I just discovered this very useful site as I begin a small timber frame project, which will be my first. It is a shed roof canopy to protect our two back doors from Western Massachusetts snow and other weather. I've attached a plan.
I'm just a hand-tool woodworking hobbyist and a very amateur carpenter, so this is a daunting undertaking. But, one step at a time.
Step one was getting the timbers from my driveway to my garage without killing myself or my two young children. Wasn't easy.
Step two, I believe, is creating the footings for the two 8x8 posts. I had assumed I would be digging a couple feet down and pouring concrete piers, but having clicked around here for a couple hours last night, particularly on Jay C. Whitecloud's very generous and informed posts, it seems as if stone plinths set in a bed of rocks, with the bottoms of the posts scribed to the stones, is an alternative. That's an appealing alternative, because who wants to pour concrete, and see it on their patio every day? And I have a friend with a lot of big stones on his land.
Is there a single resource -- a book, a web page, a posting -- that will methodically walk me through this option?
That will tell me whether it is appropriate for my structure, and all the relevant details -- how deep to dig, how to choose the stones, how to scribe the posts to them, how to attach the posts to the stones, how to raise the frame onto them, etc?
In other words, can I do this? And how?
Alexander Layne wrote:Jay C.,
And can I really just eliminate the knee braces? I thought they were important for preventing racking, but if I don't need them I certainly don't want to bother with them.)
Jay C. White Cloud wrote:
I would suggest ridding yourself of those intrusive upper "knee braces" (unless you really like the looks of them..) Some folks like the aesthetic of "knee braces" and there is nothing wrong with that.
Nevertheless, they do get in the way often of good fenestration (doors and window placement)...They only work in compression, and do not "strengthen" a frame as most assume they do. Actually, when the really do their best work (or at there strongest) is when they are in a "horizontal configuration" at the floor, lintel, and roof levels, or at the base of posts acting as "buttress." They also work better when much longer than typically found in contemporary timber frames. Anything 3' and shorter is more a "fulcrum" stressing joints then a really effective strengthening...
Alexander Layne wrote:Will,
Let me just clarify that this structure has no walls or windows; it's just a canopy -- a shed roof to protect the two doors. I have attached a side view that may make that clearer.
There will be clear roofing, so as not to block light coming into that window, which is our kitchen.
When you say "anything less than 3' acts more like a fulcrum" do you mean "the joint is 3' from the post center" or "the brace is 3' long?"
...double plating is a magnificent way to brace a frame - and, in the "wall" direction of this frame, is substantially more efficient than standard knee braces. I'm so on-board that bus...
Jay C. White Cloud wrote:
When the oblique brace design is forming an 3' legs which are the "opposite and the adjacent" elements of a triangle, or this distance is less, the bracing actually starts to create stresses within the joinery during loading events that are counter productive. Braces are never measured or I should say "size labeled" by their "hypotenuse." Hope that made sense...I have edited this now 5 times and I think it is the best I can do at the moment...
Jay C. White Cloud wrote:"Frost Heave" is often a "misnomer" in many locations and not...necessarily...all that is going on. That is why the many stone walls around the world...not just New England do not move. Many of these stone walls sit on...or near...bedrock, and/or a "mineral soil," not a "clay soil." The clay soil is part of the revelation...clays are an expansive soil when they get wet...even without ice to exaggerate this expansion. Get a "bentonite" clay in a soil and you have way more to worry about than frost as this is an extremely expansive form of clay...yet has many positive uses as well.
So the real issue is clay and/or water...if neither are present you have little to worry about. So the goal of any design is finding the clays, and removing the standing water which can freeze and expand.
No water...No heave...No clay...no heave....
Could not recommend the gravel trench more!! Best foundation system yet devised and still used today on just about every continent.
Scribing to plinth stones seems totally manageable, and there are several great posts on that, but it's all the other details -- how deep do you dig the footings, how exactly do they prevent frost heave, how do the posts attach to the stones, etc. -- that I can't seem to track down.
Alexander Layne wrote:After quite a bit of research I think I'm ready to give up on avoiding concrete for the footings. Everywhere I read says you need concrete down to below the frost line to avoid heaving in the winter. Jay C., I'm guessing the gravel footings at your Sharon Elementary project will work perhaps because the frame will be able to tolerate heaving? I don't know, but I can't seem to find really good specific information about how to do footings without concrete. Scribing to plinth stones seems totally manageable, and there are several great posts on that, but it's all the other details -- how deep do you dig the footings, how exactly do they prevent frost heave, how do the posts attach to the stones, etc. -- that I can't seem to track down.