Minimum Required Roof Slope by Roofing Material Type
The minimum roof slope allowed by code for any type of roof is ⅛-in-12, applicable only to coal tar pitch roof systems.
The following table provides the minimum required (allowable) roof slope for each type of roofing material mentioned in the code. The values given here (except for thatch) are taken from the model International Building Code, although you should always check with your local code authority in case there are local amendments to the code that affect required minimum roof slopes.
Specific roofing products may have different recommended minimum slopes; always check the manufacturer’s product data sheets for the actual product you intend to use, and always follow the manufacturer’s installation instructions. If roofing material is installed on a roof with a slope that is less than what is specified by the manufacturer, it will void the warranty. This is particularly important to pay attention to when using metal roofing products, such as standing seam metal, which have a multitude of profiles, attachment methods, and seam/lap/joint styles which can affect the recommended slope.
The manufacturer’s minimum recommended slope or pitch will sometimes be steeper than the minimum that is required by code for a particular roofing material.
For each type of roofing material, you can see the actual language used in the model 2018 International Building Code at the International Code Council website. This link will take you to Section 1507 Requirements for Roof Coverings. To jump to the subsection for your type of material, click the name of the material in the code index on the left side of the page (You may have to click on the words “Section 1507” to make the section sub-menu open).
For the actual language in the model 2018 International Residential Code, this link will take you to Section R905 Requirements for Roof Coverings.
As a very general rule, a steeper roof will perform better and last longer than a roof with a lower slope. Steeper roofs shed water and snow faster and are less likely to have debris accumulate on the roof.
If you need help figuring out the slope or pitch of your roof, we recommend this slope finder on Amazon.* It’s very inexpensive and very accurate.
Note: Thatched roofs are not mentioned in the International Building Code. The minimum slope given for thatch in the table is based on best practice standards prevalent in the thatching community.