Thursday, September 26, 2013


 This article is a sequence of photos depicting the basic installation process of an RV type crank up roof vent.  Installed on a sheet metal roof. This was being installed in the roof of a cargo trailer.  The installation is typical of many of the processes that must be performed.  But note, each installation might differ.  We were using a vent unit for 1 1/2 inch ceiling thickness.

STOP!!!!   Before purchasing the crank up type vent.  Consider the 12VDC powered vents such as the Fantastic brand.  I installed the crank up type, as shown.  After my first warm camping trip I quickly knew I had made an error.  I should have not tried going the "cheap" route.  Thankfully the opening/cut-out sizes was the same.  So at least the difficult part of the job was already done installing the crank vent. Luckily I was thinking ahead and had pre-wired power to this location.

In this case the interior of the trailer roof ribs were furred out 1 ½ inches to allow Styrofoam insulation and to give something to attach the interior ceiling finish skin.  This vent was being installed in the bathroom ceiling.  It was further recessed, to allow additional head room.  Wood framing was glued and screwed as needed.

12V Switched wiring and ground was run to where it can be accessed in the future should we ever wish to add a 12V fan unit in this location.  For now we are installing the basic crank up unit.  (As indicated this quickly changed)

What is shown here, including the necessary wood framing construction, layout, sheet metal cuts,  the vent installation, and clean-up, took approximately 2 1/2 hours.

Ceiling of bathroom area framed to install vent


Wood framing added to rough in size-4 pilot holes drilled at corners through the roofing skin

Once the wood frame was installed and double checked for rough in size, and location guide holes were drilled.  Using an 1/8 inch drill bit, four holes were drilled from the interior, up through the sheet metal roofing skin.  These four holes marked the four corners of the roughed in frame.

Moving to the exterior, the four guide holes were located.  Using a straight edge, and a marker, a cutout was marked on the exterior size of the roof skin.

While several method could be used to start and complete the sheet metal cutout we chose to use a 1 ½ inch metal hole saw to cut four holes through the roof skin roughly inside the marked square, and near but not on the marked lines.

Outline of cut out marked (notice the small corner pilot holes
1 1/2 inch hole saw punched through roofing-Sheet metal cutting started


We used sheet metal shears or snips to make the roof skin cut out.  The pre-drilled 1 ½ inch holes made this job much easier to start and complete with a clean edge.  Note: Sheet metal shears do come in 3 different cutting styles.  One makes a straight cut, another makes a left turning cut, and lastly the third is used to make a right turning cut.  While you might fight it and get the job done with just one style, there is much to be said for having the proper tools.  Having all 3, makes this job simple and produces a very clean and accurate edge.


Inside view of completed cut out-Blue sky.  Committed now!












Vent unit dry fitted


Once you have the roof skin hole cut.  Dry fit the vent unit in the hole.  Mark around its outer perimeter on the exterior of the roof.  Then pull the vent unit back out.  Next using sealing clay tape (Comes in a kit with the Clay Tape and Screws), gently press the tape around the hole cut out, slightly overlapping the line you just drew.  Once you have the clay tape in place re-insert the vent unit into the roof cut out hole.  The clay tape should be showing about ¼ inch all around the screw flange of the vent unit.   The clay tape should show through all the vent flange screw holes too.  Once all is in place, start screwing in the screws (Hex Head ) through the vent flange.  Continue through the clay tape, through the roof skin, and into the wood framing on the interior side.  Start the screws in the middle of each side and work toward the corners to avoid puckering the sheet metal and creating a leak point.  We used a hex driver in a battery hand drill for this step. We set the screw break on the drill to break free once just snug and the clay depresses slightly.  If you don't have that luxury, finish off the tightening by hand so you don't over tighten, strip the hole, or break off a screw.


Once all the exterior screws are in place you should have a weather tight installation.  In our case we will complete our installation by installing the interior finish ring, once we have finished installing our finished ceiling panels.

Completed installation-Vent unit sealed with Clay Tape Sealing kit, and screwed through roof into the wood framing

  Below is the finished ceiling and the trimmed out shower

Trimmed out shower and finished ceiling.


1 comment:

  1. Thank you so much for sharing on this very nice awesome illustration i truly appreciate it.

    Iko roofing


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