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install new roof on top of old?
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posted
We have a townhouse with a flat tarpaper build-up roof that is approximately 25-35 years old and has been actively leaking despite multiple attempts to fix the problem. We have received numerous bids for this project and it is amazing how much they vary. While they all agree we need a new roof and to use 'modified bitumen' some want to place this new roof on top of our existing roof and others want to completely remove the old roof down to the wood and then install the new roof. We are only going to be living in this house for five more years and therefore want to minimize our costs, but also do not want there to be any further problems or damage. Anyone ever dealt with this question? We could really use some expert input! Thanks.


Audrey
 
Posts: 1 | Registered: 23 June 2006Reply With QuoteReport This Post
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Without seeing the existing roof, it's difficult to answer. A lot depends on the condition of the existing roof, and the presence or absence of iregularities, and then there are some flashing issues, I'm sure, that have to be dealt with. If you install the new roof over the existing without removing it, you'll have to 'fess up when you sell the place...and what you save now, you may end up losing then.

Did anyone mention an EPDM roof, which is a rubber or neoprene membrane, often installed without adhesives and held in place with stone ballast?


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Where do you live and under what building code do you reside?

If under the International Residentail Code, then you have no choice but to completely rip off and remove the existing roof and install a new one if your current roof has deteriorated to the point of leaking.

Period.
 
Posts: 453 | Registered: 19 July 2005Reply With QuoteReport This Post
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Take it from me dont go with the lowest bid.the storm we had last year I had 2 leaks after 800 dollars latter and me putting tar on my roof an inch thick now i have 8 leaks. check out how is going to do the work before you commite to anything.good luck. I didnt lay it on top of my old roof I removed it myself to save some money but it is costing me a lots more if only I payed just 4 hundred more I might be with no leaks.
 
Posts: 14 | Location: ellisville Ms. | Registered: 28 June 2006Reply With QuoteReport This Post
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Hello,

"Actively leaking" and "multiple attempts to fix the problem" imply years of on again, off again leaking below. Years of leaking means wood rot. Wood rot means movement and flexing in the roof deck. Installing new material over an unstable base will lead to more leaks, possibly within the five years. I highly recommend removing all existing roofing to view and repair wood sheathing as needed. Hidden flashing can be viewed for rusting, missing, etc.

In the wide world of roofing, these built-up flat roofs have about the shortest life span of any type of roofing and must be done right just to get their minimal life expectancy.


InspectorMark
 
Posts: 87 | Location: OmahaNE | Registered: 26 July 2005Reply With QuoteReport This Post
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While we do mostly commercial roofing, we do deal with flat built-up roofs a lot. Our advise to anyone wanting to go over the old roof with either a modified bitumen or a rubber (EPDM) membrane is quite simple. If it was or is wet it usually needs to come off. For starters, the moisture can be trapped between the built up layers and it will not evaporate once you cover it. Besides that, the trapped moisture will still leak inside the building whenever you have extra weight on top due to standing water or snow loads pressing down from the top. The third factor would be the deterioration of the insulation and substrate (deck and rafters). And last, any manufacturer will not issue a warranty on the new system if the old holds trapped moisture. Hope this helps in your decision.
Carol
 
Posts: 1 | Location: Detroit, MI | Registered: 30 June 2006Reply With QuoteReport This Post
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I have dealt with maintaining and repairing flat roofs for many years and there are a few considerations to think about. 90 percent of flat roof leaks occur in 10 percent of the roof. That 10 percent is usually the flashings and penetrations. Replacing the roof as is will not solve a faulty flashing design problem. You need to find the problem with the existing roof before committing the same mistake over again. Second, if the existing roof has leaked and absorbed water it likely weighs 3 times or better what it's dry weight was. Additionally, even if dry, you need to be sure your roof deck construction will support the additional weight of another complete roof. If, as you say the existing BUR is 25 years old it has likely reached it's lifespan. Finally, you need to be especially careful adding another layer of insulation and a second impervious moisture barrier (roof membrane) as you could create a dewpoint somewhere within the two roofing systems. This could cause a condensation issue which will be nearly impossible to rectify
 
Posts: 245 | Location: Annville, PA | Registered: 03 July 2006Reply With QuoteReport This Post
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