any carpenters here?

[feralfreak]

are there any carpenters here? ive been trying to get an answer to something on roof framing in relation to rafters and ceiling joists, but i cant seem to find one, my question is:

[Baby Brian]

I'm not licensed but I do know that normally you can NOT simply join dimensional lumber like how you're wanting. Even if they were longer, the lumber will not be thick enough to transfer the load. This is why they only come in certain lengths. Once you get longer than that, then you need to start looking into either supporting them in the middle or switch to engineered trusses/metal beams.

[kevindhca]

Factory built trusses connect the butted ends with metal plates stamped into the wood.

You can do the same thing with 2 - 3 ft pieces of wood. Butt the ends together and join with the wood on the side of the truss.

Many home built trusses use strips of plywood for the joining piece, easy and fast if you have access to an air stapler.

With any long span, be sure to use an adequate number of braces. There should be at least one V on each side of center to ensure the center of each roof face doesn't sag over time or with snow loading.

[Little_annie]

ok i ask a little builder freind i know " the joist can in no way be lap jointed to make the span.

[feralfreak]

i should have mentioned an interior wall running the length of the house, does that change anything?

[Baby Brian]

Factory built trusses connect the butted ends with metal plates stamped into the wood.

You can do the same thing with 2 - 3 ft pieces of wood. Butt the ends together and join with the wood on the side of the truss.

Many home built trusses use strips of plywood for the joining piece, easy and fast if you have access to an air stapler.

With any long span, be sure to use an adequate number of braces. There should be at least one V on each side of center to ensure the center of each roof face doesn't sag over time or with snow loading.

[kevindhca]

Those trusses go beyond just having braces like you're describing. If you look at any section you'll see that except at the corners there are always three pieces of lumber meeting at each of those plates. The angle of the cross braces matter, as do the size of those nail plates. It's all triangulated to transfer the loads correctly- and more importantly engineered.

I've also been in plenty of houses that did not have those V or horizontal braces. Most were build before they started using smaller 2x10 & 2x8 beams though (and are still standing today). Additionally, I have taken classes in Architecture and found you can do the older conventional (open attic) framing for the same cost as engineered trusses (filled in with braces). The difference is using bigger more expensive wood and cheap labor to frame it, or expensive engineering/bracing with cheaper wood.

As for your interior wall. The house I'm currently living in also has an interior parallel wall running down the middle of the house. It is NOT load bearing and my ceiling joists do run the entire length as I had described above (two 2x10's running the entire span & 24" on center). I do have horizontal bracing towards the outer ends though, but I know this is more for supporting the roof trusses though, not for holding up the ceiling joists.

Lol at engineered.

At work when we see something stupid, we know an engineer was involved.

Good roofs have been built for a long time before engineers got involved.

A roof truss is not complicated and the minimum specs for the species and dimensions of wood used are easily looked up.

Overkill is often cheaper than professional help.

As long as you stick to accepted maximum spacing like 16" centers it's going to work.

[diaper baby 76]

engineered truss is cheap if you consider your time is worth anything plus quality,I'd go to a place that builds trusses tell them your span plus linear feet that's important believe it or not and your local codes and snow load requirements are important too,sure you can scab but two boards together with 2 boards 4 ft long centered over the but joint cross nailed, but it's not code in a heavy load that's the spot it will fail regardless of the A bracing,why not spend a little have it done right!!!

[willnotwill]

We've built up beams for floors with multiple layers of dimensional lumber.

[Dill_Pickle]

My, let's see, 1930's house had a load-bearing center wall.

[kevindhca]

We've built up beams for floors with multiple layers of dimensional lumber. There are approved practices.

And no Kevin, just making sure things are 16OC guarantees squat. There's always been more to designing roof systems than that (engineered or skilled housewright).

I know what's involved, I've built many roofs.

Standard spacing of roof trusses is 24". Spacing at 16" will produce a structure that exceeds any required specifications.

The peak structure is what holds a roof deck up, not the v bracing.

For long span roof deck stringers, 2"x6" should be used. The ceiling stringer is usually 2"x4" and the v bracing is to hold it up as a long horizontal piece has a tendency to sag.

If high loads are expected, the pitch of the roof deck needs to be increased accordingly.

A well designed roof structure should have a steep enough pitch to shed the load well before any dangerous loading occurs.

The only thing a factory built truss offers, is time saving.

With a crane truck you can do the whole roof in one day.

