That s a lot of extra weight putting added stress on the roof decking.
Why not to add a second lkayer on a roof.
You need to tear off the roof and install a new one.
Also two layers of shingles are going to attract a lot more heat than just one layer which can lead to the shingles prematurely deteriorating.
That in itself eats away at the savings.
Adds value a brand new tear off roof can add to your home s resale value and is a major selling point.
Plus depending upon the size of your roof you ve added multiple tons of weight which could pose a big problem if there is significant snow accumulation.
Doing a second layer right means a lot of prep work goes into the overlay anyway and flashing which remember is the most vulnerable point on your roof is harder to guarantee.
That second layer of shingles won t last as long.
There are already two layers of shingles on your roof most building codes only allow two layers of any type of roofing on your home.
Reasons why you should not add a second layer of shingles it will shorten the lifespan of your roof the second layer of shingles will trap heat which can result in the decomposition of both roof layers.
You re essentially adding a second roof on your house and that added weight puts stress on the roof decking which is especially worrisome in our climate that gets heavy rain and snowfall.
This step is important because it brings the underlying surface back to a level height consistent with the rest of the roof plane.
Install a course along the snapped line then install succeeding courses using a guide or a snapped line.
The savings you re going to see may be in the range of a modest 25.
Add a layer of shingles over the newly repaired area before you install your second layer of shingles.
The second layer is also more difficult to install properly compared to new shingles.
So if there are already two layers the choice is made for you.
This will force you to replace your roof earlier than expected.
What to do if the old roof is not straight if the existing roof has wavy horizontal lines you can take out the waves by snapping a horizontal line 1 2 inch below the shingle bottoms of one course.
For instance instead of just one roof on your home you now basically have two.
This is mostly due to the fact that a brand new roof traps much less heat than a roof with multiple layers.
Manufacturers believe that layering the roofing diminishes the overall performance of the roof.
That helps your final layer of shingles look flat with a proper installation.
Extra heat causes shingles to curl and break down much more quickly.
