I would like some opinions. Does doing a recover cut down on the life of the shingles? If so how much? 10%? 20%? 50%? And what techniques have an affect on that percentage? Adequate ventilation ? A new layer of underlayment? Is a new layer of underlayment recommend or a bad idea?
The condition of the old roof being roofed over is the biggest factor and in a recover a thicker shingle should be used in the first place.
Quality oriented companies don’t do recovers as a general rule.
3 tab still flat and in decent condition being covered by 30year minimum dimensional
The big things I look at are when deciding if a roof over is possible is the condition of the shingles and how much flashing work there is. To do a roof over properly the new roof will still need its own independent flashings (not just butted against the old and caulked/tarred) to do a proper roof over job IMO. Some jobs with lots of flashing details would be nearly as labor intensive to do all the flashings correctly as it would be to just rip the whole thing off (best option).
While I do believe a recover won’t have the exact same lifespan of a single layer roof in the exact same situation I don’t feel like it will have a significantly shorter life either (provided its done properly). I’ve usually do one or two every year and some of them are over 10 yrs old now and still look brand new and they were done with “30 yr shingles”.
As mentioned above…the quality of install and condition of existing substrate and shingles are critical. Correctly installed the mfg warranty is 100%.
Personally we don’t do shingle overs/ Recovery. If a customer is dead set on going over their old roof we walk away.
Unless the roof is pretty much wide open with no flashing or valleys I wouldn’t recommend it. If not, all of the flashing details take more labor dealing with the old shingles and flashing still in place vs. A clean deck. If you have valleys on the roof or have any issues at the eaves you are relying on the old shingles as underlayment instead of ice and water shield adhered to the deck. Imo they are more trouble than they are worth.
MPA is right.
All valleys, walls, protrusions need to be treated as new.
You cant just roof over them…
Yes, as usual it’s the details.
I wouldn’t want the extra weight on my roof. OSB is saggy enough with one layer.