Roof stiffness?!

Good morning!

I raised my high post cape few days ago and last friday, dropped in the last purlins, I was setting wedges around the dovetail mortises of the purlins this week-end and I mentionned that the frame is not "rigid" on the second floor. I mean if I try to shake the queen post I can feel the roof system shaking

My question is: is that normal?!

It's my first timber frame buidling and I have used the high post cape drwaing from chapell's book, adpated to my needs, I reduced from 24x24' to 20x20' keeping the same timber dimensions exept that I have one center post instead of two..
Also I didn't peg the joint external post to rafter, thinking that it was not enough wood left on that bird'speak which is 4x4", so far I set a screw from the top to hold it in place, strongbacks were just fine to raise the bents.

Can you guys tell me more about your experience in roof system bracing and stiffness? it looks like my braces in the first floor are doing their job, their are tight.



Thanks in advance for your help Neil

Yes, typical. Just standing and someone walks around with a load or some thrust, it can be felt. Of late, I have been using plank wall construction and the amount of movement is greatly reduced. No wall bracing just 2" plank mortice into top and bottom plates with splines and GRK screws into the edges of the planks in place of traditional peg. Once you have the other components in place things will stiffen up.

As Tim says, this is common. Timber frames while strong are not stiff. Most people (including many timber framers) don't realize this. Just like in stick framing, the structure's stiffness must come from the sheathing in most cases.

I really wish this had been posted before we built. Our original plan had been to raise the roof timbers using a sheerlegs mounted on the first (second in American English) floor. When we lifted the sheerlegs in place and put the first piece under tension, the frame started to rack and we had to rapidly change plan. At the time my wife was concerned that the structure would never be rigid, but now that it's sheathed it's solid as a rock. A few nerve-wracking moments though.

Presumably the inclusion of more uprights and bracing elements (as in "traditional" European styles... think English Tudor, French Colombage etc) would lead to a stiffer frame before sheathing. Certainly the French carpenters that looked at my timber-framing books were concerned that there weren't enough bracing elements in the roofs.

Hi again!

thanks for your comments, makes me feel confident
I just went back to my frame after work this afternoon and I tried to see how much of the frame was moving by pushing on the queen posts again. It looked like the all frame is vibrating, even if my braces on first floor are pretty tight. So I tried to screw back some long 2x5" braces outside (like you can see on the first bent on the picture and bracing both sides it looks like the frame is stable then..

So my conclusion, reading in addition your comments, it will become stiffer with the sheeting and i guess i'm gonna make it technicaly more braced while I'll build up the walls. Roof will come along I guess. I keep you posted

If you've seen the pictures of our frame, there was a point where the centre posts were just floating... the roof beams not having been lifted at that point. Striking a post with your hand at that point made the whole post vibrate for a few seconds. Once the roof beams were in, the vibration was reduced, and once the rafters were nailed on it basically vanished.

The first thing that most first-time visitors to our house do is to whack the posts before commenting on how solid it is. This is mildly disconcerting, but also very satisfying.

This frame still had some wiggle in it even with the roof bracing. https://www.youtube.com/watch?v=NLD8-CEmTLE

It's the whole package. Don't sweat the wiggle. Once it's all laid with boards, or plywood, it's stiff enough. And isn't what makes a timber frame strong the fact that it can move a little? That's why the ancient temples and churches and ? stand for so long being exposed to earthquakes and hurricanes and ? They do move a little bit. And that's the beauty of it. My 2 cents. but I'm always learning.
dave

Interesting frame Timbeal, I'm finishing at the moment what we call here "stavlinebygg" in Norway, a lot similar to this one, especially with those "rotkne" braces inside.

Yes i agree collarandhames, got that idea in mind as well!! but working alone from the beginning, I have some extra thoughts sometimes probably what we call the positiv stress!

In, what I call, traditional timber framing we use continuous plates, not interrupted plates as Steve designs.

I feel that a continuous plate make a building stiffer to begin with, and when braced properly very ridged.

Jim Rogers

I'll probably choose that technical solution in my next frame Jim, one thing I have been pointing yes.

Neil- how you making out with that? Stiffened up yet? There was a derelict barn near us that someone pulled the vertical siding off. And guess what, first wind storm which happened to be the next day, the thing fell over. Timberframes are strong, real strong, but a little bounce on a new frame is part of it. Do you draw bore? Do you drill braces once in place and posts are plumb? (we do! seems to work really good) We use 1 1/8 pegs a lot. At least 1". Let us know how you are making out? A link to the build would be awesome!