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Question DetailsAsked on 2/7/2017

We have noticed worsening horizontal cracks along plaster walls on 1st floor of home. Is this serious?

Home has full basement, which has previously flooded, but has since had flood control system placed. Cracks began appearing shortly after we bought home and had flood control system placed. Flood control system includes interior drain tile placement, creation of Sump pit with pump and re-grading of lawn/lot to fix negative pitch on which house sat

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2 Answers


Could be a number of reasons for this - would take an inspection by a civil/structural engineer and maybe a geotechnical (soils/foundations) engineer as well to tie down the cause. Here are a number of common causes of this, which might give you a hint if you are able to look around outside and under the house to look for signs of house/foundation settlement or cracking, soil bulging or cracking around the house, things out of plumb or level, etc:

1) insect damage in the house framing - maybe preciptated by the high moisture from the flooding, because most wood damaging inspects like damp wood conditions.

2) rot - ditto to above

3) house sits in expansive soils, and dropping the water level and removing the outside ponding has caused the soils to dry out, shrinking and resulting in foundation settlement and/or cracking. Or worse, in expensive soil areas drying them out with drainage causes cracking, then in the rainy or snow melt season those cracks let MORE water down by the foundation and cause the soil to expend with the wetting, causing foundation issues. Most common in the western part of the midwest - from the Rocky Mountain Front Range (and in localized parts of the rocky mountain states in the rockies as well) about 200-400 miles east of the front range - so from Canada and Dakotas down through WY, NE, CO, OK into Texas generally, with some occurrences in the next states east of those. Would normally exhibit foundation wall cracking and/or tilting if causing house cracking.

4) foundation failure due to excessively wet soil over a long time - basically the house is "sinking" a bit. Normally in clay and fine-grained river bottom soils. Would normally exhibit foundation wall cracking and/or tilting if causing house cracking.

5) drainage system under slab was not properly guarded against infiltration of fines into the drain pipe so it is "piping" or washing the fines from the underlying soil with the water it drains out, resulting in settlement of the foundation. If this is the case, the sump would have a significant amount of soil fines (mud/silt) in it - not just the normal sump pump "slime" but actual soil grit buildup, and quite significant - probably to the point of the pump discharge having noticeable fines piling up at the discharge point as well. Uncommon, but does happen in clean fine sand and silty soil areas like river bottom lands. Would also normally have cracking and/or settlement of the basement slab, and maybe foundation wall cracking.

6) framing issues which may or may not have been related to the flooding issue, or may be just normal cracking of drywall because of the long-term sagging of the joists and beams - especially if the cracking is in intermediate non-load bearing walls NOT over supporting posts or beams or walls in the basement. Note normal floor joist sagging causing cracking in overlying walls normally cracks only interior walls that parellel the floor joists - not ones going crosswise to the joists.

7) localized foundation wall failure - which would exhibit (if unfinished basement walls) pretty visible cracking in the foundation wall before you saw much cracking on the first floor.

You can find a fair number of previous questions with answers about specific foundation issues in the Home > Foundation Repair and Home > Foundation Waterproofing links in Browse Projects, at lower left, but if you don't have specific basement/foundation symptoms those may not help you much - but there area fair number of cracking drywall ones which might help.

Horizontal cracks would normally indicate settlement of that wall, with the cracking being most pronounced or "open" in the middle between supports (other than floor joists) under it - so commonly indicates (ignoring rot/insect damage) sagging/failing foundation wall if in occurring in outside walls, or rotting or sinking support posts or sagging support beam in the basement if occurring in interior walls. It can also happen in non-load bearing walls that do not have supporting walls under them - because even non-load bearing walls generally carry some load even if not intended too because they are VERY rarely built to be truly non-load bearing. Quite common in non-load bearing mid-house interior divider walls under roofs with snowloads which end up carrying some of the load from the trusses in the attic over them just because they come up tight under the trusses even if not connected - though in those cases you usually have diagonal cracking at the bedroom and bathroom doors which are parallel to the roof trusses as well.

One other possibility - if only straight horizontal cracks along drywall sheet boundaries, could be just a bad tape job (or not taped at all) and are only architectural cracks. Obviously, if spreading noticeably over a relatively short time (days or weeks or a few months versus many years) then they demand more attention than very slowly developing ones, which are commonly just patched over every 3-5 years or so as they develop.

Also - Generally - there are always exceptions - but straight (within 1/8-1/4 inch but relatively straight and not real jagged) drywall cracks vertically or horizontally are USUALLY not structural unless they also go through concrete or brick walls. The diagonal ones are usually what you see due to structural or sagging framing issues, normally initially originating at the top corners or doors and windows and then as the movement progresses developing diagonal cracks in the "field" of the affected walls as well, then into the corners as the problem advances. However, there are probably exceptions to that - though offhand I can't think of having seen one myself except in walls with relatively independent panels which conceal what is going on behind - like wood or plastic interior architectural wall panels. Tongue and groove finishes also do odd things because of their highly assymetric load carrying capacity.

Typical engineer visit (Search the List category is Structural Engineer - only civil engineer category AL has in Search the List, but if a foundation specialist is needed structural engineer will have one in the company or know one he can call in to consult on the issue. Visit cost typically around $250-1000 range depending on whether one or two engineers have to look at it, and on whether just an evaluation on-site or a simple remedial design need to be done too. Of course, if a real serious problem then cost can run up to several thousand $ more than that.

If you wanted, you could post a couple of photos of the worse cracking to get opinions on how serious it looks - use the Answer This Questions yellow button right below your question, then at the top bar of the UYour Answer box that pops up, the left-most yellow icon lets you post pictures in GIF, JPG, or PNG format. I understand JPEG (from Macs) also works but I can't guarantee that. If you do so, I will respond back with my 3 cents worth on how serious it looks to me - caption as interior or exterior wall if not evident from doors and windows.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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