flange24 inches (61 cm) below gradeextending 12 inches(30 cm) out at right
anglesto the foundation.Thisflangewill preventrats fromburrowingunderthe
floorslab and chewingtheirway throughvulnerableplacesinto the plant suchas
throughfloor drainsor expansionjoints.If the building has a basement of cellar,
its floorshouldbe tied directlyto the solidwallfoundation. Thiswill createa
solidbox that will be an effectivepest barrier.
Anotherrodent deterrentis to construct a clear stripalongthe outside of an
external wall that is about30 inches(76 cm) wideand 4 inches (10 cm) deep.Line
this stripwitha heavydutyplasticsheetto prevent weedgrowthand fill with pea
gravel(small diameterrounded stone)that will not bridgewhen the rodenttries to
burrowthroughit. It will keepcollapsing and discourageburrowing.
Otherrodent preventionfeatures for exteriorwallsincludethe shieldingof
outsidepipingand wiresto preventclimbing. Accordingto AFIS(1952), rodents
can:
∑ walkalong or climbup vertical wires;
∑ climbthe insideof vertical pipesnot morethan 3 inches (76 mm) in diameter.
Thiswouldincludedownspoutsor otheropendrainpipes on the outsideof the
building;
∑ climbthe insideof vertical pipes not morethan4 inches(102mm)or less
than1.5 inches(38 mm)in diameter;
∑ climbthe outside of vertical pipes of any size if the pipeis within3 inches
(76 mm)of a wallor other continuoussupportfor a rat;
∑ jump26 inches(660mm)vertically and up to 48 inches(1.2 m) horizontally
froma flat surface;
∑ drop50 to 80 feet (15±25m) without beingkilled;
∑ burrowverticallyin the earthto a depthof 4 feet (1.2 m).
Theeasiestwayto discourage these incursionsis to utilizemetalshieldsto
preventthe rodents fromgoingaroundthemor installthemoverwiringto
preventrodentsfromobtaininga foothold.
If concrete block construction is considered,careshouldbe takento make
surethe hollowcores are blocked to prevent rodentsand insects fromgaining
accessand free roaming throughthe wall interiors. Thiscan be accomplishedby
fillingthe blockcenterswithmortar when laid and making sure the tops of the
wallsare not left open.Thiscautionapplies to internalwalls as well.
Whenconcrete block is selectedfor exterior wallsthenit shouldbe of the
high-density type.Volcanic ash or cinder blocksare not acceptablefor food
processing facilities.Theyare too porousand will absorb moisture and bacteria
and may allowthemto penetrate directly to the core of the block where they are
virtually impossible to dislodge. Low-density concrete block is not
recommendedsince moisture, bacteriaand mold can penetrate the surfaceand
createsanitationproblems.However, a goodquality sealercan close the pores
sufficientlyto overcome thesedisadvantages. Evenwhen sealedin this way,
low-densitywallsstill requirea goodmaintenance programto remain effectively
sealed.
Improvingthe designof walls 187