Author Topic: Several ? and Site Built Truss ?  (Read 8088 times)

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Offline peteh2833

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Several ? and Site Built Truss ?
« on: June 28, 2008, 07:13:33 AM »
I bought your 20x30 1.5 story plans. I have the piers done and will be starting to frame soon. I'm using a steel beam down the center which will rest on several piers. The beams on the outside will be 3 2x10's with plywood. The distance between each pier is roughly 7'6". Is it ok to attach the joists to the outside beams instead of placing them on top?? The joists will then go across to the steel beam. I will sister the joists together over the beam. The joists will only be spanning 10 feet. I understand the rest of the subfloor and wall framing. I have done that before. I have never done the roof trusses or gable end walls. The plans show site built trusses using 2x6x16's Correct?? I plan on making the loft a complete floor. Can I use bigger rafters, 2x8x16's and not have to sister anything to it like it shows in the plans? Will 16' material work for the rafters and what will the over hang be? I planned on using a ridge board and no beam. I will use collar ties and then I want to finsh the ceiling with tongue and grove pine ceiling. Thanks Pete Halli
« Last Edit: June 29, 2008, 05:01:13 PM by peteh2833 »
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Offline Redoverfarm

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Re: Several ? and Site Built Truss ?
« Reply #1 on: June 28, 2008, 07:54:04 AM »
peteh2833 I am not familar with the plans but IMO the 2X8 or even 2X10 would be better suited for the rafters.  The main reason would be to allow enough room for insulation.  With a 2X6 vented you will only have about 4-3/4"(with the air chase for vented) and with R-19 compressed to that demension you will drop down to a R-17-18.  Not knowing where you are at but would this be enough in the roof? 


Offline MountainDon

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Re: Several ? and Site Built Truss ?
« Reply #2 on: June 28, 2008, 08:46:20 AM »
Pete, I don't have answers regarding the joists or rafters. However, the question of compressing fiberglass insulation was raied. Here's an Owns-Corning chart chart that shows the effects of compressing...





originally posted in this thread..
http://countryplans.com/smf/index.php?topic=3527.msg39278#msg39278
Just because something has been done and has not failed, doesn’t mean it is good design.


Offline peteh2833

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Re: Several ? and Site Built Truss ?
« Reply #3 on: June 28, 2008, 09:30:40 AM »
The camp will be built in the northerwestern mountains of PA. Average snowfall is about 80 inches a year. Pete
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Offline Redoverfarm

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Re: Several ? and Site Built Truss ?
« Reply #4 on: June 28, 2008, 09:53:38 AM »
Depending on the amount of use I would opt for a bigger rafter so that you can at least get in the mid 20's to 30's R-factor.  If not you will loose most of your heat via the roof.  Your snow fall is about the same as ours maybe a little less. Another option would be to use the smaller demensional rafter and then scab 1-1/2" onto that but I don't know what the $$$ difference would be in comparison to just using larger width lumber.  If you used 2X8 and then put 2" ridig for insulation you could get the R-30 in 6" cavity plus 1" air baffle. Just my $.02 worth.


Offline peteh2833

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Re: Several ? and Site Built Truss ?
« Reply #5 on: June 28, 2008, 11:26:53 AM »
Thanks. I'll proabaly just go with the 2x8x10 rafters since it isn't much more in cost. Will 16's be long enough??
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Offline Redoverfarm

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Re: Several ? and Site Built Truss ?
« Reply #6 on: June 28, 2008, 11:54:13 AM »
peteh2833 maybe these two sites will help in figuring out you roof layout.

http://www.get-a-quote.net/quickcalc/gable_rafters.htm
http://www.blocklayer.com/Roof/

I would run it through the calculator but I wasn't sure of the pitch, overhang, gable overhang and etc.. I never used the first one as the second was more user friendly.  Just enter the info in the apprioate space and it will give you the run and the likes.

John


Offline peteh2833

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Re: Several ? and Site Built Truss ?
« Reply #7 on: June 28, 2008, 01:07:55 PM »
Thanks. I'll wait and see if John has an answer to any of my questions. Pete
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Offline John Raabe

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Re: Several ? and Site Built Truss ?
« Reply #8 on: June 29, 2008, 07:52:04 PM »
First, the floor joists. Since you are adding a mid span beam your floor joists can be 2x8 @16" or 2x10 for better insulation.

The detail I show has the joists sitting on top of the beams. That is so you can bring plumbing waste stacks down the outside wall and make a bend without having to chop out the beam. If you can layout the plumbing to avoid this I don't see any other problem - there will be a slight loss of insulation at the wall edge. (R-5 rather than 25-30).

For the roof rafters you can perhaps do the timber framed open beam ceiling that I show as an option on p. 9 of the booklet. I use 2x12 rafters there to have room for good insulation (R-30 to 38). Note that I show a built-up beam used as a collar tie with every 2nd rafter (4' o/c). That collar tie can be raised up to 1/3 the way up the rafter and still do its work of counteracting the desire of the rafters to spread at the base. If you push it higher than this you start to compromise the triangulation of the rafters. This is why I've done trusses for a higher ceiling.

However, here is a perhaps better option...

Since you are doing a full 2nd floor and will tie the outside walls together with the floor system all the length of the building, you can balloon frame with taller studs. Instead of 12' studs, frame those sidewalls with 14' studs (finger jointed) giving you a 2' higher sidewall before the rafters start up. This will give you a wider more usable upper floor and you can do a full cathedral ceiling w/ the timber style collar ties every 4'. If you set the bottom of these ties at somewhere between 6'-8" and 7' you should not be more than 1/3 of the way up the rafters.

