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dean1484
dean1484 GRM+ Memberand PowerDork
10/29/13 9:33 a.m.

Ok This is getting out of hand.

First off they are no "flat roofs". They are properly referred to as "low sloped roofs" Calling them flat roofs has lead to builders actually building them flat and this is where problems start.

The price of flat roof replacement is HUGLY dependent on if it is insulated underneath or if it uses insulation above the deck. With the new energy code and then the stretch code piled on top of that replacement costs are getting rather expensive. Not that it is a bad thing but $20 / foot roofs are now the norm. You can put down a $7 a foot roof but you will get what you pay for.

Asphalt roofs of the 80's generally were 20 year roofs. Coal tar pitch roofs (commonly confused with "asphalt" roofs) will last 50 -100 years and are self sealing. Both look the same to the untrained person but are very different animals with respect to quality.

Yes flat roof require inspections and some maintenance but again proper design from the beginning will greatly reduce this.

Another misconception is that flat roofs are flat. Properly installed roofs are 1/4" / ft or 1/2" / ft sloped as required by code. You can go as low as 1/8" per foot and still have good drainage but the margin for building movement and settlement etc is much less.

EPDM AKA rubber roofs are good. They have become the industry standard. In the last 10-15 years they have changed over to using adhesive tapes for the seaming and flashings with pre applied adhesives that are MUCH better than the old style where you were basically applying a contact adhesive and then calking the seams. Another improvement is the elimination of uncured EPFM flashings. AKA "form flash" This was great for flashing weird shaped things but because it is uncured it will deteriate with prolonged UV exposure

The current EPDM roofs can easily be installed to last 20-30 years. Manufacturers are not offering 30 year warranty's on specific designs. I tend to design my roofs to a hybred standard where I call for the flashings and the seams to be done to the 30 year standard and the field of the roof to the 20 year standard. One of the down sides to EPDM is that animal fats are very destructive to it. Petrolium based products are much less so but prolonged contact is not recommended.

Cheap flat roofs from home dep are just that cheep and you are lucky if you get 10 years. The reality is you get a window guy to install windows and plumber to install plumbing and an electrician to install wiring. But for some reason in residential jobs most general contractor think they are qualified to install low sloped roofing. Nope not the case for the most part. People also seem to go cheap with flat roofs. This is stupid. It is your homes first defense against the weather. They will purchase $5,000 light fixtures and bathroom fixtures but go cheap on there roof and wonder why it only lasted 10 years. Idiots!!!! And it leads to a lot of the misconceptions about flat roofing that I see here in this thread. Like anything else in life you get what you pay for.

PVC roofs with non directional fiberglass reinforcement are an excellent roof when you have to worry about ponding water as the seams are heat welded together and are actually stronger than the field sheet. The same manufacturer of this product also make pool liners. One of the down sides to it is that it is VERY slippery when there is frost on it and even water or dampness can make it a little slick. PVC does not like to be exposed to Petroleum based products and it also does not like to be in contact with cement as both extract the plasticizers from the sheet and it gets brittle.

Now, lets tale a look at the premium low sloped roofs. I am a huge fan of the cold process built up roofs. They are similar in appearance to the old built up roofs but the technology is very different. With BUR roofs the asphalt or coal tar pitch was providing the waterproofing and the felts were providing dimensional stability with the gravel surfacing providing UV protection as well as protection from foot traffic. Cold applied roofs the felts are the actual waterproofing material and the mastic (that goes down cold) is really just a adhesive holding it together. A flood coat is then spread over it and gravel applied again for UV protection as well as protection from traffic. I like these systems as they provide redundancy and are tough as nails. You can latterly hit them with a ax and it will not damage it.

A more "normal" type of roof system all be it an old style is the coal tar pitch roof. It has been the standard for more than 100 years. Many roofs of this type that used copper base flashings I have seen last 75 years. The key to all of them is that they had enough slope to drain properly. The nice thing about this is that it is "self sealing" the coal tar softens in the summer and will flow a little. This allows it to re seal any damage or ware it may experience.

