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#33224 - 10/26/15 01:52 PM Can't Find A Joint For This
ATC Offline
Member

Registered: 07/26/12
Posts: 15
Loc: The Emerald Triangle
I can't seem to find any info on some good joints for a top of rafter to girt or top plate.

This is for situation where there are dropped shed roofs on either side of the main barn.

Here is a picture of what I'm looking at:



I have a couple ideas, but I'm wondering what is the standard.

Thanks


Edited by ATC (10/26/15 01:52 PM)

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#33225 - 10/26/15 02:28 PM Re: Can't Find A Joint For This [Re: ATC]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Hello ATC,

"Shed Dormer" common rafter systems today are typically (my experience grant you) "let in" with a simple housing and instead of a trunnel attachment (if any in many historic cases) they are attacked with a structural lang/screw such as produced/spec'd by Simpson, GRK, et al.

These are the fastest joinery modalities usually and easiest to place "in situ." there are others that also have housings, toggles, leggings, and even "tusk tenon" systems, as well as "wedge blind dovetails," half doves, lap joints, etc.

Regards,

j
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#33226 - 10/26/15 02:49 PM Re: Can't Find A Joint For This [Re: ATC]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Here are some links to pdf you may find of value...

https://ncptt.nps.gov/blog/historic-amer...-plate-2001-14/

https://ncptt.nps.gov/blog/historic-amer...-plate-2001-15/

https://books.google.com/books/about/Historic_American_Timber_Joinery.html?id=_k-XAAAACAAJ

There are many others, especially if doing searches in other languages, as well as great reference books...
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#33227 - 10/26/15 04:00 PM Re: Can't Find A Joint For This [Re: ATC]
ATC Offline
Member

Registered: 07/26/12
Posts: 15
Loc: The Emerald Triangle
Thanks for that info.

I'm a "conventional" General Contractor, so I use Simpson products quite a bit. But for this one, I'm trying to go a little more traditional.

I had thought of a wedged dovetail, but depending on the size of the rafter, it would probably have to be wedged from the outside. This plan is for 4x6 rafters, and a 4x6 mid-height girt to hold them.

I've been looking for that book by Jack Sobon, "Historic American Timber Joinery", and Amazon doesn't have it anymore. I just found out I can purchase it through the Guild. Sweet.

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#33228 - 10/26/15 06:13 PM Re: Can't Find A Joint For This [Re: ATC]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 480
Loc: Vermont
Quote:
I'm a "conventional" General Contractor, so I use Simpson products quite a bit. But for this one, I'm trying to go a little more traditional.


Hi ATC,

Going "traditional" is more than ameberal. It is our general rule that all frames must "work" in a "traditional context." This holds true whether we are doing a "new build" or facilitating a "historic restoration/conservation/reconstruction" project.

Now with that stated, having studied these structures over the decades, we all get to see where they are "potentially vulnerable" to weather, tectonic, and other aging effects. So it is advisable (and always makes our PE very happy) to "add/augment" the frame with elements of modernity that "strengthen the frame at weak/vulnerable points. "Uplift events/loads" on eaves is a common one. Now this can be achieved with pegs and wedges, yet even then we still will add the "strengthenings" as a "backup" insurance policy to those "rare events" that inevitably are subjected to any structure...especially ones as enduring as timber frames.

Quote:
...This plan is for 4x6 rafters, and a 4x6 mid-height girt to hold them...


That is a very common format, and we just finished another "Asian style" pavilion with 4x4 on 4/10 pitch. This is on a 7.2 metre by 4.8 metre (~16'x24') to bay frame. The common rafters just "sit" on the ridge beam, yet are house in a simple notch ~ 50 mm deep at the eave cord/plate. This forms a typical "hung roof" assembly as you would commonly find throughout Asia on simple farms structures of all types. These rafters would be shingle with wood or stone, and often additional stone would be used to weight the shingles down, there by adding mass to the building thus pinning it to it's stone plinth foundation. We opted for a "standing seam" metal roof on this frame (now common) yet the rest of the frame is traditionally built with no pegs at all and only 14 primary wedges (and gravity) holding the frame together. Now to appease (rightfully so) the PE there are Simpson Lags on each rafter at ridge and eave, and a "structural drift pin" securing the posts to the stone plinth foundation.

I believe in your case a similar arrangement would be advantageous, and if forgoing the "modern fasteners" just use "toe nailed" trunnels as a securing method. These could (should?) come in from the sides and not be larger than 20 mm (~3/4") of a wood such as Dogwood, Hornbeam, or Locust.

Jack's book is great, but much of the guidance you need (I think) can be gleaned from the PDF files I share above.

Good luck and do post more pictures when you are done!! grin
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