I live in a very moderate southern California climate with an average rainfall of only 15 inches (38cm) / year. My roof is asphalt shingle and the pitch is 1/3. In two places I have vines growing up walls and then spreading out on the roof. The vines lie directly on the shingles and cover sizable areas. The vines do not adhere to the roof - as ivy would - but are held in place by gravity and friction. My questions are: 1. Do the vines impede water shedding and so promote roof failure? I haven't had any leaks and the vines have been there for years. 2. Are the vines shortening the life of the roof somehow or actually prolonging it? 3. Do the vines have any significant insulation value? 4. What other concerns might I have? Thanks.

banitthedog; While the vines may be shading the shingles from UV rays, they are most likely causing more harm than good, They aren't supposed to be there and could be promoting insects, mold, mildew,excess dirt and impeding water drainage. Since you really can't see what is going on underneath the shingle, it would be better if they were not there.

In general vines on the house/roof can cause many different types of problems.

Rodents use vines as a way to gain entry, climbing the vines and making holes in places like soffits or fascia and moving into attic space, where they cause all kinds of havoc.

Depending on what the vine is, it can excrete substances that can cause deterioration in the asphalt. In addition leaves and other detritus can get caught in the vines and cause damming, and the detritus will rot, and the rot can spread to the roof. Further, the vines can creep under the shingles, lifting and breaking them, and ruining your seal, in addition to giving the wind a way in to tear or break the shingles.

Vines do provide shading, and I have read that they decrease heat by 15 degrees or more. I just don't think it is a good idea to grow them on your roof, unless the roof is specifically designed to support such growth, as in a sod or vegetative roof.

-Rosalinda

If you want to keep them, I would build a trellis over the roof.

As the other commentors have mentioned, any sort of growth on the roof is probably doing more harm than good.  The vines can trap moisture and cause mold and rot to form fairly quickly.  I'd suggest keeping the vines off the roof and the exterior walls. 

At the risk of pissing off builders I could learn from, It sounds as though your dry climate could help discourage any potential rot or moisture buildup.  With quick solar evaporation and plant transpiration and minimal rainfall, I would argue that moisture and rot really play limited roles in your climate.  My concern here would be to assure there is no physical damage.  How much could this vine weigh and is my roof capable of handling the vine load in addition to its existing load?  Are there are signs of physical damage?  A trim from time to time might help balance the need to protect your investment vs. need to protect plants/life - if it's worth the trade off to you. 

Greetings,

The problem is that the roots(?) penetrates the shingle fabric and breaks it down causing premature replacement of the roof. Moisture also enters the picture as the foliage holds moisture close to the shingles more or less continuously. Air moisture content may or may not contribute.