Flat Roof Leaks
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Flat Roof Leaks


In this video, we will show you how to find
and diagnose a flat roof leak . There are two types of flat roofs. The ones that leak
and the ones that are going leak. Additionally, many flat roof leaks are misdiagnosed and
many times, unnecessary expensive repairs are performed. The owner of this flat roof
has had flat roof leaks since the day the building was purchased which was roughly 10
years ago The building owner employed many roofing contractors to make roof repairs which
included the installation of new roof membranes, installation of new flashing, and the installation
of new top reflective sealant coating. After all these repairs, the roof membrane still
leaked. The building owner and his secretary would control the roof leaks with buckets
The last roofer decided to get an opinion from a building scientist Marko Vovk (that
would be I) to help diagnose the roof leaks. The roofer cut the roof membrane and found
trapped water. Water was running between roof membranes and leaking at two different room
locations below. While on the roof, I asked the maintenance
man to bring me a 5 gallon bucket full water. I threw several cups or water to an upper
elevation brick wall. The water beaded off. I ask the maintenance man who sealed the brick.
He said, that 10 years ago, when they bought the building, the previous owner disclosed
that the window at this location leaked and it was repaired. He wasn’t sure about and
brick sealing. He stated that since this repair, the window has not leaked. Well it was quite
obvious that somebody 10 years ago knew it was the brick that was leaking and not the
window. This is why they sealed the brick with what appeared to be a water resistant
coating. While on the roof, I walk over to the location where one of the roof leaks was
occurring. A brick higher elevation roof wall also existed at this area. I threw several
cups of water onto this brick. This time, the water was absorbed or sucked into the
brick. Brick and mortar joints are naturally absorbent; this is why you need weep holes
in brick. This brick upper roof wall did not have weep holes. This brick wall was once
an exterior wall of an older building. The building roof that has the two flat roof leaks
was an addition that was built over 20 years ago. The brick was getting saturated during
long duration rains. This wall also faced the southern and western exposure which is
more susceptible to weather. The water was getting sucked into Brick and mortar joints
and running down that back side if the brick in the ¾ capillary space. This newer addition
building had roof joists that rested on pocket ledges that were cut into the brick 20 years
ago. Instead of water running down into lower levels, it escaped at these cut pockets. This
was going to be an easy fix. Simply by sealing the exterior brick would fix this leak. I
did warn the owner that when you seal brick, it no longer breaths and the potential, of
brick spalling may occured. I told the owner to control indoor humidity by running a dehumidifier
during cold climates. The reason for this is that if you have high indoor humidity it
will travel to the exterior through a vehicle called vapor diffusion. If the brick is sealed,
it will act like an exterior vapor barriers. During the winter, it is cold, it freezes,
and brick Spading can occur. The second leak
diagnostic was also simple. Directly above
this second leak was 12 year old H VAC unit. We cut into the roofing membrane at this location
and encountered moisture. I asked the maintenance man to be bringing me a second 5 gallon bucket
of water. This time, I dumped it into the HVAC unit fan area. It wasn’t long before
the water started dripping into the room below. In the room below you could see a roof fasteners
rusted and dripping water. The secretary said, the roof would leak for several days after
rain storms. This leak existed for 12 years due the HVAC installation contractor not being
a roofer. This roof top unit had a roof duct penetration that was poorly sealed. The HVAC
installing contractor created this leak 12 years ago. This was also an easy repair. The
HVAC unit needed to be lifted and roof membrane needed to be replaced. Sometimes when looking
for leaks you need to apply some building science knowledge, not just roofing knowledge.
Sometimes, roof leaks are not roof membrane related as they were in this case. Please
subscribe and watch my other videos.

34 thoughts on “Flat Roof Leaks

  1. Uprated.  Brilliant!  (And good guitar!)  My parents in South Euclid, Ohio could really have used you.  The creepy, haunted Craftsman's Bungalow they owned for 40 years had a leaky roof, and more.  They couldn't afford it, but they kept getting new roofs.  It did NOT help.  Also, I don't think they ever paid that house off, and it was only 19,000 USD when they got it.  That, you couldn't have helped with.  🙂

  2. Check out my new video. This one is finding flat roof leaks. This flat roof had two leaks and it was not the roof that was leaking. Sometimes you need to think out side the box..

  3. I own a 2 story, brick 1905 build. On the top story, along our north/western wall, we have water coming in through the brick mid-wall. Any ideas why that could be happening? It is a semi-flat roof with what I'd say is about a 1-12 pitch with knee walls on the north and east facing. It's a corner building with buildings attached on the south and west sides. The building on the west side, where the leak is, is only a single story structure. Any help would be appreciated.

  4. Having problems with leaks? Need to seal your roof? Not wanting to replace your entire roof?
    Check out our solution for those problems: https://www.youtube.com/watch?v=qtgpGeYZUIk

  5. How does a brick wall without weep holes pass a building inspection? I would hire an attorney if I owned the building.

