# Tear off the old roof or not? Please advice



## ChicagoGuy (Jun 21, 2010)

Hi,

I have an 80+ years old 2-flat brick building in Chicago south side. The roof is 22'x60' flat with tar on the top. The roof never leaked since I purchased the property 5 years ago. However it started to show old age; blisters, ripples, and some cracks. I don't want to wait until the roof leak to start repair. So I have a number of roofers went up to the roof and gave me estimates. Some told me that the old roof had to be removed. Some said they could lay bitumen membrane over the old roof. I have no idea who to believe. I found all of them from yellow pages. Hence I don't know who to trust.

Those who told me that old roof has to be removed were concern about the weight. Does those thin membrane weight that much? Also, how thick should the membrane be to make the roof leak free for 10 to 15 years?

Please advice.


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## Grumpy (Oct 29, 2008)

I've worked on numerous roofs that you have described... and yes it should be torn off. weight is a concern yes. However I post a question to you, how can you have a good roof placing a new roof over an old bad roof? The answer is you can not. All those ridges, blisters and wavyness will carry through (at least partially) to the new roofing membrane.

Furthermore there are codes that govern how most trades are to operate. In the fine city of Chicago these codes are often ignored, especially for roofing. However the code was changed from 3 layers of roofing down to two layers last year. Therefore you are most likely currently far in excess of the maximum number of layers of roofing material allowed. Any additional layers would likely be against the law. 

Thicnkess is mostly meaningless when it comes to material, and a 10 year roof is a complete waste of money in my opinion if you are tearing off. You shoudl opt for no less than 1 5 year roofing system, preferrably a 20 year rated roofing system if your budget allows. How the roof is installed is equally, if not more, important than the materials used. We typically no longer use modified bitumen, although it is a decent product. I however prefer white reflctive single ply membranes such as TPO and PVC which do not require to be coated every few years, meet the current city of Chicago reflectivity code. Furthermore these membranes can be installed without open fire, like modified bitumen uses open fire. 

If you choose to go with a single ply you would want no less than a 60 mil membrane. If you choose to go with modified bitumen opt for a 3 ply (base sheet, base sheet and granulated cap sheet) both would be a 15 year roof. 

Now would also be a good time to address your insulation which is probably next to nothing. I also suggest the gutter always be replaced with the roof (assuming it is not brand new).


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## AcclaimExteriors.com (Jul 5, 2010)

I agree with Grumpy Completely. :thumbup:


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