Hail storm roofing repair question

[Larry Browning]

My small rent house received enough hail damage to get a insurance check to do the repairs. There are no current leaks, but there may be soon if I do not put on a new roof. There is only 1 layer of shingles now. As I was growing up (back in the 60s) it was common practice to simply add a second layer but never a third. This is what I have been planning on doing with this roof. However, I am finding that this practice seems to be frowned upon these days, but I cannot get anyone to tell me exactly why it is a bad idea to add this second layer. Every estimate always want to remove the existing shingles before putting on new, but they really don't know why. It seems to me that 2 layers should be better than one, even if the first layer is not in the best of shape. The current layer is not curled up or broken and from the ground looks pretty good. This is a small rent house with a very simple roof (no valleys).
Why is it a bad idea to add the second layer?

[Jason Roehl]

Larry, there are a couple reasons to not add another layer of roofing. First and foremost is the heat. Two layers hold a lot more heat, leading to premature failure of the roof (how much is up for debate, but it could mean 15 years instead of 20). Second is because of future leaks. If the top (newer) layer develops a leak at some point, chances are that the bottom (old) layer won't leak at the exact same spot. Rather, the water will run between the layers until it finds a place to leak through the bottom layer. This makes troubleshooting leaks in the top layer much, much more difficult, if not, impossible.

That said, if you go the second layer route, to make them look good, the proper technique is to "nest" the top layer in the existing shingles. In other words, the top of your first row of new shingles would butt up to the bottom of the second row of the old shingles (you would have to cut this first row), then the top of the second new row (first full shingle) would butt up to the bottom of the old third row. This way the new shingles will all lay flat on the old shingles.

[Randy Cohen]

there can be weight issues...is the roof framing capable of supporting the weight of another layer of asphalt shingles?

[Pat Germain]

Having multiple layers of shingles also makes the next replacement job more difficult and more expensive. Of course, if you don't plan on owning the home then, it may not be a problem. However, prospective buyers will flag this as a potential problem. The days of ignorant buyers are going away. Almost everyone hires an inspector and watches HGTV. ;) And they don't like multiple rows of shingles.

When you could throw away things for free, ripping off two or three layers of shingles wasn't a big deal. Now that you typically have to pay to dispose of a whole roof of old shingles, it's going to cost you more with multiple layers.

By the time you add up the extra work, extra time and extra disposal fee, it equals bad idea. FYI, my father put a second layer of shingles on his house in Oklahoma several ago. It looked like dog doo as soon as it was done and it's looked worse every year since. I don't think they followed Jason's advice during installation. Also, it gets very hot in Oklahoma. As Jason pointed out, I think the two layers of shingles seriously cook in the summer.

[Von Bickley]

Larry,

Preferred method is to remove old shingles. You'll get a much better job.

[Larry Browning]

Are these new things that have been "discovered" within the last 40 years? I am still hung up on what used to be a normal accepted thing to do. But now is somehow a shoddy practice. Why is this? Roof technology hasn't changed that much in 40 years has it? My dad was never one to skimp on quality, this just does not compute for me.:confused:

[Joe Pelonio]

Are these new things that have been "discovered" within the last 40 years? I am still hung up on what used to be a normal accepted thing to do. But now is somehow a shoddy practice. Why is this? Roof technology hasn't changed that much in 40 years has it? My dad was never one to skimp on quality, this just does not compute for me.:confused:
Larry,

When I was young I helped my Dad do several roofs too, and in most cases we went over the old ones with the new. It's not so much that roof technology has changed, but that over the years ideas change based on experience over a longer time.

Asphalt roof manufacturers have proven that a cooler, ventilated attic leads to longer shingle life. When you go over it again, the lower layer acts as an insulator. Heat does not radiate into the attic space as well as a single layer. The upper layer then becomes hotter than it would otherwise, so it won't last as long as new shingles in a single layer.

[Tom Godley]

Years ago almost all roofs were of the simple 20 year "three tab" design - and it was normal to add a second layer on top of the old with a layer of felt paper between - some were of the mind that the felt was not needed. Normally you would cut off the tabs from some new shingles and fill in the first row on the roof -- this would give you a flat surface to install the roof all the way up. If you are going to use three tabs I see no problem with this at all -- you do need to use longer nails to make sure they are actually nailed to the roof.

The weight is not an issue unless something is incorrect in the structure -- modern shingles use a fiberglass base whereas years ago they were paper impregnated with asphalt and actually were heaver per square.

The 50 year three layer shingles that I installed on my current home after ripping two layers off, are heaver and thicker than any two layers of regular three tabs would ever be.

There are many ways to look at this -- And you will get an expert on each. Some modern designs as well as SLP built houses have no ventilation for the roof at all - some designs add one in very warm climates. Houses with great snow load may need extra protection for ice dams - while others are subjected to great winds.

I remember reading years ago that the use of felt paper did not provide any protection for the roof once installed - but it is always used??

When in college - too many years ago :) -- I did rehabs and I remember being surprised that other than having twice the trash the actual roof removing work was about the same. Maybe twenty five years from now when they take those roofs off they will have some use for them other than the dump.

[Stephen Beckham]

Larry,

I've got a set of 30 yr shingles sitting in the yard waiting for good enough weather to have mine re-done. I currently have two layers of 25 yr on the roof now. The second was added as a cheaper alternative to removing the first layer (by previous owner through storm chaser roofing company) and according to the fella doing mine - the top layer only being six years old should have lasted a lot longer. He said he's done lots of roofs - and most of the two layers he's removed are being replaced earlier than they should have been.

He went on to tell me to check with my insurance company - they might not cover a new roof if I put a second layer on because of expected early failure (he's right - USAA doesn't allow layering in a job they are replacing - I can do it if I choose, but if they find out, they do not have to cover next repair).

He told me that most shingles have a small print that says warranty is void if not proper installed (which layering is considered not proper to some companies).

He told me that my attic should be cooler after removing the two layers and adding the ridge vent - the objective is for the attic to be at same temp as the outside - most get extremly hot requiring more A/C.

He told me that it's common practice for storm chasers to encourage layering because it's quicker and their gone by the time it fails. (I can't find the guys who put my second layer on - so their warranty isn't worth the paper printed on).

One last note - your insurance company is going to hold out a 'depreciation' - That is yours! Some companies do not tell you about it. It's a reserve (lack of better words) to insure you fix your roof. Once complete, they'll refund the rest of that back to you as well. Most will hold that out to ensure you don't just take the roof money and spend it versus actually repairing the roof. Just FYI - something I learned on this little venture.

Steve