Just as in wall framing, HUD and DOE also suggest spacing floor joists and roof rafters up to 24 inches apart rather than 16 inches. Again, you will save money on lumber and labor. You will also be able to install more insulation, making your home more energy-efficient and saving on heating and cooling costs for years to come.

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If you found this tip helpful, you might also want to read this:
Don’t use headers in non-load-bearing walls
Use steel studs for non-bearing walls instead of wood
Use metal studs for complex framing challenges