The hardest parts about blending a new addition into an existing house is the siding, roofing and flow of the addition. If the addition is going in an area where the siding is not an exact match or the roof on the addition is new tying into a 10 year old roof, it’s a dead giveaway that work was done. If the siding is painted, it’s easy to match but if it’s vinyl siding that is no longer made and one of your big concerns is about the addition blending in, we would recommend replacing all the siding on the house so it ties everything together. Taking a similar approach to the roof, if your existing roof has a lot of years on it and you are dead set on it matching, this would be the time to replace the existing shingles to match the roof.