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Question DetailsAsked on 4/15/2015

What is causing cracks in my drywall AND wood doors/trim?

Moved into a 12 year old home (about 4000 sqft) in burbs from a condo in Chicago last summer. At walk through and inspection, walls looked great. Fast forward: most of winter our home's humidifier was not working. During that time, many cracks in drywall, nail pops, and wrinkled drywall tape appeared. All appeared aesthetic but on large scale.

Resolved issue & also purchased an additional floor unit to help with first floor and finishd basement (avg RH now ~40+%). Now, even more cracks and pops are appearing along with small hairline cracks in doors and wood the wood itself, not at the seam.

Furnace guys said too dry and we needed different humidifier (purchased the floor unit to save $'s). Different contractor said too little humidity, humidifier ok, but needs to be moved to outflow side. Insulation guys said house is too sealed and humid and we need electric ventilation system.

Old owners could not have experienced this yearly! Something's different. Help!

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1 Answer


IF you know the old owners or can contact them, you might ask if they had any such problem in the past, if they used the humidifier on the furnace (or floor mounted one), or had a lot of house plants or open aquarium in the house that might have resulted in much higher humidity when they were there.

And I presume you have checked around the house for signs of settlement such as sagging or cracked exposed joists, open foundation cracks or several closed ones (especially diagonal), diagonal cracking at corners of doorways/windows, jamming windows or doors, etc.

Humidifier (in-duct type) DEFINITELY should go on the outflow side, otherwise you are going to rust up your furnace, and also possibly cause mold in the filter assuming the return flow goes through the filter. HOWEVER - it needs to be installed in a location or with ducting modification such that if it leaks water that water and water vapor from the unit (when fan is not running) does not run down into the furnace and rust the blower/motor/controls/furnace housing out.

Ideally, in new construction the humidifier should be on the outflow side AFTER ("downstream") from the A/C evaporator also to reduce the amount of moisture condensed there (and not remove the water you had just put into the air), if you have central air. However, if "upflow" from the evaporator but downflow from the furnace that is not fatal, as long as the humidistat measuring the humidity in the air is downstream of the A/C evaporator coil so it is using the actual humidity in the airflow AFTER the coil has removed a bunch of the moisture to determine whether to run or not. However, the added moisture precipitating out on the coil will promote corrosion and quicker failure. [Note - using upflow/downflow as being before or after the furnace or evaporator - not referring to upflow/downflow type furnaces here]. If the humidifier is "upstream" of the furnace - on the return duct, then if it is not moved to the supply duct I would keep a close eye on that area and the furnace air supply "box" or intake area, to be sure you are not forming mold or rust, and maintain the humidifier as specified in the instructions.

One thought - in residential building, excepting in extremely dry climates like deserts, additional humidification is generally not needed with a normal sized family for the size of house (as opposed to say 1 person in a large house) - between bathing, washing, cooking, plants, body evaporation and respiration you generally get enough humidity to stay in the desireable 35-45 or 50% range, or may need just a small boost with a floor humidifier - whole-house residential (as opposed to commercial building) units commonly cause as many or more problems than they solve, and since the owners rarely maintain them as necessary, commonly cause furnace damage and in-duct mold as well.

Clearly, if the cracks and splitting wood were occurring in prior years, you almost certainly would have noticed it during your walkthrough - so yes, likely "something" different is going on.

Cracking trim and door veneer is a common sign of only very low humidity (say below 20% or so) - drywall hairline cracking generally perpendicular to the wood framing it is nailed to is too. In high humidity, unless so high it is causing warping of the wood I have not see trim distress other than rusting nails - door veneer can sometimes bulge and delaminate in quite high humidity.

However - wrinkled drywall tape - as in bunched up across the joint, not diagonally stretched so it is "pleated" or "zebra striped" at a diagonal as occurs during shear movement along the joint, and popping nails from swelling wood or rusting nails working their way out are generally signs of wetness in the wall, not low humidity - so a possible mixed story here.

First thing I would do - Get a decent humidity gage (Springfield, Meade, Oregon Scientific are some commonly available names I would trust) for about $20-40 to see what your "real" humidity is if you are going off just a strip gage, and check it in various parts of the house, especially if this is occurring mostly on one level or HVAC zone - which might be indicative of more of a circulation issue than overall household humidity. For instance, upstairs/attic living spaceswithout bathrooms up there commonly have this problem, whereas the lower floors with kitchen and baths might be fine. and of course, basements commonly have the opposite issue - too high a relative humidity because the cold ground causes condensation on the foundation and slab.

Also - look around and see if occurring only on one wall of the house, whioch would normally be indicative of settlement of the framing or foundation - though in that case most or all the trim cracking would be through the nails, and door facing cracking would be at edges/corners where it is jamming or dragging as the door opens and closes.

Then you would know for certain whether your problem is low or high humidity. Also, bear in mind, it will take the framing in the house and wood trim and such a couple of weeks to perhaps a couple of months to come back up to normal humidity from the higher house humidity, especially since your house, from its age, should have vapor barrier under the drywall so it takes a long time for the moisture to permeate the framing.

Where you go from then - unless it is clear you have excessively high or low humidity and lessing it acclimate to your current humidifier situation, is a tough call.

One final thought to throw into the pot - I left it till last to give you several possibilities to consider, but I think this might be your answer if the assumption is right - if this house was vacant last summer, and the A/C was left off or at a high temperature setting, your house could have picked up a lot of moisture during the summer - which was then removed by the furnace running this winter without a humidifier, so the relative humidity could have gone from near 80-100% down to maybe 20-30% - which would definitely make for the right conditions for a lot of wood shrinkage and cracking, so once you stabilize the humidity further signs may taper of to zero over the next few months. Once you convince yourself this is not a structural problem, this might be a case of wait and see if it gets worse after the winter is over.

Answered 4 years ago by LCD

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