How do I keep ants out of my house?

Seal cracks around the foundation, windowsills, door frames, and utility penetrations with silicone caulk, keep trees and shrubs from touching the roof or siding, and fix any moisture problem — leaky pipes, clogged gutters, poor crawlspace ventilation — that softens structural wood. Store sweets, syrup, and pet food in sealed containers and wipe up trails with soapy water, since ants leave pheromone trails other workers follow.

When should I seal cracks against ants in New Hampshire?

Early spring, before ants emerge from overwintering — typically February through March in southern NH, well ahead of the May start of the active season. Sealing later still helps, but a head start closes entry points before scouts establish a trail that recruits the rest of the colony. Moisture correction isn't seasonal the same way; fix leaks and improve ventilation year-round, since damp wood stays attractive to carpenter ants whenever they're active, right through the October frost.

Does ant prevention actually work, or will they just find another way in?

It works, but only as durably as the moisture fix behind it. Removing wet, rotten wood is a genuinely effective deterrent against carpenter ants because it eliminates the habitat they need, not just one entry point. Sealing cracks while ignoring an active leak just delays the problem — the ants (or a new colony) return to the same soft wood once a new crack opens.

What attracts ants to a home?

For carpenter ants specifically, moisture-damaged wood is the draw — they nest in it even though they don't eat it. For most ants generally, sweets, honeydew from aphids, pet food, and food residue on counters or floors are the pull. That's why prevention pairs moisture correction (the structural fix) with sanitation (removing the food that keeps foraging ants coming back once they're inside).

Why do carpenter ants matter so much in New Hampshire specifically?

UNH Cooperative Extension identifies carpenter ants, alongside termites, as the state's most troublesome structural pests — four species live in New Hampshire, and the damage from an established colony can be extensive before it's noticed. The state's older housing stock, damp fieldstone basements, and heavily wooded suburban lots create exactly the conditions carpenter ants need, which is why moisture control carries more practical weight here than it might in a drier region with newer construction.

Do carpenter ants actually eat the wood they nest in?

No. Unlike termites, carpenter ants excavate smooth galleries in wood to build nesting space, but they don't consume it for food — they forage outside the nest for sugars and proteins. This matters for prevention because the fix isn't about protecting wood from being eaten; it's about keeping wood dry enough that it's not soft enough to excavate in the first place.

What moisture level makes wood attractive to carpenter ants?

Roughly 15% moisture content or higher, per NC State Extension research on carpenter ant biology. That threshold is common in sill plates near foundation leaks, roof decking under a slow leak, and any wood that stays damp from clogged gutters or poor ventilation — which is exactly why fixing the moisture source, not just the visible ants, is the durable prevention lever.

When are carpenter ants active in New Hampshire?

May through October, with activity peaking in July, based on Northeast regional data from Rutgers NJAES. Activity slows and stops as the first hard frost arrives in fall. That gives a practical window: seal in late winter before the season starts, and treat July sightings as a signal to check for the moisture source rather than just the ants themselves.

Will trimming trees and shrubs off the house actually help?

Yes. Branches touching the roof, siding, or eaves are a primary route foraging ants use to reach a structure without ever crossing open ground, per UNH Cooperative Extension. Cutting that contact doesn't stop every ant, since some still travel along the foundation or through soil-level gaps, but it removes one of the easiest paths in and makes trailing activity easier to spot early, before a scouting trail turns into an established indoor problem.

PreventionAnts

Ant Prevention: Moisture Control Stops NH's Top Pest

TL;DR

Fixing moisture and sealing entry points is the HIGH-VALUE, durable play against carpenter ants — New Hampshire's top structural pest alongside termites. The catch is patience: it works over a season, not overnight, and it fails if the leak that drew them stays unfixed. Spraying visible ants while ignoring a damp sill plate just treats the symptom.

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NH License #782664Family-owned since 2017Updated Jul 2026

NH's top structural pest
Carpenter ants, along with termites
UNH Cooperative Extension carpenter ants fact sheet (Eaton & Maccini).
Wood moisture that attracts them
15% moisture content or higher
NC State Extension — carpenter ant biology and control.
NH activity season
Active May through October, peaking in July
Rutgers NJAES fact sheet FS1101.
The real entry route
Branches touching the roof, siding, or eaves
UNH Cooperative Extension — trimming vegetation off the house cuts foraging ants.

The honest verdict

Does this actually work?

HIGH-VALUE and durable — carpenter ants strongly prefer wood at 15%+ moisture, so removing that moisture removes the habitat, not just the symptom. Slow to pay off (a season, not a weekend) and useless if the underlying leak is never fixed.

Works — High

Evidence: UNH Cooperative Extension names carpenter ants and termites NH's most troublesome structural pests and centers its guidance on moisture elimination and vegetation-contact removal rather than spraying. NC State Extension documents the 15%+ wood-moisture preference directly, and Northern Woodlands confirms removing wet, rotten wood is an effective deterrent.

