You've got to do a tearoff. Especially if the shingles are buckled. Metal has to go over a flat surface. And you've got to inspect the sheathing. Get your ladder and shingle shovel out and you can do the tearoff. Putting the metal down isn't that hard either. We did it on our barn.

Thanks Holly. We are in our 70's now. We used to do everything ourselves but the garage has a cedar home built over it (which my husband built) and the drop on one side from the roof is over 40 feet. I'm not going to let him do the work this time.

We had a metal roof (steel shingles) installed 2 years ago and we had them remove the original layer of asphalt shingles that were about 15 years old. They were buckling bad and we were afraid any heat buildup in between would further the problem and create an issue with the new steel shingles. Plus I felt the added weight was an issue.

Check to learn about the metal roof warranty if you place it over old shingles.

The steel shingles we installed were nearly double the cost of an asphalt roof shingle; however we felt it was worth the cost since we're in a high wind and hail area. It was definitely worth the added cost for us. Many in our area are going to the steel shingle.

Check with your Fire Marshall.

Sue

When I checked into the metal roofing all of the installers told me they leave the singles in place and put 1X6 treated lumber across them to attach the metal to. Not sure if that is the correct way or not but I couldn't afford it at nearly double the price of quality shingles.

Having done installations on a primary roof instead of a tear down, I have never repeated this mistake.
I have replaced roofs three times in three different states using asphalt and cement tiles. I looked at metal tile on the last home but we lived in a high end neighborhood and it would have not meshed.

Our present home was owned by a couple who were in their 80's. They left me a packet of their repair costs. I can see that were taken several times by a few . Prices were inflated and workmanship was poor.
Some contractors assume homeowners are.... gullible.
Shop around for more quotes. Measure the work area and price out how much the material cost should be.

I have measured 800 and told I need 1200.
I recently did a basement insualtion install and measured 710. I was told I had 1200 for a three day install.
I hired the company who said I had 750 sqft and it was a two hour installation.

Good Luck
Be informed

I want to thank you all for your responses. We priced the metal supplies with asphalt and at Menards, the price in materials was only $200 more for metal. That surprised me since all of our estimates were coming in twice the amount for metal.

We had even put out an add where we would pay for the materials and insurance if a experienced roofer would want a side job --- no takers on that though.

But then we got a local company which is highly recommended who will do the job at an affordable price (metal over existing shingles.)

BTW, we are out in the middle of nowhere so do not have to worry about fire marshalls or crazy permits and regulations. There are definitely advantages to living in the country.

Can it be done...yes. Most metal manufactures will allow for this application with a slip layer of some sort and/or batten/purlin installation.

I prefer that we tear off all the old asphalt to help with the performance of the metal roof in this case.

Thanks for all of your advice. We had the roof put on (over the existing shingles) last week when there was a warm spell and before the snow came.

We were told since the underlay was in good shape and the shingles were not coming loose that keeping them in place would increase the insulation. Anyway -- it is done.

"BTW, we are out in the middle of nowhere so do not have to worry about fire marshalls or crazy permits and regulations. There are definitely advantages to living in the country. "

You can say that again !

"BTW, we are out in the middle of nowhere so do not have to worry about fire marshalls or crazy permits and regulations. There are definitely advantages to living in the country. "

LOL