling joists. I've also used vertical 2x's going from the strongback and ceiling joists to the rafters.

[Don_P]

A quick check in the book, Table R502.3.1(1)
Southern Yellow Pine or Douglas Fir #2 or better on 12 inch centers will span the 24' with a 30 psf live load as a FLOOR joist ;).

Deflection is going to push an inch.

Sizing the rafters requires the snow load in pounds per square foot.

Rafters on the floor requires details not prescribed in the codebook. Outward thrust on the tails needs to be restrained. This is usually accomplished by nailing the joist alongside the rafter tail. When you set up on top of a floor deck that restraint needs to be provided by something of equivalent strength. A typical hurricane tie and a kneewall don't do that, a brace would probably need to go through the floor to lap onto the joist. There are Simpson straps that could do that also. A kneewall supporting any of the roof load on that 24' span is out. The inspector needs to be on board with any of that.

[Joe Carola]

So Joe, Are you saying that after running the joists (2X?) I can lay the decking on the joists then add a plate on top of the decking then tie into the rafters?

Only if you're using it for storage space. Since you said this.

Hi, I'm a novice builder and I'm bulding myself a 24' x 24' workshop. I'm considering stick framing the roof vs. trusses roof for greater attic space / storage/ possible office etc.

You can't use 2x's for Office space. The last 24' garage I framed with a room above, I used 3-1/2 x 14" I-joists @ 12" o.c. This was all spec'd on the plans, so I can't tell you what you can use.

[Joe Carola]

A quick check in the book, Table R502.3.1(1)


Rafters on the floor requires details not prescribed in the codebook. Outward thrust on the tails needs to be restrained. This is usually accomplished by nailing the joist alongside the rafter tail. When you set up on top of a floor deck that restraint needs to be provided by something of equivalent strength. A typical hurricane tie and a kneewall don't do that, a brace would probably need to go through the floor to lap onto the joist. There are Simpson straps that could do that also. A kneewall supporting any of the roof load on that 24' span is out. The inspector needs to be on board with any of that.

Don,

I frame rafters on top of 2x joists that have a box with one or two plates using just hurricane ties with and without a kneewall.

I frame rafters on top with no hurricane ties and just angled braces along side the ceiling joists.

I frame rafters on top of the joist and decking with hurricane ties and no kneewalls.

I'm not the Architect or Engineer, but this is how I have framed them so far. I think I used bolts about 10 years ago on a hip roof that had angled braces going into the ceiling joists.

[lonestar]

Hey Don, I looked up the table and it looks like you are correct! I can use 2x12 douglas fir #2 to span 23' or #1 to span 24' 8" on 12" OC.

I'm assuming I can still use a 2x6 rafter with a 2x8 ridge board?
No snow load here in south Texas

I would plan to build a knee wall to close in the room but It sounds like it cannot transfer any of the roof load. How would I accomplish this other than leaving a gap between the top of the knee wall and the rafters?


Thanks for your help

Regan


A quick check in the book, Table R502.3.1(1)
Southern Yellow Pine or Douglas Fir #2 or better on 12 inch centers will span the 24' with a 30 psf live load as a FLOOR joist ;).

Deflection is going to push an inch.

Sizing the rafters requires the snow load in pounds per square foot.

Rafters on the floor requires details not prescribed in the codebook. Outward thrust on the tails needs to be restrained. This is usually accomplished by nailing the joist alongside the rafter tail. When you set up on top of a floor deck that restraint needs to be provided by something of equivalent strength. A typical hurricane tie and a kneewall don't do that, a brace would probably need to go through the floor to lap onto the joist. There are Simpson straps that could do that also. A kneewall supporting any of the roof load on that 24' span is out. The inspector needs to be on board with any of that.

[Richard A Hetzel]

2x's WILL span 24' if used as ceiling joists in a garage.
He was talking about an office and storage up there, so that's at least 40 psf live load. He can build it with 2x12's on 12" centers with good wood, and only have something more than an inch of deflection. Wow. And at what cost for premium length 2x12's for a substandard floor? Whjy not hang a trampoline up there and use that for a floor...it'll probably be stiffer.

Some people just don't want to listen, so in that case, I stop talking.

When using I-joists with a rimboard, you don't need any squash blocks or web stiffeners.
That all depends on the concentrated loads coming down on the joists. The TJI catalog I have calls for them under certain loading conditions, and my guess is a 24-foot roof might produce those loading conditions.

[Joe Carola]

That all depends on the concentrated loads coming down on the joists. The TJI catalog I have calls for them under certain loading conditions, and my guess is a 24-foot roof might produce those loading conditions.

Richard,

How does a 24' roof sitting on I-joists produce more of a load than a two story house that has first floor walls, second floor joists,second floor walls and roof? Or a one story 24' wide house that has first floor walls and a roof sitting on top of the joists? Both one and two story houses don't require squash blocks or web stiffeners on the outside walls.

Why would a 24' wide roof require squash blocks or stiffeners?

[Don_P]

Lonestar,
There is the beauty of "design". You pick a load path and design to that, the codebook then says you build to that load path.

Real life doesn't care what you call the load path, it chooses the real load path. Those two are supposed to be the same. So, you are right in building the kneewall short. Never seen that done though. In reality we build multiple load paths. When something unintended becomes load bearing it can do funny things if that element isn't strong enough. I've realized after a tug not to open a door or I'd be wearing the second floor. Termites in the wall had turned it into a load bearing column.

