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Author Topic: Timberframe barn repair question  (Read 6849 times)

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Offline JanPaul

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Timberframe barn repair question
« on: March 28, 2009, 03:34:39 am »
I could use some advice on an issue with a timber frame barn repair.

We're planning on repairing our timberframe barn, probably built about 1892 (see the Barn pic). 



The main structure is solid and well built, six bents with awesome 18" hand-hewn main timbers, plates 55' long without a scarf anywhere.  However, the front loft (with the lower sloped roof), with the open lean-to below, was added in the 1920's as an afterthought and is not properly timber framed nor braced. That section, as can be seen in the photo, is presently held aloft by short 7 ft posts which rest on the ground and support the bottom plate, and have no braces. This front section has developed a lean and is causing stress on the main structure. So want to remove that front loft and rebuild it with a proper timber frame, and we figure on giving it proper rigidity by using six bents, with posts which run all the way from new footings to the roof and are tied in to the posts on the existing six bents in the main structure.

The front of this overhanging section is open all the way across the width of the barn, and provides a great working area in bad weather.  We're in Ontario, and get maybe three or four feet of snow, although the way the weather comes in, the main structure shelters this open lean-to section pretty well, so there's usually about a foot or so of snow-pack at the base of the posts.

What's got me scratching my head is figuring out whether we can adequately weather and rot-proof the exposed butts and the lower three or four feet of the new white pine posts, which we plan to rest on sono-tube footings, anchored with rebar or embedded plates. The existing short posts (which these full-length posts would replace) are cedar and rest on the ground without footings — so every 15 years or so, when they got weathered, they were replaced as needed, one by one. But once we switch to full-height posts, that won't be an option . . .  so that's got me wondering if the old timers didn't have it right to begin with . . . but THAT gets me back to an unstable frame. . .

If anyone has any thoughts on how to come at this, or seen an approach that works on a barn like this in their neck of the woods, I'd be much obliged.

Thanks in advance,

JanPaul

Offline Jim_Rogers

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Re: Timberframe barn repair question
« Reply #1 on: March 28, 2009, 07:25:17 am »
I inserted your picture for you.


There are several ways you can do this. First of all you could increase the roof overhang and hopefully this will help the posts to not get so much weather on them. But that means you'll have to increase the size of plates and rafters in order to support more load.

The next option would be to just paint a wood preservative onto your posts.
When I did my fence out front, many years ago, I cut some white pine 4x4 posts and then painted them, the bottom three feet, with a wood preservative and then placed them into the ground, and back filled with crushed stone. This way the surface water can drain into the hole and there isn't wet soil against the post. I read this procedure in a fence installing book. And it has held up for many years.

The next option and maybe the best option is to plan on future post repairs.

This can be done several ways. Design the joinery so that you can remove the post in the future.

Or use the short pole system.
This system, I was told by the guy who showed it to me, was found in old barns in CT, and is not a new method.

What you could do is make the bottom several feet of your posts, above the sono tube footings, out of pressure treated wood. And you sister a set of 2 by's onto the sides of the pressure treated stock to joint and overlap the regular white pine posts.

I have this drawing to show you:



And the text with this drawing says:

This drawing shows how a short pressure treated pole is below grade and a regular non treated pole is above grade, with two pieces of pressure treated 2 by stock nailed or bolted onto two sides to secure the poles together.
If the pressure treated pole ever rots away, you just jack up your building and replace only the lower short pole.



Now in your case you might want to make the sistered 2 by stock on all four sides to insure that the posts don't separate at all.
And make the pressure treated pieces tall enough so that only that portion will be in the weather.

Then as mentioned later on if the pressure treated section rots out, you can just hold up your barn roof and remove the rotted section and replace it with a new piece.

Hope this has helped you with some ideas to solve your situation.....


Jim Rogers
 
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Offline moonhill

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Re: Timberframe barn repair question
« Reply #2 on: March 28, 2009, 07:47:25 am »
Hi JanPaul, interesting dilemma.  How is the space under the add-on used?  Could you place a full concrete wall in place of the exchangeable cedar post, or do you need it open?  Old barns are changed frequently through out their lives.  If the pine is missing its sap wood they will last longer, place the butts at the bottom, more of the sap wood will be sawn off.  In stead of sono-tubes use a frost wall or a rubble trench with a grade beam poured on top.  Sono-tubes bother me, they are susceptible to frost movement.  It looks like you have drainage off the back of the picture into the hard wood valley, the rubble trench needs drainage to daylight. 

How are you planning to attach the six new rafter to the existing old barn?  If there is any chance of movement this connection could be stressed. 

I wonder if you could put siding on the full length post, with an air space, maybe just the out side faces or go for it an side the whole post, as protection from the weather.

Tim
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Offline witterbound

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Re: Timberframe barn repair question
« Reply #3 on: March 28, 2009, 08:45:18 am »
Why don't you just use the tube for concrete up to 4' above the ground, and put your post on it there?  Or build a small square form for the concrete post bottom, and cover it with a thin layer of stone?

Offline Rooster

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Re: Timberframe barn repair question
« Reply #4 on: March 30, 2009, 12:50:18 am »
Hey there,

I have used Jim's idea on a few projects, and I agree with Tim, I am not a big fan of sono-tubes.  And when it comes to the "old timers" getting it right.....you have to remember that the "farmer" who added that addition in the 20s, was fulfilling a need at that point.....not building for the "long haul".

"As long as this thing lasts longer than me ....after that, I don't care what happens!!"

Sound familiar?  He probably never expected it to be "useful" to anyone else, let alone have someone who would want to "restore" it.  To the farmer it was a tool of farming, not a piece of history to be cared for.

Ok, I'll get off my "soap box".

I have a suggestion for your support "system".  I would divide the new frame and supports into three separate levels or stages.  Each stage increasing in "rot resistance" as you decrease in elevation.  I would start  by using treated posts made from the lower portions of used utility poles.  These are "real" pressure treated and will last forever!! I would auger out holes, place them on top of a 6in X 16in concrete pad called a "cookie" below frost line.  Cut the tops off level to each other 6-8 in above final grade.  Then run a "sill" or "cap" beam the length (horizontal) of the building on top of the posts made out of the same treated material.  This will tie them all together and help eliminate some of the "wandering" of the "post on post" connection. 

The next stage is the exposed posts, which you mentioned you wanted to be part of the bent system.  First I would talk you into making this into two separate frames...upper section, and lower section.  The lower section would be the one exposed to the weather. It would have 6 separate bents made up of posts, tie-beams, diagonals, and a "top plate" which will also act as the "sill beam" for the upper section of frame.  The lower section of frame could be made out of white oak which will last longer than exposed pine.

The final stage will be the upper section (pine frame) which will rest on top of the white oak "sill" frame, which in turn rests on top of the treated beam, supported by the treated posts, on top of the concrete pads......"in the house that Jack built"...

The down-side is material availability in your area, and extra time and energy to build.
The up-side is that it will be stable, look appropriate for the building it is attached to, and you will get an "At-a-boy" from the "old-timers".

Good luck!

Rooster
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Offline thecfarm

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Re: Timberframe barn repair question
« Reply #5 on: March 30, 2009, 08:15:06 am »
That's a nice picture. Like the Ford tractor, I think it is, too, 8 or 9n, Not many NAA around. I see they put a nice foundation under the barn. Around here most of the older barns was put on big rocks and or granite. Good luck with your project.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79