Ash vs. oak - your thoughts!

[Jim Mackell]

I need to make a floor joist for a restoration project. The joist will be 6 feet long, 3 inches thick and 11 inches tall at it's tallest point. The ends taper down to about 5 inches. The ends carry a lot of weight and thus there is a lot of internal stress on the joist. The original cracked from the stress. The original - from 100 years ago - was oak. To be archivally correct oak has been recommended. BUT, it's been my experience that oak cracks or splits much too easily (lesson learned from splitting firewood) and I have been recommending ash as a replacement. I can't alter dimensions and I can't reinforce with metal and I can't use any of the modern laminates. So, which would you recommend, oak or ash? Thanks!

[Cody Colston]

If dry, the Oak (White Oak) is probably the stronger of the two, structurally. Green, Ash is moe stable because it contains less moisture. it's also lighter for that reason.

I don't think you can beat White Oak for strength. If straight-grained timber is used, any checks are really inconsequential because they will be along the grain.

[Kevin Begos]

Remember that ash has some flexibility.
This from a U Florida wood description:

"The white ash is also known as American Biltmore or cane ash. This tree is most famous for being the best wood for baseball bats and other sports equipment such as tennis racquets, hockey sticks, polo mallets, and playground structures. The reasons for white ash being the most popular wood for these items is that it is tough and does not break under large amounts of strain."

But for a floor joist? Not sure. It might bend but not break, but then you'd have a bent floor joist....

[Glen Butler]

I assume since it is a joist, that there are several others than have not broken. Therefore, you pretty much answered your own question. The original joist was oak FROM 100 YEARS AGO. Go with the oak. They want oak, the original was oak and from what I can tell did an adequate job. If nothing else someone 100 years from now will have to replace a joist. Ladeefrickenda.

[Chip Lindley]

A joist 11" tall, tapering to 5" ends, in effect gives you only a 5" tall joist. Poor engineering in the original building. That is the problem, not oak or ash! Either hardwood is plenty sturdy.

[Peter Quinn]

Are the joists visible? There seem to be a lot of restrictions. Is this part of a hysterical society restoration? If so, use oak, do what they want, it makes them happy to believe that old buildings should be maintained as artifacts.

If these are people of reason, insist on imbedding a steel fliftch plate in the joist, or mending plates near the five inch ends. What difference could it possible make having steel buried in a ceiling?

[Tom Rick]

100 years is not bad..

Can you perhaps increase the size of the joist just a hair?
Is there a reason the joist failed outside of just floor loading?
Did it fail with deflection as would be expected from under size/under strength joist, or perhaps split where there was a poorly placed spike or poorly designed joint?

[Stephen Cherry]

The ends carry a lot of weight and thus there is a lot of internal stress on the joist. The original cracked from the stress.

It may be time to call in a structural engineer.

[Dick Strauss]

Jim,
I'd use oak again.

The original 2" per foot taper is probably what caused the cracking. In essence you are exposing the end grain and leaving it unsupported at the ends (as Chip said it is really a 5" joist). If you could find a piece of oak with the grain that closely followed the taper, you'd be much better off. I suspect that you have a hard time finding a piece of oak that big.

[Tom Scott]

A joist 11" tall, tapering to 5" ends, in effect gives you only a 5" tall joist. Poor engineering in the original building. That is the problem, not oak or ash! Either hardwood is plenty sturdy.

Not exactly true. There are two things working in a joist: moment and shear. Moments are higher in the middle of a joist. This is where the depth helps. Shear is higher at the ends. It may be that the reduced section works. I've seen this a lot in old timber structures. More depth at the end is better, but may not be required.
An engineer could certainly help if you need justification.

[Brian Tymchak]

A joist 11" tall, tapering to 5" ends, in effect gives you only a 5" tall joist. Poor engineering in the original building. That is the problem, not oak or ash! Either hardwood is plenty sturdy.

Just for grins, visualizing this joist as a very thick, very shallow shelf, according to sagulator (http://www.woodbin.com/calcs/sagulator.htm), the results come out within .001" per foot deflection of one another. Parameters: materials =white ash, white oak, 72" length x 3" deep x 5" thickness.

Brian

[Jeff Duncan]

I'd be inclined to stay with what was original...as previously stated it's lasted 100 years already so? On the other hand if it failed long ago from improper design (ie it's an undersized joist), or more weight has been put on it than it was originally designed to support, I would strongly suggest having a structural engineer get involved. There's not enough info provided to really make a educated opinion on your particular situation, but keep in mind once your work is done you own it. If it fails (or even worse if it fails and someone's injured) guess who's taking the blame:eek:

Now the oak they originally built with I believe would have been green, as it's now fully dried you'll either want kiln dried, or possibly better from a originality standpoint, reclaimed wood for your replacement. Either way that's not a large size and readily available.

good luck,
JeffD

[Jim Mackell]

Thanks for all the responses. At this point we're having a hard time finding either oak or ash in the required size and (horror of horrors) may actually have to laminate one! Yes, this is for a "hysterical society" project where to the extent humanly possible, materials and techniques must follow the original. Thanks again!

[Jeff Duncan]

Hmmmm, that's not a large size for oak. Not sure where you are in Maine, but I'm sure I could get that pretty easily in my area. Last time I called about big white oak pieces it was for 10" by 10" beams for a restoration project. Called up a local reclaimed lumber place and they didn't even flinch;)
Even new kiln dried lumber should be available. Course when you only need 1 short piece it may make it tougher?
good luck,
JeffD

PS if you don't have any luck PM me and I'll call a couple of my suppliers on Monday.

[Brendan Plavis]

Structurely speaking, the oak can span longer distances. The modulus of elasticity for White ash is 1249 kg/mm² which for my span charts, if I am converting this correctly should be 1.249 which is about the same as Spruce. Swamp White Oak(using this data, so I can show you the difference in spans(since 1.249 and 1.251(white oak) essentially are spanning the same +/- a couple inches) on the other hand is 1446 km/mm² so 1.446.

Since I dont have the data for (4x)s Ill use the example of a 2x6:

The ash can span, at a joist spacing of 16", a maximum of 8'-10".

Where as Oak can span, using those figures, a maximum of 9'-4".

As you can imagine, this is from Beam to Beam.

Sorry, since I wasnt sure the spieces, I had to just use random spieces.


You can find data for all different woods at: http://www.csudh.edu/oliver/chemdata/woods.htm

That is where I got the figures from(between that and the use of a span chart, which can be downloaded off the net...

-Brendan

[Scott T Smith]

Jim, was the oak joist that split quartersawn (when viewing it from the 11" face)? If so, the cellular orientation for a flatsawn joist may lend itself to being less likely to split.