Reasons to Clean
Although the general direction of air in a house is upward and out through the attic, the quality of attic air can still cause problems for those living below. The primary reason is moisture. Warm air hits cold attic surfaces, and condensing moisture promotes the growth of mold and mildew on surfaces like rafters and roof sheathing. Growth can be accelerated by wide temperature fluctuations, blocked ventilation and small roof leaks. If broken screens or vents have let animals or birds into the attic, attic dirt can be high in allergen and possible disease.
Before working in the attic, open windows or vents to allow fresh air in as much as possible. Block doors or hatches to other parts of the house with plastic sheeting, and ventilate attic space for 30 minutes to an hour or longer before going to work.
The watchword for homeowners cleaning attic space on their own is "protection." Personal protection -- an N-95 respirator or heavy dust mask, goggles, protective clothing and gloves -- is a primary concern for everyone coming in contact with attic dirt and dust and bleach or other recommended cleaning chemicals. Turn off heating, cooling or ventilation systems with attic pipes or vents. Use microfiber cloths to remove more dust than paper towels or conventional fabrics. A vacuum cleaner fitted with a high-efficiency particulate air filter assures removal of contaminants, although a heavy-duty dust filter may be adequate for an attic that is merely dusty.
For a thorough cleaning, remove all items stored in the attic. If you cannot do that, gather items in the center of the floor, clean off dust and dirt and wrap them in plastic to protect them from cleaning chemicals.
Cleaning Animal Damage
If you see droppings or other signs of animal damage, spray them with a solution of 1 part bleach and 10 parts water, and pick them up with a towel or rag for disposal. Do not sweep or vacuum them because this can spread potentially disease-carrying dust. You can sweep, then wash down with bleach solution the surfaces that have no visible animal damage.
Pull out dirty or wet insulation batts and bag them in plastic for disposal. If most of the insulation is soiled, remove and replace all batts. If insulation is loose, sweep or vacuum it up and dispose of it all. Put down new insulation after you have cleaned the surfaces underneath. If you have had animal damage, thorough disposal reduces the chance that vermin will remain behind.
General Surface Cleanup
You can sweep or vacuum all attic surfaces. If they show the dark blotching or streaking that suggests mold, wash them with bleach solution as well. Ventilate the attic thoroughly between washing sessions and after you have finished. You can keep surfaces cleaner with clear sealant. Let that dry thoroughly before moving stored objects back into the attic.