Ever see this type of splitting in a ridge board?

[Backcheckrage]

This house was built in 1950's. We are in an earthquake prone area. The ridge board is a 25mm X 200mm sawn timber supporting purlins which in turn support a concrete tile roof. There is this weird split to the bottom end which I can't imagine why this would be. A theory could be a combination of deterioration and some seismic activity? Anyways, I thought I would share. I've not seen this type of splitting before.... any ideas?

 

[Ron]

This is ungraded, rough cut lumber. Looks like a grain defect in the lumber. The concrete tile has no waterproofing underlayment so it is likely that you have a lot of moisture cycling (wetting and drying), which exacerbates the grain defect over time. Virginia Tech in the US has some good timber/lumber resource material as does the American Wood Council. Look up grain loosening.

 

[msquared48]

I agree with Ron. This is not due to seismic activity.

The tear is so uniform it almost looks like Cedar, but probably is not.

Mike McCann, PE, SE (WA)

 

[oldestguy]

Agree with above. However, the board for that application has no use other than for aligning the rafters.

 

[MacGruber22]

However, the board for that application has no use other than for aligning the rafters.

I don't feel that is strictly true. I think a better version of your comment is that the defect in the photo does not affect the roof structure capacity. I can envision a few other types of defects in the ridge that would be unacceptable and compromise rafter stability.

"It is imperative Cunth doesn't get his hands on those codes."

 

[berkshire]

Looks like a quarter sawn log where the center of the tree was brash.
B.E.

You are judged not by what you know, but by what you can do.

 

[calvinandhobbes10]

Not seismic. Attic looks in good shape.
Don't think you should mess with it unless (1) you see other problems or (2) they want to replace the roof for other reasons, in which sheathing and shingles will reduce seismic weight, add a roof diaphragm, and give an opportunity for a water barrier.

 

[hokie66]

berkshire,
Have never heard the word 'brash' used in this context. What does it mean?

 

[Archie264]

Here's a link: Brash

From the link:

"...brash wood breaks suddenly and completely across the grain with brittleness in fracture and with a comparatively small deflection. Consequently it absorbs relatively little energy in bending. Wood that is characterized as tough, on the other hand, breaks gradually, with continued splintering, and only after comparatively large deflection in bending has occurred."

 

[dik]

Unless the collar ties have failed, the member is subject to little or no stress other than compression perp to the grain... unless the compression terminating along the line of the bottom of the roof rafters has caused splitting because of the change in stress from the bottom of the ridge member to the underside of the roof rafters.

Dik

 

[msquared48]

Seems very odd to have that happen with the collar tie construction showing - probably only a 4 to 6 foot span for the ridge beam, and very little deflection - unless the collar ties were added after the tile roofing was installed?

Mike McCann, PE, SE (WA)

 

[Ron]

The issue showing is not stress related! It is a function of the lumber grade and moisture cycling. Has nothing to do with induced stress.

 

[dik]

Very interesting split if only due to moisture changes. I guess the roof rafters could restrain the material above by friction sith the moisture changes affecting the material below. Ron: have you encountered this condition before?

Dik

 

[hokie66]

Archie,

Thanks for the definition. From that description, which says that "brash wood breaks...across the grain", that doesn't seem to be the issue here, as this broke with the grain.

 

[Backcheckrage]

Thanks for the replies everyone. Appreciate the insightful comments. I don't think it's stress related at the moment. And good to know about "brash". Cheers.

 

[berkshire]

Hokie66 ,
I agree that that the timber did not break across the grain which is the usual definition of brashness, however Brash lumber can be harder and less flexible than the good timber adjacent to it The only way to tell would be to pull the piece down and try to break it.This timber appears to have split on a growth ring very cleanly , and from the straightness of the split it appears to be a nice piece of wood, sometimes a failure of this type will show up when the lumber is felled. Starting off as an end shake that nobody spotted when the lumber was sawn. If that split does not travel any deeper into the ridge timber than it has , I would not mess with it.
B.E.

You are judged not by what you know, but by what you can do.

 

[msquared48]

Ok. I am trying to understand the cause for the condition in the member.

Could the brashness be caused by a very dry year followed by a very wet one, causing a weak plane in the growth rings, existing the splitting we see here?

Mike McCann, PE, SE (WA)

 

[msquared48]

Another question would be is this condition either species or region specific?

Mike McCann, PE, SE (WA)