Repairing dryrot in structural beams

I am looking for some insights from anyone out there who has some experience with repairing large beams with dryrot. The beams look like they are about 16-18" tall, 12" wide and probably 35-40' long. They reside underneath an old country store, are made of fir and it looks like none of the rot goes completely through the beams, although a couple go a little over half way. The largest rotted area thus far covers about 5-6' of the length, about 50% through in the middle, tapering out to zero on the ends of the 5-6' sections. The bad sections are almost exactly in the middle of the span. I cannot see or measure any sag thus far, but I want to shore up the bad spots before it starts sagging. I already know the cause of the rot I need some ideas on good repair techniques to restore the "cancerous" areas. Thanks in advance for any tips you can pass along. regards, Joe.
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Rotted wood is gone, there is no repair. You will have to add "sisters" (ie patches) to the bad areas. Depending on the usage and loads, you should be able to keep using the building.
Don't do it yourself, get at least two estimates from experienced contractors.
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"bw" wrote:

Very good advice.
This project requires far more than a little OJT from a previous job.
Lew
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On Fri, 27 Mar 2009 03:52:19 +0000, Lew Hodgett wrote:

Oh, I don't know. I've had the same problem twice, on a workshop floor and a porch, and I fixed it myself both times.
I bought "sister" beams the same size as the rotting ones. I got them long enough to reach piers as well as the solid portions of the old beams and attached them to the old beams with lag screws.
One such repair was 5 years ago, the other 10. So far so good.
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guy jumping off the empire state building at floor 50: so far, so good.
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"charlie" wrote

Nothing wrong with Larry's fix ... particularly since the sisters spanned the same piers as the old beam.
When possible, LVL's are a good choice for sisters; they come in various sizes, are lighter, and can be "laminated" together with a nailing pattern to make a bigger beam, which makes them easier to get into tough spots. Simpson strapping is often also required to attach the sisters to the faulty beam, and the piers.
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charlie wrote:

Sistering a beam is a perfectly acceptable repair, as long as you do it to code or have it vetted by an engineer. By supporting the ends of the sisters on piers he's being quite conservative.
My main concern with the beams in question would be the size of them--they're heavy enough that if they get away from you they can do some serious damage and if they're going into a confined space then some specialized fixturing might be needed to move and position them safely. It's one thing when you and a hundred Amishmen are carrying one on your shoulders, it's quite another when it's you and a long ton of beam in a crawlspace.
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Larry Blanchard wrote: ...

... So you're suggesting he "sister" a 12x16 40-footer in there???
Sure...
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On Fri, 27 Mar 2009 14:02:45 -0500, dpb wrote:

I must have missed that. Sorry, you're right. That's a bit much to tackle yourself. The largest I worked with was a 20' 4x12.
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Larry Blanchard wrote: ...

Yeppers..._IF_ (the proverbial "big if") this really is that massive a structure and loadings are anything approaching what it must have been designed for it definitely needs an engineer's evaluation if the expected continued usage is anything like that.
OTOH, if it is an old industrial/manufacturing building and is now simply being used as nothing more than a light fabrication or store, it's quite possible even as they are they're more than adequate and nothing would actually be required to be done.
Either needs a competent structural evaluation imo if there's anything significant going to be done to make it worth the investment as well as the all-important issue of safety when dealing with anything of that size...
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They were cleaning up to remodel an old grocery store in town on the square. The workers heard some creaking. They ran out of the building. The building collapsed. I thought I read termite infested. They hauled away the rubble, tore out the old slab and built a new buidling.
On Thu, 26 Mar 2009 16:54:47 -0800, Joe Brophy

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Joe Brophy wrote:

There's nothing you can do that will restore anything other than the exterior appearance w/ patching.
You have only the basic choice of either adding sufficient shoring underneath via pilings or similar (w/ the attendant adequate foundation support for them, of course) or adding other structural material in a way tied to the solid portions of the existing beams to carry the other load.
For something the size you're talking about, that would be a healthy beam in it's own right other than steel plate bolted thru or similar.
In a beam of that size, it would be possible I would think to engineer a bottom tension rod that could be attached on both sides of the damage area, but anything approaching an optimum solution would take an engineer to evaluate and design both the structure and the attachment details.
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On Thu, 26 Mar 2009 16:54:47 -0800, Joe Brophy

Best to replace the beams with rot-resistant beams. Second choice is to sister the beams
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Phisherman wrote:

12X16 40-ft sisters??? Yeah, local BORG will send 'em right over or he can go get 'em hisself w/ the little rental truck...
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wrote:

Pop holes in the foundation and run new beams in between the old ones. Use steel - it will last longer and is likely cheaper (particularly if you can get fabbed engineered trusses)
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As others have said, you cannot make a structural repair by smearing bondo, wood filler, epoxy, etc on the beam. If you have intentions of an alternate method to carry the loads you can make a decorative repair of the finishes. You might also consider interior columns or a pair of cross beams to catch those timbers back where they are not hurt..
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