Wooden support beam question

[Dinsdale]

My wife and I looked at a 1911 craftsman style home the other day. We aren't considering it due to the floor plan and location, but I had a question about something we saw.

In the basement, the main support beam was wooden, and was supported by several adjustable metal columns with screws on the tops of them. The sides of the beam had several places where "gaps/cracks" were visible running lengthwise, tho not for the entire length ofthe beam.

My wife thought these a sign of structural problems. I wasn't so sure, and was at least willing to get an expert's opinion (if we had been interested in the house). I thought I remembered hearing that it was common for wooden beams to show such signs of stress at some point with settling, but there was no problem so long as there were not signs of ongoing settling. And the plaster walls and ceilings looked quite solid throughout the house.

I wish I had brought my camera. Sorry.

[Stranger On A Train]

Originally Posted by Dinsdale

In the basement, the main support beam was wooden, and was supported by several adjustable metal columns with screws on the tops of them. The sides of the beam had several places where "gaps/cracks" were visible running lengthwise, tho not for the entire length ofthe beam.

My wife thought these a sign of structural problems. I wasn't so sure, and was at least willing to get an expert's opinion (if we had been interested in the house). I thought I remembered hearing that it was common for wooden beams to show such signs of stress at some point with settling, but there was no problem so long as there were not signs of ongoing settling. And the plaster walls and ceilings looked quite solid throughout the house.

The cracks in the beam are probably the result of shear flow (interlaminar shear due to bending), indicating that the beam was not adequately supported, hence the jackstands installed later to support the beam. This is fairly common in older houses that were constructed prior to standardized building codes. (Also be aware that the beam was probably untreated lumber, and possibly age seasoned rather than kiln dried as modern construction-grade lumber is, and so will be more prone to thru-cracking as it ages.)

Wood is nature's natural long fiber composite material, and as a result is very strong (yellow pine is slightly stronger per weight than steel) but like all composite materials it is only as strong as its largest flaws. Modern wood beam construction is almost exclusively laminated materials like Glulam(TM) or laminated veneer lumber, which limits the size of innate flaws and the degree to which they can propagate.

Whether the structure is compromised or not would have to be evaluated by a structural engineer, which you should do if you were planning to buy the house. If the beam is adequately supported by the jackstands, and they have adequate footing so that they won't sink faster than the house does, it's probably not an issue. However, looking at the wall and ceiling plaster is not a good indication; especially with plaster & lath construction, as it is relatively easy to patch cracks and since the surface is never as smooth as gypsum board it is difficult to tell if there is an inherent flaw. A better indication is looking at the squareness of door frames, especially those that are most effected by the deflection of the beam. An experienced inspector should be able to tell you if there are indications of excessive settling, but again, a structural engineer should be consulted to assess the adequacy of the required supports.

Stranger

[Dinsdale]

Wow - thanks!

[herm]

if it is a solid wood beam the cracks you see are probably due to the wood drying out and "checking" or cracking from the internal stress of the beam shrinking. Not necessarily from stress of the house.

[TriPolar]

I realize this is an old thread, but I haven't really looked at this forum and maybe I can get some discussions going.

The type of wood, and how the beam was cut are factors in the structural integrity of beams with checking and cracking. Some woods like oak are very susceptible to checking usual with cracks opening at the end of beams. Oak beams are sometimes wrapped with a steel band at the end to prevent this. But I've seen oak beams over 200 years old that probably had their initial splits when they first dried, and haven't continued splitting or weakened since then. My current house is made from white cedar, and several purlins have longitudinal cracking. Center cut cedar beams with fairly deep cracking will not lose strength because of the long tight grain. With other soft woods cracking can be a serious problems where the openings continue to grow over time. Even with serious cracks in beams, it's usually easy to reinforce the beam with steel plates to preserve it. In the case mentioned in the OP, if the wood is otherwise intact, a steel beam could be inserted under the wooden beam to hold the load between posts, and the wooden remains, only bearing a compressive load.

[Sal Ammoniac]

I'll second what you said, TriPolar. I don't think I've ever seen a wooden beam of any size in a vintage house that didn't have visible cracks. But that said, there are cracks and cracks. If the cracks look fresh and new, and are accompanied by obvious deflection in the beam, then maybe you should worry. But old cracks that look like they've been stable for a long time? No particular worry. All old houses have them.