I’m following the plans from Jack Sobon's book, “Build a Classic Timber Framed House” but would like to build on a concrete slab as per James Kachadorian’s book “The Passive Solar House. (The floor will be some sort of fancy concrete finish that my wife is in charge of) Thus I am eliminating all the floor joists, sill girders and sills from the plan, they no longer seem necessary.
So my questions are:
1. Can I indeed remove the aforementioned pieces or am I missing something about their functioning?
2. If it’s OK to proceed without the floor beams -- can I just plant the posts using an elevated post base that’s set into the concrete? Any suggestions for brands that can handle the weight or will I have to have the bases custom made?

Also:
I have 5 acres of mostly Douglas fir and some Western Red Cedar on the Olympic Peninsula and would like to build entirely from what’s at hand without buying any additional wood. However, the lumber list calls for grades 1 and 2 and specifies hardwood for posts and braces. I don’t know what the grades mean but I assume they indicate quality.
More questions:
1. How do I know the grade of the wood that I mill?
2. Isn’t Douglas fir good enough for posts and braces or do I really have to go buy hardwood?
Thanks

The answer to #1 is yes you can remove these as the concrete slab will and can do the same function that is support the posts.
You should plan on re-enforcing the concrete below where the post will be setting, completely down to the footings.
There are methods of attaching posts to concrete slabs. Some have been posted here on the forum in other threads. You'll need to do a search for post to foundation connections.
Also, there are post to concrete connectors sold by Simpson strong tie company. There is a link here somewhere to their site where you can find all types of connectors for this type of use.
As to the weight factor if they can't handle it they might have to be custom made by a local welder in your area.
As to the grades of lumber, I'm sure you can understand that you or your sawyer can mill a 2x6 from your own stock with a 3 or 4 inch knot in it. But it wouldn't be strong enough for just about anything. This is why grades rules were adopted. You could get a rule book from the Western Wood Producers Association and read up on the rules for grade 2 and once you understand them you can then select and mill good trees into proper strength timbers.
If you aren't going to personally mill the timbers then talk to your sawyer and see if he understand these rules. If he doesn't then either you have to educate him or find another sawyer who does understand them, and have him mill your timbers.
As to whether or not you can substitute Douglas fir for oak, you might have to have a structural engineer review this. You'll need to find one from your area who is familiar with timber frame construction. You can go to the TFG home page and select the resource guide and do a search for engineers and see if there is one in your area.
Good luck with your project.
Jim Rogers

Thanks for your response Jim
As I will be cutting and milling the lumber myself, I ordered the lumber grading guide. Thanks also for the other words of wisdom.

My understanding is that, at least in Washington State, you have to have a certified stamp on those timbers or the county building department will not approve. To get a WWPA certified stamp, the particular mill has to be an authorized WWPA mill. I would contact your local building department for assistance. -Patty

I too am going to build a house using Kachdorian's passive solar concept and would appreciate any thoughts about the design. Our house footprint is an L; we plan to have the solar slab as the foundation for the short leg of the L only. I have also been thinking about using the "faux" slates for shingles which are apparently made from old tires. (I like the idea that they are recycled.) Anyway,I was wondering if anyone has had experience with them on SIPs.

Here in the northeast the lumberman's association that issues grade stamps to mills told us that they wouldn't issue a grade stamp to a portable sawmill. So I can't get one.
To overcome this problem when a building inspector wanted grade stamped timbers, we (the customer and I)hired the association's traveling graded to come here to my sawmill yard and inspect and grade stamp all the timbers.
This then satisfied the building inspector for the town where the barn was going to be built.
If you contact the WWPA ask them about hiring a grader who will travel to your site and inspect your timbers.
When he arrives he'll want to look at every timber and every face of every timber so be prepared to lay them out so he can look at everything. He'll also want to know which are posts and which are horizontal timbers as different grade rule apply to these timbers. At least they did when he came here to my yard.
Good luck with your project.
Jim Rogers

A timber frame PE licensed in WA is next door in ID. Philip L Hart
E-mail Address(es):
hart101@imbris.com

He will do an outstanding job and will negotiate the $$$.
Have fun.

I have always found it very curious that the Very last Timber Element to have left the Residential Building in the North East -- the Timber Sill -- is also the very last Element Modern Timber Framers seek to incorporate into their Frames.

Beyond merely providing a place for the Post to land, a Sill acts to spread the Point Loads, And, to help the Frame survive the erosion, and, sometimes, the outright collapse of sections of the Foundation.

In the Modern House the Foundation is often one of the more temporary aspects.

In general, Softwoods can be substituted for Hardwoods in most every case, (including braces) however, Dimensions do need to be refigured. I don't remember what Spans Jack's Design addresses or what Sizes he calls for, and why he specs Softwood for Horizontal members and Harwoods for Vertical, rather than vice versa.