Joist span and spacing is set by your local building code.
Clearance from grade to floor joists.
When building a house or even a deck it is important to confirm you have the correct joist sizes spans and spacing before you get started.
A huge bonus of building a freestanding grade level deck is that a building permit isn t required as long as the deck s area is 200 square feet or less see 2015 irc r105 2 work exempt from permit 10.
When wood joists or the bottom of wood structural floors without joists are located closer than 18 inches or wood girders are located closer than 12 inches to exposed ground in crawl spaces or unexcavated areas located within the periphery of the building foundation the floor assembly including posts girders joists.
So the minimum is 18 for floor joists and 12 for wood beams within the building foundation according to the internaitonal residential code.
Section r502 10 of the international residential code states that header joists can be the same size as the floor joists when the header joist span isn t greater than 4 feet but if the header joist span is more than 4 feet you ll need to double the header joist and ensure that it s capable of.
The minimum clearance between the ground and the wood structural floor joists and girders is primarily for prevention of wood rot that is caused by wood being too close to the moisture in the soil.
While most residential construction uses 2x8 joists with 16 inch spacing there are many other factors you need to consider when determining the proper joist span length.
Working space or clearance distances that may allow 0 on 1 3 sides but always requires working space at least at the front or at front rear if access to a blower or filter are at the unit rear side.
Protection of wood and wood based products from decay shall be provided in the following locations by the use of naturally durable wood or wood that is.
Joists have at least 18 clearance to exposed ground and girders have at least 12 clearance.
Floor levels getting the floor level wrong can lead to on going moisture problems.
Where the header joist span is than 4 trimmer joists and the header joist shall be doubled.
It can also bring serious building code compliance problems and potential drainage problems due to an insufficient height of the floor above ground and lack of fall to the drains.
The table excerpt above is simply a sample and may not be valid for your region.
Clearance from combustibles ranging from 0 to 18 to 36 typically depending on the fuel type electric gas oil.
The clearance from grade to the bottom of floor joists in enclosed areas such as crawl spaces under a house is per the crc irc 18 r317 1 location required.
Additional support for the floor joists is achieved by nailing the ends of the joists into headers.
2 lumber grade all joists are bridged sample floor joist span table.
