Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces.

What is a good R-value for a roof?

Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces.

How do you calculate the R-value of a roof assembly?

To calculate the R-value, you simply add together the total thickness (in inches) of each insulating material within your roofing system: “For each different material, multiply the thickness by the standard R-value per inch for that material.

What R-value do I need for flat roof?

Polyurethane Roof Insulation R = 7.2 Polyurethane in sprayed-on foam is a high R-value choice for flat roof insulations. The American Chemistry Council Center for the Polyurethanes Industry reports R-values of up to 7.2 per inch.

How do you calculate R-value?

It is simply the thickness of the insulation in inches divided by the thermal conductivity of the insulation. For example, a two inch thick sheet of insulation with a thermal conductivity of 0.25 Btu•in/h•ft2•°F has an R-value equal to 2 divided by 0.25 or 8.0.

Can you have too much insulation?

It is possible to over-insulate your house so much that it can’t breathe. The whole point of home insulation is to tightly seal your home’s interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That’s when mold starts to grow.

How do you calculate R-value in engineering?

The R value is the thermal resistance to heat transfer of a given thickness of a given material. To find the R value of a material, one divides the thickness of the material in question [x], by the coefficient of thermal conductivity [k]. Note: Attention must be given to the dimensional homogeneity of the equation.

How do you calculate R-value in construction?

Multiple layers. In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added: R-value(outside air film) + R-value(brick) + R-value(sheathing) + R-value(insulation) + R-value(plasterboard) + R-value(inside air film) = R-value(total).

What is the R-value of 4 inch Styrofoam?

5.0 per inch
STYROFOAM extruded polystyrene insulation is rated at an R-value of 5.0 per inch at 75°F.