  6. you smart and know your trade well sir. your droping beautiful gems of knowledge in this video. im subed now looking forward to more videos and more knowledge for u to bestow upon us. thanks for you video. and helping us out. take care.

  7. I don't have a hvac on my roof but I will look under the membrane under the roof hatch to see if that was done correctly because the leak has occurred in the same spot for two years straight on the third floor ceiling. do you have to replace the membrane with new membrane if there a collected water underneath?

  8. clevelandmarko what is the best flatroof material the roof has very little slope and will be getting foot traffic since the roof is also a porch ,thanks

  9. propaganda video this idiot is first blaming new roof and later states how brick was leaking stay away from people like this

  10. Great video! I have fixed many residential Counter-Flashings around chimneys only to discover, a brick seal was all that necessary. Brick above the roof is no bueno, but stone is worst!

  11. Sorry I don't know how to send a private message on here but I need your help in a building located in saint Louis, MO . Please get back to me. Thank you

  12. If you make a flat roof with a tiny degree to let water run off, using concrete like they use in swimming pools, is it not then "water proof"?

  13. I am laying a flat fibre glass roof onto an irregular quadrilateral area of 9 m2 that has no sides the same length and no angles the same. All walls are the same height and level. If corners in clockwise sense are labelled ABCD then side AB is 3.42 meters long, BC is 1.76 meters long, CD is 3.05 meters long and DA is 3.13 meters long. Angles are 99.5, 105, 83 and 72.5 degrees respectively (A,B,C,D). The roof is going to be flat so I am running timber joists (2 x 6 inch cross section) across. I start all perpendicular to wall CD so that from corner D up side DC, I go up 38 cm and place the timber beam perpendicular to wall CD to rest above wall AB. So I go up 38 cm at first and then every 40 cm so the joist lengths are: 3.11, 2.92, 2.73. 2.54. 2.35. 2.16. 1.97 meters and then I have 27 cm to corner C. This is since the angle the first beam makes with side AB at corner A is now 65 degrees so the joists get shorter by 19 cm every time. On the other wall AB the spacing between the beams is therefore 40/sin(65) or 44 cm (instead of 40 cm as in wall CD). OK so far so good. Now after securing these joists to the light concrete wall (it is a single walled aerated Y tong block wall system of 10 cm thick wall around) I want to put tongue and groove OSB3 boards (plywood). These will have a 2.5 cm of foam insulation sheets, and also there will be insulation between the timbers. What I am now struggling with are the following questions (1) I wish to give this flat roof a slight slope from wall AB to wall CD. It is a ruled surface I know so I need to raise it more in the wider sections. I was thinking about using FURRINGS or FIRRINGS in timber. Do you know much about them or when I should use them. I want to give the roof a slight angle (three sides will have raised edges but one is a drip edge). (2) some roofers told me to stay away from fiber glass because the roof may sag in the middle over the years. I do not think this is the case. Also this roofer said "I would stay well away from fiber glass unless you do it yourself and apply the resin generously". Why? (3) I am wondering if you have any other advice?

  14. very good video. i deal with alot of repairs that half the time are windows or non sealed brick.

  15. this is something that you can apply on wet roof, after removing old stuff https://www.youtube.com/watch?v=OilBBWHzY9U

  16. Excellent, Marko! Brilliant…Amazing how problems get solved when you get the right person involved. Thanks for posting so many informative videos about many different topics. I have learned a lot from you over the past year. Again, many thanks—Mike

  17. Thanks for the video Mr. Marko. How would an interested person become a building scientist. As soon as I heard you say "building scientist" my ears perked up. I'm a jack of all trades and I love diagnosing problems not to mention I used to wake up early as a kid just to catch the Mr. Wizard show before I read a page or 2 or 10 of popular mechanics magazine back in the 80s when I was a little brat. Science & building has always been my hobby.

  18. I live in an old loft. The building is 100 yrs old. Its was once home to Holsom Bread. The building is called, The Bread Factory here in Chattanooga Tn. My brick wall leaks and sometimes it's really bad. 6 people have looked at it since Aug.2017. But nothing done. Its starting to grow green and black mold. Its awful, I like the loft and want to stay but I can't believe they haven't been aggressive with fixing it. Last time it leaked so bad water sprayed out of 3 holes at 3am, it was a mess. It's a flat roof building. I recommend a brick master but they keep having just roofers look at it but that's all they do is look at it while it grows green and black fuzzy spots. I need help they need help. I'm at my wits end.

  19. Great video! Its amazing how many builders are unaware of the value building that specialize in building enclosures. As a fellow building envelope consltant, I appreciate your sharing your knowledge with the public. BTW, what location was this project?

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