How do I fix a sagging floor in an older New Brunswick home?

A sagging floor in an older NB home almost always traces back to one of three causes: failed or undersized floor joists, a failed or settling support beam in the basement or crawlspace, or deteriorated wood framing due to moisture damage — and the repair approach, timeline, and cost depend entirely on which problem you're actually dealing with. Getting a professional assessment before any repair work starts is not optional here; the wrong fix wastes money and can leave the underlying cause to worsen.

In NB's older housing stock — the post-war bungalows common in Moncton, the turn-of-century homes in Saint John and Fredericton, the older rural farmhouses across the province — floor framing was often undersized by today's standards. Lumber grading wasn't enforced consistently before the 1960s, and many homes were built with spans that worked marginally well when new but have developed bounce and sag over decades of loading. Sistering new joists alongside deteriorated or undersized originals is one of the most effective repairs: new structural-grade lumber is nailed alongside the existing joists across their full span, doubling the carrying capacity and stiffening the floor significantly. Sistering a typical floor costs $3,000 to $8,000 for a moderate area of floor, depending on joist length, access difficulty, and how many joists require treatment.

If the issue is a failed or insufficiently supported main beam in the basement — which often shows up as a broad, gradual sag in the middle of the floor spanning the width of the house — the repair may involve installing a new steel or engineered wood column under the beam's midspan, or replacing a deteriorated wood beam with an LVL or steel equivalent. A new steel column with a proper pad footing typically costs $1,500 to $4,000 installed. Replacing a failed main beam is a larger undertaking at $4,000 to $10,000 or more depending on the beam's size and the shoring required during replacement.

Moisture damage is the most serious scenario. NB's spring snowmelt and Maritime humidity create conditions that attack floor framing from below, particularly in unventilated crawlspaces and unheated basement areas. Rot in floor joists, sill plates (the lumber sitting directly on the foundation), or rim joists (the perimeter framing) is common in NB homes that haven't had adequate moisture control. Replacing rotted sill plates and rim joists requires temporary jacking of the structure, which is specialized work. The moisture source — ground vapour infiltrating an unsealed crawlspace, drainage problems at the foundation, condensation in an unvented crawlspace — must be corrected at the same time as the framing repair, or the new wood will rot on the same timeline as the old.

For minor sagging in older NB floors with settled main beams, temporary and permanent jacking is sometimes used to slowly raise the floor back toward level. This must be done gradually — a maximum of 3 mm (about 1/8 inch) per week — to avoid cracking plaster walls or breaking connections elsewhere in the structure. Rushing this process in a hurry to get results causes more damage than the original sag. A contractor experienced in heritage home renovation will understand this pace.

Budget $3,000 to $15,000 for most residential floor repair projects in NB, with the low end covering sistering work in an accessible basement and the high end reflecting rotted sill plate replacement, main beam work, or moisture remediation combined with structural repair. Add 20 to 25% contingency for any pre-1970 NB home — once you open up the floor system, additional hidden deterioration is common. A structural engineer assessment ($500 to $1,000) is worthwhile before any repair work begins on a significantly sagging floor; it identifies the true cause and prevents expensive misdiagnosis. Always confirm WorkSafeNB coverage with any contractor doing this type of work, as crawlspace and basement structural repairs involve confined-space and fall hazards.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Thirty Four Renovations
• Gionetterenovations