Construction Design-Insects and Rodents

When I purchased my old home, the 1952 Cape in late 2018, the basement area looked good.  Someone took the time to paint all the concrete walls and floor and cleaned everything up to look nice.  Shortly after we moved in, the cat caught a mouse and then the following summer, the basement became a bug gathering place.  Ants, spiders and other bugs apparently wintered in another area and returned to my house in the spring.

How do all these critters get into the house?  Usually, it’s the areas lacking in water management details and where air leaks occur.  Gaps, cracks and holes in the building envelope.  Another reason for taking the time to do a really good job with the water and air management details, bug and rodent control.

This is the spot where I think the mouse got into my home, I’m surprised the cat didn’t find its way to the outside here as well.

The carpenter ants prefer damp areas.  This is the rim joist that was behind a set of concrete steps.  It had been getting wet and not drying completely for decades, the ants had a colony established and every summer they would come into the house to say hello.

In the spring of 2019, I started to change the water and air control layers of my home from tar paper, which works well for water management when the details are correct but does nothing to control air.  I moved to a self-adhered WRB or house wrap product called Henry Blueskin.

I used a primer specifically designed to seal the Blueskin to areas where the bond may be questionable.  The concrete foundation was one of those areas.  I recently checked that connection, after 2+ years, the bond is still holding.

Sealing the mouse hole!

Performing air sealing on the inside can also help control the bug population.  This is rigid XPS foam cut and sealed with canned spray foam at the rim joist area.

Did the water and air management improvements help control the rodents and bugs in my home?  I have not seen another mouse, and it’s rare I see spiders and ants inside the home.  I’m not completely done on the exterior, I still have one side left to reside, but the insect numbers are way less than that first year.

I talk a lot about the control layers on my blog.  Once a home is built, going back to change these layers will usually require disassembly of the structure, an expensive change.  Getting the detail right when building new is very important.  Improving these details on existing homes only happens occasionally, like when residing or during a gut remodel in a room or area of the home.  I recently heard the phrase, plan now or pay later, a great saying for many areas in the construction industry, but particularly fitting for the control layers.  Getting these details right solve so many issues, including rodent and bug problems.

2 Replies to “Construction Design-Insects and Rodents”

  1. Randy,

    As you improve the building envelope on your house what have you observed in terms of lower energy use and increased comfort? When I did the thermal improvement on my house in MSP in 2006 the first thing I noticed was the house did not cool down as fast in winter after 10:00 PM when the thermostat set back. I had a conversation with a building scientist friend about this at the time and he said I was on to something. When he worked with NYSERDA they would sometimes conduct this exercise on homes to be weatherized. Right before the weatherization they would after sunset set down the thermostat and observe the rate of indoor heat loss. After the weatherization they would do the same. By taking into account the Delta T for both the before and after weatherization they would get a snapshot of the thermal improvement for the project.

    1. Hi Doug,
      I have a ways to go on my home, I still have to take care of the attic/ceiling on the upper level. One thing that did happen, my natural gas furnace was replaced a couple winters ago. The original was a 100,000 btu that seemed to keep the home comfortable as long as you weren’t next to an outside wall. I downsized to an 80,000 and haven’t noticed any change in comfort but have seen a reduction in fuel use. I haven’t seen much of a reduction in the blower door number even though I’m 3/4 through with the install of the Henry Blueskin and new windows, I’m sure nearly all the leakage is in the lid.

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