Split-Level Home

Split-levels (including side-splits and backsplits) are defined by half-storey offsets—great for zoning space, but hard on the building envelope.

Common Canadian variants: - Side split: one wing is 1-storey, the other is 2-storey (often with a tuck-under garage) - Backsplit: looks like a bungalow from the street, with extra levels stepping up at the back - 5-level backsplit (GTA): multiple stacked levels with more seams, stairs, and utility routes

Why the seams fail: A split-level can sit on more than one foundation depth (basement vs. slab/garage vs. crawlspace), so freeze–thaw movement isn’t uniform. Inside corners and step-downs can open up cracks at cold joints and expansion joints.

Pest implications: - Pavement ants use slab cracks and joints as direct routes from soil into living space - Air leaks at seams can pull food odours and warmth, increasing mouse pressure at the lower levels - Moisture at step foundations can support wood-destroying insects where framing gets wet

Inspection cues: - Vertical cracks at inside corners of the “split” - Gaps where brick/siding changes height - Slab cracks near patio doors or garage transitions - Efflorescence or staining on foundation walls

In many side-splits, the upper floor extends past the foundation wall below (a cantilever/overhang). The space between joists becomes a sheltered cavity that’s hard to insulate and air-seal perfectly.

Why it’s a pest magnet: - Insulation batts can sag over time, leaving warm voids - Exterior soffit seams give mice a protected entry point - Condensation can form on cold surfaces in winter, increasing moisture

Inspection cues: - Cold floors above the overhang - Noises in the floor system at night - Droppings or nesting material near HVAC/plumbing runs - Damaged or loose soffit panels under the cantilever

Best-practice retrofit: Improving performance usually means removing the underside soffit, air-sealing the subfloor/rim area, and installing continuous insulation (often closed-cell spray foam or rigid foam sealed at edges) before reinstalling a tight soffit.

Split-levels behave like short chimneys: open stairwells let warm air rise quickly to the top level. That creates positive pressure up high (pushing air out) and negative pressure down low (pulling air in).

Why it matters: - The lowest rim-joist/sill areas act like a vacuum, pulling in cold air, odours, and pests - Air leaks at the top of the house can push warm, moist air into the attic - Unlike a simple house, split-levels can have multiple rim-joist lines at different heights

Where to focus sealing: - Rim joists (solives de rive) in the basement, any crawlspace areas, and the lower family-room level - The sill plate-to-concrete interface - Service penetrations (cables, pipes, ducts), especially around the garage and mechanical room

Practical outcome: Better air sealing at rim joists reduces drafts, moisture problems, and the scent/heat cues that attract mice—while also reducing attic conditions that favour overwintering flies.

Backsplits and side-splits often have multiple rooflines meeting at valleys and roof-to-wall intersections. These areas trap snow and debris—especially during Canadian winters.

Ice dam chain reaction: - Heat loss melts snow higher on the roof - Water refreezes at colder eaves and valley edges - Meltwater backs up under shingles, wetting fascia and sheathing

Pest implications: - Chronic damp wood supports carpenter ant satellite nests - Tiny gaps at soffit returns and roof vents allow cluster flies to enter to overwinter

Inspection cues: - Staining/peeling paint at fascia and soffits - Dark, damp insulation in the attic near valleys - Repeated icicles or water staining at level-change walls - Loose or missing flashing where a lower roof meets a tall wall