Commercial Construction Detail: Installing Membrane End Laps (CT-22)


Hello CertainTeed Family, 

I’m back again to teach you and your team another modified bitumen installation detail. In this session, I will detail the steps to properly prepare membrane end laps (Construction Detail CT-22).

As we all know, an end lap is the point where one roll overlaps a previously installed roll; typically, for capsheets, such as a Flintlastic® SA Cap, this overlap is 6” (minimum). If not properly installed, these areas are susceptible to a capillary condition which could lead to water incursion into the structure. An important step necessary to ensure a watertight seal is to use our FlintBond® SBS-Modified Adhesive, Caulk, or Trowel Grade to secure the cap sheet. 

As I like to say, “if you don’t see blue, there is something you have to do,” so if you don’t see the top blue facing of either our installed Flintlastic SA NailBase, SA PlyBase, or SA MidPly sheets, you will need to apply our FlintBond SBS Modified Adhesive – Caulk or Trowel Grade – in a uniform bed, the entire dimension of the endlap.

For a successful installation, please follow the steps below, and then watch my quick demonstration video to see it in action. 

Let’s Get to Work!

1. Make sure all side and end laps are installed with the slope of the roof to ensure that no laps are installed against the flow of water. 

2. Position the new roll to overlap the existing roll a minimum of 6”, creating the end lap. It’s helpful to score and leave the release film in place until you are ready to adhere to the end lap. 

3. Adhere the new roll, up to the end lap. 

4. Next, to remove the T-lap, use the selvage dimension of 3” as your guide. Cut the installed sheet on an angle to as close to the 6” dimension as possible – I recommend leaving approximately 5.5” to avoid overcutting. 

5. To avoid the T-lap on the next course, make a similar cut on the opposite corner on the sheet being installed. 

6. Again using the selvage dimension of 3” as your guide, cut the top sheet on an angle, 5.5”. 

7. Make all T-lap cuts in the same direction, starting about 3” into the roll, cutting out.

8. When the new roll overlaps a granulated surface, as with Flintlastic SA Self-Adhered Membranes, apply FlintBond SBS-Modified Adhesive – Trowel or Caulk Grade – to the entire 6” overlap ensuring a minimum of ¼” FlintBond bleed out. 

9. For aesthetic purposes (not required for warranty), broadcast CertainTeed color-matched granules into the FlintBond bleed out.

Nice job, you and your team have learned yet another crucial installation detail. If you have any questions, you can submit via this form or leave a comment below. 

For additional information on CertainTeed products and installation, please visit, or go directly to our Flintlastic SA Installation Manual

Be on the look-out for my next blog and video post detailing the installation method for edge metal flashing (CT-01). 

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Commercial Roofing Construction Detail: Base Flashing The Outside Corner Of A Parapet Wall (CT-10)

Commercial Construction Detail: Base Flashing the Inside Corner of a Parapet Wall (CT- 09)

Happy Building, 


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