16' material for the rafters will give you an overhang of 12" or so. You can always plumb cut the main rafters and add a 2x6 outrigger nailed into the rafter for whatever tail length you want. This can be more cost effective than getting long 2x12's and having to notch much of it out.

For your heavy snow load I would check with an engineer who can review all this and determine your slope reduction factors. If you don't want to do 2x12 rafters you will likely find 2x10 is structurally sufficient (my charts stop at 40 psf). The engineer might OK 2x8's if you have a metal roof.
« Last Edit: June 30, 2008, 06:50:39 PM by John Raabe »
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Offline peteh2833

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Re: Several ? and Site Built Truss ?
« Reply #9 on: June 30, 2008, 02:34:11 AM »
Thanks John for clarifing that. I was going to use 2x6x10's for wall studs. Should I go higher? What size joists would you recomend for the upstairs floor? I'm going to leave the floor joists exposed on the first floor. I'll do tongue and groove flooring on the 2nd floor. I'll probably go with 2x8's or 2x10's for the rafters. Thanks Pete

PS Could the trusses be built on the ground like Tennessee Pride did? It looks like he built them on the ground using 2x6's and plywood for Gussets and then used no ridge board. Is this possible? Also can the trusses be built like in you plans. 2x6's with collar ties and a 2nd 2x6 attached with a gusset? Which is the best way to do it??
Here is the link to Tennessee Pride's Cabin  http://countryplans.com/smf/index.php?topic=3194.msg34095#msg34095
« Last Edit: June 30, 2008, 10:58:33 AM by peteh2833 »
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Offline John Raabe

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Re: Several ? and Site Built Truss ?
« Reply #10 on: June 30, 2008, 07:08:11 PM »
When you do roof trusses you don't have a ridge board. It looks like TP used skip sheathing under a metal roof. They probably hoisted the trusses up with ropes and held them in place with a piece or two of the skip sheathing. There is helpful information in the House Framing book on bracing and such if you haven't done this.



When you are doing floor framing and want to expose the joist framing, and will use 2x6 T&G decking, then you can usually safely double the designed joists and place them twice as far apart. IE: the framing plan calls for 2x10 @ 16" o/c with 3/4" subfloor. You could probably do 4x10 @ 32" o/c w/ 2x6 decking.

It sounds like you may be planning a major redesign of the plans and you would be wise to work with a local builder or designer to make sure all the parts you want to change are working together and detailed properly. While CP members can give suggestions and tips, a redesign of the structure is outside the realm of help we can provide online.

« Last Edit: June 30, 2008, 07:22:59 PM by John Raabe »
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Offline peteh2833

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Re: Several ? and Site Built Truss ?
« Reply #11 on: July 01, 2008, 02:40:43 AM »
I am trying to stick to the plans as close as possible. Just trying to do it correctly. I thought the plans called for 2x12x20's on the second floor? I have the framing book by Wagner. Sometimes the probelm I run into is with the availability of materials. I went to the local lumber yard yesterday and to get 2x12x20 DF and they had to be ordered. No problem but to get any other size except for 20's I had to order the whole lot, like 100-150. So I looked into LVL's and the company recommended 2 1'3/4x11"7/8x30 LVL's on each side for the beam. Other than that I will stick to the plans. The sheet that has the site built trussess out of 2x6x16 is what I was going to use. Are they just lifted into place and supported until the roof sheathing goes on??? Thanks for the time. Pete
« Last Edit: July 01, 2008, 05:17:57 AM by peteh2833 »
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Offline John Raabe

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Re: Several ? and Site Built Truss ?
« Reply #12 on: July 01, 2008, 11:16:57 AM »
Yes, that order of 2x12's is more than you need. Remember that the plans use balloon framed 2x6 framing with the joists supported on a let-in ledger (loft floor details Sht. 5). The loft floor framing plan (Sht. 3) has a layout for double 2x12's with T&G decking on top. You could use the LVL beam suggested by the supplier there instead of the double 2x12's. Have him check the chart with a 4' spacing.

The trusses can be built on the deck of the loft floor and lifted and tilted into place. They only need to be raised over the kneewall. If you have a local truss company they can build the trusses for you. They will likely be lighter and delivered to the loft deck. You just tack a brace or two onto the trusses to hold them in place while the sheathing is nailed off.

If you do just the change above that should work fine. The problem comes when too many changes are interrelated and interdependent. Then it's easy to "walk off the plank" so-to-speak. ;)
« Last Edit: July 01, 2008, 11:30:39 AM by John Raabe »
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Offline peteh2833

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Re: Several ? and Site Built Truss ?
« Reply #13 on: July 01, 2008, 01:29:49 PM »
No other changes. They wanted me to use the LVL's for the beams on the piers but It will be cheaper to use 3 2x12's. I just haven't decieded on site built trusses or prefabed. I would like to build the site built wants like in your plans. I can use 2x6x16's and no ridge beam. If I read the plans correctly you then attach another 2x6 with gussets up to the collar ties?? Correct.
« Last Edit: July 02, 2008, 02:19:23 AM by peteh2833 »
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Offline John Raabe

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Re: Several ? and Site Built Truss ?
« Reply #14 on: July 01, 2008, 08:38:59 PM »
That interior 2x6 is not structural and can be added after the roof is up. It is there to add depth for insulation. If you used foam insulation you may not need it.
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