7B Ch5 Cheat Sheet: Subterranean Termite Treatments

🎯 Top 5 Traps

1

Plenum crawl space = NEVER liquid termiticide. The crawl space serves as the HVAC duct — termiticide odor circulates with heated/cooled air through living areas. Termite baits are the alternative. Non-plenum crawls require duct inspection and outside-air ducting before treatment.

2

Subslab heating ducts: low pressure (less than 30 psi at nozzle), rod from OUTSIDE. High pressure backs termiticide into the duct. Drilling through a duct is never the procedure. Reconsider treatment entirely if ducts have cellulose material, soil/sand bottoms, or standing water.

3

Foam insulation below grade lets termites BYPASS soil barriers. Termites don't eat foam — they tunnel through it to reach wood. Owner must remove foam at least 6 inches above AND below grade. For foam-filled hollow blocks, soil treatment fails entirely — termite baits are the answer.

4

Borates do NOT stop termites tubing across treated wood. They're stomach poisons — must be ingested. Highly water-soluble (leach out if wet); no contact residual. Effective indefinitely only when treated wood stays dry. Bonus: also protect against powderpost beetles and wood-decay fungi.

5

Wells/cisterns — sandy soil LESSENS contamination potential; dry weather INCREASES termiticide movement. Counter-intuitive on both counts. In dry weather, termiticide travels along cracks and fissures in the soil. Standard practice: remove soil to footing onto plastic sheeting, treat, dry, replace.

🔢 Numbers You Must Know

Number

What It Represents

less than 30 psi

Maximum nozzle pressure under or around subslab heating ducts (prevents back-flow into duct)

4 inches

Minimum cut height above floor for wooden members extending through basement concrete; also concrete-footing height above grade for wooden porch piers

6 inches

Minimum amount of rigid foam insulation board to remove ABOVE and BELOW grade for inspection and treatment access

15 minutes

Sump observation period after removing some water — if water level rises, delay treatment for drier soil

4 gal / 10 lin ft

Soil treatment rate along outside of foundation wall for dirt-filled concrete porch

1 gal / 10 sq ft

Flood rate for accessible soil under porch slab

2 to 4 inches

Untreated soil or impervious-barrier cover over treated soil in basements with exposed soil floors

🔀 Easily Confused

Pair / Group

Distinguishing Feature

Plenum vs Non-plenum crawl space

Plenum: crawl space IS the HVAC duct — no vents/access doors in foundation; never use liquid termiticide. Non-plenum: standard treatment is OK, but inspect ducts, repair leaks, and duct outside air before treating.

Borates vs Wood injection

Borates: water-based, absorbed into wood fibers, stomach poison, indefinite if dry. Wood injection: aerosol/liquid emulsion into termite galleries, bonds with soil particles in galleries for some residual; surface treatment is short-term only.

Wells inside vs outside foundation

Inside foundation walls: do NOT treat the soil beneath the structure. Outside: treat sparingly and only after considering distance, soil type, water lines, and label/local distance requirements.

Sandy soil vs heavy soil

Sandy: LESSENS termiticide movement potential. Heavy/cracked/dry: termiticide moves CONSIDERABLE distances along cracks and fissures, especially in dry weather.

Hollow block / tile / rubble vs poured concrete

Hollow / tile / rubble: termiticide can leak through, vapor escapes from uncapped block tops — seal cracks, use low pressure or gravity in voids. Poured concrete: standard methods OK.

Mechanical alteration vs Soil treatment vs Baiting

When liquid termiticide isn't safe (wells, plenum, foam-filled blocks), rely on mechanical alteration (cut and replace wood, install access doors), baiting, or direct wood treatment — possibly together.

🧭 Special Situation Decision Guide

Situation

Recommended Approach

Critical Constraint

Plenum crawl space

Termite baits; no liquid termiticide

The crawl IS the air duct — odor circulates through living quarters.

Non-plenum crawl space

Standard trench/rod after duct inspection

Repair air-duct leaks; re-duct units to outside air; ensure ventilation.

Subslab heating ducts

Rod from outside; low pressure (less than 30 psi); horizontal rodding when radiant pipes are in slab

Reconsider entirely if duct has cellulose, soil/sand bottom, or standing water. Close vents, run fan, check each drilled hole for airflow before treating.

French drain / sump pump

Drill test holes; turn off pump; remove some water; observe sump 15 minutes

If water level rises, delay treatment until soil is drier. Watch sump during treatment for termiticide.

Wood through basement floor

Cut wood at least 4 inches above floor; treat soil; pour concrete around remaining wood

Don't try to chemically treat buried wooden supports alone. Lower step of stairways: replace with concrete if possible.

Dirt-filled concrete porch

Tunnel along foundation wall, remove dirt, install access door; treat exterior soil at 4 gal / 10 lin ft and accessible subslab soil at 1 gal / 10 sq ft

Same principles apply to stoops, sidewalks, and driveways. Add masonry pier supports if tunneling weakens the porch. Foam applications often most useful here.

Wooden porch with ground contact

Cut wood above ground level; place supporting concrete; replace wooden piers or set on concrete footing 4 inches above grade

If replacement isn't possible, treat soil per label and treat soil all around base of pier.

Hollow block / tile / rubble foundation

Seal cracks/openings; seal poor mortar joints; low pressure or gravity for void treatment

Termiticide leaks through voids; vapor escapes from uncapped block tops.

Wells / cisterns / springs inside foundation walls

Do NOT treat soil beneath the structure

Rely on mechanical alteration, baiting, and direct wood treatment.

Soil near foundation walls near wells/cisterns

Remove soil to footing, place on plastic sheeting, treat outside foundation, dry thoroughly, return to trench

If well is extremely close, consider not treating that wall (with written permission of owner). Comply with local distance rules.

Rigid foam insulation board below grade

Owner removes foam 6 inches above AND below grade; trench and treat soil; backfill

Termites tunnel through foam to bypass soil barrier. Hidden from inspection.

Foam-filled hollow block foundations

Termite baits

Voids cannot be properly treated; soil treatment fails because termites enter through cracks in the footing.

🪵 Wood Treatment Quick Reference

Wood treatment is most commonly used as a supplement to soil treatment or baiting — and as a fallback when soil treatment is unsafe (well/duct contamination risk).

Method

Mode of Action

Limitations

Borates

Water-based dilution absorbed into wood fibers; stomach poison — termites must ingest. Effective indefinitely if wood stays dry. Also protect against powderpost beetles and wood-decay fungi.

Will NOT prevent termites from tubing across treated wood to untreated portions. Highly water-soluble — leach out if wet. Generally no contact residual.

Wood injection

Aerosol or liquid emulsion injected directly into termite galleries. Termiticide bonds with soil particles in galleries for some extended residual.

Difficult to saturate all wood fibers via aerosol injection. Surface treatments are short-term barrier only — not equivalent to soil treatment. Not a replacement for soil treatment.

💡 Memory Hooks

Plenum: "Plenum = pneumatic = air = no liquid." If the crawl space is moving air through the house, liquid termiticide is off the table.

Subslab ducts: "Under 30, never through." Less than 30 psi at the nozzle, and never drill through a duct.

Foam insulation: "Six and six." Remove foam 6 inches above AND 6 inches below grade. Termites tunnel through, not eat through.

Borate limits: "Tubing crosses, borate misses." Borates don't stop termites from building tubes across treated wood — they only kill the ones that eat it.

Wells in dry weather: "Dry cracks travel further." Termiticide moves greater distances along cracks and fissures when soil is dry. Sandy soil reduces this risk; cracked clay magnifies it.