Works when

Roof and plumbing leaks are fixed and gutters kept clear so structural wood stays dry
Basement, attic, and crawlspace ventilation is improved to prevent condensation
Branches and shrubs are trimmed so nothing touches the roof, siding, or eaves
Cracks around the foundation, windows, and utility penetrations are sealed before the spring emergence

Fails when

Visible ants are sprayed while the moisture source that drew them stays unfixed
Sealing happens over an active structural leak instead of after it's repaired
Vegetation is left touching the house, giving foraging ants a bridge
Sweets, pet food, or spills stay accessible even after entry points are sealed

At a glance

Ants follow moisture and trails — remove both and most colonies never establish

How it works

Moderate DIY

Prevention removes what carpenter ants need to nest — damp, softened wood — and cuts the physical routes ants use to reach the structure. Sealing entry points and trimming vegetation deny the trail; fixing leaks, improving ventilation, and clearing gutters deny the moisture. Neither is a chemical intervention; both target the conditions a colony needs to establish rather than the ants themselves.

Vital stats

Time: A weekend for the sealing and trimming pass; moisture repairs vary from a day (gutter cleaning) to a longer job (roof or plumbing leak)
Best for: Homes on wooded lots or with older, damp construction — the fieldstone foundations and settling sill plates common across southern and central New Hampshire.
Cost: Low for caulk, sealant, and vegetation trimming; higher if structural moisture repair (roofing, plumbing, ventilation) is needed

Carpenter ants are New Hampshire's top structural pest, tied with termites, and the reason is almost always the same: damp, weathered wood. Unlike termites, carpenter ants don't eat wood — they excavate galleries in it to nest, and they strongly prefer wood that's already softened by moisture at 15% content or higher. That's the crack in the problem prevention can actually exploit. Dry out the wood a colony would need, and you remove the reason it settles there in the first place.

The second half of prevention is just as physical: ants trail along structural elements, so cutting the vegetation bridges that touch your roofline and caulking the cracks they use to get inside stops the scouting before it becomes a colony. None of this is instant — it's a season of moisture repair and sealing, not a weekend spray — but it's genuinely more durable than treating the ants you can see while the leak that drew them stays open.

Step by step

How to do it

Walk the perimeter and trace any trail to its entry point
In late winter or early spring, before ants emerge, walk the foundation and follow any existing ant trail backward to where it enters the structure. Mark each entry point.
Tip: Check at dusk or with a flashlight along baseboards and window frames — carpenter ant trails are easier to spot in low, raking light.
Caulk every crack around the foundation and openings
Seal cracks around the foundation, windowsills, door frames, and utility penetrations with silicone caulk. Use concrete-rated caulk on foundation cracks specifically.
Caution: Sealing over an active leak just traps the moisture behind the wall — fix the leak first, then seal.
Trim vegetation off the house
Cut back trees and shrubs so no branch touches the roof, siding, or eaves. This removes the bridge foraging ants use to reach the structure without crossing open ground.
Tip: Re-check after major growth spurts in late spring — a branch that cleared the roofline in April can touch it by June.
Move firewood and dead wood away from the house
Store firewood off the ground and away from the foundation, and remove stumps or dead wood nearby — all attractive nesting sites for carpenter ants.
Tip: A raised rack at least a season's distance from the house keeps firewood dry and out of ant range at the same time.
Fix the moisture problems that soften structural wood
Repair plumbing and roof leaks, improve ventilation in basements, attics, and crawlspaces, and keep gutters clear so water doesn't pool against the structure.
Tip: A moisture meter reading wood at 15% or higher is your cue that it's currently attractive to carpenter ants — prioritize drying that spot first.
Keep mulch and soil off the siding
Pull mulch and soil back from direct contact with siding, since built-up organic material against the house holds moisture against the wall.
Tip: A few inches of clearance between mulch and siding is usually enough to break the moisture bridge.
Wipe indoor trails and seal food sources
Clean any indoor ant trail with soapy water to break the pheromone scent, and store sweets, syrup, honey, and pet food in sealed, washed containers.
Tip: Rinsing recyclables before storage removes another food source that keeps foraging ants coming back.

What you need

Tools & materials

Silicone or acrylic-latex caulk
Seal cracks around foundation, windows, doors, and utility penetrations
Avoid brittle latex caulk; concrete-rated caulk for foundation cracks specifically
Low-expansion foam / standard foam
Fill larger gaps — low-expansion indoors, standard foam for exterior use
Pair with caulk for a finished, weather-tight seal
Door sweeps
Close gaps at exterior and garage door thresholds
Check for visible daylight under the door as a quick test
Moisture meter
Identify structural wood at or above the 15% moisture threshold that attracts carpenter ants
Check sill plates, window sills, and any wood near a known or past leak
Dehumidifier
Keep basements and crawlspaces below the humidity level that keeps wood damp
Pair with fixing the actual leak, not as a standalone fix
Sealed food containers
Deny foraging ants access to sweets, pet food, and pantry items
Glass or hard plastic with tight lids
Pruning shears / pruning saw
Trim branches and shrubs off the roofline and siding
Use a stable ladder for anything above reach

Stay safe

Safety first

Applicator
Caution
Use a stable ladder for eave and roofline trimming or sealing work, and don't overreach — most DIY fall injuries happen from stretching a ladder position rather than moving it.
General
Low risk
For an active indoor ant trail, baits and spot treatments outperform broadcast sprays because carpenter ant colonies are better controlled at the nest — see the ants chemical method page for that approach.
Children
Low risk
Keep any pest-control products stored away from children and pets, and store food attractants (sweets, pet food) in containers kids can't easily open into ant-accessible messes.
General
Low risk
If ant products are ever ingested or cause irritation, contact the Northern New England Poison Center at 1-800-222-1222, available 24/7.

