TF on split-level floor - ideas?

[ShimodaLife]

Hi All, I'm working with an architect (no TF experience) to design my mountain TF, and he has come back with a split-level concrete foundation to work from. He doesn't know anything about TF, but I'm determined to make this work, so I wonder if anyone has any experience with split-level foundations, and how to make a TF work on this base. Right now I'm looking for general ideas about how to frame this out.

You can see the cross-section below. Dimensions are in metric, so I'll approximate a bit:
Length: total length of building (cannot see): 55ft
Depth: total depth is 24ft; upper section is 9ft; lower section is 15ft
Height: height of back wall (mountain side) is 8ft; height of middle wall is 13ft (from upper base); height of front wall is 9.5ft.

Second image below is my original design, which has a clerestory roof. I wonder if I can get him back to that direction...

Thanks in advance, JT



 


 

[Don P]

What is typical for the area, can you post some local houses you like?

The rear retaining wall holding back a surcharge looks a little optimistic. The front footing seems shallow if that is fill right in front of it (single hash marks). The underfloor, is there access?, seems shallow for future service.

[ShimodaLife]

Thanks for your interest, Don. 
I don't have pics of local houses. The retaining wall (and concrete foundation) is engineered for the ground it sits on: 1 meter of loam (single hash) and 1 kilometer of solid rock (double hash). The underfloor is typical crawl space for Japan, just big enough to get plumbing an electrical in.

As for building a frame on two levels, I'm wondering if I just build it as it it were one level, but the upper posts are shorter...

Hope this helps.
JT

[ShimodaLife]

I wonder if these quick-and-dirty trials are heading in the right direction, structurally speaking. 

Some notes:
- The layout follows the dimensions mentioned in the first post, with the concrete foundation as spec'd. 
- The braces were a quick copy-paste, so are not exactly the right size, but their placement is important.
- The braces on the upper deck extend above the cross-beam, intentionally to allow more head space below.
- on the lower deck, one cross-beam is intentionally missing, as there is a small staircase there to move between levels and I need the headroom.
- as for roof, I'm thinking maybe a rafter-style (standard 2x framing, not sure of the vocabulary) to minimize the weight.

Thanks.
JT


 


 


 

[Ianab]

Looks like the braces cover each axis, so that's a good start. 

I wonder if you can incorporate the rafters into a better "triangle" with the central wall and the top plates? A roof truss is a structural brace in most construction, here you would have 2 half trusses, but the extra bracing idea would still apply. 

You need to put the rafters there, to hold the roof up, but they can also serve as bracing at the same time?

[ShimodaLife]

My architect is continuing to push the split-level design, but now we have a tri-level concept. First change of course is the height of the lower part, which is only 1.980M (6'6"). Under there is only the bathroom and a pantry, but still a little low. I haven't seen many TF samples looking anything like this, and worry there's a structural reason for it. Hmmm.

Thoughts?


 

[everythingwood]

I am not an engineer but I'll give it a go.

I think if you are building into a steep hillside a tri-level makes a lot of sense to maximize living space in a narrow building.  I see no structural reason you can't build a tri-level timber frame.  Actually a tri-level gives you even more opportunities to add bracing... making more triangles for stability.

I agree you need to increase the ceiling height in the lower level.  in your architects latest drawing the lowest level shows a post approximately mid-span.  If you put posts at these locations on the third level and bring the uphill wall to the same height you can put tie beams across the plates.  This breaks up the long run of rafters on the downhill side of the building and takes a lot of sideways thrust off of the tall knee walls on that side.  Now you have even more braces you can add.  I imagine anywhere in Japan you have to design for earthquakes and more bracing would be better.

Also, with a length of 55 feet and 6 bents your spacing between is only about 11 feet.  That's pretty short.  You should be able to do this with 5 bents, giving you a spacing of 13.75 feet.  This would give you fewer posts in your living space.  

[JRWoodchuck]

The little bit that I've read about Japanese timber framing is they traditionally don't use braces because of what happens with them in earth quakes. They use wedged through tenon mortises I believe. I know that's not the original question just something I noticed about the design. 

[ShimodaLife]

The little bit that I've read about Japanese timber framing is they traditionally don't use braces because of what happens with them in earth quakes. They use wedged through tenon mortises I believe. I know that's not the original question just something I noticed about the design.

You're right, JRW. But I'm building a western timber frame because I don't have 10 years to devote to learning the intricate cuts and tenons a JP version requires. And believe me, it's no easy task even getting this thing designed. The build itself will be a piece of cake, relatively. Thanks for the comment.