Architekwiki
  • Home
  • WIKI
  • Start Here
  • Resources
  • Other
    • Reading List
    • Ochre >
      • Ochre
      • Ochre KB
      • Ochre FAQs
      • Ochre Help
    • Details
    • The 3 Aspects
    • About
    • Subscription FAQs
    • Terms of Use
  • Subscribe
  • Home
  • WIKI
  • Start Here
  • Resources
  • Other
    • Reading List
    • Ochre >
      • Ochre
      • Ochre KB
      • Ochre FAQs
      • Ochre Help
    • Details
    • The 3 Aspects
    • About
    • Subscription FAQs
    • Terms of Use
  • Subscribe

Architekwiki

A Resource For Architects
Click here to get good stuff in your inbox

Categories

All
Business Development
Business Management
Design
Detail
Miscellaneous
Project Management
Resources

Archives

January 2023
November 2022
October 2022
July 2022
June 2022
May 2022
April 2022
October 2021
September 2021
August 2021
June 2021
May 2021
February 2021
January 2021
December 2020
November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
April 2020
March 2020
February 2020
January 2020
December 2019
November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012

Flat Roofs

5/28/2018

 
Flat Roofs

Flat Roofs Don’t Leak

Flat roofs have a bad reputation for leaks, but I don’t think flat roofs leak. My experience is that any leaks aren’t due to poor roofing or poor roof materials. The leaks are due to the flatness of the roof, which encourages use of the roof for HVAC equipment. 

Here is why that is a leak-producing situation, and what you can do about it. 
​
​
Flat roofs don’t leak. 
What leaks are the holes you put in the roofing and poor roof terminations. 

Some Actual Cases
​

First Case    A technical school had a 25 year old built-up tar and gravel roof. Maintenance was nonexistent. I could see the surface of the felts that made up the roof. The gravel and flood coat had completely eroded away. That’s not where the leaks were. In fact I have never seen a roof leak in the field of the roof. The leaks were at the exterior roof edge where the joints in the gravel stop had created cracks in the roof membrane due to expansion and contraction of the metal gravel stop. 

The school was re-roofed with edge conditions that met the roof manufacturer’s recommendations. 

Second Case   A seven year old school had leaks in a corridor and some offices on the first floor. Checking above the drop ceilings showed there were no penetrations through the roof above. A trip to the roof, however, made it obvious that all these leaks were along the back wall of the gym. Ahh, the flashing at the higher gym wall. Nope the flashings were intact and the counter-flashing was a copper design that I recognized from Graphic Standards; it looked perfect. After testing with a garden hose, the culprit was the mortar joint where the counter-flashing entered the brick gym wall. There was a hairline crack where the brick and copper met. The rainwater rolling down the masonry wall was flowing right into the hairline, back into the wall where it hit solid mortar, then went under the flashing and down the face of the wall and onto the ceiling. 

The counter-flashing was removed; the offending joint sealed; and a surface mounted counter-flashing installed with a mastic backing and a 45 degree ‘kick’ at the top to receive a non-setting sealant. 

Third Case   A manufacturing building had a leak in the middle of the floor. The culprit was pretty obvious. Directly above was a rooftop HVAC unit. The base flashings looked OK, but clearly there was a leak. After the flashings were redone...the leak was still there as though nothing had changed. We had the roofer check his flashings with a garden hose. No leaks. The rooftop unit was letting rainwater in through joints in its casing. No gaskets! 

Adding gaskets was extremely labor intensive for the HVAC unit manufacturer. 
Flat Roofs
​What You Can Do
​

Intersections are the weak link. Pay special attention to where the work of two trades intersect. Mason and roofer. M/E contractors and roofer. Skylights and roofer. Siding / panels and roofer. 

Use big-name roofing manufacturers. Use manufacturers that include roof edges and flashings in their warranty and that publish recommended details for those conditions. Then make sure you get those details. 

Don’t put stuff on the roof. Whenever you can, put HVAC equipment inside or on the ground. It is more expensive, that’s why most buildings have the stuff on the roof. But it is better.

Space equipment so that the roofer can do a good job. This means being aware of what’s going to be on the roof. Then making sure every item has 30” clearance for the roofer to do his work. A diagrammatic roof plan is a good way to express the requirement. An accurate roof plan is even better. If you have consultants, make sure they know what you want.

Specify tall curbs. HVAC equipment needs base flashing around the curb that it sits on. Give the roofer a chance to do a good job. Specify 12” (min) high curbs. 

Design tall equipment platforms. When you have a large piece of equipment sitting on a raised platform, it will still be there when re-roofing is required. Raising it up makes roof maintenance possible. It may make the equipment more visible. You can solve that, but you can’t re-roof in 16” of headroom. And make sure the structural posts holding the frame are round. There are foolproof flashing details for ‘round’.  (Square is rarely square.)

Don’t use pitch pockets. Make the M/E contractors use pipe boxes instead. You should specify the pipe boxes and have the roofer install them. Here is a company that specializes in all types. Pitch pockets eventually leak, and quite soon if you have more than one item per pitch pocket. There are four items per condensing unit.  

Don’t attach piping and conduit to flashings and copings. Re-roofing is much more complicated, disruptive, and expensive when you let M/E contractors run items across the roof. There is always a way to run it below, but it’s cheaper to screw up your roof. 


​I am hoping you won't run into any of these situations like I did. Luckily, most of them were found re-roofing someone else's design.
Picture

Comments are closed.
    Resources

    Start Here

    YouTube Channel

    Join The Mailing List

    Terms of Use
    Your use of Architekwiki is implicit agreement with the 
    ​
    Terms of Use.
    Thank You for your donation

    x
    Get Good Stuff in Your Inbox
    Picture
    Subscribe

    RSS Feed


    Archives

    January 2023
    November 2022
    October 2022
    July 2022
    June 2022
    May 2022
    April 2022
    October 2021
    September 2021
    August 2021
    June 2021
    May 2021
    February 2021
    January 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    June 2014
    May 2014
    April 2014
    March 2014
    February 2014
    January 2014
    December 2013
    November 2013
    October 2013
    September 2013
    August 2013
    July 2013
    June 2013
    May 2013
    April 2013
    March 2013
    February 2013
    January 2013
    December 2012
    November 2012
    October 2012

    Categories

    All
    Business Development
    Business Management
    Design
    Detail
    Miscellaneous
    Project Management
    Resources

Picture

Picture
VISIT ARCHITEKWIKI'S RESOURCES
​
START HERE
ABOUT
SIGN UP
TERMS OF USE
Architekwiki | Architect's Resource | Greater Cincinnati 
© 2012-2022   Architekwiki​