Taking a closer look at the roof

When looking at a house to buy, the

first thing that many buyers will

consider — once they’ve decided that

they’re not ‘a little too good for the

neighborhood’ or vice versa — is the


An asphalt shingle roof, by far the most

common type of roof, can look pretty

good from the ground, even if it’s 15 or

20 years old, if shingles aren’t actually

missing here and there, don’t seem to

be curling or cupping at the edges, and

aren’t covered with black stains or

green moss.

And speaking of moss, we have noticed

that many a home owner’s memory can

get a little mossy when they are required

to disclose the age of the roof, so a

closer look may be required to determine

the actual age of the shingles, or at least

to make a reasonable guess.


Shingles can vary widely in quality and durability, depending on the manufacturer. We have seen fairly new shingles cracked or split, a problem called thermal splitting or tearing. This can be worse in colder climates, often due to freezing and thawing — like Ithaca’s infamous potholes — but usually, it is the fault of a cheap, poorly manufactured shingle, or improper installation.


We are often asked about the black stains or green moss visible on many roofs. Once again, the cold, damp climate is usually the culprit, but not always. Chemicals added to some of the newer shingles can help reduce the growth of black algae, the black staining often seen on shingles. In cheaper shingles, black stains can also be caused by the leaching out, or bleed-through, of the asphalt itself.

Moss, algae or lichen is often found on shingles under an overhanging tree or on a north facing, shaded roof. Moss will hold moisture and trap sediment which will reduce the life of the roof and should be removed if possible. Lichen and black algae are thinner and less of a problem. It may be best to leave them alone, especially if the shingles are older.

Cleaning up

All of these can be gently cleaned and hosed off — from the top down of course — if the shingles are in good shape, but extreme care must be taken not to damage the shingles. Power washing is not recommended, and it’s probably a good idea to hire a professional to do the job; wet roofs can be very dangerous. There are chemical products available for cleaning roofs but these could be harmful to the environment, and no matter how it is cleaned, the problem will probably come back over time. Once again, we urge you to hire a professional.

Another solution may be a strip of zinc. When attached along the ridge of a roof, it produces metal salts when washed over with rain, and will help control the growth of moss and algae.

Sagging roof

A sagging roof on a newer house could be a big problem, but on an old house it’s very common and not too alarming. Older homes were typically under-framed originally, often with full sized two-by-fours on two, three and even four foot centers. The rafters have sagged over time, but we rarely find broken rafters once we look in the attic. One way to eliminate the sag is to remove the roofing material and reframe the roof — very expensive!

Another method is to install a new, properly shimmed metal roof over the old one, but if you can live with the sag, the existing framing can be reinforced in the attic to stabilize the roof and prevent further sag — much cheaper!

Multiple layers

Also, multiple layers of roof materials may or may not be a problem. A second layer of shingles can be added over the first, only if the original layer is in good shape — no curling or cupping edges. You should never add a third layer, although we once saw a roof with six layers — five asphalt layers and the original cedar shake roof! The weight of this roof was tremendous and it’s a miracle the rafters weren’t sagging more than they were.

One problem with multiple layers is that the flashing is usually not renewed with the new layer. Flashing — not to be confused with exposing oneself in public — is the thin metal material, usually aluminum or copper, that makes the transition from shingles to the siding or the walls of a chimney. Tin was often used before aluminum came into use, and that can rust away.

Valleys, the area where two roof lines meet, also were often done with tin. Now we see mostly aluminum in valley areas, or commonly, just the shingle material itself, woven into the valley properly. Valleys and flashing are always the first place we check if we find evidence of a leak.

Campbell and Davies LLC    201 Dey St Suite 211 Ithaca, NY 14850   

607 216 0036    fax 607 216 0402   campbellanddavies@yahoo.com   


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