Classic Mistakes

Classic Mistakes

When inspecting firestop installations you can’t look at an assembly and say that it is done correctly without conducting destructive testing. However, in some cases you can tell that it is not done right just by looking.

Check out these Classic Mistakes photos and see if you can tell what is wrong just by looking. Email us at if you are not sure, and we will send you the answer.

This is a 1 hour rated gypsum wall that will tie into the concrete sheer wall behind it. Look at the head of wall joint. It is firestopped with 3M’s FD150.

Can you tell what is wrong with the firestop installation?

This is a 1 hour wall and you are looking at it from the unfinished room side. The opposite side is the corridor. From the corridor side of the wall the installation looks good at a glance. Firestop is installed the full circumference around the cables, and the cables are rigidly supported as required by the UL listing. The installer used an intumescent material that matches the submitted UL listed detail. When the wall is complete these MC cables will not penetrate the room side of the wall, so technically this is a membrane penetration rather than a through penetration.

Do you know what’s wrong with this installation?

This is a 2 hour block wall, and these are non-dampered ducts. Let’s say the duct on the left is 16”x32 and the one on the right is 26×38. The installer used the proper depth of mineral wool and the proper depth of firestop sealant. They claim they are done.

Can you see what is missing? If you ask for the answer, you should know you will get two answers: a short one and a rather long one.

This is not firestopped yet. But unless something is changed before the firestop is installed this will not be a compliant application.

Do you know what needs to be changed?

This is an edge of slab joint, and we obtained an Engineering Judgment for this installation because of the over sized joint. There is one thing that is wrong that creates two critical problems. Perhaps in the short term there is little chance of a problem.

But long term as the exterior of the building warms and cools through the changes in the day, and the changes in season, there is a potential for this installation to fail.

This is a 4” sleeve that stands 5” off the floor. There are three 1-1/4” innerducts. The installation has 4” of mineral wool and ½” of an intumescent firestop sealant.

If this installation were placed on a UL furnace we guarantee this application would fail.

For the sake of argument, let’s say we take the pillows that are protruding from the wall and we slide them back in, and we install an intumescent sealant or putty in the spaces between the conduits and the block.

We still have two other problems with this installation.

This is a 3” CPVC pipe through a 2-hour concrete floor. There is a 4” sleeved opening, 4” of mineral wool and ¾” of STI’s LCI.

Do you think this is installed right?

This is a ½” conduit through a 1 hour rated gypsum wall. This is another application where from the opposite side of the wall the installation is firestopped, and without destructive testing it looks compliant.

Do you think this is installed right?