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WHAT DO YOU GUYS THINK ABOUT OVERLAYING AN EXISTING 20 YEAR ROOF WITH A 30 YEAR DIMMENSIONAL.IVE BEEN IN BUISINESS 7 YEARS AND I THINK ITS OK.JUST WANTING OTHER PEOPLES OPPINIONS.I KNOW ABOUT IF ITS CURLING OR ROTTED WOOD EXISTS ITS NOT A GOOD IDEA IM TALKING ABOUT IF ITS IN GOOD CONDITION BUT NEEDS CHANGING. :rolleyes:
 

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brad23 said:
WHAT DO YOU GUYS THINK ABOUT OVERLAYING AN EXISTING 20 YEAR ROOF WITH A 30 YEAR DIMMENSIONAL.IVE BEEN IN BUISINESS 7 YEARS AND I THINK ITS OK.JUST WANTING OTHER PEOPLES OPPINIONS.I KNOW ABOUT IF ITS CURLING OR ROTTED WOOD EXISTS ITS NOT A GOOD IDEA IM TALKING ABOUT IF ITS IN GOOD CONDITION BUT NEEDS CHANGING. :rolleyes:
It's hard to know if rotten wood exists unless you strip. In the snow-belt, the usual place rot exists is at the eaves, especially if there is any ice-damming happening, and this is very difficult to see from the attic.

Secondly, the top layer will never lie as flat and clean if it is laid over another layer of (old) shingles.

Thirdly, each layer of shingles (regular) weights 2-3 lbs. per sq.ft., and dimensional shingles can weight up to 6 lb. per sq.ft. Most building codes do not allow more than 2 layers of shingles (equivalent to 6 lbs. per sq. ft. dead weight loading) on regular construction. If you want to have more weight than that, you usually have to reinforce the roof structure. For instance, tile and slate roofs (which usually weight 10-15 lbs. per sq. ft) require bracing and structural support to be engineered into the house frame. Failure to do so will cause premature aging of the frame, as it will end up supporting a greater weight than it was engineered to support.

Our practice is to always tear off the existing roofing, inspect the sheathing, replace any sub-standard wood, apply the appropriate underlayment (Ice-and-water shield in specific areas, other underlayment in low-risk areas), and ensure that the ventilation is appropriate. The customers pay for this, but we must be doing something right since much of our business comes from referrals.
 

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I prefer not to overlay and will only overlay if the existing shingles appear smooth, uncurled and the wood seems okw hen walking on the roof. I always prefer a tear off for the reason P mentioned. When tearing off the roof you can address each and every situation that may be occuring with the roof. You can't do this with an overlay.

Overlay is acceptable in some areas and not acceptable in other areas. In Chicago it is acceptable and commonly requested but I always try to push the customer to a tear off for the reason before mentioned.
 

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I do a lot of recovers, I always check the areas known for damage and if repair is needed I repair it, it's simple to go back over with new three tabs to even the roof up with existing. If there is a lack in ventilation I walk the large areas feeling for weakness, on plywood it could be delamination, OSB hasn't been a problem except for roofers not paying attention or blowing and going.
If the roof is feeling to soft for my liking I'll recommend a tear off.
Ventilation is something I always address and easily make a sell because hardly anyone talks to a HO about it. And I get letters from them later on thanking me because their utility bills go down.
Another area to talk to the HO about is the bridgeing that goes along with metric shingles over standard [3tab or earlier dimentionals] that shows up after a good hot summer. If three tabs are really wore out you probably won't get much bridgeing. Sometimes the three tabs are metric, old Elks and a few others, then you just butt and run.
Most people who want to recover are doing so to sell their homes, but a lot of older people can't afford a tear off and if the roof isn't in to bad of shape it will still look pretty decent with a recover.
It's rare that I only do one recover in any neigborhood I am invited into, good work sells more than a good line.
 

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I have a second layer on my home, and all tho I was planning on re-roofing this year, it's not because it's done but rather because I'm going to re-side also and want to do both, prolly will be next year now tho.
the second layer is now 6 months older than the first layer was when i did the lay-over and I never had any wind damage, leaks, etc.

So I know for a fact they work if properly done.
I to always push the issue that it's better to re-roof rather than lay-over,
but if a re-roof simply is not in the home owners budget than a lay-over is an acceptable solution.
 

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if the customer only has the budget for a layover, thats what we give them, we explain the advantages of the full rip. at the end of the day. its the clients choice. i would not walk away so someone else could do the job....ps if the old roof is in good shape, there is no problem, also roof overs shorten the life expectancy of a roof.
 

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if the customer only has the budget for a layover, thats what we give them, we explain the advantages of the full rip. at the end of the day. its the clients choice. i would not walk away so someone else could do the job....ps if the old roof is in good shape, there is no problem, also roof overs shorten the life expectancy of a roof.

Do you have any links to sites that have done studies showing the life span of a lay-over is less?

In my personal experiences thats not true, which is why I'm asking.
 

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Do you have any links to sites that have done studies showing the life span of a lay-over is less?

In my personal experiences thats not true, which is why I'm asking.

INTERESTING, i do not have any studies to referance, i will however due some research, my primary reason for assuming layovers affect the lifespan is the fact that ventilation plays a vital role in the life and quality of lumber, sheathing, and roofing, any material that has airflow and temperature moderation will generally fair better than without. when a roof is layed over it stands to reason that there will be less airflow, greater likelyhood of condensation, higher temp swings, these factors will surely have some effect on lifespan. i have roofed for many years, that does not mean i am correct in my assumptions, it is just a conclusion that i have drawn based on experiance. i would welcome others opinions.G
 

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DavidC
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I can't quote any specific studies either, but I do agree with what Gene is saying. I recall a description of the problem from an ancient magazine article, so old it was actually printed on glossy paper....

In the morning the sun comes up and goes right to work heating up the top layer of shingles. They insulate the next layer for at least a little while. As the top layer warms they also expand, ever so lightly rubbing across the stones of the next layer.

Eventually the heat reaches the next layer and they start to expand, rubbing their stones against the smooth bottom of the upper layer.

As the sun lowers into the western horizon the top layer starts to cool..... same thing in reverse.

So between the weather on the outside and the friction from beneath, your new roof over is wearing from both sides.

I always tell customers that the stripping will help the new roof last longer and price accordingly. If I find that I can only sell the job by roofing over, then that's what I sell.

Good Luck
Dave
 

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DavidC
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Good read Gene, thanks for posting that. The last sentence sums it up well.

In my earlier years we stripped plenty of roofs that were multiple layers. Seems like most of them had wood shingles under everything else. 3 or 4 layers were common, 8 was the record for me. Sometimes the house would sigh when we stripped them.

Good Luck
Dave
 

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Did a QUICK search, turned this up, it basically agrees with what i suspected was the case...G

http://www.jfminspections.com/roof-over.htm
That was some good reading, as was your and Davids response,
Thanks again.

I do re-roofs also, but only once I am unable to sale the job as a re-roof and this info- will surely help with my sales pitch in the future.
 
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