Attic Trusses

[Curtis Johnson]

Allen:

Trusses can be made to carry wider spans without center supports. I changed the bottom chord to simulate a deeper bottom chord which I am sure a truss manufacturer would use to carry any required floor loads for the "attic" or "bonus" room.

Yes, it could be manually framed but a center support might be required depending on spans and planned floor loads. Totally up to the designer and/or home owner.

[Allen42acj]

Curt
In one of his post, thought he said it was going to have a floor rather than an Attic truss.

26' wide, I-Joist will make it.

[Curtis Johnson]

Allen:

It looked to me like he wasn't sure ... maybe you're right.

Yes, I joists will work. In my Boise info (Western BCI Residential Floor Span Tables), for live load deflection ltd. to L/360, a 3-1/2" x 11-7/8" BCI 90 2.0 will span 26'-6" and would need to be 16" O.C. I am sure TJI's and similar products would be rated about the same.

I am curious Allen, approx. how fast could you frame a project like this and be ready to sheath the roof, install sub fascia, etc. ... just install the ceiling joists, rafters, ridge beam and knee walls .... ? Of course I realize you may have slowed down a bit working in the office all the time and drinking .......?...... by the lake - let's assume you're in your prime and got it all together!?!

[Allen42acj]

Curt
I would say about 1 week I would be pretty much done roofing it.
About 2 days to get the attic floor on,another day or 2 to get the rafters on and sheathed.

Never promise how long it will take, Go as fast as I can and do not worry if it takes me longer than expected (I get paid by the job)..
Most people like that , if a builder has to have it done in an exact time and a few days will kill him, not someone I want to work for.

That's the problem not working, it will be a killer if I have to..

[Curtis Johnson]

Allen:

With attic trusses, and assuming a garage with an average length ... say about 30', with a crew of 3, they could be set, braced and fascia installed
in a day with sheathing on the next morning and probably the subfloor in the bonus room as well. A high ball crew that works together well could probably do better. That is the advantage of trusses.

The advantage or savings is reduced with more complex roofs where lots of hardware needs to be installed etc. and layouts and connections are more difficult. There can be added boom truck time for setting larger trusses. The cheapest truck time around here that I know of is $80 per hour with most truss companies providing the first hour or so free (included in the truss package cost).

[lbuttery]

doing plans with trusses instead of stick is far cheaper also

on an 8,000 sqft house with 12:1 pitch roofs my sub added $4000 to the estimate to do the condocs if the roof was to be stick built versus trussed.

he would have had to calculate all the point loads etc for stick built where with trusses, we added "truss specs to be supplied by vendor" and were able to submit the permit and later added the truss specs.

Lew

[Allen42acj]

Curt
I work alone..
That keeps me from working with trusses..

[tlsapp]

Allen, The first picture shows the first large attic truss being set on a 4000 sq ft plus house .
The date/ time is 9/24/2007 / 09:47:26 am. On the right side, you can see that the garage trusses have already been set that morning.

The second picture was taken the next day, the crew is starting to nail on sub- fascia. The date/time is 9/25/2007 / 09:36:36 am

This is about an average time for this size house.

[TeaMan]

Thanks Curtis. That looks like a great Idea. I'll give it a try. Funny you would suggest that I speak to my truss manufacturer. I just hung up with him before I read your reply. He is looking at how he can do just what you suggested. I didn't think I could replicate it on my software, but you proved I can, so I will try. I'll be nice to get some dimensions so I can see if I need to go to a steeper pitch.

Alan, If I can do this with attic trusses, I won't have to put floor trusses above the garage and the cost will be considerably cheaper than going that route. My only concern is insulation, but if I use closed cell foam, I can get a good insulation value.

TeaMan

[Allen42acj]

I am not saying trusses are not faster.
I thought Tea was going to to use scissor trusses over a floor system.
Then it would be like doing a Cape, why bother with trusses?

[tlsapp]

The bottom line is:
Trusses are faster and give you more design flexibility in you first floor plan,
but conventional framing will give you a lot more room and more design flexibility in your second floor plan

[TeaMan]

You guys are absolutely right. Trusses give more flexibility, but stick built or sisors trusses over a stub wall give more room. Allen, my first plan was to use stub walls and sissors trusses to give me more room. I didn't think with the 8 in 12 pitch that I could get enough head room with attic trusses. After talking to a truss manufacturer, he assured me that he could get a 7' to 1.5 foot ceiling height with 14' to 16' room width over my 23' garage. This is all I would need to do what I want up there being a media room. I think you and I talked directly on this and I appoligize for not posting that I was looking at the costs and being willing to sacrifice a bit to cut some costs.

