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octavious Reader
10/28/13 1:31 p.m.

Currently searching for a new house. A couple have popped up with flat roofs instead of the normal pitched roofs. Obviously these are on older homes as it is not a design I have seen much of lately. I don't know anything about a flat roof. In my internet search it looks like they need to be checked and are covered with tarpaper, tar, and gravel.

Does anyone have a flat roof home? Can anyone tell me anything about maintenance, problems, things to look out for, and/or questions to ask should we go see one of these houses with a flat roof?


Tom Suddard
Tom Suddard Event Marketing
10/28/13 1:42 p.m.

I know that they aren't as "good" as normal roofs. Sorry, that's about all. I managed to find a house with a pitched roof, and I'm thrilled.

Tom Suddard
Tom Suddard Event Marketing
10/28/13 1:43 p.m.


Giant Purple Snorklewacker
Giant Purple Snorklewacker MegaDork
10/28/13 1:44 p.m.

In reply to octavious:

I imagine they are not really "flat", maybe a 3-5% taper to allow water to flow?

I think if they are in good shape and can drain properly they would be preferable because... instant deck!

mtn UltimaDork
10/28/13 1:56 p.m.

I'd be worried about snow mostly. You probably wouldn't have to worry about that too much in Nashvegas.

1988RedT2 UberDork
10/28/13 2:14 p.m.

More often found on commercial buildings around here. Best is EPDM.

Duke UltimaDork
10/28/13 2:16 p.m.

Old style "flat" roofs were built up out of layers of tar paper and asphalt. They were exceedingly low-tech and very subject to not only weathering but poor installation and repairs.

That being said, I wouldn't let it scare me away from a house that I liked. What I would do is contact a small commercial roofing contractor and ask them how much to tear off the existing roof down to the sheathing / deck, then put down 3" of rigid polyisocyanurate insulation board, a cover board over that, and a fully adhered 60 mil non-reinforced EPDM rubber membrane. This is a 20-year (officially) to 30-year (probably) roof and is a relatively easy to work and relatively maintenance-free material. Ask them to budget to replace 15% of the sheathing as well.

Then use that to negotiate the cost off the asking privce for the house.

ClemSparks PowerDork
10/28/13 2:17 p.m.

Note, I'm not a qualified answerer because I have not had a flat roof.

Here where I'm at (plenty of precipitation, including some snow and ice) I would not want one because you have to rely on mechanical sealing to keep from having leaks. Leaks lead to rot, mold, and other structural and health catastrophes (along with the associated financial implications).

With a generously pitched roof, physics takes care of preventing the water infiltration without having to have a perfect seal.

I'd say the majority of flat roofs around here are found on commercial and/or industrial buildings. A common situation here during thunderstorm season: One finds himself needing to walk around a mop bucket in the middle of a shopping aisle or production floor that is collecting water from a roof leak.

I would imagine in an arid climate, a flat roof may be an acceptable choice. There may be other positives about them as well...I'm just looking at them from a maintenance standpoint and generally see them as something to avoid (for me...where I'm at).


stuart in mn
stuart in mn PowerDork
10/28/13 2:27 p.m.

By and large, flat roofs aren't perfectly flat - they have some pitch to allow water to run off, and they can be used in areas with heavy snowfall if the roof structure is designed correctly.

Modern EDPM rubber membrane roofs are pretty bulletproof - I have it on my back porch roof (the slope is about 2" over 12 feet) and it works fine.

10/28/13 2:28 p.m.

i have had one, if you have trees around you have to keep the roof swept off, and it was about twice the cost of a regular roof, they are built up "membrane"

spitfirebill UberDork
10/28/13 2:47 p.m.

My advice for a flat roof residence is don't do it. I think architects design them (for houses) when they get bored.

I've been in a lot of old commercial buildings with "flat" roofs that have failed. Let a little water in and the end won't be far behind.

HappyAndy SuperDork
10/28/13 4:04 p.m.

I own a flat roof home and I hate it. I would never do it again, seriously. Mine is extra flat, it has barely any visible pitch, and when it rains the flow of water to the one and only drain is so slow that all the leaves and other stuff that winds up on the roof washes to the edge of the drain and dams up the drain. The drain pipe doesn't actually clog, but the dam of crud makes a large puddle on my roof that has led to leaks. BTW mine is the EDPM rubber type, and its not all that old.

This reminds me that I'm overdue to get up there and clean things up again. It needs to be done atleast twice a year.

dean1484 PowerDork
10/28/13 4:09 p.m.

I do roof design for a living and lets just say that there is alot of misinformation out there about them. Drop me a pm and i can answer any questions you nay have.

For refrence i just finished designing a 150,000 square foot one.

Large or small comercial or residential it does not matter. The short of it is a properly installed one that is maintained will serve you well. They are definitely more needy than a standard sloped shingle roof but i would rather inspect and service a flat roof on a house than change the oil in my porsche.

RX Reven'
RX Reven' HalfDork
10/28/13 5:21 p.m.

I owned a home in California with one for ten years. I never had a huge problem with it but I did need to get on the roof multiple times each fall to clear the leaves.

The single mom that lived next door to me wasn’t much for getting on roofs; fancy, fancy lady. Anyway, one time, the fire department kicked in her front door while she was at work so they could shove a steel rod through her ceiling a bunch of times to let the standing water drain.

