Author Topic: 20X40 cabin - foundation plan  (Read 12558 times)

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Offline retiredmarine

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Re: 20X40 cabin - foundation plan
« Reply #25 on: September 03, 2015, 05:48:57 PM »
Ok that makes sense..I get the snowshoe visual.  Nothing hanging off the floor joists the run across the cabin (2 - 2x10x10) 20 ft wide cabin.  I'm going to hang decks off either side of the 40 ft runs for a front and back porch.  Thought I'd hang those joists off the girders.

Offline retiredmarine

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Re: 20X40 cabin - foundation plan
« Reply #26 on: September 17, 2015, 05:43:15 PM »
Ok lets move to the top of this project... straight to the top - the roof.  I found this picture and it's the exact roof I want to use.  remember the cabin is 20X40 and there is a 8' covered porch on each side.  Anyone want to take a shot at the components of this roof? engineered truss?   Thanks in advance!


Offline garyc

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Re: 20X40 cabin - foundation plan
« Reply #27 on: September 17, 2015, 06:29:07 PM »
Ok lets move to the top of this project... straight to the top - the roof.  I found this picture and it's the exact roof I want to use.  remember the cabin is 20X40 and there is a 8' covered porch on each side.  Anyone want to take a shot at the components of this roof? engineered truss?   Thanks in advance!



It looks like a standing seam metal roof. Big $$$$!It takes special tools and a crimping machine to install. The advantage to this roof is your fasteners are hidden and can be used in a low pitch roof.    They do make a snap on standing seam roof that is cheaper. menards does sells the snap on. https://www.menards.com/main/building-materials/pole-barn-post-frame-materials/steel-panels/premium-pro-snap-steel-panel/p-2044892-c-5717.htm?tid=732349041227881606
If it wasn't for bad luck . I would 't have any luck at all.

Offline Don_P

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Re: 20X40 cabin - foundation plan
« Reply #28 on: September 17, 2015, 07:40:48 PM »
Certainly can be a truss. It can also be 10' sidewalls with a ridgebeam and stick framed rafters. The porch rafters rest on the same top plate then out to a post and beam support. It can also be ridgebeam and stick framed for the main roof and monochord trusses for the side porches.  All the beams should be properly sized and supported.

Offline retiredmarine

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Re: 20X40 cabin - foundation plan
« Reply #29 on: September 18, 2015, 07:30:48 AM »
Am I reading this right?

http://www.southernpine.com/app/uploads/SS_15-20L.pdf

Table 15-30 (30spf Ground snow load)
20' span of supported roof framing (width of structure)
Clear opening 24' (the max available on the table)
3 -1/2X16 ridge

if so then with a structure that is 40'long I would need to plan a support at the 24' point of the ridge and add the remaining 16 foot of ridge to complete.

Offline John Raabe

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Re: 20X40 cabin - foundation plan
« Reply #30 on: September 18, 2015, 08:44:42 AM »
Here are some diagrams to explain how a load trace is done. You start at the peak of the roof and follow these loads as they accumulate ultimately to be carried by the foundation and supported by the earth of the site. At each step the beams, posts, joists and rafters will have certain limits to what they can carry.

You build from the ground up but design from the sky down.

One of the first subcontractors to get local help from is often a home designer or engineer. They can likely use local materials and design loads to help you make a practical support structure.

https://www.google.com/search?q=ridge+beam+load+tracing&rlz=1C1CHFX_enUS620US621&es_sm=122&tbm=isch&imgil=7_xQOX7g0HUQUM%253A%253BWRBlBCKvCsEVeM%253Bhttp%25253A%25252F%25252Fbct.eco.umass.edu%25252Fpublications%25252Fby-title%25252Fsizing-engineered-beams-and-headers%25252F&source=iu&pf=m&fir=7_xQOX7g0HUQUM%253A%252CWRBlBCKvCsEVeM%252C_&biw=1366&bih=643&usg=__j0r-7lwusYZJUkuwtuUn2LTDlgw%3D&ved=0CCkQyjdqFQoTCOey2_rxgMgCFYQDkgodzgcDPQ&ei=liz8VeePDISHyATOj4zoAw#imgrc=BGHU8baQMSlWKM%3A&usg=__j0r-7lwusYZJUkuwtuUn2LTDlgw%3D
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Offline retiredmarine

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Re: 20X40 cabin - foundation plan
« Reply #31 on: September 18, 2015, 08:50:08 AM »
John thanks.. totally get the concept and the math of load transference..  now it's a matter of choosing material that doesn't take a giant to move and still gets the job done  .. oh yea and looks nice..

Offline Don_P

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Re: 20X40 cabin - foundation plan
« Reply #32 on: September 18, 2015, 11:37:49 AM »
The looks nice part is a glulam. I rolled through your southern pine span tables quickly, it looks like the glulam they are using has a bending strength of 2400 psi and stiffness is 1.7. Off the top an LVL is going to come in around 2800 psi and 2.0E so may reduce size a bit... although the southern pine table took a load reduction I wouldn't, a pile of wet snow is heavy and it only has to happen once.

Offline retiredmarine

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Re: 20X40 cabin - foundation plan
« Reply #33 on: September 19, 2015, 08:20:43 AM »
A bit of figuring on the cost and weight of that construction has convinced me to go the truss route.  Here's what I'm thinking after looking at the truss tables.






Offline Don_P

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Re: 20X40 cabin - foundation plan
« Reply #34 on: September 19, 2015, 11:41:08 AM »
The steeper the outside pitch and the shallower the inside the stronger a scissor truss gets. It looks like a 10/12 pitch in the photo above.

I would set the side roofs on the main roof to gain more pitch, it'll hold water and fail sooner at the pitch break at those pitches. Just let the scissor designer know what you are doing. I would try a sketch at 6/12 outside main roof, 2/12 interior,3/12 sidesheds and see how high they crawl up on the main roof visually.


Offline retiredmarine

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Re: 20X40 cabin - foundation plan
« Reply #35 on: September 19, 2015, 11:56:14 AM »
Don,

If I understand what your saying you're suggesting that I use a 6/12 pitch on the main roof and a 3/12 pitch on the side sheds. And then when I attach the side sheds attach them to the main trusses instead of setting them on the wall?

I don't quite understand what you mean about the interior pitch.  Is that the pitch of the interior members - the "scissors"?  and when you say it looks like a 10/12 pitch in the photo your talking about the real photo and not my sketches right?

I'd like to keep as much openness inside as I can so I'm trying to pick something that only has enough room for insulation and no more so I can keep the ceilings high.

Offline Don_P

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Re: 20X40 cabin - foundation plan
« Reply #36 on: September 19, 2015, 08:41:20 PM »
Yes, what looks like a 10/12 to me is the original photo in the thread. If you want high ceilings inside start with a steeper pitch outside. The stresses on the members and the joints goes down as the pitch increases as well. The porch roofs will intercept the main roof faster if the main roof is steeper.  Steep roofs are not as much fun to work on.

Yes, the interior pitch is the "scissors", and yes the side sheds land on a ledger across the topside of the main roof

Offline retiredmarine

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Re: 20X40 cabin - foundation plan
« Reply #37 on: September 21, 2015, 02:13:40 PM »
Don,

When your right your right... The pros are great to deal with... truss selection ...Done!