Clearance From Grade To Floor Joists

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.

Clearance from grade to floor joists.

Joists have at least 18 clearance to exposed ground and girders have at least 12 clearance. Framing of openings require a header and trimmer joists. Floor levels getting the floor level wrong can lead to on going moisture problems. 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.

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. 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. Clearance from combustibles ranging from 0 to 18 to 36 typically depending on the fuel type electric gas oil. So the minimum is 18 for floor joists and 12 for wood beams within the building foundation according to the internaitonal residential code.

Additional support for the floor joists is achieved by nailing the ends of the joists into headers. 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. 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. Where the header joist span is than 4 trimmer joists and the header joist shall be doubled.

2 lumber grade all joists are bridged sample floor joist span table. Decks not exceeding 200 square feet in area that are not more than 30 inches above grade at any point are not attached to a dwelling. 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. 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 table excerpt above is simply a sample and may not be valid for your region. Looking at this table you will see there is a choice in the size of floor joist 2 x 6 2 x 8 2 x 10 or 2 x 12 and there is a choice in the joist spacing 12 16 or 14.