Bottom line, I wouldn’t refuse to own a home with a flat roof but I would require a significant discount to offset the added effort, lack of attic, and the esthetic message that says, we stopped at nothing to shave every penny off of the construction costs.

petegossett UberDork
10/28/13 5:48 p.m.

Our building we live in(circa 1898) has a minimal pitch on the roof. We installed a thick white rubber-like roof and have been very happy with it. Get someone who knows what they're doing, and it should have a 15-20 year life easily.

benzbaronDaryn Dork
10/28/13 6:47 p.m.

Around the SF bay area they are popular, you should see the amount of water my neighbor pumps off of his roof, serious amount of water sitting on top of the roof. They are a terrible design and don't have any provisions for drainage. You can have them modified to run down spouts. Around here they spray some white foam or something on the roof.

Lancer007 New Reader
10/28/13 7:20 p.m.

Here is Arizona its very common. Its less surface area for the sun to heat up, and mine is coated with a white reflective polymer that also weather proofs it for the 9 rainy days a year here. Though it does have a slight pitch so the water does run of mostly. If I lived anywhere with any appreciable rain or snow I would opt for a pitched roof but they aren't terrible as long as you inspect for any tears or places water is settling or getting in.

gamby UltimaDork
10/28/13 7:48 p.m.

This one is in a neighboring town. As someone who digs modernism, it tickles my fancy pretty well:

That's in Lincoln, RI, so it has to be built to survive snow.

BoxheadTim PowerDork
10/28/13 8:13 p.m.

Looks like it needs more garages, but other than that, it looks like an interesting house.

Gearheadotaku UberDork
10/28/13 8:34 p.m.
RX Reven' wrote: The single mom that lived next door to me wasn’t much for getting on roofs; fancy, fancy lady. Anyway, one time, the fire department kicked in her front door while she was at work so they could shove a steel rod through her ceiling a bunch of times to let the standing water drain.

What? More info if you've got it.

alex UberDork
10/28/13 11:01 p.m.

I live in a "flat" roof house built in the 1880's and have a 3-storefront commercial building from the 19-teens with a flat roof also. They're incredibly common in St. Louis city. We have a lot of old buildings, and I'm guessing flat roofs outnumber pitched roofs by close to 2:1. Generally speaking, they need major maintenance every 20-30 years, possibly some patching in between, but even that's unlikely these days.

If they're not incredibly rare in your area, that means you have plenty of qualified roof guys to do the maintenance. I wouldn't let a flat roof scare me away from a house I liked.

SVreX MegaDork
10/29/13 7:34 a.m.

I couldn't disagree more with most of this thread.

Yes, I have a flat roof, yes, I've been in construction for over 35 years, and yes, they are a PITA.

The problem is the difference between theory and real life.

There is a lot of good theory in this thread. Yes, a well constructed flat roof can serve it's purpose well.

But that is pretty much an oxymoron in residential construction.

Residential construction is cheap, and flat roofs are expensive. Therefore, it is extremely common for corners to be cut in residential flat roofing.

Overspanned wood framing members will sag, and pool water (which will seep in). Homeowners will buy cheap E36 M3 at Home Depot for re-roofing, and you get granular rolled roofing (which is crap). People unfamiliar with flat roof technologies will not know how to properly detail joints, undersize drainage, poorly seal seams. Maintenance will generally only be performed when a leak has already started.

Flat roofs are often used as bad solutions to problems they couldn't otherwise solve inexpensively (like a porch roof which would have run into the 2nd story windows if it had any pitch. Rather than going through the expense of moving or modifying the windows, a flat roof is (poorly) installed).

Even professional contractors are clueless. Most professional residential contractors with 20 or more years experience have only done a flat roof 2 or 3 times.

Qualifier: If I lived in Arizona (maybe FL, or some other locations), I would have a different opinion. Flat roofs are common enough there that the work force is well familiarized with the techniques.

I wouldn't let it scare me away, but I would have at least 2 separate qualified commercial roofing contractors inspect it before assuming it was any good. If it needs works, assume commercial roofing costs, not residential.

octavious Reader
10/29/13 7:42 a.m.

Wow. Thanks guys. I knew I would get some good info here. I won't derail the discussion on flat roofs, but the house I asked about is out of our search. The garage wasn't big enough.

Residential flat roofs are pretty rare here. Which makes me wonder if the roofers in the area even have any experience in them. I wouldn't mind doing the required maintenance on a roof, but I really had never considered one on my residence before.

From a cost perspective is the difference between having to have a flat roof retarred every 20 years or new shingles put on a pitched roof? I assume they are probably about a wash after that many years.

SVreX MegaDork
10/29/13 7:51 a.m.

20 years?

Flat tar roofs will never last 20 years.

I am re-tarring my flat roof every 2 months.

I will replace it as soon as possible with a pitched roof.

Duke UltimaDork
10/29/13 7:59 a.m.

Having a flat roof retarred every 20 years is exactly what leads people to hate flat roofs. That's when they leak and it is much more insidious than is apparent at first.

But if you replace the crappy built-up roof with a quality commercial rubber roof like I described, right now it will be about $6 or $7 per square foot depending upon your area. But it will last 20+ years with almost no maintenance but an annual inspection. Although it is better to have the roof sloped for positive drainage (and you can do this with tapered insulation board that slopes as little as 1/8" per foot) a properly-installed EPDM roof isn't harmed by standing water and tolerates ponding very well.

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