Author Topic: Attic Trusses Vs. Ridge Beam and Rafter  (Read 4910 times)

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Offline ColchesterCabin

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Attic Trusses Vs. Ridge Beam and Rafter
« on: June 08, 2012, 06:22:51 AM »
Here I am planning the next stages of my build and I was wondering on different peoples opinions on truss or putting in a ridge beam with rafters. I am very virgin to building and I am looking for pros and cons of each, ventilation plus or minuses, etc.....

Please looking for honest imput on this thread.
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Offline Redoverfarm

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #1 on: June 08, 2012, 08:13:00 AM »
Here I am planning the next stages of my build and I was wondering on different peoples opinions on truss or putting in a ridge beam with rafters. I am very virgin to building and I am looking for pros and cons of each, ventilation plus or minuses, etc.....

Please looking for honest imput on this thread.

Personally I prefer engineered attic truss.  No bearing support needed.  More bang for your buck so to speak by using all the available space.  If there is a down side it would be cost associated vs. beam and rafters.  But then again maybe not.  As far as ventilation I doubt that there is much difference if standard insulation practice is followed. 

Offline ColchesterCabin

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #2 on: June 08, 2012, 08:48:51 AM »
Either way I go the design calls for 24" O/C, my new question is how many of the trusses would have to baffelled for air flow? Cabin is 1624'. Is there a formula for air flow based on sq footage or something, cause I can't see having to baffel every opening from the eaves to the attic above the top fllor???
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Offline Squirl

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Offline Redoverfarm

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #4 on: June 08, 2012, 09:11:46 AM »
I believe it is in the neighborhood of 1 sq ft of soffit vent per 150 sq ft of attic space.  If you went with a beam and truss and wanted to make a loft then every rafter bay would have to have vents. On a attic truss it would be vented to the ceiling in the loft space.  The vents are only needed if you are putting insulation that would normally close off the bay.  So if you used an attic truss w/5' kneewall then that point where the ceiling meets the rafter would have to be vented.  The area behind the kneewall up to that point would not if the kneewall was insulated.  There would be a dead space behind the kneewall that the air could move up to the ceiling area from the soffit and out.  The styrofoam vents "raftrmates" are only about $.50-.75 each and are designed for 24"OC. Some truss's can be designed with a 3' kneewall. Again same principle applies just a little longer venting from that 3' intersection w/rafters and up over the ceiling space.  Anything above the ceiling needs no baffles unless you insulate heavily which would block off the rafter bay.  Make sense?

Offline ColchesterCabin

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #5 on: June 08, 2012, 10:40:53 AM »
Yeah I have approx a 2' - 2' 6" knee wal before my trusses, 1 1/2 story so therefore kind of like a calthedral ceiline so every second rafter vented from soffet into small the small roof attic above the ceiling, correct? then if my theroy is correct I can use either a ridge vent or attive vents on the end wall?



to show what I'm looking at?
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Offline Redoverfarm

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #6 on: June 09, 2012, 03:40:25 AM »
I believe what you are showing is a "vaulted parrallel chord" truss rather than a "attic truss".  This is what I call an attic truss and what I was explaining regarding the insulation and rafter bays.  So depending on the style of the truss dictates the manner in which it is vented and insulated.


Offline ColchesterCabin

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #7 on: June 09, 2012, 05:26:44 AM »
My Bad Red, did I mention I am a virgin with all this building stuff (terminology and all!) but then the same theories would apply though wether attic or vaulted parrallel chord truss, every second rafter from soffit to above ceiling to allow proper air flow. But is there any advantages vs disadvantages. I am thinking of engineered trusses so someone elsee qualified does the load bearing math calculations plus they appear to be less labour intensive to install, stand them up and away we go.

Plus not being a huge fan of heights yet :) factors in the decision as well. this way I can put in my loft flooring brige the gaps and with my 2 foot knee wall can virtual work of the loft floor and not scaffolding, maybe a step ladder or two.
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Offline Redoverfarm

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #8 on: June 09, 2012, 07:33:57 AM »
My Bad Red, did I mention I am a virgin with all this building stuff (terminology and all!) but then the same theories would apply though wether attic or vaulted parrallel chord truss, every second rafter from soffit to above ceiling to allow proper air flow. But is there any advantages vs disadvantages. I am thinking of engineered trusses so someone elsee qualified does the load bearing math calculations plus they appear to be less labour intensive to install, stand them up and away we go.

Plus not being a huge fan of heights yet :) factors in the decision as well. this way I can put in my loft flooring brige the gaps and with my 2 foot knee wall can virtual work of the loft floor and not scaffolding, maybe a step ladder or two.

I am wondering what your pitch is.  Another question is what is the demensions of the rafter bay from the bottom chord to the top.  That may be a determining factor in the amount of insulation you can put there.  Generally R45-50 for ceilings.  That is pretty thick stuff so I am not sure how much room you will be left there for air flow.  Like I stated the baffles are cheap and they should be put in every rafter bay.  None required on the kneewall just from on top of your top plate to the ridge.  As far as vents you will have to decide.  I like ridge but others may differ.

With attic truss you need no floor joist for your second (loft) floor as they are made into the truss. But that will not work with your 2' kneewall. With the attic truss the kneewall is made in the truss and sits upon your wall top plate.

Just some more to digest.  If building was fattening we all would be over weight. ;)
« Last Edit: June 09, 2012, 08:46:12 AM by Redoverfarm »

Offline ColchesterCabin

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #9 on: June 09, 2012, 02:13:25 PM »
red design calls for I believe 11/12 pitch. the thickness of the joist appears to be approx 1ft which would require venting. I was thinking/hoping I could get away with every second rafter. I though about the attic truss but then I would lose 2' or so on each side on 16' span plus the loft look wouldn't be the same feel when you were on the first floor looking up the staircase or above the entrance when you come through the door.

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Offline Redoverfarm

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #10 on: June 09, 2012, 02:37:25 PM »
I believe that someone recently was faced with the same problem.  If my memory is correct it was in the last 6 months and the truss company made him a attic truss which did not sacrifice the space.  Might take a little looking but might be worth the gander @ http://countryplans.com/smf/index.php?topic=11727.msg157131#msg157131



Offline dablack

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Re: Attic Trusses Vs. Ridge Beam and Rafter
« Reply #11 on: June 12, 2012, 10:52:00 AM »
Yep, that was me.  When all was said and done, they are giving me 19' on a 26' span with a 4' overhang on one side (porch area) and 1' on the back.  So the width of the truss is 31 feet.  I'm getting a 19' wide room in that 31 feet.  A bit of that room will have a ceiling height of less than 8'.  No big deal.  I like the extra room width.  Plus, it is simple to set them.  I haven't gotten to that point yet, but it should be interesting. 

Austin