Does two layers of shingles improve the life of the roof?

Jack from South Carolina asked:

I recently purchased a house built in 2004. After the builder installed the 30-year shingles, the POA did not approve the color. Rather than remove the shingles, the builder put another layer of 30-year shingles on top of the shingles that were just put on. My question is how long will this roof last since the first layer was new. 

A: Regarding your question, a house with two 30-year roofs does not mean it's a 60-year roof.  I don’t know if that situation has been lab tested. The roof-over-roof does not diminish the function of the overlay roof. However, the warranty is only for the top layer. The only down side of having two layers of roof is that when you do need to re-roof, you have an extra layer to remove. You cannot install a third layer of roofing. It will cost about one third more for your roof removal.

Answered by John Stout of Go Roof Tune Up