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#33878 - 07/31/16 10:03 AM joist pockets on exterior porch?
tburt Offline
Member

Registered: 07/31/16
Posts: 7
Hi all, I'm fairly new here & just wanted to say that I've really appreciated all the information on these forums...so thank you!

Here's the background on my question: I am building a 24'x36' workshop with a concrete 24'x24' foundation and the remaining 12' cantilevered out to (3) locust posts. The concrete section has an 8x8" sill (hemlock) and will be fully enclosed. The cantilevered section will share the roof system (ie. covered), but will be open on three sides.

This "porch" will have 2x8" joists (white oak) notched & dropped into pockets on the hemlock sill. They will reach across and attach to a 6x8" beam (also white oak), but this is where my question begins...

I would love to avoid using hangers for that joist/beam connection, but I am worried about cutting pockets because of the risk of creating a "wet" zone and promoting premature rot. It's true that this connection will be below a roof, but it's at the gable end of the building & will receive some windblown rain & definite snow.

Does anyone have experience with joist pockets in a similar exterior environment? Is there a way to design them to avoid this water issue? Is flashing with ice & water (or similar) an option? Weep holes? Any insight would be greatly appreciated...thanks!


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#33880 - 07/31/16 09:27 PM Re: joist pockets on exterior porch? [Re: tburt]
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1872
Loc: Maine
Looks like a nice project. You could put a copper cap over the sill that houses the joist, or another modern material, ice and water, EPDM, tarred paper. How about soffit or tusk tenons on the end of the joist, mortices in the face of the sill instead of drop in pockets.

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#33881 - 08/01/16 09:31 AM Re: joist pockets on exterior porch? [Re: tburt]
Hylandwoodcraft Offline
Member

Registered: 03/23/11
Posts: 141
Loc: Western NY
As timbeal suggested, any joint at the face will be better than a drop in joint. Just out of curiousity, I wonder how long weep holes would stay open before being filled by mud wasps or some other bug. Other than that random thought, weep holes seem like a good idea as well.

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#33882 - 08/01/16 10:22 AM Re: joist pockets on exterior porch? [Re: tburt]
Dave Shepard Online   content
Member

Registered: 02/19/06
Posts: 706
Loc: Alford, MA
Exposed sill connections in Dutch barns used weep holes.
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#33883 - 08/01/16 02:30 PM Re: joist pockets on exterior porch? [Re: tburt]
tburt Offline
Member

Registered: 07/31/16
Posts: 7
Thanks for all the great ideas. I like the tusk tenon, though assembly might be an issue unless I cut a slope into the top of the mortise so it could be inserted at an angle...maybe that's a solution?

As of now I'm leaning toward drop-in joists, and spending some extra time on the flashing. Dave, it's good to hear that weep holes have been used historically, though I hadn't thought of them filling up with insects, etc over time. What do you all think about using a gouge to make a sloped channel at the bottom of the pocket? Like this:

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#33884 - 08/02/16 07:22 AM Re: joist pockets on exterior porch? [Re: tburt]
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1872
Loc: Maine
You could tusk the outer sill and have the inner one be drop in, insert the tusk and drop the other end making for a simple install. I find mortises easier to cut than drop in pockets, less material to remove.

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#33885 - 08/02/16 09:26 AM Re: joist pockets on exterior porch? [Re: TIMBEAL]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 470
Loc: Vermont
Hello,

Joining late and like many of the suggestions thus made...

As for "cladding methods"...copper, or even slate are exceptional methods as they allow (when installed properly) an air layer away from the wood that promotes drying while still protecting the wood from the ravages of exposure.

An "encapsulation method" that lays directly on the wood such as modern latex paints, tarring, or plastic roof wrapping materials, very often inhibits proper drying and promotes interstitial moisture buildup and decay. A good tradtional oil finish however, tends to protect yet stay exceptionally permeable.

Weep holes, drain slots, and other such methods are very traditional and effective...if...(as suggested wisely) maintained properly and kept clear of "wee beasties" that like to live in them. An occasional inspection by annually and a reaming to insure proper clearance is necessary for them to stay functional.

By far, the best (in my view) of the suggestions is to have all these members facilitated as slanted (thereby draining) housings and a "free tenon"...soffit or tusk...that will lock the frame together better than any other jointing modality.

Yatoihozo (the Japanese form of "free spline tenon") are a broad and diverse joining method also found throughout most of Asian single plan multi directional joint unions. So the issue of assembly is not really an issue or challenge at all. Now you get the bearing strength gain of a housed joint, and the massive strengthening of a "through tenon" with wedge that allows further tightening in the future if necessary. Securing the spline in place can be a "modern method" of using a structural adhesive...or a traditional method such as Shachisen. A cotter, key, or drawing wedge can pin this joint well within the receiving timber.

The video below demonstrates aspects of this and several other "free tenon" and layout methods as well that may be helpful.


[video:youtube]https://youtu.be/72LIWyuMQSk?t=578[/video]


Edited by Jay White Cloud (08/02/16 09:28 AM)
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#33886 - 08/02/16 04:03 PM Re: joist pockets on exterior porch? [Re: tburt]
D L Bahler Offline

Member

Registered: 05/17/10
Posts: 946
Loc: Indiana
Copper is actively anti-microbial, meaning it naturally inhibits rot from forming where it is contact with the wood, or where it has leached into the wood. In contact with wood, it also will form various poisonous compounds, most notably copper sulfate which is one of the commonly used chemicals used in preserving wood today since the banning of creosote and arsenic in most applications. It has the disadvantage of attracting moisture, but this is offset by its antimicrobial nature.

I personally like to avoid methods that will require faithful follow-up maintenance because I know that this realistically won't happen most of the time, and that people don't want the added responsibility of having the crawl under the house and clean bugs out of tiny little holes.
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#33887 - 08/02/16 09:31 PM Re: joist pockets on exterior porch? [Re: tburt]
TIMBEAL Offline
Member

Registered: 12/10/07
Posts: 1872
Loc: Maine
Run an air line to each hole with a timer to give a burst of air once a week.

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#33890 - 08/06/16 09:23 AM Re: joist pockets on exterior porch? [Re: tburt]
tburt Offline
Member

Registered: 07/31/16
Posts: 7
They always say the simplest solution is usually the best, so in that case I've decided on Tim's air-hose-linked weep holes with digital timer....figured it would also add to the overall aesthetic, too smile

I really ended up going with drop-in pockets & a gouged channel at the bottom. I've been leaning toward copper option for the flashing and after reading DL's post, I'm re-convinced to shell out for some good function and beauty.

Thanks again to everyone for their input and ideas! It's starting to look real.

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