Timber frame top/conventional frame bottom

[roycroft]

Hi, folks.
I'm brand new here, and hope this post isn't inappropriate. I'm an experienced woodworker, but have never done any timber frame construction. I bought a new house a year ago that has a small shop, which I am using as my wood shop. The building is 14'x28' (~4.3mx7.3m), and has a conventional stud wall frame. The wall framing is fine, but the roof was both underbuilt and sagging, and needs new shingles.

The pitch is low, with almost no overhead storage room, and based on that, as well as the structural defects, I've decided to reframe the roof from scratch, and as I'd like to have more open space overhead, I thought that a timber frame roof would both function well for me and would look good. I also need more storage in the shop, and have decided on a gambrel roof so that I can create some storage lofts above the main shop and have a large open space in the middle. I may even install a cupola to enhance natural air flow in the summer.

My initial design idea is to install some tie beams spaced 8' apart, that land on the existing wall plates. I would then install some summer beams to support the loft floor joists and the roof support structure (which I'm still working on).

My immediate questions are two:

1. What would be a good way to attach the tie beams to the existing structure's wall plates. I would prefer to not have visible fasteners such as hurricane plates, but if that is what is necessary I can work with that. A sub-question would be whether I should think about reinforcing the stud walls where the tie beams land, i.e. install additional studs or a post inside the stud wall? I want this to be safe, but economy of materials and economy of floor real estate are inportant.

2. While doing my design, I'm designing from the wall plates up to the peak of the roof to get the overall structure sorted, then I anticpate I'll need to start doing calculations from the top of the roof down to the tie beams to determine the loads on each member so I can calculate the timber sizing. Is this the general way timber frame structures are designed, or is it a good way to do so?

Thanks, and I hope not to be too much of a bother. I'm pretty self-reliant when it comes to learning, but I do need to be pointed in the right direction at times, and that's what I'm asking.

I should be able to post a rendering of the initial design at some point soon, but I don't have that ready quite yet.

Cheers.

--Stephen