Three ways to deform
The word curling covers different shapes, and they do not tell the same story.
- The edges turn up. The shingle takes the shape of a cup. The top has dried and shrunk more than the bottom.
- The centre bulges and the edges dip. The shingle arches its back. This is common on shingles at the end of their life.
- A ridge lifts several shingles. The deformation follows a straight line or forms a wave. Here the shingle is often not the cause. What lies underneath has moved.
Telling these shapes apart helps find the cause, the first step with any of the shingle problems.
The causes
Age. Year after year, the sun drives the oils out of the asphalt. The shingle hardens and shrinks. On a roof nearing the end of its useful life, every slope curls, the south one first.
Attic heat. A poorly ventilated attic overheats in summer. That heat speeds up the aging of the shingles. A roof that curls well before its time calls for a look at the soffits and vents.
Moisture. When moist air from the house condenses under the decking, the wood swells and shifts. The panels lift at their joints and push up the shingles. You then see straight raised lines, evenly spaced.
Installation. Too few nails, or nails badly placed, leave the shingle free to deform. Wrinkled underlayment, or underlayment installed wet, creates waves that show through.
What happens next
A curled shingle does not heal. One thing leads to another.
- The raised corner gives the wind a grip. The adhesive strip lets go.
- The shingle flaps, tires at the nail line and breaks.
- Wind-driven rain gets in under the raised edges.
Repair or replace
A few deformed shingles in one area can be replaced, as long as their neighbours are still flexible. We need to lift them without breaking them to slide the new ones in.
If the curling is widespread, a repair no longer makes sense. The roof needs replacing, and the cause has to be fixed at the same time. Redoing the shingles without dealing with ventilation or moisture sets up the same problem for the next roof.
Frequently asked questions
Do curling shingles mean the roof will leak soon?
Curling shingles do not necessarily mean a leak right away, but the risk goes up. Raised edges let in wind-driven rain and tear off more easily. Have us look at the roof without waiting for the first ceiling stain.
Why are my shingles curling on only one side?
The slope most exposed to the sun ages first, so the roof curls on that side first. A single side affected can also point to a local problem, such as a bathroom fan blowing into the attic under that slope, or blocked soffits on that side.
Is it normal for a roof under ten years old to curl?
No, a roof under ten years old should not curl. Look at attic ventilation, moisture, installation or the product. Get out your contract and the warranty, and ask the roofer who did the work to come and see.