In this case if the floor takes roof load you're in trouble. If it was mine I would tie the kneewall studs to the rafters and floor well. Here's where we're gonna send that deflection packing :). IF you design each kneewall as a 24' girder and in effect suspend the floor from it...
On the backside run an angled brace from the top of the wall in the center, nailed across the backsides of the studs down to the exterior walls. Sheath the face in well nailed osb, making a roughly 24'x4' tall girder truss out of each.


Joe, I'm not going to say I haven't built with rafters on a plate on a raised floor either. Nor am I going to say millions haven't been built that way, but it is usually wrong. I wasn't corrected till I took a class under Dr Woeste. This is hopefully gonna be clearer than mud.

In a typical ridgeboard roof, the vertical gravity load is transferred down the rafters along their axis. This produces a horizontal force at the level seat cut trying to push the walls apart or slide the rafter off the wall. The codebook calls for the ceiling joist to be firmly attached to the rafter if you are building prescriptively. Look up table R802.5.1(9) titled "Rafter/ceiling joist heel joint connections". In that table you will find how many nails are required between the rafter heel and the cj according to to slope, span and load. Notice nail size.

If you nail a plate to the floor and then nail the rafter to the plate... you've got 2 or 3 nails in the connection, those holding the plate to the floor, resisting the horizontal component of the load. In the table, it is a rare connection that takes that few nails.

Doing the math for this particular situation it needs at least 6 .131 gun nails. There is about 500 lbs thrust horizontally. The typical hurricane ties are rated for uplift but do not restrain in that thrust direction. Check their load direction before thinking they will prevent thrust. Framing angles can work if they can get adequate nailing. Angled braces or straps can also do the trick.

This is the math I was taught for that situation put into a calc, it's more conservative than the codebook though. That isn't usually a bad thing, you'll pull the trigger a couple extra times or go to a slightly oversized strap or brace.
http://www.windyhilllogworks.com/Calcs/Sloped%20Rafter%20Design%20for%20Bending1.htm
The span is the span of each rafter, half the bldg width.

edit; Table R802.5.1(2)
SYP rafters on 24" ctrs... #2 2x6 can span 12'3"

[Richard A Hetzel]

Richard,

How does a 24' roof sitting on I-joists produce more of a load than a two story house that has first floor walls, second floor joists,second floor walls and roof? Or a one story 24' wide house that has first floor walls and a roof sitting on top of the joists? Both one and two story houses don't require squash blocks or web stiffeners on the outside walls.

Why would a 24' wide roof require squash blocks or stiffeners?
Like I've said, I want to see it in writing from the manufacturer. I hear people say "I do it all the time" all the time, and guess what, they are often wrong all the time.

[Joe Carola]

Like I've said, I want to see it in writing from the manufacturer. I hear people say "I do it all the time" all the time, and guess what, they are often wrong all the time.

Richard,

You're an Architect, how do you draw one and two story homes using I-joists? How have you drawn a set of plans with rafters sitting on top of the joists? When you draw plans using I-joists, do you have it in writing the manufacture that you have to use squash blocks and web stiffeners on outside walls?

I can say that I frame like this all the time because I frame off Architectural plans approved by the town using I-joists. I've never once had to put squash blocks and web stiffeners on the outside walls before, and never seen it in writing that I had too. So far the way I've been framing is right.

[Richard A Hetzel]

My Trus-Joist McMillan catalog clearly shows that squash blocks are required when load is coming down from above. Look at the detail in the center of Page 8 of their online catalog: http://www.ilevel.com/literature/TJ-4000.pdf

Approved by the town means nothing. You don't for a minute believe they check such things, do you? A detail should have been shown on the architect's plans, or at least he should require that the joists be installed in accordance with their manufacturer's written instructions, and if he did so, he is covered, and he who installed them incorrectly is not.

[Joe Carola]

My Trus-Joist McMillan catalog clearly shows that squash blocks are required when load is coming down from above. Look at the detail in the center of Page 8 of their online catalog: http://www.ilevel.com/literature/TJ-4000.pdf
.

Richard,

Page 8 shows an interior wall, not and exterior wall like I'm talking about. Scroll down to page 10, it clearly shows that you don't use squash blocks or web-stiffeners on an outside wall with rimboard like I've been talking about.

[Richard A Hetzel]

You're right, Joe, sorry...I was mistaken.

[luftweg]

I was wondering why no one has considered using some sort of steel?
Say 14 or 12 guage -- which can also be constructed in 'I' or 'boxbeam' configurations if needed. I think you'll find that a 12 guage, 12 inch deep x 2.5 wide steel joist at 16OC can span 24' at l/480 deflection with 10 dead, 50 live load)...

Or, what about constructed wooden box-beams? You can make up these very deep (up to 48"), with marine plywood as webs (staggered) on both sides of dimensional lumber flanges (chords) and web supports (though, for a single 24 foot boxbeam, flanges would have to be doubled up to bridge gaps)... Say, stagger 16 foot and 8 foot, 2 x 6 flanges, top and bottom, with 2 x 6 web supports, with 3/4" staggered marine (or baltic birch, if you're rich) plywood.... A 16" deep boxbeam may be more than enough (may be able to go 14")...
Ahh, but this would all have to be approved by any inspectors, and although they are not too too hard to construct, it would still be somewhat time-consuming... Might be more desirable to just go for manufactured trusses....
doh!... Also bearing support through the lower wall might need to be bolstered in ANY event....?...

Why not just put posts and a center beam under the middle of ceiling joist span if you're trying to go cheap, and the ridge beam above, so you can gain the open space.....?

[bighammer]

holy sh*t, are you kidding me..an Architect admitting he was wrong..glad we have that in writting...lol....Richard you are very talented and I am glad that you are even wrong..sometimes.....=)