This is generally cheaper than building with a larger dimension of lumber. It is possible, however, to add pieces of wood onto the rafters to fur them out to allow for more insulation. So if your rafters are only 5 1/2" deep, that is all the space you have for insulation. Roof insulation for 1 1/2 story homes (a home where you have living space in the attic) is typically installed in the rafter spaces. In making your choice, consider how you will insulate your insulate your roof. Another option are 2 X 8 rafters spaced 24 inches o.c. The table states that 2 X 6 rafters spaced 16 inches on center (o.c) can span a maximum distance of 13 feet 5 inches. Looking through the center of the table, we can find a couple of options. Let's use this example and find a size of rafter that will work. So if your house is 26 feet wide and the roof ridge beam is centered on the house, you will need a rafter that can span 13 feet. The maximum spans in the table above are for the horizontal distance the rafter can span (NOT the diagonal distance or actual length of the rafter). This table is simply a sample and may not be valid for your region. Sample Maximum Spans (feet-inches) Douglas Fir or Larch, No.1 or No.2 with 31.3 psf of Snow Loading Let's look at the sample table below which shows maximum rafter spans for a snow load of 31.3 pounds per square foot (psf).įraming Table for Maximum Roof Rafter Spans If you live in a region that gets winter snowfall, contact your municipal building department to find out what maximum snow loads you need to design for.ĭepending on your region, you may need to design for a maximum snow load of anything between zero to 65 pounds per square foot (or roughly 0-3 kPa). All roof framing tables are organized by maximum snow load. In most regions, the first thing to consider before sizing the wood framing members for a roof is the maximum snow load that the roof will have to bear.
Open rafter ceiling how to#
Initially, we will discuss the framing of gable roofs so that we can learn the basics of how to size a roof rafter, beam or joist. Each rafter is in turn fastened to the top of the exterior structural walls.Īs we discussed in Exterior House Designs there are many different house roof types. Along the top center of the house there is a beam to which are attached the rafters. The image below shows a cross-section of our simple 12' X 13' house from the joist span tables section of this tutorial. Let's consider a basic gable wood roof framing design. (Be sure to add soffit vents and ridge vents in EACH joist space.)ģ) consider how you’ll heat the space.Continuing on from Part 3: Floor Beam Span Tables of Residential Structural Design, we will now look at roof rafter and beam design. Wiggling that into place will take some skill.Ģ) New attic batt insulation can be installed between each joists, but keep 1” air space between the insulation and roof sheathing for venting.
Installing the beam will be difficult because it could weigh 17 lbs. You may be luck, because the existing strongback probably has some footing under it at each end. The new posts will need adequate footings. The new ridge beam will need a notch so it can fit tight to the roof joists.)Īfter the new ridge beam is in place and supported with a NEW post at each end and each joist clipped to the beam, then the existing ceiling joists and temporary supports can be removed. (This is going to be somewhat difficult because the existing ridge beam is slightly lower than the roof joists.
Open rafter ceiling install#
In order to remove the ceiling joists and vault the space, you’ll need to install temporary supports under all existing roof joists, remove the existing vertical supports under the ridge beam and then slip a NEW ridge beam in under the existing ridge beam. Yes, you can remove the ceiling joists and “vault” the room, but you have several issues: 1) unusual structural system, 2) loss of attic insulation, 3) heatingġ) The existing roof joists are supported by a complex set of ridge beam, intermittent vertical supports and a “strongback”.
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