Exclusion and Sealing: A Room-by-Room Order of Work

Step one: the foundation and the sill

The foundation line is the first and most important pass, because swarmers land on damp wood there and rodents use the cracks and gaps near the ground.

Walk the whole perimeter with a torch. Look at where the brick or block meets the sill, where a pipe or vent enters the wall, where a crack runs from the ground upward, and where soil or mulch has built up against the siding. Mark each opening with a pencil so it can be recorded.

Seal the ground-level gaps after the wet ones are dealt with. A sealant over a wet sill will hold the water in, and the wood behind it will stay soft. Dry the wood, check the drainage at that corner and then close the gap.

Step two: the crawl space and the cellar

The crawl space or cellar is where the moisture, the wood and the pipes meet, and it is where a colony or a rodent route is most often hidden.

A cellar with an open drain or a sump needs the same checks. The sump lid should close, and the drain should have a trap that is not dry. A dry trap can let insects in, and it is a simple fix.

• Check the sill and the joist ends for soft wood, mud tubes and frass
• Look at the vent openings, and fit hardware cloth where a vent has no screen
• Check the pipe penetrations and seal any that have a gap around them
• Note any standing water, damp insulation or a dripping pipe, and record it for repair
• Check the access door for a gap at the bottom, and fit a sweep if one is missing

Step three: the utility penetrations

Every pipe, cable and duct that passes through a wall is a possible gap, and most are small enough to be missed from inside the house.

Check the gap around each water pipe, gas line, electrical cable, air-conditioning line and meter box. A gap wider than a finger can let in a rodent, and a gap around a cable can let in insects and air. Fill the gap with a material that suits it, and where the gap is large, fit a collar or a metal plate before the sealant goes on.

Do not seal a gas meter box or a flue without checking the clearances first, and do not block a vent that is needed for combustion or moisture control. The purpose of the seal is to keep pests out, not to change how the building breathes.

Step four: the kitchen, the bath and the back of the appliances

Kitchen and bath work is about the gaps behind the appliances and under the sinks, which are the warm, damp spaces that roaches and ants find first.

Pull the dishwasher and the refrigerator out where possible and check the wall and floor behind them. Seal cracks in the wall behind the cabinet, and seal the gap where the countertop meets the wall. Check the space under the sink for pipes that come through the floor, and seal around them with a material that will not crack with the water.

The bath is checked at the tub edge, the drain and the gap at the floor. A bathroom fan that vents into the roof space should have its duct checked, because a duct gap can let in air and insects from the attic.

Step five: doors, garages and the attic

Doors and garages leak at the bottom and the sides, and the attic is where rodents and wasps enter through the roof line and the soffit.

A rodent in the attic must be removed before the openings are closed, or it will be sealed in and will find another route. The order is trapping, then sealing, and the technician will confirm the animals are gone.

• Replace worn door sweeps and threshold seals on every exterior door
• Check the garage door seal along the bottom and the sides, and replace it where light shows through
• Fit hardware cloth to attic and soffit vents, and check the screens for holes
• Look for gaps where the roof meets the wall, and seal any that are open
• Check the attic for droppings, nests and gnaw marks before sealing it closed

After the seals go on

A sealed building needs a short check each year, because seals wear, doors shift and new penetrations are added.

Walk the outside once a year and look at the sweeps, the screens, the sealant at the foundation and any new pipe or cable. A household that adds an air conditioner or a satellite cable should have the entry sealed at the time of the work.

Keep a simple log of what was sealed, the material used and the date. The log is useful for the next check and for a technician who is asked to confirm the work.

Gaps on masonry and on clad walls

The gaps that matter differ between a masonry wall and a clad wall, and the sealing method should follow the material.

A masonry wall is sealed with mortar, sealant or a metal flashing where the masonry meets the sill or a window frame. Cracks in the mortar joints are followed to their end, and the sealant is chosen for its ability to move with the wall. A clad wall, with vinyl or fiber cement siding, has gaps under the trim, at the corners and where the siding meets a window or a door. Those are sealed with a flexible sealant or a trim cap.

The technician checks the material before sealing. A sealant that stays flexible on a wall that moves in the heat is a better choice than a rigid filler, which can crack and open the gap again.

Materials that stop a rodent and materials that do not

A rodent chews through many sealants, and a gap that is closed with the wrong material can reopen in a few weeks.

The right material depends on the hole. A small crack in a brick joint needs a sealant. A hole in a vent needs mesh. A gap at a pipe needs a collar, mesh and then a sealant, so that a rodent cannot reach the foam from outside.

• Hardware cloth or metal mesh, which a rodent cannot chew through, for vents and holes
• Steel wool packed into a gap and then sealed over, which resists chewing better than foam alone
• Expanding foam, which a rodent can chew and which should be covered with mesh or metal where it is exposed
• Caulk, which is a sealant rather than a barrier and should be backed by mesh where a rodent could reach it
• Wood filler, which is not a barrier and can be damp and soft after a season

Commercial receiving doors and dock seals

A commercial building that receives goods has its own sealing points, and the receiving door is the most important of them.

A dock seal or a roll-up door with a worn bottom seal lets in rodents, insects and air, and the gap is often the largest in the building. The technician checks the seal along the bottom, the sides and the top, and notes any damage to the door track. A worn seal is replaced rather than patched, because a patch tends to fail at the next cycle of the door.

A receiving area also needs a clear rule for what stays closed. A door left open during the day for ventilation is an open route, and a fan or a screen that allows air without allowing pests is the usual answer. The owner decides, and the report records the choice.

Balancing sealing with ventilation and moisture

A sealed building still needs air, and a sealing job that traps moisture can make the wood and the crawl space worse.

Vents in a crawl space, a roof space and a kitchen or bath are there for a purpose. They let moisture escape, and closing them without advice can make the wood wetter. The sealing plan keeps vents in place and fits them with mesh or a screen, rather than closing them. Where a vent is closed for a reason, the reason is written down.

The same rule applies to exhaust fans. A fan duct that vents into a roof space should be checked, because a gap in the duct can let in insects and humid air. The fix is to vent the duct to the outside and seal the joint, not to remove the fan.

Keeping a sealing record that is useful later

A sealing record lists each opening sealed, the material used, the date and the check that followed, and it is the document that shows whether the work is holding.

A useful record has a line for each opening. It names the location, such as the north sill behind the air conditioner line, gives the size of the gap, names the material and records the date. A second column shows the check at the next visit, with a note if the seal is intact, cracked or bypassed. Over a season, the record shows which openings keep failing and where the next work should go.

A household that keeps the record can hand it to a technician, a landlord or an insurer without a briefing. It also helps the household's own maintenance, because a worn seal on a door or a cracked sealant at a corner is easy to find when it is already on the list.