[kevindhca]

are there any carpenters here? ive been trying to get an answer to something on roof framing in relation to rafters and ceiling joists, but i cant seem to find one, my question is:

when you have a span longer than the length of a joist, lets say 25 to 30 feet just for the sake of the question, and you arent going with ceiling trusses, just dimensional lumber, how would you connect the joists together? ive seen where they are lapped with at least 4 inch but ive only seen one side, the side where they are also nailed to the rafter and the rafter plate, but not the other side, and because of the lapping there is an offset so one joist ends up an inch and a half away from the rafter on the other side, what do you do there? is there a picture you know of that i can see?

Here's the technical reasoning why you can butt joint the ceiling stringer.

Picture the load on a triangle, as the top peak gets pushed down it tries to pull the bottom stringer outward from both ends.

Items under tension are very strong even when made of multiple pieces.

The joint just needs to be constructed in a way to make it difficult to pull apart.

A butt joint is acceptable for tension loading.

[Bettypooh]

As an expert on the subject I have to disagree with the above. I have built several roofs with rafter spans exceeding available lumber lengths and there are codes regulating what is acceptable practice for joining the sections. First is a minimum 3 to 1 (and newer codes call for a 5 to 1) ratio diagonal joint* nailed and glued with scabs in both sides which are a minimum of 3' in length past each side of the end of the joints, also glued and nailed, of the same material as the rafter. There may be only one joint in any unsupported span of the rafter and joining is not allowed where single runs of appropriate material can be obtained** A better method than a diagonal join is a "Trois d'Jupiter" which is a zig-zag joint used in timber framing that is self-locking, although you'll still need the scabs to keep the inspector happy. And of course the rafter width will have to be appropriate for the span involved. An alternative I use and prefer is to design in a double LVL beam halfway in the span, edges ripped to the roof angle, then use rafters which match that width. You get a much stronger roof that way provided you can support that beam correctly. You will have to level-notch the rafter bottoms to receive hangers at the upper side of that beam.

[kevindhca]

@Betty, the code book won't help you here, maybe physics class instead. No way is there deflection load on the ceiling stringer.

The defection load is in the roof deck transfering the load to the walls.

In fact you can build a good strong roof without the ceiling stringer or v braces.

Vaulted ceilings.

I think I can calculate loads and stress correctly. I did hang a car from the ceiling inside an auto parts store.

[Bettypooh]

Look up the word "sciolist". Lots of folks have done lots of things and gotten away with them by guessing or luck or empiracal experience. One must have knowledge to know the difference. And yes, butt joints on unsupported horizontal framing components are addressed in the Code books- better quit while you're ahead.

[kevindhca]

Don't have to look it up, already know what it means.

I never guess. Nothing I've built ever failed.

Not quite sure how calculating loads, breaking strength, load ratings, etc. equals luck or guessing.

Where I work adequate is not good enough. The work must be reinforced and armored to survive severe impact.

When people who have no knowledge or caring are using the structures, dangerous overloading is common, the installation must be able to survive excessive loads so that if failure occurs, it's the fixture that fails, not the installation.

To get the work hanging large heavy items from the ceiling in an open store with customers around, one must be able to provide evidence that all factors have been considered.

Even one little close call would mean never doing that type of work again.

Agreed, leaving the discussion for now. I believe I would like working with you. Competence is hard to find these days.

[Dill_Pickle]

Betty and Kevin:

I think the issue is confusion...the only beams that don't get deflection loads in a normal wood-framed house are the vertical ones (in first order theory only) and parts of trusses that don't support a panel, meaning not the ones that support the roof or the ceiling.

[Wet Knight]

Lol at engineered.

At work when we see something stupid, we know an engineer was involved.

Good roofs have been built for a long time before engineers got involved.

A roof truss is not complicated and the minimum specs for the species and dimensions of wood used are easily looked up.

Overkill is often cheaper than professional help.

As long as you stick to accepted maximum spacing like 16" centers it's going to work.

[Wet Knight]

i should have mentioned an interior wall running the length of the house, does that change anything?

[Bettypooh]

[BabyJune]

You'd have to use a "truss" system to distribute the load over such a long span--in other words, a series of criss-cross braces to support the load. The design would have to be approved by a structural engineer and a building inspector.

[Wet Knight]

[feralfreak]

i came up with a drawing, is this what y'all are saying would be the right way?

[Wet Knight]

i came up with a drawing, is this what y'all are saying would be the right way?

[feralfreak]

will that ceiling joist pattern work for doing floor joists? or does it matter if the floor joists are lapped and the ends of them where they are under the outside walls off by an inch and a half on one side?