grapes on house: bad idea?

Are grape vines on a house a bad idea? What about on a trellis about a foot away from a house? (Where the tendrils could still touch the wall and provide an ant bridge.) How far away should it be?

grapes need some support in form of a trellis, but this trellis can be put directly onto the wall. But be warned - grapes need regular pruning.
Sorry, this link is to a german page, of a trellis manufacturer, but it is loaded with good pictures.

On an earth covered roof, grapes can grow laid flat on the dry soil. They need to be rooted in deep soil on the ground and allowed to climb to the roof. Grapes thrive when the night temperatures don't go too low. The thermal mass of the roof moderates the extremes.

Nice! Because if they grow over the flat roof, they'll shade it in summer when the sun is high overhead and giving unwanted hot light to the flat roof.

I was thinking of putting a vertical trellis in front of the large south-facing windows for the grapes that are near our building. They are currently fully inside the adjacent greenhouse structure, so they are in the open in summer, on trellises a few feet away from the wall, and are inside a plastic greenhouse in winter.

Those old ivy covered cottages have great eye appeal, but there is a problem that is often overlooked. Ivy holds on to structures with a tendril kind thing that can corrode the surface it is holding to. Grapes employ a twisting tendril (correct me if I'm wrong). While it is not acting chemically, the growth and expansion of these tendrills can get into small cracks and crevices and enlarge them. Bigger hole, more rain damage. A home is a considerable investment for most folks. Protecting it would be prudent.
Erecting a trellis gives the vines something to hold onto without endangering the home. In order to access the wall of the home, 2-3 feet would allow a person to move behind it. 3-4 feet offers room to move with lush vine growth.

I hate ivy. Grapes, ivy and other climbers should be kept off of conventional asphalt roofs. They send tendrils under the shingle tabs and the buildup of leaf litter causes damming. As leaves decay, the acid further damages the shingles.

Many vines will find their way behind roof gutters. They emerge at the top, in behind the drip edge and then go to the sunny roof. As the vine grows, it pushes the gutter off of the house. Water can now run all over the fascia since the drip edge is rendered ineffective. The stems of the vine often have water flowing down them, just like with those Japanese chains that replace downspouts. Often the vines are climbing the wall or some structure attached to it, so now the roof overhang is rendered useless as water follows the vine and wets the wall. I've given that speech to many pruning customers in order to convince them to keep vines under control.

When Ivy is removed from roofing, it is usually best to clip it and let the attachments rot off. If pulled, chunks of shingle are removed.