you should definitely design your structure, or any structure for that matter, with at least a 2 foot overhand at all sides. Unfortunately, people frame things with a small (16 inch or less) overhang. Sure it costs more, but the price far our weighs the protection your building will get from the elements as well as provide a great area to get artistic with exposed rafter tails and nice stained pine soffits. If the design you are trying to use as a reference does not have good overhangs, either redesign the frame, or use 2x4 sleepers across the entire roof system to get additional framing for it. Cheers!

Tim,

Continuous Top Plate- This would seem to make the rafter design and joinery easier. I'd be concerned about the availability of 20' timbers in the Adirondacks and also the difficulty of lifting them into place.

Top Guard- Is Top Guard the stuff designed to replace roofing felt?

Metal- I've been advised that metal will have to be mounted to furring strips rather than directly on a flat surface to allow "breathing" and minimize heat transfer. Is that a concern?

Collar Ties- They certainly would be head knockers though I wasn't originally planning on using the space within the rafters. I might change the pitch from 8/12 which matches the pitch of the nearby main camp building to 10/12.

Tie Beam Placement- Haven't worked that out, understand the some? space from the plate joinery is necessary. Posts will be along enough to give 8' clearance from the floor to tie beams

Thanks,

Carl

Brad,

Would appreciate any plans and pictures. Thanks also for the "vote" for continuous top plates.

Principal rafters and too much meat- Just read in a Bensen book that the for the top of a post cross section was three joints with no more than 50% involved.

20' timber should not be a problem, 40' could be but still possible.

Roof Top Guard is a brand, I believe, and yes it replaces tarred paper/felt. I am about to put some down in stead of tp, and a metal roof directly on top of that. I am after the additional mass of the roof surface to keep the metal from changing temp too quickly and easing the sweating problem. I don't see any problems with doing this, maybe someone will point out a reason.

Collar beams, even so, someone may one day, and what a bugger it would be.

Tim

Thane,

No apology is necessary. The rookie nature of my questions was evident. The good news is that I am not new to chisel and mallet having built a number of dressers, tables, etc. using traditional joinery. Though the scale is different, many of the principals are similar. I also have built two Rushton style small boats from the late 1800's which might not be relevant to timber frame construction except to illustrate my desire to use traditional techniques.

"read several more books" is a great suggestion, you might notice in my original post a request for reference materials. SInce then I have acquired and read the Benson and Gruber book besides the Chappell book. Any other suggestions? I'm not too worried about the joints which are, I undertand, central to this form of construction; right now I'm more concerned about sizing and spacing of the components, deciding which tools I HAVE to have, deciding whether to use local Amish milled Hemlock or second growth Douglas Fir sold by a lumber suppler, etc.

"Start small" - The idea of a "training structure" makes sense, though age and approaching infirmity probably mean this barn will be my first and last timber frame structure (unless I can get some help).

In summary, I really do appreciate your "$0.02",

Carl

Thanks Carl,
Not sure how far along you are but have you considered a ridge beam and common rafter design? The ridge beam being simply a third plate with which to rest the top end of the rafters on. Just birds mouth both top and bottom ends of the rafters and lag them down. No notches are required in the plates as the outward thrust has been eliminated by the ridge beam. As for bracing, just brace as if it were a wall from the plate to the king post which sits atop of the tie beams.
Also, there is a Simple Beam Calculator which has been seen a few time on this forum and is very handy for these simple structures. I can send it to you if you don't already have it.

Thane

Carl,

20' plates shouldn't be a problem. I would be careful in selecting a mill though, as most only saw boards, and their mills often don't cut square. I would bet a good percentage of them don't even have a square in their mill. As far as raising them, do a search on the forum for parbuckling.

I can imagine which Benson joint you're referring to, and I'm not a big fan. Nor am I fan of some of the joints in the Chappell book. Buy a copy of the Historic American Timber Joinery book from the Guild, and also check out Sobon's books. They're both essential reading.

There's really not a lot of good reasons to truck doug fir across the country, when you've got at least a dozen different species you could build with locally. You can even use a dozen different species in your little 16x20.

Unless you have very tall kneewalls, I think you can skip the ridge. You'd also be point loading the tie beams with 1/2 the roof load, so you'd have to beef up the tie beams a lot.

Thane,

A search for "Beam Calculator" shows only you recent post, please send it on to me when you can.

Carl

Carl,

Try this link:

http://www.forestryforum.com/members/donp/beamclcNDS2.htm

Ok, that's the one I was talking about.
Thanks Kevin