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bamaranch 03-29-2010 10:07 PM

span beam under code
An addition was built onto our home about 20 years ago. It is a vaulted ceiling, with an exposed beam (covered by trim box), and a span of about 20 feet.

Noticed that it is starting to sag a tad in the middle. Considered putting a remedial underneath it myself. A friend suggests the undercode (2 ply 2x8s) can be extracted and a new one inserted. Suggests that the roof can be temporarily propped up with supports/jacks.

Is this doable?

Seems complicated. In addition to the rafters needing to be cut away from the beam, wouldn't there be roof sheathing (ten penny) and even roofing nails in those 2x8s? Can that be yanked out?

kelley4180 03-30-2010 09:10 PM

Seems like cost/benefit will be a consideration. How much more is the extract and replace than the remedial support beam? I imagine if you'd look to sell, the idea of disclosing the remedial beam may be unpleasant, whereas with a rebuild, there's nothing to disclose if it's all code.

Seems doable though. The contractor would need a lot of brace supports to keep that roof up for a while. I've not seen that done, but theoretically dooesn't seem insurmountable.

Daniel Holzman 03-30-2010 09:43 PM

You indicate the beam has been there 20 years, and is starting to sag a little. Sag is normal in a beam that old. What is your basis for concluding that you need to do anything at all? Have you evaluated the beam to see if it meets current code? There are many options for strengthening a beam if in fact it is not adequately strong, replacing it is a drastic measure that should be undertaken only for very good reason.

Jim F 03-30-2010 09:58 PM

Dan, who would be the first person to call to evaulate sagging beams.

BJLower 03-30-2010 10:59 PM

Information from a posting from a while ago
If I recall correctly the posting was made by someone that wanted to move the kitchen in his home into a larger room. He was worried the the 2 X 10 floor joists might sag under the additional weight that he wanted to put on them and asked if he could put particle board down the sides of the floor joists to prevent sagging from occurring.

Why this site is so good, a professional architect answered his question.

Naturally he told him first that particle board doesn't have a grain so isn't supportive.

Then he gave the formula that architects use, that I wish I'd written down and even noted to him that the number was “best estimate” when wood was involved. Different types of pine have more strength and that the longer the span the greater the possibility of a weak spot, etc. He did finish by telling him that the wood used to make support joists is high grade.

He told him that if he “glued and screwed” a 2 inch strip to the bottom of the 2 X 10 floor joists that he was afraid would sag, that that would make them into 2 X 12's that under the formula increased the “anti-sag” strength by 177%. (I used the formula to check the difference between a 2 X4 and a 2 X 6 out of curiosity and the increase was close to 1,000%)

Just to make sure, when the architect told him to “glue and screw” he was referring to Elmer's glue and that the screws would act like wood clamps to hold the strip until the Elmer's dried. Not all DIYers took “Wood Shop” in high school and have actually built furniture, or the most common Senior Year project of a Grand Father clock, that other than to hold the clock works themselves in is built completely with Elmer's glue that is actually a copy of the glue that they made from horses long ago and used to build furniture some of which is still in perfect condition after hundreds of years of use.

If I'm following your description correctly that would be a fairly simple way for you to add the “anti-sag” strength.

Without pictures how to repair (actually temporarily hold) the minor sag that you already have is something that I can only try to give you a “best guess” on.

You'll have to take the minor sag out of the beams long enough for the glue and screw to set which is 24 hours. It would actually be better if you push the sag even farther than being just straight again, but I doubt that is a possibility

The trick that you would have to figure out is how to use something like the metal joist supports that are threaded so that you can use then to lift joists (normally these are used in basements of older homes and are left in place) to take the minor sag out of the beams while you glue ans screw the added strength.

I have to note that the existing beams have already developed a curve to them that is going to try very hard to stay curved.. The thicker the piece that you glue and screw the more strength you will have against the beams curving back to the way they were. They will curve back no matter what you do. However, the amount of curve (at least at the “best guess” that I can make from the information I have)
should be at the “doesn't matter” point at the beams will need to be boxed back in.

I hope I got that right. You ran me past my bed time and my brains already headed in that direction.

If you need any more information or explination shoot me an email and I'll do the best that I can for you.


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