Drywall Cracks in 40 year old home

[cse1]

I have inspected a 40 year old 2 story home with drywall cracks extending diagonally from several interior wall openings in one particular area of the home. The 2nd story wall cracks are directly over the 1st floor wall cracks. There is a crawlspace with masonry piers on concrete footings. There is evidence of previous moisture in the crawlspace but no standing water and a poly vapor barrier. The lot slopes moderately from back to front. The crawlspace soil appears to be clay but does not look like it could be the cause of the cracks. Any thoughts on what might have caused the cracking?

 

[ChipB]

Differential settlement. Typically what I see around here, is a main girder beam suppported by masonry piers centrally located in the crawlspace. The rest of the framing is supported by the exterior walls. So you've got 50% of your load going to the piers, and 25% going to each of the exterior footings. If the exterior is a foundation wall, it is continuously supported, so the soil pressure is significantly less than that of the interior piers. Assuming the soil is the same across the house footprint, the middle of the house experiences more settlement.

Put a level on the underside of the floor joists to verify they are sloping towards the interior.

 

[Focht3]

A 40 year old pier and beam house that only recently began to experience problems? Something has changed - things to look for include:[ol][li]Plumbing leaks[li]Large trees near distressed area[li]Grading changes within the last 5 to 10 years that could have adversely affected site drainage[li]Structural damage (damaged pier, beam, etc.)[li]Modifications to the structure within the last 10 yearsExcessive floor loads (unlikely)[/ol]Do any of these seem likely to you - for this house?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[ERV]

It has been my experience that cracks diagonally off of door openings are the cause of horizontal movement of the wall. Check doorways for plumb and exterior walls perpendicular to the subject wall. I have also noted that some older structures will move excessively (racking) during periods of strong winds, often returning close to plumb.

Differential settlement can also produce cracking of this sort. Check first and second floors for deflection.

Are any of the doors affected by this, such as opening or closing, uneven gaps around door and jambs? If doors are all the same in relation to each other then it is a racking problem. If the doors at opposing ends of the wall are affected opposite in relation to each other then it is a settlement problem.

 

[catanzarope]

cse1,

Diagonal cracks can be related to settlement of the foundation, however they are most commonly the the result of differential downward movement of the wall - or more precisely the downward movement of the floor on which the wall is set. Let the crack orientation direct you to the forces acting on the wall - remember Mohr's circle !!

In buildings with crawl spaces, I often detect excessive atmospheric humidity and moisture in the timber beams and floor joists. Excessive moisture causes excessive creep and also results in favorable environment for fungal decay, which of course weakens wood and causes it to deflect (or crush) more.

The deflection of the joists or timbers can be determined by pulling a few stringlines along the length of these members. Crushing at a support is fairly obvious - but don't confuse crushing for an intentionally notched end. Determine the size and spacing of the joists - is the floor system satisfactory?

From up top, a simple "jump up and down" should enable you to gage just how stiff the floors are.

The humidity in the crawl space should not be above 55% and the moisture content of the wood joists/beams in the vicinity of 15% max. You can probe the joists/beams with an awl, meat tenderizer or other sharp/pointy metal object - hard wood is obviously stronger than soft, punky wood.

If you detect rot or insect infestation, excessive deflections or crushing call a structural engineer.