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Re: Repairing sagging floor

From: info@builderswebsource.com
Category: Structural
Remote Name: 63.198.181.43
Date: 14 Jan 2001
Time: 09:23 PM

Comments

A 3" sag is huge for a floor! I am concerned that this may be a converted attic on top of ceiling joists that weren't designed to carry sufficient dead and live loads.

The building code requires that floor joists be sized large enough to ensure that the total deflection is less than 1/360 of the total unsupported length. For example, a 12-foot unsupported floor span (based on direction of joists) should deflect no more than approximately 0.4", and that's under full "live" loads.

Without knowing the unsupported span or other live/dead loads on the floor, we cannot estimate the remedy. If you reply, let us know the approximate length of the floor joists as well as their size and spacing. From that, we can make some recommendations.

In general, it sounds like your existing joists are undersized and need reinforcement. This will likely involve jacking up the sagging portion, running one or more additional joists in parallel with existing joists, and securing them to the original joists with staggered 1/2" hex bolts on approximately 16"-18" centers. You'll probably also want to run a bead of construction adhesive (such as Liquid Nails or PL400) along the top of the new joists to bond to the subfloor, particularly if you don't want to nail through the top of the floor. The glue will help to minimize floor squeaks.

This procedure will involve removal of ceiling underneath. Your task may be further complicated if there is electrical wiring or plumbing that cuts through the existing joists.

Your situation is very serious and should be rectified immediately. A floor that sags 3" could collapse. Depending on your level of skill and available time, this sounds like a job for a competent general contractor. Calculations must be run based on the building codes to determine the level of structural reinforcement required.

Let us know the measurements and we can provide a "ball park" estimate. Also, let us know what type of lumber you have available in your area, such as Douglas Fir, Hemlock, or Pine, as this affects the strength of the joists and must be factored into the equation.

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