Anyway I have typed way to much here. Like I said PM me if you have questions. I ran the metal shop and was the chief estimator for a large commercial roofing company for 10 years and then jumped back over the fence to the engineering / design side of things. I have been in the field for 35 years. You know you have been doing it for tow long when you are starting to replace roofs you put down when you started. LOL

SVreX
SVreX MegaDork
10/30/13 5:09 p.m.
dean1484 wrote: First off they are no "flat roofs". They are properly referred to as "low sloped roofs" Calling them flat roofs has lead to builders actually building them flat...

You don't see the contradiction in that statement?

The OP is not asking about good design or theory (which you are obviously well versed in). He is asking about buying an existing house with a flat roof.

There absolutely ARE many, many "flat" residential roofs out there, and MOST are not built in acceptable manners. 38 years as a contractor.

I purchased a house a few months ago with a flat roof. It was BUILT flat. Unfortunately, the rafters are over-spanned. They sagged, and the roof now ponds water 1" deep (which leaks into the garage).

I have no idea what you are talking about when you say it is a "misconception that flat roofs are flat". It is not a misconception. It is a FACT that many roofs are flat, lack positive drainage, or worse (like my house), regardless of what the building code says.

Your design recommendations for proper construction of commercial grade roofs are good, admirable, knowledgeable, and correct. They are, however, irrelevant in this thread.

But I'll thank you anyway... I will use some of your advice when I re-build my roof.

SVreX
SVreX MegaDork
10/30/13 5:16 p.m.

One more thing...

An excellent Architectural shingle roof can be installed in most of the country for $200 per square (100 SF).

Your "budget" roof of $7 per SF would cost 3.5X that. Your $20 per SF benchmark would be $2000 per square (10X good residential roofing cost).

This is why residential flat roofs are typically roofed poorly. People simply can't afford that.

Poor quality residential flat roofing is a standard, not an exception.

alex
alex UberDork
10/30/13 6:32 p.m.

I think what it comes down to is this: if flat/low pitched roofs are common in your area, especially if they're on old buildings, it's likely that they're built properly and there will be contractors in the area that know how to work on them the right way.

And SVreX, I don't really think it's fair to use your improperly constructed roof as an example of why they're fundamentally flawed. Again, there's been a flat (low pitched) roof on my house since the 1880s, and there are tens of thousands of other buildings like it in St. Louis and other old cities across the country.

SVreX
SVreX MegaDork
10/30/13 9:45 p.m.

In reply to alex:

I agree with what you said. I believe that is pretty much what I said earlier.

I did not intend to use my single bad roof as evidence of fundamental flaws. I am using my 38 years experience as a contractor, having worked on hundreds of bad roofs (all with similar problems), as evidence of the fundamental flawed nature of residential flat roofs. It's not the roof, its the culture of cheapness among homeowners (and contractors) related to them.

My roof was just a good example of the problem.

I can build them well. EPDM, PVC, and cold process are all methods I am intimately familiar with. I am also aware these types of roofs are rare on residences, for cost reasons.

As I have noted, based on my experiences, I would be suspicious of a residential flat roof. I would get it carefully inspected by qualified commercial contractors.

alex
alex UberDork
10/30/13 11:48 p.m.

All fair points. Your professional input is certainly appreciated.

Curmudgeon
Curmudgeon MegaDork
10/31/13 7:49 a.m.
gamby wrote: 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.

I love this architectural style. Having said that, I prefer that my roof be low maintenance therefore I have a house with a pitched roof and probably always will.

1988RedT2
1988RedT2 UberDork
10/31/13 7:57 a.m.

Off-topic:

My house was built in 2001 and wears a high-quality "dimensional" shingle with a 30 or 40-year life expectancy. Why then did the roofer use a cheesy plastic pipe flashing that crumbled away and allowed water to pour in after only 12 years? You ARE the weakest link. Good-bye!

spitfirebill
spitfirebill UberDork
10/31/13 11:50 a.m.

I work with a E36 M3 load of engineers. There is a difference in flat and level.

Curmudgeon
Curmudgeon MegaDork
10/31/13 2:58 p.m.
1988RedT2 wrote: Off-topic: My house was built in 2001 and wears a high-quality "dimensional" shingle with a 30 or 40-year life expectancy. Why then did the roofer use a cheesy plastic pipe flashing that crumbled away and allowed water to pour in after only 12 years? You ARE the weakest link. Good-bye!

Yeah, I've bitched before about exposed nail heads. NOTHING pisses me off more than sloppy workmanship when it's just as easy to do it right.

