removing sills seems to be common today, where the posts are instead bolted down to the foundation below some how.
But I've never been a fan. I'd sooner put in a framed floor. It's not that hard to make a wood floor strong enough to support a truck, lots of bans around here have them.

How far apart are the purlins?
It is very common practice on granaries in the southern Germanic areas to have a purlin roof, and it's also common in Sweden. The granaries of Switzerland and Austria are very closely related to the log houses of Norway and Sweden. I've seen lots of granaries in the Canton of Bern framed like this -the purlins supported only by the walls and spaced about 4 feet apart. This supports a board roof, onto which wood shingles are nailed (today its often ceramic tiles)

The purlins are 24" oc. I agree with you on the sills, I'd rather have them, but its a compromise for time and cost so I can afford to put more of the features I want into the house later. It's unfortunate, but alas, thus is life, eh?

From my limited experience (one house built) I would strongly advise the use of sills. I didn't and have regretted the decision more than once. For a four post frame it might not be useful, but the moment you need to align multiple posts (ie. 3 or more in a row) the sill saves a lot of effort. You could always still pour a slab, and make a ramp over each of the sills for the entrance... although this would preclude ever pushing a vehicle into or out of the garage!

If you're planning on raising as bents, bear in mind that your centre posts create a hinge point for the girts. Either you have to size the joints so that they can take the lateral forces and lift the girts, or you have to lift all three posts simultaneously ensuring that the force is distributed evenly... again... this is the voice of (recent) experience! :-)

Hi everybody,
I'm having some questions about the rafter and purlin spacing and sizing, and am hoping someone can point me at a resource and walk me through the process.
Thanks,
Devin

What's the snow load for your area?

Our ground snow load is 40psf.

Great, now we need to understand the sizes and spacing.

I have measured your version 8 drawing. I see that the purlins are 4x4's and are 2' on center in the rafter plane but 1' 9 3/4" on center in the run of the rafter. And the unsupported span of 11'. Is that right?

I'll assume it is. And that would give the area each purlin is supporting to be 19.9375 sqft, round up we'll call it 20 sqft.
20 sqft x 40 lbs live load and we'll assume a 10 lbs dead load for the future roofing materials for a combined load of 50 lbs per sqft to be 1000 lbs. (20 x 50 = 1000).

Next we need to understand what type of wood the purlins will be made out of. Your first post says "rock maple". Is that correct?

Jim Rogers

Jim,
Thanks for spelling the math out for me, I'm starting to see how it comes together.
The rock maple supply I have is "free" but the more I dig into it the less free it gets, with trucking and sawing; its almost as costly as buying EWP from the mill down the road from me, and I'm within their free delivery range, so they'll drop it on the property with no charge.
Long story short, I haven't settled it yet, but it looks like either EWP or rock maple. As always, any advice is appreciated.
Devin

You'll be a happier man with EWP.

You'll have no bones left after working with hard maple.

Well, since you asked, you will enjoy working pine. What you will experience working rock maple I can't say for sure. Probably not much joy.