Sunday, January 11, 2015

Rodent Exclusion

It's always been quite annoying setting mouse traps throughout the basement, finding little droppings around the HVAC system, and discovering the occasional occupied trap only after the putrid smell of rotten rodent permeated the basement.  Yum.

Hoping to put an end to the mild infestation we began poking around the basement looking for and plugging up any entry point. One suspicious and mysterious spot is our crawl space, we know woodchucks and squirrels had made it into the house via this space once upon a time. It's incredibly difficult to get to the exterior wall of the crawl space from the inside so we decided to apply some construction techniques from the outside.

The particular part of the wall that concerned us was under the front porch. There were a couple of spots under there where animals had burrowed through the rock wall and gotten into the crawl space. In the past we had simply taken out a few of the porch floor boards and poured concrete into the holes. In hindsight this probably wasn't the best approach, although at that time our living situation warranted a quick fix.

There is a handy guide to rodent exclusion techniques on the interwebs here:

They outline methods for both rats and mice.

The approach we decided to take was to build a concrete curtain wall with a hardware cloth upper extension.  We wanted to be as close to 100% positive that this would no longer be a trouble spot as we could.

The design calls for a 1 foot wide trench, a poured footer, and a 4 inch backing wall tapered up to the existing foundation. I aimed for a 36" deep trench but only got about 24" deep in some spots. This projects took us the month of November to complete working weekends and holiday breaks.

Step 1, destruction!
We tore off the porch floor boards. All of them except the ones that ran under the supporting pillars. They were toe nailed in from the sides so we had to slide a sawzall under each joist and cut each board free.

The rotted porch steps were also dismantled. These will eventually be replaced with steps and a railing that match the wrap around porch on the back of the house.

Step 2, dig.
The trench was dug the entire length of the porch plus under the door from which the pictures below were taken. Some cats decided to stop by to see what was going on.

Step 3, setup shop.
To combat the cold temperatures for a good cure we wrapped the work area in plastic and plugged up gaps around the bottom with insulation and dirt. We tried to keep the inside temps above 40 degrees Fahrenheit to help the concrete hydration process. Using a space heater and insulating the fresh pours helped during the frigid nights. We weren't overly concerned with the strength of the final wall as it wasn't' structural.

Step 4, pour.

The mixing station was at the end of the porch where we combined hot water with 60 lb bags of concrete in 5 gallon buckets stirring with a shovel.

I should note that before pouring any new concrete we did some repairs to the rubble stone foundation. We used S-type mortar to place rocks back into and fill holes where the old mortar had failed. So maybe that was step 3.5?

The footing was poured first with a wire mesh flashed up the back and sides to connect the future wall.

Next a simple form for the wall was dropped into the ditch and supported. This form held the concrete in place while it cured to form the tapered barrier wall against the stone foundation. 1/4" hardware cloth was tucked up underneath the siding and down into the top taper of the concrete to form a barrier for any remaining exposed wall.

The form was gradually moved down the length of the ditch to complete the wall a piece at a time. 

 The footer was extended down the wall preceding each new vertical section.

Step 5, bury all the hard work.
It's a shame to cover up all that hard work but we are glad to bury it and be done. The dirt was compacted as it was replaced in the ditch and the floor boards were placed back on the porch. We numbered each board before we took them off so they would go back on in the same spot. There were a couple of cold days on this project but it was completed before the extreme cold weather started kicking in this year.