I had a house which developed a leak next to the chimney. Turned out the flashing was butted together in a corner and the 'roofer' just wadded silicone in the corner when it would have been so easy to put a small piece of flashing in the corner behind the top two. I know this because that's how I fixed it 5 years in. Jerk.

gofastbobby
gofastbobby New Reader
10/31/13 3:28 p.m.

There's two kinds of flat roofs. Those that leak and those that are going to leak.

Edit: I don't read entire threads sometimes before posting. oops.

benzbaronDaryn
benzbaronDaryn Dork
11/1/13 12:27 a.m.

I'm with SV on this one, I live in an area where flat roofs are prevalent and I see people with 2-4 inches of water sitting after a rain storm. They just don't have any drainage and if they do it is plugged by leaves. Around here they do something called a "foam roof" and there are specialists. I don't understand why they were made, I guess SV is probably correct that a flat roof is a bad solution to an expensive problem.

If you ever saw my neighbor running two pumps to drain the water, it is literally a waterfall worth, hours of pumping in the rain. I can't imagine the damage a failure in the roof would cause. You can keep a flat roof.

captdownshift
captdownshift GRM+ Memberand Reader
4/22/14 7:27 a.m.

rhino line said roof in question, set up solar powered pond sumps along the lowest sections and and never worry about it again

<--- has been looking into making a home out of sea containers

drainoil
drainoil Reader
4/22/14 8:17 p.m.

If you start out with a solid leak free dry roof, and keep it that way you should be good to go. As already posted here, some homes look really nice with a flat roof. When I think of flat roof homes, I think of 1950' s atomic retro cool. But if are looking to buy a home with an already shot flat roof, might want to pass.

As long as we are talking roofs, how about all the crappy shingles out there that are on pitched roofed homes? 30 or 40 shingles that need replacing after half their advertised life expectancy.

Almost forgot, a buddy inherited property with a 20 something year old mobile home ie: flat roof, and that hasn't ever leaked from what we can tell.

SVreX
SVreX MegaDork
4/22/14 8:38 p.m.

"advertised life expectancy"...

That's a misnomer. People hear what they want to hear.

Roof shingles do not have an advertised life expectancy. When people buy a "20 year shingle" they want it to last 20 years. But they never actually read the warranty.

Virtually all roofing manufacturers warrant their products against manufacturer's defect. They do not warrant them against wear and tear.

A 20 year shingle means it is warranted against manufacturer's defect for 20 years. No warranty on the wear.

Fun, huh?

Kramer
Kramer Dork
4/23/14 9:45 a.m.

Here is my dad's storage building. Both the 50x50 building with the lean-to on the west side, and the 70x30 building north of it. Notice on the north portion, which used to be a Kaiser dealership, there is water standing on the roof. And leaks all over inside.

The 50x50 portion also has a "flat roof," but it doesn't hold water or leak. Obviously the pitch is different.

Takeaway: too little pitch, and you're more susceptible to leaks.

 photo CherryStAerialPic.jpg

N Sperlo
N Sperlo MegaDork
4/23/14 10:03 a.m.

To make it short, a friend lives in an old lofted warehouse. As cool as the place is, the roof is a mess. He had the roof that was regularly re-tarred covered with a "better" roof. The "better" roof started leaking in less than ten years. The ceiling is built under that roof, so when it leaks, it shows. Where it shows is not necessarily where the leak is. Now since the roof is leaking and the footage is high, it will cost over 20k to fix.

Pain in the ass for sure.

Duke
Duke UltimaDork
4/23/14 10:11 a.m.

A properly installed flat roof - technically, they're called "low slope" since they are not usually installed dead flat anymore - WILL NOT LEAK.

The key words there are "properly installed". That's the part where owners need to understand that you need a good, manufacturer-certified roofing contractor to do the work. Not 3 guys in a pickup truck.