Curtis, I have been working with the attic truss for a couple nights and failing miserably. The help article I have on them is very useful, but I'd really like to form ones like you did with a sloped ceiling. When I add ceiling planes to the 2nd floor, they show up above the roof since the roof is setting on the 1st floor walls as it should. If I draw them on the 1st floor they won't allow me to create attic trusses because of the flat ceiling rule. Even if I ignore the error message, the ceiling planes don't show up on the second floor or the bonus room area. Maybe this is a limitation with HDP 8.0 and is available in Chief. If you have any more ideas, please shoot them my way.

Hey all, I appreciate all the help here. It's been a great learning experience and gotten me a long way down the road with this issue.

TeaMan

[Curtis Johnson]

TeaMan:

In my example, on the 2nd floor level, with roof already build and knee walls in, what I did was draw a CAD line parallel with one of the roof planes and about 12" or so into the attic space to give me an idea of how far above the 2nd floor level I would need to start the ceiling planes for the vault.

Next, I drew another CAD line from the intersection of the first CAD line with the bonus room side of the knee wall and then drew it up past the center line for the room. I think I replicated these (reflec ?) to the other side as well and then pulled a measurement to the intersection of the vaulted ceiling lines from the floor to see what the ultimate ceiling ridge height would be.

Then, for my example I just assumed what I did would be OK, I drew in the ceiling planes (on the 2nd floor level). When you first do this, CA will draw the ceiling plane based on the outside wall height (my roof was drawn based on first floor wall heights so the ceiling planes used the same plate height). You need to select the ceiling plane, open the dbx, and change the settings to get it to move up in the z axis. Or, you could do more CAD line work and determine the difference between the bottom of the ceiling plane in X-section versus the elevation of the intersection line of my vault CAD line with the knee wall ... and then transform-replicate and move the ceiling plane up that way ... either way works.

Once you get one roof plane up where it belongs, you can make a copy and reflect it about the center line of the room to get one on the other side ... or ... do it the hard way as I did with the first one. Once the ceiling planes are where you want them, draw your truss and hopefully it will look similar to what mine did.

One thing about getting the ceiling height where you want it ... if you prefer more height ... is to have your truss builder put in a higher heel on each side. You could play around with this by moving your roof planes up and doing the CAD work to see how things would work.

Another option, using a combination of trusses and a 2nd level floor system to get more ceiling height is to build short outside walls and then scissor truss off of them. Your knee walls would be manually built in this case. Sometimes there are many ways to skin the cat.

I would really like to see the truss design you and your truss builder come up with for your project. If you could post a pdf or image of one of the trusses, that would be great. I am most curious about the member sizes/locations ... especially how he does the bottom chord(s).

[TeaMan]

Thanks Curtis. I had the stub walls in also as you suggested, but the ceiling planes gave me a bit of a problem. I think I understand your explanation and will give it a try.

At this time the truss MFG is looking at a flat ceiling. I'd like to get a picture to send him as yours to see if he can do a vaulted one. I think I would gain a little in height and the character of the room would improve.

We are working with a 12" energy heel which should help as you suggested. I'm not getting the look I would expect though because I'm using a 11.5" bottom chord in my example and it takes up the heel area. I am thinking I may have to increase my distance off plate for the roof to 24" to get a 12" heel above a 12" bottom chord. I'll have to give it a try, but it may mess up the rest of the roof. Maybe there is a way to do it just for the bonus room. I'll have to investigate.

I'm curious on chord sizes the MFG comes up with too. I'll definitely either post a PDF or outline them as the design shows if I can't get a good picture. I should be helpful if anyone is doing something like this.

TeaMan

[Curtis Johnson]

Teaman:

The final truss design for this sort of truss may in fact entail using different bottom chord depths in a single truss. I think I remember seeing one design on a project I did some consulting on where the bottom chords below the bonus room were either 2 x 10 or 2 x 12 and that when they got to the vertical members at the edges of the bonus room, they stepped down to 2 x 6's or something less than in the center. Your truss guy could confirm whether or not they'd actually do something like that. Apparently the "mending plates" (a Simpson Strong-Tie product) are capable of doing quite a bit of work depending on their size and location of member connections.

It would be nice if we could manually edit trusses in CA but the reality of the matter is that it is an exercise in futility as Chief is not meant to be a structural design program.

So, we have limitations of what we can do with some of the program features. That is where are ability to create CAD details comes in handy. For trusses, the easiest thing to do is to get them professionally designed and then paste in one or more of their drawings into the plan if needed or as desired.