For an older home the deflection usually exceeds the current code requirements.
Floor deflection standards.
Codes also specify how much floors are allowed to bend under load a measurement called a deflection limit.
Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection.
Divide the total span of the floor joists in inches by 360 to determine the maximum amount the floor can give in the middle under a live load of 40 lb sq.
For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360.
If the floor deflects more than the 0 4 inches or 0 6 inches the floor is deflecting more than what the standard allows and does not meet code.
Relatively longer spans and higher loads have the potential to make differential deflection problems in floors more pronounced.
Figure 2 live loads and deflection limits are set by code.
Consequently better built homes use stiffer deflection standards often l 480 or l 720.
Ft plus any.
If the span of the joists is 10 feet between supports then the deflection should not be more than 1 3 between the center and the end.
If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6.
Many tile contractors can judge a floor s deflection by walking around.
This sets an allowable first floor live load of 40 psf a dead load of 10 psf and a deflection of l 360.
For example for a 30 foot span l deflection of up to 1 5 inches in a single floor member would be permissible.
Serviceability the actual long term deflection of a normally reinforced slab or beam in the typical floor of a multi level office building depends on a large.
Frequently there is misunderstanding regarding deflection between joists.
To calculate a specific value the tile council of north america tcna offers a standard formula.
The irc says that floors must deflect no more than 1 360 of the floor s span.
This is essential in a flat slab or plate where the mid panel deflection relative to the supporting columns is the sum of the column strip deflection and the two way panel deflection.
An l 720 floor would deflect only half what an l 360 floor does and would be far less bouncy to walk on.
For example a floor with a span of 10 feet must deflect no more than 1 3 inch or 120 inches 360 inches.
The china in the sideboard rattling as you walk across the dining room floor is not a mark of quality construction.
The l 360 standard means that the floor should not deflect more than the span divided by 360.
