Being a homeowner myself, I was doing some research on what the telltale signs are for replacing you roof. I did some research, and The Money Pit summed up the symptoms of an old roof best. You can read the entire article here. I have summarized the main points:
Missing Granules. If granules are missing on the surface of the shingle, exposing the asphalt or fiberglass mat below, it can decrease the life of your roof. Areas of missing granules indicate it might be time to replace the roof.
Buckling. A number of factors can cause shingles to buckle. If buckling is caused by wrinkled felt below the shingle, a roofing professional can simply remove the affected shingles, cut the wrinkle and replace the shingles. If the cause is poor ventilation, you’ll need to add ventilation to the attic space to allow heat and moisture to escape and keep attic temperatures lower.
If buckling shingles go untreated they will begin to crack and tear and will need to be replaced immediately to avoid significant damage to the roof or roof deck which can lead to leaks and rotting.
Curling. Curled edges on shingles can be a result of improper fastening (such as high nails or too few nails), poor roof ventilation or lack of a back-coating on the shingles. Curling is more common in organic shingles such as wood and will often start at the bottom edge of the shingle. Contact a roofing professional as soon as possible to avoid further damage to the roof
Rotting. Rotting is caused when the mat at the core of the shingle absorbs moisture. Replace rotted shingles with ones made from non-organic compounds which resist moisture and are less likely to rot. To determine if a professional is needed, look for shingle irregularities. Depending upon the roof, these irregularities appear as discoloration, black spots or large spaces of missing color granules. If these signs are present consult a professional
Blistering. Blisters are sometimes found in non-organic shingles and are caused by trapped moisture in the shingle. If blistered shingles break open they can leave shingles susceptible to other damage such as granule loss, color fading and may even lead to water leakage and should be replaced. A punctured blistered shingle will be easily spotted because it will likely appear to have black spots.
Ceiling Spots. Stains on your indoor ceilings may be caused by a leaking roof. Check your attic to find the source of the leak, and examine the rafters for leaks that travel away from the original source. On the exterior, check the chimney and vents for cracks in the flashing.
Problems specific to wood shakes include
Moss/Algae growth. Algae can reduce the long-term performance of the roof. Replace damaged shakes with moss/algae resistant ones.
Splitting. Splitting can be the result of natural aging or caused by stress, such as walking on the roof. Small cracks can be caulked, but larger ones require the damaged shakes to be replaced.
Termite damage. Wooden shakes provide sustenance for termites. To exterminate termites, the home must be tented and fumigated. After the termites are gone, replace the affected shakes with new ones.
All tear off asphalt shingles can be recycled on the lower mainland at Gemaco’s Shingle Grinding Facility. To find out where to recycle the rest of your roofing and demolition waste in BC check out Recycle BC’s Recyclopedia.