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Author Topic: Feedback: Foundation, Wall, and Roof design  (Read 540 times)

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Offline SPDM

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Feedback: Foundation, Wall, and Roof design
« on: January 22, 2017, 01:09:13 pm »
Greetings,

The forestry forum has been a fantastic resource to me. Based on the information posted, I now know how to use SketchUp, how to design mortises and tenons in SketchUp, and I even built a few simple timber framed structure. The journey up to this point has been fun and educational. I believe that I am finally ready to take the next step; build my own timber framed house based on Jack Sobon's book.

I came up with a few drawings of the foundation, wall, and roof systems. These are my initial draft. Having never design a house, I could be way off. I seek your feedback on the designs. Hopefully this will also contribute to the body of knowledge on the forestry forum. At the very least, point to the "what not to do" as I discover them myself.

Foundation design:


Roof Design:


I removed the the tie beam to better see the profile of the roof/insulation.

Some design consideration and explanation:
  • I wanted 2' of overhang to minimize rain hitting the siding as I will be using board and batten
  • Code in my area is r17 on walls/foundation and r49 for ceilings,
  • The 2x4 on the roof are skinny side up to minimize the height of the facia board (not sure if this is a wise idea or not),
  • The above grade portion of the foundation will be parted,
  • There will be 11 rows of concrete blocks, and
  • Most of the 2x4s will be store bought however I do have a sawmill which will enable me to mill true 2x whenever required.

Any feedback would be greatly appreciated. I am sure some of the design decisions I made will leave some of you wondering what the heck. My only explanation for these is that I don't really know any better (yet).

Thank you
Shawn

Offline ljohnsaw

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #1 on: January 22, 2017, 01:28:41 pm »
Nice SketchUp work!

From a construction perspective:
(disclaimer - I am not a builder by trade, just a DIY guy that has built a lot of stuff and learned from my mistakes...)

I see a problem with the actual enclosing your frame.  You show wrapping from the inside out starting with sheet rock.  That means you need to quickly apply all your layers before you get any weather.  That could be daunting.  Others have suggested that you fir out your stud wall with some 5/8" plywood strips to allow you to come back later and slip your 1/2" sheet rock behind your timbers.  Make sense?

On your EPS sub grade?  Is that sub-grade rated?  Do you/should you provide some sort of sheet covering (like house wrap)?

So your beam that the rafters are sitting on is cantilevered out via tie beams?  It makes for a great way to keep your insulation envelope intact but does two things - make for a somewhat weaker roof and hides a large structural element.  Why hide it?  Isn't that why you are doing timber frame - to show off the wood?

On the roof, you probably should extend your rafters down to the end of the eaves.  That looks  a little weak with the 2x4s.  You get snow, right?  What will the roof be, metal?
John

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64'

Offline SPDM

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #2 on: January 22, 2017, 02:10:53 pm »
Thank you John for the great reply.

The 5/8 plywood strips are brilliant! It would certainly relive the stress of having to quickly put up the wall sheeting for fear of weather. The 5/8 strips are placed on the perimeter and the felt goes directly against the strips of plywood? Just build out from there?

I choose the drop ceiling insulation design to increase the R value and prevent having to heat the attic area. However, your concerns about snow load definitely resonates with my gut feeling (65 psi for my area). Switching to an insulated roof design: I could re-gain the view of the joinery and a third usable floor. However I would have to heat the attic.

I will definitely be using metal roofing - I don't want to have to climb back on the roof for the rest of my life!

EPS foam appears to be ground contact rated according to my research. However Type 1 EPS cannot be used under slab due to lacking in crush strength. Years ago I applied parging to my garage wall directly over the foam board with mesh support. But to be honest, I wasn't exactly paying attention to codes and best practices back then. I will look into adding a layer of house wrap it for sure.

Thanks again John.

Offline Jim_Rogers

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #3 on: January 22, 2017, 02:14:38 pm »
Current design of roof overhang:

 

 

Not sure how you're going to make it two feet.

Jim Rogers
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Offline SPDM

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #4 on: January 22, 2017, 02:47:04 pm »
Hi Jim,

I am tried recreating roof system outlined in this thread without insulating the roof. I see that I may have more work to do in figuring this out. The extra 12" of horizontal overhang will weaken the roof.

I will redraw the wall and roof insulation design using 12" of overhang.

Just as a side note to forestry forum dwellers, Jim is the one creating the timber frame drawings for me. I'm just the monkey tacking on the extra bits and hopefully not screwing Jim's careful calculations.

Thanks Jim!



Offline ljohnsaw

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #5 on: January 22, 2017, 02:51:45 pm »
Jim,
That looks good for where there is a tie beam, but how are the rest of the rafters supported between the tie beams?  They look too high to be supported by the beam that tops the wall.
John

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64'

Offline Jim_Rogers

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #6 on: January 22, 2017, 03:29:31 pm »
 

 

Each attic ceiling joist extends beyond the wall plate and then a "raising" plank is placed on top of the attic ceiling joists. The rafter foot sits on those, so that the combined load is spread out over many joists.
I'd have to take a picture of my model in order to show them better. But the rafter's are different lengths based on the location of the rafter.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline SPDM

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #7 on: January 22, 2017, 03:41:42 pm »
Working on updating the roof based on both your comments.

Here is a view of the rafter plate from sketchUp:


Ignore all the extra stuff on top of the frame.


Offline Jim_Rogers

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #8 on: January 22, 2017, 04:42:21 pm »
That appears to be it.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline SPDM

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #9 on: January 22, 2017, 04:55:45 pm »
Thanks Jim

Here is a better view without the clutter:



Offline SPDM

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #10 on: January 22, 2017, 07:07:49 pm »
Does extending the overhang weaken the cantilevered roof?




Offline ljohnsaw

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #11 on: January 22, 2017, 08:25:10 pm »
Does extending the overhang weaken the cantilevered roof?

(Image hidden from quote, click to view.)
Yes, of course it does.  You are adding additional roof area (snow load).  Is there any way you could add horizontal supports from the eve back to the wall, where you will be attaching your soffit?  That would make a pretty strong triangle shape.
John

Just North-East of Sacramento...

SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 38" cut Bandmill up to 64'

Offline Rougespear

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Re: Feedback: Foundation, Wall, and Roof design
« Reply #12 on: January 22, 2017, 11:34:33 pm »
I love you beautiful drawings - very easy to image what you're trying to accomplish.

I'm making a quick observation: I've framed many common truss roofs with an 18" overhang accomplished using trusses with a 2x4 top chord and 2' on-center and not worried about snow load.  So I don't see why you couldn't do that by simply nailing 2x4s on top of the common timber-framed rafters... if you're really concerned you could up size to 2x6s.
Custom built Cook's-style hydraulic bandmill.