I would take the old roof off. It gives you a chance to see the sheathing and it removes a few tons of stuff off the structure. If you're moving in the time frame stated, 30 is 18 years more then you need.
Ron

I agree w/ Ron it's best to strip the existing, but of course it's a lot more money. If you go the re-cover route, insist they cut back the existing shingle overhang and run new drip edge. I would also insist on 30# felt when going over existing. 30 yr or 40 yr? The 40's might make a better selling point but the life expectancy of any shingle is dependent on where you live despite mfgr's claims. The fasteners will have to be longer to penetrate the sheathing. An experienced roofing outfit will know that , but i would mention it anyways as some will use whatever is in back of the truck. Im assuming you are checking the roofing outfits you are considering by getting references and looking at their work.

---I noticed at HD that 15# and 30# are virtually the same price.---

Per roll, yes. A roll of 15# felt is twice as long as 30# felt.

There is absolutely NO benefit to adding felt over an existing asphalt shingle roof. It's wasteful and will only add more junk to the landfill when it has to be removed again.

A tear off is the best choice. AND, proper attic ventilation is much more important then worrying about 15/30 felt over existing shingles. Without proper venting, shingle warranty is void and the house will suffer from heat/moisture damage.

Find a roofing professional with certified credentials.

Michael

A circa 1910 rental property I owned in the '80s still had its original wood shingles--and four extra layers of asphalt ones. No leaks.

Still, I'd strip the roof and probably use a #30 underlayment. 30 year shingles should be fine.

Watch the roofers like a hawk. The last place I built, they tried slipping in some 20 year shingles instead of the specified 30-year ones. "Just a few bundles, is okay?" Sorry.

The benefit to adding a layer of felt is dependent on location. It might not be necessary in your area, but in hot climates the old shingles will dramatically lessen the life of the new shingles w/o the felt barrier. I've seen it on many applications in our area when the new felt was omitted, been doing this for awhile. Proper ventilation is key regardless and is something that has always been an issue in our area, improperly vented attic space.

The house in Sedona AZ; 90's typical summer and lots of subfreezing in winter, so I imagine that would warrant 30# felt. The original old 3-tab shingles have lasted 30 years, are flat & tight and, just looking pretty shabby. The roofer is trimming the edges back 2" and installing new drip edge.

DWPC

I am a roofing contractor as well as a PE. Since I am in WI and could not possibly bid on your project - here are my 2 cents.

1) Stay away from Felt - period. Felt winkles which will show through the singles and it does not breath so it rots your decking. Since you are looking at GAF products go with Shingle Mate at a minimum (same price as felt) but I would recomend Deck Armor since it will breath.

2) Do not do a layover - complete tearoff

3) Ventilate, ventilate, ventilate - this is how you extend the life of the roof. Contractor should show you slide chart with attic SF which will tell you how much Fascia and Roof vent you need. Error to the high side.

4) 3 tabs made today do not last like they did 30, 20, or even 10 years ago. PE's and Archtects spec shingles by weight. Asphalt is the waterproofing in shingles but the price of oil has gone up if you have not noticed. All suppliers GAF included have reduced Asphalt and added stones to keep the weight up. Current average roof life span is 8-10 years nationally.

4) Make sure ice and water extends 24" from inside of warm wall. This most likely means 2 rows at 36" wide unless you hace no eves. I have seen contractors cut a roll in half and install only 18".

5) $800 to upgrade to 40 year is a steal - GAF's 30 and 40 look identical only the package is different. Make sure this is not a bait and switch.

6) GAF admits to a 1 in 100 truck load defect rate. Defect shows up in year 8 to 10. Base warrenty runs out in year 5. Coincidence I think not. Certainteed and Owens won't admit thier defect rate I would assume higher than GAF.

7) Take the Systems Plus Warrenty at a mininium. Extends material coverage to match shingle lable. Make contractor provide documented proof that warrenty card was mailed in. Consider going Golden Pledge - GAF will independantly inspect job and certify workmanship. Only deal with contractors that have done Golden Pledge and can show inspection reports. Score is 1 to 10 with 10 being the best. If they can show lots of 10's you know they can install properly. Improper installtion or failure to mail in card are the top 2 reasons warrenty is denied.

8) Contractor should agree to all of above in writing. If not find a new contractor.

We are in the process of obtaining quotes for a reroof (asphalt shingles)I am getting confused by the different contractors. Some say to reroof over the old shingles, some say strip off the old shingles. Also, some are pushing the polymer underlayment, while others say felt is just as good. We live in Southern California where our temps can be as low as 30 degrees in the winter and as high as 110 degrees in the summer. What's the best and most economical feasible reroof?