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

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.

How do I calculate the R-value in my attic?

It will most likely be a fiberglass batt, so multiply the thickness in inches by 3.2 to find out the R-value (or the R-value might be visible on a product label). If the insulation is a foam board or sprayed-on foam, use any visible label information or multiply the thickness in inches by 5 to estimate the R-value.

How do I calculate roof insulation thickness?

To calculate the total R-value of a roof assembly, find the total thickness in inches of each type of insulating material within the system. For each different material, multiply the thickness in inches by the standard R-value per inch for that material.

What R-value do I need for flat roof?

We recommend having at least 20 r value worth of material for optimal energy efficiency.

Do roof shingles have an R-value?

No more than R-1.6 for standard shingles

So, if you're using 3/8-inch shingles, the installed siding will have an R-value of (at most) about R-1.3. If you are using thicker 5/8-inch shingles, the installed siding will have an R-value of (at most) about R-1.9.

How to Calculate U-value

Do metal roofs insulate better than shingles?

They're more energy efficient than asphalt shingles. Not only does metal roofing provide excellent insulation during the cold season of the year, but metal materials also reflect sunlight, helping keep energy costs of the home down 40-50 percent during warmer months.

Does a metal roof insulate better?

Technically, there is no difference in the insulation value of a metal or shingle roof. While metal roofs are efficient at its ability to resist heat transfer it is exposed and absorbs just as much heat as a shingle roof.

How thick should the insulation be on a warm roof?

Achieving a U value of 0.20W/m² (meaning your roof will be better insulated than your walls) will need 120mm thickness of rigid foam or 200mm of mineral wool or natural insulation. Hitting amazing levels of 0.13W/m² will need 300mm of mineral wool or 180mm of rigid foam.

What insulation is best for flat roof?

Roofing professionals emphasize that the choice of flat roof insulation should feature the appropriate R-value. The most expensive and highly recommended insulation is Polyisocyanurate (Polyiso) rigid foam. Extruded Polystyrene (XPS) is also an optimal choice, along with Expanded Polystyrene (EPS).

Is it worth insulating a flat roof?

Adding insulation to a flat roof will help keep the heat in, making the room beneath more comfortable while helping to keep your bills down.

How do I work out how much insulation I need?

To work out the amount of insulation required for a floor, first you need to calculate the Perimeter Area (PA) ratio. This is calculated by dividing the exposed perimeter given by the floor area.

Can you put too much insulation in attic?

It's possible to over-insulate an attic as too much will cause moisture buildup and eventually result in mold. Eventually, adding more insulation leads to diminishing returns in trapping heat as well.

How many inches of insulation should be in my attic?

The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.

How many inches of insulation is R38?

R38 - 10.25 in - Fiberglass Insulation - Insulation - The Home Depot.

How thick should flat roof insulation be?

An uninsulated flat roof has a U-Value of around 1.5 W/m2K. When insulating one, you're aiming for a value of 0.25 W/m2K or less. To achieve this, you should insulate your flat roof with insulation boards totalling around 150mm thickness.

Is 50mm insulation enough for a warm roof?

You can use two sheets of 50mm but it is not enough to comply with current regulations. You will not achieve the correct "U Value" which is the thermal resistance. In a nutshell your roof could end up with condensation (interstitial). Ideally if using Celotex you need a minimum of 120mm.

Can you insulate on top of a roof?

Insulated roof assemblies can be vented or unvented. There are lots of different ways to insulate this type of roof, but one of the best methods calls for the installation of rigid foam insulation above the roof sheathing.

Can you put insulation between joists on a warm roof?

The general advice we give is that you should always insulate between and above the rafters (warm roof) or between and under the rafters (cold roof).

What U-value do I need for a warm roof?

To comply with Part L of the building regulations 2010, all roofs to rooms (except those in unheated buildings) should be thermally insulated to a maximum U-value of of 0.18 W/m²K.

Do you vent a warm roof?

A warm flat roof usually does not require ventilation. What space do I need to allow for the ventilation? To ensure sufficient ventilation, enough space must be provided to allow for the movement of air, preventing the risk of condensation forming within the roof.

Do you need a vapor barrier under a metal roof?

Without one, water can get trapped in the wall, which will produce moisture and ultimately other issues like rot, mold, and trouble with thermal performance. Vapor barriers are recommended for under metal roofs.

What are the disadvantages of a metal roof?

How much R value do I need?

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.

Does a metal roof make your house colder in winter?

A metal roof acts as an insulator and it naturally reflects the sun's UV radiation. This will keep you home cooler in the summer and warmer in the winter.