Timber flat roof construction usually consists of structural joists topped with a decking of plywood or a similar sheet material.
Flat roof joist definition.
I joists are used extensively in residential floor and roof framing.
2 are indicated below.
Live load is weight of furniture wind snow and more.
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.
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.
In the warm flat roof construction there is insulation packed into every possible space where air can flow.
Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no.
Joists and rafters must be strong enough not to break when loaded.
Joists are traditionally made from timber.
They are ideal for long spans including continuous spans over intermediate supports.
A roof joist is a structural member which provides support for the roof and distributes its weight so that it is even.
See the table below.
Dead load weight of structure and fixed loads 15 lbs ft 2.
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.
If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6.
Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground.
1 ft 0 3048 m.
Unlike stiffness live loads and dead loads are added together to determine minimum design values for strength.
Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection.
The pitch is governed by the roof covering and the required rate of rainwater discharge.
1 psf lb f ft 2 47 88 n m 2.
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.
For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360.
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.
