**Contents**show

Multiply the load per square foot by the total area of the roof. If an example roof is 10 feet by 20 feet, the total area is 200 square feet; multiplied by 40 pounds per square foot equals 8,000 pounds. This number represents the total load that your roof must carry.

## How much support does a porch roof need?

Typical decks are designed to support 55 PSF (lbs per square foot). Porch decks require 25 additional PSF for roof loads for a total of 80 PSF. As a result, most decks have inadequate footings to support a new porch roof.

## How much fall should a porch roof have?

The minimum pitch for a roof is 1/4:12, which translates to 1/4 inch rise to 12 inches of run.

## What is the weight load of a roof?

After reviewing local building codes, the dead load for normal shingled or wooden roofs is a minimum of 20 pounds per square foot, while it’s closer to 27 pounds per square foot for a more sturdy material like a clay tile or metal roof.

## How do you calculate roof span?

Follow a similar procedure as shown below:

- Rafter run = external width between the wall plates divided by two.
- Rafter span = rafter run divided by cos °.
- Overhang = eaves width divided by cos ° (add dimensions for brick veneer).
- Ridge strut = rafter run times tan °.

## How much overhang should a porch roof have?

Typically, a porch overhang should be at least 12-inches long. However, they can range from two feet to very minimal in length depending on the area’s climate, so be sure to account for the amount of rainfall you might expect. Drier climates require minimal overhang length and wetter climates require longer overhangs.

## How do you calculate load capacity?

Calculating Load

- Add together the wattage capacity of all general lighting branch circuits.
- Add in the wattage rating of all plug-in outlet circuits.
- Add in the wattage rating of all permanent appliances (ranges, dryers, water heaters, etc.)
- Subtract 10,000.
- Multiply this number by . …
- Add 10,000.

## How do you calculate building load?

Dead Load Calculation for a Building

Dead load = volume of member x unit weight of materials. By calculating the volume of each member and multiplying by the unit weight of the materials from which it is composed, an accurate dead load can be determined for each component.

## How do you calculate square footage per load?

Divide force by area to calculate the pressure exerted. Continuing with the example, divide the elephant’s 5,940 lbs by 3.14 square feet to calculate the pressure of 1,891 pounds per square foot. Divide the little girl’s 55 lbs by 0.0009 to calculate her pressure of 61,111 pounds per square foot.

## How do you calculate the slope of a roof?

How to Calculate Roof Pitch in Degrees

- First, you need to measure the run of your roof. …
- Next, you need to figure out the rise. …
- Now, divide the rise by the run. …
- Then, divide 1 by your tangent.
- Finally, multiply this result by 180/π and you’ve calculated your roof pitch!

## How much pitch does a patio roof need?

The short, simple answer is 2:12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles.

## Should front porch slope?

Make sure the porch floor has a slight slope to it—between 1⁄8″ and ¼” per linear foot for tongue-and-groove floors. (If the porch is deeper than 8′, use a slope closer to 1⁄8″ per foot to avoid a pronounced slant.)

## How much weight can a porch roof hold?

While the average roof can withstand 20 pounds per square foot, there’s a huge range in the weight of snow: Fresh, light snow can weigh just 3 pounds per square foot… so your roof may be able to hold over 6 feet of it. Wet, heavy snow can weigh 21 pounds per square foot… so a foot of it could risk collapse.

## How much does a roof weight per square foot?

Table of Roofing Material Weights

Weight of Roofing Materials | ||
---|---|---|

Roofing Material | Pounds per Square Foot (lb/ft2) | Pounds per Square (100 Sq. Ft.) |

Asphalt Shingles “3-Tab” or “Strip” | 1.95 lbs | 195 lbs |

Asphalt Shingles “Architectural”, “Dimensional”, or “Laminate” | 3.05 lbs | 305 lbs |

Asphalt Shingles “Luxury” | 4.25 lbs | 425 lbs |

## What does 20 lb roof load mean?

Roof load (live load) design is affected by the shape of the roof whether it is flat, curved or pitched. … The North Zone design live load equates to 40 pounds per square foot, the Middle Zone equates to 30 pounds per square foot, and the South Zone equates to 20 pounds per square foot.