Any reputable New Jersey powerwashing contractor will be using some type of chlorinated detergent to adequately remediate mold, mildew, or other organic matter from your siding. The main ingredient used at http://www.thompsonpowerwashing.com/ is Sodium Hypochlorite. This is the main ingredient in household bleach you might use in clothes whitening. It may be a higher strength used for pressure washing. This chemical reacts favorably in warmer temperatures. It works also in the cold but it may require a longer dwell time to get the same effect. You will not be charged more for winter months. Since winter is not as busy, the contractor will appreciate the work, even though it requires more time. The same holds true for roof cleaning.