Trusses vs Stickbuilt

[buening]

Unless you are familiar with the IRC/IBC or build homes for a living, I would highly recommend buying pre-manufactured trusses. Even if you are out in the country where inspections are minimal, if you have any collapse due to roof or attic loading you will not likely get an insurance payment. If anyone is in the garage at the time of collapse, you'll likely have a hefty lawsuit against you for failure to comply with building codes.

There are ways (as have been discusses already) to avoid using trusses, but be prepared to get out your wallet because it won't be as economical. As a structural engineer, you would be amazed at what I have to clean up from Bob the Builder who thought he could use his backyard engineering to fabricate something....only for it to fail and then cost him 4x what it would have if done correctly.

 

[buening]

H

As a fireman, I can tell you that we are very cautious about interior fire attacks if there are lightweight trusses involved.

At what point do you see the truss in a garage during a fire (assuming it has a finished ceiling)? A 2x6 stick framing compared to a 2x4 truss may last a slight bit longer, but wood is wood and if the fire has gotten to the roof then an extra 1.5" isn't gonna add much time. That's just my opinion though.

 

[blkhonda1991]

At what point do you see the truss in a garage during a fire (assuming it has a finished ceiling)? A 2x6 stick framing compared to a 2x4 truss may last a slight bit longer, but wood is wood and if the fire has gotten to the roof then an extra 1.5" isn't gonna add much time. That's just my opinion though.

i believe drywall itself has a rating of 1/2 hour for 1/2" and 1 hour for 5/8"

 

[KMR Construction]

as far as span you would need a 2x12 hem fir 16" o.c. for the ceiling joist thats a 20lb live load and 10lb dead load

 

[Skyline]

At what point do you see the truss in a garage during a fire (assuming it has a finished ceiling)? A 2x6 stick framing compared to a 2x4 truss may last a slight bit longer, but wood is wood and if the fire has gotten to the roof then an extra 1.5" isn't gonna add much time. That's just my opinion though.

I did say that a finished ceiling can add the fire protection you need. But wood is not wood. One of the main fire concerns with lightweight wood trusses is the connection points. In a fire, the metal connection straps fail VERY rapidly. Once one connection goes, the whole truss goes. While a conventional framing system can take a pretty good fire load before collapse, a lightweight wood truss will fail in a few minutes.

I have seen many structures where these trusses are left exposed, especially in garages, so that was the reason for my post.

 

[hidollartoys]

as far as span you would need a 2x12 hem fir 16" o.c. for the ceiling joist thats a 20lb live load and 10lb dead load

My IRC does not list 2x12 in joist span tables. 2x10 is the largest listed??????

 

[sharage71]

Hidollar,
Thanks for that info but I'm feeling somewhat confused on how to use the conversion factor. My shop would be 24' wide. Can you give me an example of how the conversion works? Could I use a 2 x 6 x 20' and make a rafter tie? Would I need to go to a 2 x 8?Looks like it would make the ceiling approximately 2 to 3 foot higher. Trying to cut costs but I want to be safe and pass inspection also.

 

[Doug B]

http://www.garagejournal.com/forum/showthread.php?t=25411

Check out this guys framing....it might work for you.His garage is wider,also.

 

[hidollartoys]

Sharge, Your first post questioned the "ceiling joist" span. Are you talking "ceiling joist" or "rafter"? These are two different structural members. The two span tables are different. Could you verify which you are questioning? This thread has mixed Joist and Rafter so I can see how you might be confused.

 

[sharage71]

Sharge, Your first post questioned the "ceiling joist" span. Are you talking "ceiling joist" or "rafter"? These are two different structural members. The two span tables are different. Could you verify which you are questioning? This thread has mixed Joist and Rafter so I can see how you might be confused.

Hidollar,

The question is about the horizontal member that connects the two walls from spreading. The rafters are not in question. I would like to raise the joist up to make a 20' collar tie ( cathedral ceiling ). This would allow me to save a dollar plus get extra headroom and maybe some light storage ( depending on the size of the wood ). Doug B sent me the link to a build that will be similar to mine. I would like to do it stick built but purchasing the longer span seems expensive ( 24' ). From what I've read trusses are great if you don't want any storage. If you want storage and trusses then you shell out anyway.

 

[hidollartoys]

Sharge, I understand the issue now. If you use rafter ties you have to de-rate the "rafter" span. Meaning you have to up-size the rafter. As you move the rafter tie higher away from the wall top plate the span capacity of the rafter is reduced. The table does not allow for a rafter tie to be placed above the wall plate heigher than 1/3 of the total ridge height. On your building , if the ridge height is 6 feet (assuming a 6/12 pitch) then the rafter tie cannot be more than 2 feet above the top plate. Again assuming a 6/12 pitch ,the rafter span figures to be 13.25 feet. Look at the span table and determine the rafter size and spacing to span 13.25 feet. but you have to use a conversion factor which reduces the span by .67 (span in feet per table X conversion factor = actual span). This actually requires you to "up-size" the rafter or decrease the rafter spacing. Be sure that you use the right table for your application which takes into account live load, dead load, snow load and ceiling application.

If you PM me with your phone# I will contact you and assist in sizing based on the 2006 IRC.

Mike

 

[sharage71]

Hidollar,
I PM'd you with my number. From what I've drawn on graph paper it looks like a
20 foot "rafter tie" would only move up 1 foot vertically giving me a 9 foot ceiling.

 

[sharage71]

Hidollar,

Thanks for your help in detemining the rafter span. Your knowledge was most helpful !!

 

[hidollartoys]

Thank you for the kind words. Happy New Year.