Brand new roof or re-roofing with molding problem ?

My house was built in 1986, about 3000 sqft, 2 story and colonial style. I noticed some black stains on the roof and was told that it was molding. No leaks(maybe not yet ?) and no shades or tall trees around. When I got roofers for an estimate, some said it's ok with re-roofing meaning putting new shingles over the exiting ones. Others said they need to take out the old and put down the new shingles. Can I have your expert advice on this ? Thanks.

Public Comments

1. At any rate.... the molded area will have to come out because it can be bad for the health and could spread to the rest of the house.. If roofer number one can get rid of the mold by removing part of the roof.. then go that route.
2. Now I am no expert, but I have been a carpenter allmy working life (I am 76 now) Those that have told you to replace with a new roof, might be right? If the roof has been on your house for 25 years more or less, I would say replace, I am not too much on putting a second layer of shingles on a roof. It involves removing the tabs and then nailing new shingles over what is left. I don't like it because it only adds weight to the roof, and sooner than latter you are going to have to have that roof removed, then the cost to have the roof replaced will cost more because they (the roofers) will have to remove a double layer of old roofing. My suggestion find a reliable roofer and trust him (go to your bank and ask them who is a good roofer)
3. I would recommend pressure washing the molded areas clean, let the roof dry then install a new roof over the existing.