Leak in flat roof (C) D Friedman Roof Leak Diagnostic FAQs
Questions & answers on finding & fixing the source of roof leaks

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Roof leak diagnosis & repair questions & answers:

Diagnostic FAQs about finding and repairing the cause of roof leaks that show up inside or outside of buildings. Our page top photo illustrates the importance of careful inspection of roof leak clues both on the roof surface and from inside the building. A small flashing error or the wrong roof edge flashing type might alone explain leaks into the building below.

This article series provides an extensive catalog of sources of leaks in all types of building roofs, this article describes procedures for finding and fixing all types of leaks in roofs, figuring out the actual spot where a roof leak is occurring, and methods for tracking down the source of water or wet spots on ceilings or in attics. 

The first part of this article describes different types and causes of roof leaks - clues about how and where to look for the causes of a roof leak. The second part of this article discusses how we track an actual roof leak backwards to its probable source or entry point on the roof.

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Questions & answers on how to diagnose and repair leaky roofs

These roof leak questions & replies were posted originally at ROOF LEAK DIAGNOSIS & REPAIR - home.

Question: the insulation contractor cut a hole in our roof then "patched it" - is this a leak risk?

The company that we used to upgrade out attic insulation FORGOT to call us to let us know they were coming. They couldn't get to the access panel for the attic, so they cut a section of our shingles and the board underneath. Is this common practice? Can it lead to roof leaks or something worse in the future? Please advise. Thanks so much! - K.B. 8/19/2013


I guess the insulation contractor didn't want to have to argue with you about charging extra to come to the job twice, but speaking just for myself I'd have been reluctant to chop my way into a home without prior permission.

In fact IF the roof was properly repaired and sealed after the installation you should be fine. But I would not assume that an insulation contractor knows much about proper roof repair work. Why not ask a local roofer to take a look, both from inside the house and from outside on the roof surface, to see just what was done and how it was repaired.

Indeed an improperly repaired roof cut can lead to leaks later on, and un-detected such leaks can wet insulation, cause indoor mold or lead to a general mess and costly repairs. So let's make sure the repair to the roof was correct. Send along photos of the roof from inside the attic and from the roof surface and I may be able to comment further.

Question: flat roof leak diagnosis

(Aug 15, 2012) said:

Iintially roof was flat and cemented then water leakaged from the full roof and aroud the walls . I repaired applied the flat squire tiles on the roof and roof is flat. But water leakaging from full roof and around the walls . Please suggest me what I should do to stop this


Sorry Ram but I don't understand from just your note what kind of roof is presently installed nor what roofing material is on the roof surface. Use the CONTACT link found at page bottom to send me photos of the roof from outside, from the roof surface, and more photos of where you are seeing leaks and we can perhaps offer more useful comment.

Certainly from what you describe it sounds as if a do-it-yourself roof job has some problems, perhaps with improper material installation or use of the wrong material on a flat or low slope roof.

Question: corrugated asbestos sheet roof leaks

(Feb 12, 2013) Mrs M Tokley said:
My double garage is roofed with corrugated asbestos sheets, about 25 - 30 yrs old. I believe part of this is leaking. Is there any coating I could apply to leakproof it rather than re-place it? I had the covered area between the house and the garage re-felted very recently and the roofer told me that if there are still some leaks it will be because the asbestos garage roof has become porous and leaks. He tells me it would be very expensive to dispose of old asbestos, so I would like to repair it if possible. Any advice please?


There are several elastomeric roof coatings that can be sprayed on to a corrugated roof surface that may extend its life. But if the cement asbestos corrugated sheets have deteriorated enough to become soft you should replace the roof or install new corrugated metal roof atop what's there.

Question: leaks showing up in lower floor ceilings

(Sept 5, 2014) Dervan Drysdale said:
My two storey house has rain water leaks in the ceiling of the first floor in the kitchen which is directly under the bathroom upstairs.This happens only when it rains so I ruled out bathroom leaks. The question is; How could rain water leaks shows up on the ceiling of main floor and not the second floor where the roof is directly above..?


Dervan, By finding a path into the ceiling via a wall cavity, pipe chas, etc, leaks from a roof can enter an attic or wall, run down the wall interior and find a path out into a ceiling below.

But as you describe a leak in a ceiling below a bathroom, I'd check for plumbing leaks with great care. Often cutting an inspection opening into a leaked-into ceiling will permit a view that answers the question of where the leak originates. Look for leaky toilet mounts, tub or shower traps, etc. by cutting an inspection opening in the most-water-stained area of the ceiling. Make the opening big enough to get a light and your head or at least an inspection mirror into the space.

Question: water stains around soffit vents

(Sept 6, 2014) Jarhead33334 said:
There are no visible internal leaks in the attic or eaves, however around EVERY vent soffit around the entire house,
it appears to be water stained.


Jar: look for seasonal ice dam leaks into the roof eaves. That's the most likely source unless you live in a climate that is free of ice, snow and freezing weather.

Also look via the attic for signs of moisture or frost or even ice accumulation under the roof deck and at the house eaves. Interior building moisture can end up in the attic where it shows up as stains mistaken for roof leaks.

Question: water stains over the felt lining visible in the loft - how do I speed up the dry-out of this area?

