Flat Roof Joist Definition

Timber flat roof construction usually consists of structural joists topped with a decking of plywood or a similar sheet material.

Flat roof joist definition. Unlike stiffness live loads and dead loads are added together to determine minimum design values for strength. 1 psf lb f ft 2 47 88 n m 2. 1 ft 0 3048 m. Joists are traditionally made from timber.

The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers known as joists that help to hold up the roof. Dead load weight of structure and fixed loads 15 lbs ft 2. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. 2 are indicated below.

They are nominally 2 inches thick actual width usually 1 1 2 inches and come in a variety of widths from 8 to 12 inches. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6. Live load is weight of furniture wind snow and more. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection.

For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. If you have a low sloped roof or flat roof of less than 2 in 12 these evenly spaced planks will be called roofing joists. Joists and rafters must be strong enough not to break when loaded. Joists are the parallel horizontal beams that run across an open space joining opposite walls in a building to support both the ceiling below and the floor above.

The pitch is governed by the roof covering and the required rate of rainwater discharge. See the table below. Wherever possible joists should span the shortest distance of the roof plan. To determine the dead load value for a given floor or roof system the weight of all permanently installed materials in a given component are added together.

Depending on the building design finished ceiling surfaces may be affixed to a ceiling joist at the bottom of the roof triangle giving a flat ceiling between the opposing building walls or the ceiling may be affixed partly to the under side of rafters and partly to the under side of rafter ties giving a cape cod type ceiling design. Some roof designs lack joists depending on how they are designed using careful manipulation of other structural members to achieve the desired level of strength and stability. A roof joist is a structural member which provides support for the roof and distributes its weight so that it is even. Because i joists are straight and true it s easier for builders to avoid crowning and maintain a level framing surface.

Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground.