Don't Overlay Shingles To the Editor: Regarding a question about overlaying asphalt shingles (On The House, 10/92): most shingle manufacturers will void the warranty in an overlay application. I can tell you from personal experience that if you do have a warranty claim of any kind, once the company rep sees that it is an overlay, he will just turn around and walk away. There are many premature roof failure problems associated with uneven roof decks and it doesn't make sense to tempt fate with an overlay. If a roof is worn out, chances are it won't make a good surface for new shingles. Get out that stripping bar and get rid of the old roof! Doug Friesen Duxborough Designs Duxbury, Mass. Nailers Need Repair To