I have a 400 square foot roof that is leaking. It is an almost flat roof next to a more slanted roof over my garage. I got an estimate from a roofer for $2800 who said the roof was shot. He said he wants to rip off the roof and the roof of the garage. There is nothing wrong with the garage roof but I guess the junction between the two roofs could be the source of leaks. I thought I'd save some money and do the work myself and just lay shingles over the existing roof. I went to Home Depot and was told that putting new shingles over old shingles was a bad idea because the old shingles would swell and crack and damage my new shingles. So I decided to rip off the roof myself. I started writing down UPC numbers of tar paper and shingle when a roofer came along and told me that I was wasting my money by doing it myself. He told me that roofing is an intricate and delicate business. He said that you need equipment that heats up the tar. He said cold tar won't last. I was just planning to spread tar that Home Depot had near the shingles. He said he would just lay shingle over the shingles that were already there for $1700.00. I told him that two people had told me that the shingles underneath will swell up and break the new shingle. He said he has put shingle over other shingle before and hasn't had any problems. He said if I wanted him to rip up the shingle that was already there he would do it for an extra $500.00 so the total would be $2200.00.
What should I do? Should I repair the roof myself or not? If I do, do I need hot tar or can I get away with cold tar, if I do need hot tar do I need to rent special equipment to heat the tar? Is it OK to just lay shingle over preexisting shingle or should the preexisting shingle be ripped up? I've also noticed that there are coatings for roofs. Should I just put one of those on instead of new shingles?
You should get a copy of the shingle installation instructions. You can get them off the shingle manufacture web site. I am looking at a GAF installation instruction that does not prohibit installing new shingles over old shingles. However, it's better not to and since you've already removed them you're already there-- Go down to the decking. In the case of a low slope roofs, you really need to inspect the decking anyway. You may likely have some soft decking that needs replacing. Most shingle instructions allow for shingle installation down to 2/12. If your roof is lower than that, you probably need a professional to install you a low-slope roofing system. You can check your slope using a builders level and tape. Place one end of the level on the roof and get it level. Then take your tape and measure down to the roof surface at 12 inches from where the level is toughing the roof. The distance measured from the bottom of the level down to the roof surface is your rise. For example, if you measure 2 inches down, then you have a 2/12 pitch. You can measure out 24 inches, measure down and divide the rise by two for a more accurate pitch determination. Low slope roofing is not your typical homeowner project. If you tackle a 2/12 re-roof, you must pay very close attention to many details. If your $2,200 guy is any good, it might be well spent money.
A roofer just told me that he knows that some of the woor under the roof has rotted underneath and that ripping it up will damage it even further and that if I don't want to pay thousands of dollars on replacing the wood I'm better off just putting a rubber roof on top of the roof I have.
Installing a new roof over rotted wood is a risk and generally not a good practice. Installing a new roof over rotten wood is likened to apply new paint over blistered and chipped paint. The new job is only as good as the surface it's applied too. You have to ask yourself the question, what if the roof decking sinks or breaks-thru? If any of those things happen, you now have a new roof over a mess. Generally, pay-me-now is cheaper in the long run than pay-me-later. Remember, your roof job is supposed to last 15-20 years. Recommend you get a second opinion from a well respected roofing contractor in the area.
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