Avoid these

Common mistakes

Why this method fails in practice.

Spraying visible ants while ignoring the moisture source that drew them
Sealing a crack without first fixing the leak behind it, so the crack reopens
Sealing over an active structural crack instead of repairing it first
Leaving branches touching the roof or siding as a bridge for foraging ants
Treating indoor trails but never addressing the vegetation or moisture outside

New Hampshire context

Ant prevention in New Hampshire

New Hampshire's older housing stock — fieldstone and rubble foundations, damp basements, settling sill plates — is close to ideal carpenter-ant habitat, and wooded suburban lots in Bedford, Amherst, Goffstown, and the Lakes Region see the heaviest pressure. Carpenter ants become active as temperatures warm in spring and cease activity as the first hard frost arrives, so the sealing work should be done in late winter before they emerge, while moisture repairs (roof leaks, gutters, crawlspace ventilation) are a year-round job that matters most before winter sets in.

Peak season

Active May–October, peaking in July; seal in late winter before spring emergence

First-frost anchor: Manchester first hard frost ~Oct 19 (50%) / Oct 29 (80%) per NOAA 1991-2020 — finish moisture repairs before winter; ant activity ceases as the frost arrives

Sealing, moisture correction, and vegetation trimming are DIY-legal statewide with no pesticide license required.

UNH Cooperative Extension names carpenter ants and termites the state's most troublesome structural pests, and its guidance centers on eliminating moisture and vegetation contact — not spraying — as the durable fix.

This method targets

Pests this applies to

When to call a pro

Ant Pest Control with Anchor

Sealing and moisture correction prevent most carpenter ant colonies from establishing, but once ants are already nesting in a wall void or roofline, the nest has to be located and treated directly — work that's often easier and more reliable with a pro. Anchor's licensed technicians combine inspection, moisture assessment, and targeted treatment so prevention actually holds.

Call us when…

Ant trails keep reappearing despite sealing and moisture repairs
You notice frass (sawdust-like debris) or hear rustling inside a wall or ceiling
Structural wood sounds hollow when tapped, suggesting an established gallery
You can't locate the nest despite following visible trails
Moisture damage is extensive enough that you suspect more than one colony

Ant Pest Control

free inspection; same-day service across southern and central New Hampshire.

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Keep them out

Fix roof and plumbing leaks and keep gutters clear so structural wood stays dry
Trim trees and shrubs so no branch touches the roof, siding, or eaves
Seal foundation, window, and utility-penetration cracks in late winter before ants emerge

Common questions

Frequently asked

Sources & further reading(5)

[1]
UNH Cooperative Extension — Carpenter Ants Fact Sheet
Carpenter ants + termites as NH's top structural pests, vegetation-contact entry route, moisture preference, wood-excavation vs. wood-eating distinction
extensionverified 2026-07-13
[2]
NC State Extension — Biology and Control of Carpenter Ants
15%+ wood moisture content threshold for carpenter ant nesting
extensionverified 2026-07-13
[3]
Rutgers NJAES — Carpenter Ants Fact Sheet FS1101
Northeast activity season: active May–October, peaking in July
extensionverified 2026-07-13
[4]
UC IPM — Ants (Home & Landscape)
Pheromone trailing behavior; soapy water trail removal and caulking as standard IPM
extensionverified 2026-07-13
[5]
Northern Woodlands — Carpenter Ants
Removing wet, rotten wood as an effective carpenter-ant deterrent
newsverified 2026-07-13

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

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Anchor Pest Services

When ants won't quit, we will.

Same-day service across Southern New Hampshire. NH-licensed #782664. Family-owned since 2017. We diagnose the pest, then treat it the right way — with a satisfaction guarantee.

Get a free inspection Call (603) 785-0118

Keep Exploring

Ant Prevention: Moisture Control Stops NH's Top Pest

Works when

Fails when

Ants follow moisture and trails — remove both and most colonies never establish

How it works

How to do it

Walk the perimeter and trace any trail to its entry point

Caulk every crack around the foundation and openings

Trim vegetation off the house

Move firewood and dead wood away from the house

Fix the moisture problems that soften structural wood

Keep mulch and soil off the siding

Wipe indoor trails and seal food sources

Tools & materials

Silicone or acrylic-latex caulk

Low-expansion foam / standard foam

Door sweeps

Moisture meter

Dehumidifier

Sealed food containers

Pruning shears / pruning saw