Hello FHB,
I’m currently forming up stem walls for a crawlspace within a flood zone. Since the project is in a flood zone the crawlspace will require flood vents. The question I have is what’s standard practice for forming the voids in the stem wall for these vents? They are installed after the pour and essentially require an 8×16 opening (i think they are sized to be compatible with CMU’s). One idea we’ve had is building a box and securing that in the form, great idea unless our boxes get a little wonky and then we’re going to be “refining” those openings with a grinder.
Thanks All,
Dave
Replies
Make a box out of plywood with outside dimensions of 7-5/8 x 7-5/8 x 15-15/8 (same actual dimensions as a concrete block). Check the required opening size against the vent that you're going to use - the block-out may need to be a bit bigger.
Cut 2 pieces of plywood cut so that they just fit the inside of your box (parallel with the wall face).
Nail one onto the forms on one side of the wall.
Slide the box onto that plywood and tack in into place.
Take the other piece of plywood, slide it into the other side of your box, and lightly tack it into place.
Raise the other side forms. Screw thru the concrete form and into the 2nd piece of plywood in your box. Your boxout for the vent is done.
TIP: Be sure to drill a couple of 3/4"-1" holes in the middle BOTTOM of the box-out. This will help vent the air bubble under the block-out when concrete is placed, insuring solid concrete around the hole you're creating. If any concrete paste finds its way into the block-out it'll be easy to chisel off after the forms are stripped.
To form a flood opening void in a log wall within a flood zone, it is common practice to construct a wooden box (typically 8 inches by 16 inches) and place it securely within the formwork before pouring the concrete. . Make sure these boxes are securely fastened for accurate alignment. Also, be sure to reinforce the edges of the box to prevent deformation during pouring. This method helps achieve a clean and precise opening and minimizes the need for post-injection adjustments.
For those flood vents, using a box in the form is a pretty standard practice. Just make sure your boxes are sturdy and well-secured to avoid any "wonkiness." If you’re worried about precision, you could also use foam blocks—they’re easy to shape and remove after the pour.