(Dec 14, 2014) sam said:
I recently noticed water all over most sides of the felt lining in the loft - called a roofer out who spotted defective cement on the ridge tiles which he said was letting the water in - this has now been re-done and hopefully it is all sealed and secure. My question is, how long can I expect it to take for the water on the felt to dry out and is there anything I can do to speed this up? I have got the loft hatch open at present to try and get air up there, will that help?


Sam the dry out time depends on

- the amount of air movement through the loft and where that air comes from;

- the humidity and temperature of outdoor air

- loft temperatures and humidity

- the materials that are wet or damp

You can speed the process by

- using a fan that increases air movement around and inside the loft
- using a fan that increases the out-venting of the loft PROVIDED that outdoor temperature and humidity are lower and cooler than the conditions in the loft

A fan blowing "out" of the loft roof hatch might help if that's the hatch you meant. I would NOT try blowing air down from the loft into the occupied space.

(Dec 14, 2014) Sam said:

Thanks for your tips, at present it is just the felt and tops of the wooden beams where the felt is touching that are wet but I think it could take a long time to dry out. I might try a fan, vents around the side seem pretty good. However I've just found something else up there - there is a pipe that goes all the way down to the downstairs toilet, not sure exactly what it's for but there was a flexible pipe that I am sure should have been attached to this, leading out through the roof.

The end is tatty and I can't re-attach it - could it be this that has actually caused the wetness, not a leak? If that pipe is supposed to exit through the roof and the flexible pipe came off a while ago, could it be that? I don't know if the pipe also carries anything from the bathroom or if its just for the fan in the downstairs loo, or something else? For now I have poked it into the top of the pipe but there is a gap around the edge - should I get this replaced? How serious is this?


Sam the pipe is probably a plumbing vent. Search InspectApedia for "Plumbing Vents" to read about that component.

If the vent pipe is leaking into the loft or leaks where it passes through the roof those conditions should be repaired.

If you block off the vent you may find drains working poorly and if the vent leaks into the building you could have a smelly or even unsafe accumulation of sewer gases. It needs to vent outdoors.

(Dec 15, 2014) Sam said:
Thanks - I don't think its leaking as such, just that if the flexible pipe has come unattached, it means the pipe is left open so anything coming up is going into the loft, not out through the roof. But as Im not entirely sure what it's there for, I don't know if that has caused any condensation. Theres no foul smell evident. I have poked the flexible pipe into the top of it for now but it isn't sealed.

Question: how can I repair drips coming off of nails visible under the roof - in the attic or loft?

(Dec 15, 2014) hubert stoke said:
My ceiling has been dripping on and off basis for the past year, it started to drip last night,
I was able to climb up into the attic last night and saw the drips coming through a nail.

How do I stop the dripping whenever there is heavy gust of rain or when snow is melting on
the roof? Are there sprays that I can use?



You can make a temporary seal around a nail puncture to slow leaks into an attic using swim pool sealant, hydraulic cement, other glues that tolerate water.

BUT this is an upside down, inside out "band-aid" approach that does not bode well.

Water continues to leak into the roof sheathing - long term this means rot

Water probably continues to leak into the space between shingles and underlayment, underlayment and sheathing, and will also run further down the roof to appear elsewhere.

Ultimately the proper repair will be done from on the roof from outside.

Question: leaks in mobile home roof

(Jan 12, 2015) Anonymous said:
My mobile home has a metal roof. There is a leak on the inside of my window. We thought we had sealed the area and water still leaks in. The tiny gutter built into the roof edge seems to be one entire piece. What can I do? We thought about new metal roofing,but,worry about the cost.



You may be able to seal the leaks with a silicone sealant applied to a clean dry surface if you can spot the actual leak points. There is also a variety of adhesive membranes or sealant coatings for mobile home roofs.

Question: leaks in ceiling near a window

(Mar 3, 2015) Fran said:
Occasionally, when we have rain with wind, there is a fall of water through the ceiling near the window. It is the middle room of a town house with a dormer above it. Builder has secured flashing. Could rain be coming in through soffit vents just outside the window?

(Mar 6, 2015) leaks are new ones was suppose to replace new boards said:
I feel like it shouldn't have leaked having it done 1 year ago especially with ice and water sheets put on the whole roof. What do you think?



We need an accurate diagnosis of the leak source in order to make a proper repair suggestion. On occasion wind blown rain can enter a soffit. But if that were the case we'd expect leak signs along much of Te soffit length. So I'm inclined to look at dormer window, flashing, and roof areas above where you see the leak as likely candidates. If you live in a freezing climate look for ice dam leaks first.

Also check for wall flashing errors above the leaky window.

Question: leaks in metal-roofed factory - what's the best repair? Bostix Flexacryl?

(May 5, 2015) Kaz said:
We have a factory with metal sheeted roof but it is old now and we are getting more and more leaks, what is the best repair for this, flexacryl or something like that?



Bostix Flexacryl is provided by the U.K. company and is intended for "general repairs or routine maintenance" - I'm doubtful that it would be appropriate or cost effective to try to coat an entire roof with a repair sealant compound.

I'd get bids from roofers for a roof-over. Metal roofing is quite light. Be sure that any proposal for adding roof layers considers the adequacy of the structure.


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