Can I use a 2x8 for a ceiling joist and rafters on a 16' span?

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When the span of a wooden beam exceeds about twelve times its depth the beam will usually deflect so much under its full safe load as to crack plastering if applied on the under side, and as floor and ceiling beams are generally used for a greater span than twelve times their depth, they should be computed by the formulae for stiffness rather than for strength.

In determining the size of floor beams the superimposed load and the span are the two elements which vary the most, the beams themselves being usually sawn to regular sizes while the spacing is generally either 12 or 16 inches. In tabulating the size of beams' for different loads, the author has found that tables giving the maximum safe span are the most convenient for general use, and with this view the following tables have been prepared, which show at a glance the maximum span for which different sizes of floor and ceiling joists should be used for different loads and spacings, and it is believed that they will be...

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Everyone wants more room in their homes. And neglected spaces like basements and attics seem to offer up free real estate for guest bedrooms, kids' rooms, or offices.

But sometimes, you need to spend a significant amount of time getting the basic "box" into shape. Attics, which usually do not have flooring, need this type of building-out.

Case 1: Attic Joists But No Flooring

Unless expressly built so, an attic's joists are meant for the ceiling below, not for any flooring in the attic.

Most houses' attics are built without flooring. However, in some cases, the joists are intentionally built substantial enough for the homeowner to later build out the attic. That is a good strategy for cutting costs for homeowners in the short term.

But in most cases, these joists were not intended to support living space.

Case 2: Existing Attic Floor For Dead Load

You may already have flooring in your attic. Does this mean you can build out? Not...

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Using span tables to size joists and rafters is a straight-forward process when you understand the structural principles that govern their use.

by Paul Fisette

© 1997

Wood is naturally engineered to serve as a structural material: The stem of a tree is fastened to the earth at its base (foundation), supports the weight of its branches (column) and bends as it is loaded by the wind (cantilever beam). A complete analysis of wood's mechanical properties is complex, but understanding a few basics of lumber strength will allow you to size joists and rafters with the use of span tables.

Let's start by taking a broad view. The structural goal of a house is to safely transfer building loads (weights) through the foundation to the supporting soil. Remember when your science teacher said: every action has an opposite and equal reaction? Well every building load has an equal "reaction load". If, when the loads of the house are combined, the house weighs more than...

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# Posted: 8 Jun 2016 12:02

I am planning to build a 14x20 cabin for use as a cook house. The location is South-Central Georgia. There is no frost line, and wind speeds of 20+mph are very rare. The soil is 12-16 inches of topsoil with clay subsoil. It will be built on a slight slope, maybe 10 inches of drop every 10 feet. There are no construction codes in my county for non-residential structures.

I would like to have the cabin elevated 2' above ground level and open underneath. It will be a single story with no loft. I don't plan to insulate, since it will only be used for occasional family gatherings. The exterior walls will be 1" thick poplar board and batten, and the interior walls will be 3/4" poplar board and batten. I am not concerned about durability of the cabin beyond 30 years. I'm old and if I'm still around 30 years from now, I probably won't be using it anymore anyway.

The following is the current specs I plan to use for construction. I have...

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Building IBC 2006 Heights and Areas Calculator "...Provides users with a web-based approach to calculating maximum heights and areas for buildings of various occupancies and fire protection based on 2006 IBC provisions. Input a given building, and allowable construction types are determined. Calculator limits building input to a single occupancy for the entire building. For multi-story buildings, maximum single floor area can be any size up to total building floor area...." Building IBC 2006 Heights and Areas Calculator INPUT Values include: "...Use Group;
Total Building Perimeter;
Open Building Perimeter;
Minimum Width of Open Space;
Building Height; etc..." For more information see ...
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Last week I wrote about an innovative foundation insulation material, Foamglas, that we used in our new house in Dummerston. This week I’ll talk about the open-web rafters we’re using to achieve a superinsulated roof.

First, a little background. There are several approaches to creating highly insulated roofs.

When the insulation is installed in the attic floor (creating an unheated attic), it’s easy to obtain very high R-values inexpensively — it’s cheap, that is, as long as you don’t count the cost of the lost living space by creating an unheated attic. Basically, you just dump in a lot of loose-fill cellulose or fiberglass on the attic floor, filling the joist cavity and more.

I’ve heard of as much as two feet of cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. being installed in this manner, achieving about R-80. To make room for a lot of insulation at the roof...

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