Do I need to replace my flat roof?

I live in SoCal. In a house with a flat roof. We’ve been here 11 years, and when we purchased it, the inspectors estimated we had another 4-5 years left before we needed a new roof.

Well I have maintained it, patched it, painted it… no leaks that I’m aware of. Not even a hint. (This is a midcentury modern house with maybe 1 inch of insulation between the roof and the ceiling inside.)

In fact, we had it patched up again last year by a reputable roofer. But it has still been years past the date the inspectors told us to get it re-roofed.

So, two part question.

1 – How can I tell if I need a new roof? Or will maintenance and patching work for several more years?

2 – If I do have to put a new roof in, should I find a way to give it even a slight angle to help with runoff? I figure even if I just have the new roofers raise on side by 6-inches or so. Let the rain slide down into what would be (I assume) a new gutter.

(If I do re-roof, I want to do it with the intention of adding a solar array on the roof shortly thereafter… solar city won’t install on my roof until I get a new one, which is probably smart.)

I’d rather ask here than speak to a roofer with a vested interest in selling his services, obviously. =)


An old saying goes: There are two types of flat roofs, those that leak and those that will.

That’s been my experience.

If you raise a section if the roof, six inched might not be enough. When I put a metal roof on my workshop, it has an angled roof, the roofing specs called for 1" height for every 12" in length.

Gotcha. I think it’s about 25 feet wide, so sounds like 2.5 feet. Not sure if that now requires dealing with the city for building codes and such.

Betcha it does. Changing the pitch of a roof, even a flat roof, is costly. The city will want their cut.

You will probably want to improve the insulation too - I bet current building codes would insist.

You’d have to pull a permit for the re roof anyways, the permit shouldn’t cost that much more. Always get a permit.

This. Or you may find yourself unable to sell.

Or, to paraphrase slightly: Every flat roof is either a PITA, or will be.

My father lived in a house for many years with a flat roof. It leaked incessantly. He and his wife (it was actually originally his wife’s house) had it re-tarred or whatever maintenance they did EVERY year, and fully re-roofed sometimes, and the leaks NEVER went away.

What I want to know is: Why are buildings ever built with flat roofs? What is the argument for them?

Well our flat roof was built in the 60’s. It was the style then, I suppose.

My house, built in 1949, has a flat roof, and we haven’t had any problem in the 10 years we’ve lived here. We did have it patched up and new skylights put in about 6 or 7 years ago.

Here in San Francisco, a huge percentage of smaller homes have flat roofs, maybe more than 50%. I always assumed that it was because there is no snow here, and that the main reason for a slanted roof is to allow snow to slide off or something like that. The roof is not perfectly flat, on purpose. When it does rain the water flows to the side and down the scupper to the drain.

Also, there are more modern ways of covering a flat roof other than tar and gravel, that are seamless and that last a lot longer.

Sloped roofs aren’t for just for snow. The vast majority of houses in many other areas of the U.S. that also get no or very little snow have traditional sloped roofs. I always wondered why flat roofs even exist for houses as well. The best answer I have been able to come up with is that many architects in the mid 20th century seemed to love to go out of their way to make their designs impractical. Like many horrible architectural ideas that caught on as fads during that period, the main cause was the misguided adulation of Frank Llloyd Wright designed buildings. He single-handedly managed to convince entire generations of architects that flat roofs were desirable for some reason and it didn’t really matter if they leaked or not because design functionality was never one of his strong suits to put it mildly.

Why you don’t want a Frank Lloyd Wright house.

The story is told in studios and bars all over the land, any time an architecture studio head feels comfortable with his students. It points out that in 1937 Mr. Wright designed a house for the industrialist Hibbard Johnson. One rainy evening, Johnson was entertaining distinguished guests for dinner when the roof began to leak. The water seeped through directly above Johnson himself, dripping steadily onto his bald head. Johnson was incensed and he called Wright immediately. “Frank,” he said, “you built this beautiful house for me and we enjoy it very much. But I have told you the roof leaks, and right now I am with some friends and distinguished guests and it is leaking right on top of my head.” Wright’s reply was heard by all of the guests. “Well, Hib, why don’t you move your chair?”

While this is true, you need to be careful about how “new” the technique is. You want it to be old enough to have been tested in real world conditions. I lived in a co-op building in the 80s that had its flat roof replaced with some whiz bang technology. When it failed (earlier than predicted), it needed to be completely removed (I forget why), at great expense.

I think the OP is wise to get opinions here rather than from roofers. However, at some point, a roofer is going to have to look at the place and he’ll tell you several ways to re-roof a flat roof. Tar, tar paper, and/or gravel is not so popular anymore - at least here in the midwest. The materials used, the degree of insulation you choose to use, the overall methodology of applying the roofing materials are quite varied today. Furthermore, roofers often suggest doing a tear-off before putting a new roof on. That’s an added cost, of course. They tell you it’s to prevent too much weight build-up and that might be so. But it might not. There’s also the cost of replacing rotten substructures, etc. And, in answer to the question, it seems to be SOP to say that a roof only has a life of x years. A leak is a pain, but deferring getting a new one can save lots of money over the years.

^^^This. The 1/12 pitch is also required for most metal roofs in order to get the warranty on most manufacturers. Many carports and patio covers still manage to go with less than this pitch, but over time, you’ll see the last six inches or so of the roof tends to blacken a bit on top by surface tension having the water staying on longer on it instead of just going on off the edge.

It wouldn’t be difficult to build some metal trusses out of 4" c-purlin or some other type of metal tubes, and attach these to your wooden frames that are already on your roof. I’ve got about 20,000 s.f. of metal roof on my self storage buildings. It’s really the only way to go, I think. Just a few simple tricks, and you can ensure yourself a water proof roof for many, many decades to come.

Of course, be aware of the retailers claiming that your insurance company will give you a 25% discount by going with a metal roof. It’s misleading as hell. It is 25% off, but it’s only on the roof aspect, and that only covers a certain percentage of the total policy. Instead of going with composite shingles again on my home, I went metal this time. It looks great. But I only saved $21.00 off of my insurance policy. That was it.

Another thing that most insurance companies rarely inform you about is also when you do get hail damage with a metal roof, chances are, you’re just going to have to live with it. It will be considered cosmetic. Unless the hail was so large, and it damages the overlapping seams so bad, to let possible water seepage in, don’t expect a check after a hail storm, unlike on composite shingle roofs, you often get a check with the slightest bit of grit coming off of it. So insurance companies love it when you go with metal.

I understand there are some really great 40 year composite shingles out now. Building wooden trusses over your existing roof wouldn’t be that big of a deal either. I had a neighbor while growing up, that had their flat roof for years. Finally after years of leaky roofs, and tar and every other new plastic product gimmick never working completely, they finally caved in and put a gable on their roof. It was the best investment they could have made for their home.