Construction R-value Calculator (2024)

FAQs

How do you calculate R-value in construction? ›

It is simply the thickness of the insulation in inches divided by the thermal conductivity of the insulation. For example, a 2" thick sheet of insulation with a thermal conductivity1 of 0.25 Btu•in/h•ft2•°F has an R-Value equal to 2 divided by 0.25 or 8.0.

The thermal resistance rating or R-Value is the measure used most commonly in the building and construction industry to determine a material's ability to resist the transfer of heat. The higher the R-Value the better thermal resistance the product will provide.

Fiberglass and rock wool batts—2x4 walls can hold R-13 or R-15 batts; 2x6 walls can have R-19 or R-21 products. Generally, batt insulation is the least expensive wall insulation material but requires careful installation for effective performance (see page 4).

Depending on where you live and the part of your home you're insulating (walls, crawlspace, attic, etc.), you'll need a different R-Value. 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.

Drywall has a relatively low R-value — about 0.45 at ½” thickness. This is similar to building materials such as siding, concrete, dirt, face brick, particleboard, wood and single-pane glass.

The R-Value of Wood

The R-value for wood ranges between 1.41 per inch (2.54 cm) for most softwoods and 0.71 for most hardwoods. Ignoring the benefits of the thermal mass, a 6-inch (15.24 cm) softwood log wall has a clear-wall (a wall without windows or doors) R-value of just over 8.

I use R-1.25/inch for R-value of framing lumber. This yields R-4.37 for a 2x4 wall and R-6.88 for a 2x6 wall. In summary, the opaque area makes up 14% to 22% of the wall assembly, yielding an R-value of 4.4 to 6.9 depending on framing thickness.

And we have three-quarter inch plywood and this plywood's R-value is also given as . 94, this is for 3/4".

Rigid foam board insulation is available in many materials, including polystyrene (R-3.8 to R-5.0), polyurethane (R-5.5 to R-6.5) and polyisocyanurate (R-5.6 to R-8.0). Since it has the highest R-value, rigid foam is typically reserved for foundations and basem*nt walls.

Can you use R13 in 2x6 walls? ›

Walls built with 2x4s: Use R-13 or R-15 kraft-faced fiberglass insulation or mineral wool insulation when the house's exterior walls are built with 2x4s. Walls built with 2x6s: Use R-19 or R-21 kraft-faced fiberglass insulation or mineral wool insulation when the house's exterior walls are built with 2x6s.

OSB (½-inch) has an R-value of 0.5 – 0.62. Fiberboard is less expensive than OSB. Fiberboard is dimensionally stable, so resistant to expansion and contraction.

R = 8.31 x 10⁷ergs mol⁻¹K⁻¹. Therefore, the value of R in the CGS system. 2: Calculate the Value of R in L(atm) mol⁻¹K⁻¹. ⇒ R = 0.0821 L(atm) mol⁻¹K⁻¹ is the required answer.

The easiest way to calculate this is to make a table with all the information you need to put into the formula. Now we can put all our numbers in our formula to find r ; r=∑(xi−¯x)(yi−¯y)√∑(xi−¯x)2∑(yi−¯y)2 =−9.3√63.6×2.9 =−0.68478681816...

Use the formula (z_y)_i = (y_i – ȳ) / s _y and calculate a standardized value for each y_i. Add the products from the last step together. Divide the sum from the previous step by n – 1, where n is the total number of points in our set of paired data. The result of all of this is the correlation coefficient r.

A reasonable R-value for a normal concrete slab can be estimated using an R-value, the thermal resistance per inch of thickness, between 0.1 and 0.2 and multiplying it times the slab thickness. For a 6-inch slab, R-value would be between 0.6 and 1.2.