You have to admit that black is a colour that attracts more the heat of sunrays than white. On the other hand, if the roof is well-ventilated, the difference on the roof’s longevity will be negligible. Even if a dark shingle attracts the sun more, the signs of aging show a lot more on a light shingle, which does make them equivalent. So colour choices remain a personal and ethical decision.
The space between the shingle butts widens and the granules chip off (especially at the butt corners).
Butt corners lift off the roof which gives a wave effect of the roof (a bit like fish tails).
Shingle butts round off and lift off (wave type).
At the edge, the shingles are fully folded on the fascia and the shingles have a tendency to break off with the wind or at the slightest contact and there is an EXCESSIVE granule loss.
A roof is considered a low-sloped roof when it measures less than 4:12. The slope determines the speed at which water or snow escapes the roof’s surface. A low-sloped roof is slower to eliminate water from its surface. This is why you have to proceed to the rebuilding of it with more caution, either with a high-quality sub-layer of Ice & Water Shield membrane (only for 3:12 slopes or depending on if there is an attic space) or in the case of asphalt-gravel roofs (tar and rocks, often 3:12 and less) it would be preferable and more advantageous to contemplate an elastomeric membrane such as that made by Soprema.
You have to ventilate your attic well because, even if your house is well insulated, there is a heat loss and under the sun the shingle itself can create heat at that place. Ventilation allows this heat to evacuate before causing either
a high level of humidity
condensation (in the cold of winter)
an ice ledge (heat makes snow melt and the water freezes again when it is exposed to cold)
etc.
IMPORTANT: ALL BATHROOM FAN OUTLETS OR DRYER OUTLETS WITH EVACUATION DUCTS GOING THROUGH THE ATTIC HAVE TO BE VERIFIED TO ENSURE THEY ARE INSULATED AND DO NOT LEAK HOT AIR IN THE ATTIC (induced heat source).
Good ventilation is created when air intake through the soffit is free of obstruction (not blocked with blown or a sheet of mineral wool – you should see the light of day at the edge when you are in the attic) and when the roof fan (air outlet) creates adequate aspiration (chimney effect).