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BRICK VENEER WALL Loose, Bulged
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DECK COLLAPSE Case Study
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DECK FLASHING LEAKS, ROT Case Study
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DRYWELLS, FRENCH DRAINS for FLAT SITES
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FLASHING ROOF WALL DETAILS
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FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FOOTING & FOUNDATION DRAINS
FOUNDATION CRACKS & DAMAGE GUIDE
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GLUES ADHESIVES, EXTERIOR CONSTRUCTION
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GUTTERS & DOWNSPOUTS
HEAT TAPES & CABLES on Roofs for Ice Dams
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ICE DAM PREVENTION
INDOOR AIR QUALITY & HOUSE TIGHTNESS
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KIT HOMES, Aladdin, Sears, Wards, Others
LEAD POISONING HAZARDS GUIDE
LEAD TEST KIT for HOME USE
LEED GREEN BUILDING CERTIFICATION
LOG HOME GUIDE
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ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
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ROOFING DIAGNOSIS INSPECTION & REPAIR
ROT RESISTANT LUMBER
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STAINS on & in BUILDINGS, CAUSES & CURES
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STUCCO WAll FAILURES DUE TO WEATHER
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THERMAL MASS in BUILDINGS
TREES & SHRUBS, TRIM OFF BUILDING
TRIM, EXTERIOR CHOICES, INSTALLATION
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VENTILATION in BUILDINGS
VINYL CHLORIDE HEALTH INFO
VINYL Siding or PLASTIC Window ODORS
Volatile Organic Compounds VOCs
WALL CONSTRUCTION BARRIER vs CAVITY
WATER BARRIERS, EXTERIOR BUILDING
WATER ENTRY in buildings
WIND ENERGY SYSTEMS
WIND TURBINES & LIGHTNING
WINTERIZE A BUILDING
This article describes defects in roof leaders or downspout systems such as inadequate number of downspouts to handle the volume of roof drainage, missing, lost, or damaged downspouts. This article series discusses how to choose, install, diagnose & maintain roof gutters & downspouts, & roof drainage systems to prevent building leaks and water entry.
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Also see DOWNSPOUT LEAKS or start this topic at DOWNSPOUT / LEADER DEFECTS; also see GUTTER DEFECTS LIST for other sources of wet basements or crawl spaces caused by problems with the roof drainage system.
The drainage requirements for flat roofs on buildings present some special problems that we describe and illustrate here.
At page top and at left our photos show a low-slope roof surrounded by a parapet. Roofs of this design will have one or more roof drains or scuppers installed.
Watch for clogs, blockage at the roof drain or scupper.
And as our photographs below illustrate, look closely for leaks and damage around the drain opening where it penetrates the roof, especially in freezing climates.
The sketch at left common leak points at flat roof drainage systems:
[Click to enlarge any image]
These emergency drains will prevent deep flooding (and risk of collapse or catastrophic building interior flooding) should the main scupper drains become obstructed by debris.
Sketch courtesy of Carson Dunlop Associates.
Interior drains on flat roofs are commonly used in urban areas. The drain runs through the building and connects to a storm drain or in some communities where it is still allowed, to the sewer system.
(Many communities have made it illegal to connect roof drains or surface water runoff drains into the sewer system because during heavy rainfall the sewer system will be flooded, resulting in discharge of raw sewage into the environment).
Watch out: debris entering the roof drain system lead to clogging and leaks into the building interior. In freezing climates a clogged interior building drain eventually freezes and bursts near the roof surface.
When the roof has been flooded due to a clogged interior building drain and the drain subsequently bursts, a huge volume of water (from the flooded roof) enters and floods the building interior.
Inspect and clean roof drain screens and drain piping at least annually to avoid this building flood catastrophe.
Sketch courtesy of Carson Dunlop Associates.
Here we illustrate just how interior drains on flat roofs become clogged, causing rising ponds of water on the roof surface. Sketch courtesy of Carson Dunlop Associates.
The combination of ponding water on the roof around the roof drain and the mechanical disturbance caused by freeze-thaw cycling act to loosen the drain connections, break the roof drain seal, and cause leaks into the building below.
When the through-building roof drain system has become clogged, even if it does not burst and lead to building flooding, it causes other building problems.
The roof structure may sag due to the added weight of ponding water.
Watch out: in severe cases of deep ponding water (or water and ice and wet snow) on a roof with blocked drainage, the weight of the water and ice may conspire with hidden rot or insect damage (such as from prior roof leaks) to cause catastrophic roof collapse - a very unsafe condition.
Sketch courtesy of Carson Dunlop Associates.
It is possible to add new roof drains to relieve ponding on a sagged flat roof, as shown at left.
Notice that the new drain extends (through the shortest possible route) to the building exterior where it is conducted to ground or to a storm drain.
Using this method permits adding a drain at the roof's low point.
When the building is re-roofed, the roofer may install tapered foam insulation to direct water to roof scuppers or to a main or new-main roof drain to prevent future ponding. Sketch courtesy of Carson Dunlop Associates.
Reader Question: roof drain clogs lead to flooding in my apartment
This is the latest picture I have of what took place yesterday while the roof tank was supposedly being cleaned. This particular picture is directly outside of widow where this canopy drain is located...in other words believe it or not it can overflow into apt. Its very close to my windows
How the building did that I will never know. Terrible disarray
However can you please offer me again your expertise on this issue as it is very scary for me to live with this condition that is totally ignored by management
This is all in addition to other picture I have sent you i. e. weep hole in brick hot spots on floors along with vibrations I inadvertently tapped 2014 as opposed to 2013 on my camera.
Don't know where to go with this or who to trust weather it be a plumber /electrician /or home inspector. - BMR 10/09/2013
Reply: recommendations to reduce the risk of building leaks due to roof drain SNAFUs
BM: There is additional important information that an on-site inspector would have to observe and then consider before offering a confident diagnosis about the roof drain overflow problem that you and your photo describe in your email. But I can offer a few comments, and also I refer you and your building superintendent to the low slope roof drain design discussion and suggestions found at FLAT ROOF DRAINAGE SYSTEMS.
Low slope roof drains are indeed subject to clogging that in turn can lead to serious, even dangerous conditions such as:
In addition to those general concerns I see the following concerns in your photo:
While an on-site expert would undoubtedly have more suggestions and could perform a more reliable inspection than anyone can do based on just a photograph, it seems to me that at a minimum your building maintenance people will want to:
On some buildings it is possible to adjust the roof slope and amend the roof drainage to convert to roof scuppers that drain out through a parapet wall to the building exterior - eliminating a good part of these clog and leak difficulties.
Whom do you trust to fix these problems? It is the building owner's responsibility to find and employ knowledgeable, reliable people; you may just aggravate the owner or maintenance staff if you are too directive, and worse, if you try to specify the exact repair then you will own the problem rather than leaving it in the hands where it belongs.
But certainly the solution to roof drainage troubles is not something to leave to an electrician and usually not a typical home inspector. A roofing contractor who has experience with low slope roofing installation and repair is where management should turn; I'd expect such a person to be in general agreement with the information given here as our views are based on guidance from roofing industry expert sources cited at References in this and each of our roofing articles.
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