And, Sperlo, roof leaks in any kind of roof almost never present themselves where water is actually entering the building, unless it is an obvious and catastrophic issue.

drainoil
drainoil Reader
4/23/14 5:21 p.m.
drainoil wrote: If you start out with a solid leak free dry roof, and keep it that way you should be good to go. As already posted here, some homes look really nice with a flat roof. When I think of flat roof homes, I think of 1950' s atomic retro cool. But if are looking to buy a home with an already shot flat roof, might want to pass. As long as we are talking roofs, how about all the crappy shingles out there that are on pitched roofed homes? 30 or 40 shingles that need replacing after half their advertised life expectancy. Almost forgot, a buddy inherited property with a 20 something year old mobile home ie: flat of, and that hasn'ter leaked from what we can tell.

Hey just going with what I've heard several others refer and describe them.

So how is it determined if pre mature shingle wear is not a factory defect?

SVreX
SVreX MegaDork
4/23/14 6:04 p.m.
drainoil wrote: So how is it determined if pre mature shingle wear is not a factory defect?

lol! Good luck with that one!

Define "premature wear" when no lifespan was ever determined or promised.

It would never win in court.

dculberson
dculberson UltraDork
4/24/14 10:28 a.m.

We have a "flat" roof on our building and it's not been a problem, but when it's $80k to replace one portion of it you hope it's not a constant nightmare! When it was re-done we had tapered insulation put on so it has a nice slope to the roof drains.

The amazing thing was, after the rubber roof from the 1980s was removed but before the new EPDM roof was put on we had a light rain and the built-up tar roof from 1927 was leak proof except for where new holes had been cut for construction work. That's an amazing life span for a roof.

SVreX
SVreX MegaDork
4/24/14 2:06 p.m.

BTW, I like this style too:

And there is ABSOLUTELY NO EVIDENCE that it has a flat roof.

It looks like a flat roof. But there is a good possibility that the walls have parapets that extend beyond the roofline. The actual roof could have a sizeable pitch on it, sloping to the rear. If that were not the case, we would probably see water stains running down the front and side.

That's how most commercial storefronts are built these days. They are pitched, but have a facade that looks flat.

A pitched roof does not have to compromise an architectural style which disagrees with it.

But I digress... on existing buildings, you get what you get, and most residential applications (except in the SW) are questionable.

NGTD
NGTD SuperDork
4/24/14 3:36 p.m.

I am in Facilities at a College. We have multiple flat roofs - yes truly flat - not even sloped insulation.

I would live in a tent before I had a house with a flat roof.

I don't even like coming to work on rainy days. We have stopped most of the leaks but our roofs are getting near end of life and they require constant monitoring.

OHSCrifle
OHSCrifle GRM+ Memberand Reader
4/25/14 7:45 a.m.
SVreX wrote: BTW, I like this style too: And there is ABSOLUTELY NO EVIDENCE that it has a flat roof. It looks like a flat roof. But there is a good possibility that the walls have parapets that extend beyond the roofline. The actual roof could have a sizeable pitch on it, sloping to the rear. If that were not the case, we would probably see water stains running down the front and side. That's how most commercial storefronts are built these days. They are pitched, but have a facade that looks flat. A pitched roof does not have to compromise an architectural style which disagrees with it. But I digress... on existing buildings, you get what you get, and most residential applications (except in the SW) are questionable.

The window at the back of the 2nd story is evidence enough for me.

Otherwise... Not a response to SVRex but to the topic..

A low slope roof with a gutter, IMHO will be more reliable than one with a parapet all around (thus dependent on scuppers or drains).. Because a plugged gutter overflows to the ground, usually. A plugged roof drain can't overflow.

It's all about maintenance. If you build anything and ignore it, you're asking for trouble. Low slope roofs need to be cleared of debris. Often.

One strategy I like is to run the "overflow" drains to someplace where you can't ignore it. Same for HVAC condensate pan (backup) drains. Don't run that pipe to the side of the house where you never see it running water to indicate the main drain is plugged.. Run it so it drips in front of the back door.

Impossible to ignore. Like an engine temperature gauge ;)

SVreX
SVreX MegaDork
4/25/14 9:32 a.m.

In reply to OHSCrifle:

That window would still easily accommodate a pitch of 6"-8" or more. Bottom line- we do not know.

I agree with you about scuppers, drains, maintenance, etc.

Since very few residential owners have anything that resembles a "maintenance program", the basic point still stands:

It is very risky to buy an existing residential building with a flat (or low pitched) roof. There are a million ways to screw it up, plus a few ways to do it well, but they are rare- statistical anomalies. Caveat emptor.

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