How much UVR protection do shade structures offer?

Shadecloths and polycarbonates are synthetic materials whose purpose is to moderate the amount of sunlight entering a particular environment.

Shadecloths
Shadecloths are designed primarily for horticultural use to control visible light for plants. Shadecloths are available in either closely woven or mesh materials. The transmission of solar UVR through shadecloth is dependent on the weave and its gauge with closer weaves offering greater protection against UVR. Shadecloths typically rate between UPF 2 (50% block) to UPF 10 (90% block) and should not be relied upon as the only form of UVR protection.

Awnings
Awnings are a form of shade structure where the canopies are usually made from dense, closely woven materials such as canvas and usually provide very good protection.

Sun umbrellas
Sun umbrellas where the canopies are made from dense, closely woven materials such as canvas usually provide very good protection.

Polycarbonates
Polycarbonate is manufactured in either clear or tinted sheeting. The main purpose of the sheeting is to weatherproof an outdoor area while allowing visible light through. Transparent polycarbonates usually have UPF ratings of 50+.

Evaluating shade structures
UVR can be scattered by particles in the atmosphere and is known as diffuse UVR. This means that apart from UVR reaching the ground directly from the sun overhead a lot of UVR an also reach the ground from the open sky. A person who was shaded from direct sunlight but could see areas of open sky may still receive UVR exposure due to diffuse UVR. UVR can also be reflected from surfaces such as water and buildings. Many types of shade structure provide little or no protection against reflected or diffuse UVR.

Standards such as AS/NZS 4399 Sun protective clothing - Evaluation and classification are intended for evaluation of personal sun protective clothing that is worn in close proximity to the skin. When dealing with shade structures such as tents, awnings and umbrellas the protective material is typically at some distance from the person. This may allow UVR directly from the sun, or scattered from the open sky or from reflecting surfaces to reach the occupant. This means that the amount of sun protection the person receives can vary depending on the positioning of the structure.

It is often useful to determine the UPF rating of the materials that comprise shade structures but labelling for a shade structure should make it clear that the UPF rating applies to the material only and not to the sun protection afforded by the structure as a whole. The reason for this is that although the materials may be effective at blocking UV, the effectiveness of shade structures is dependent on the manner in which they are positioned in relation to the sun and the manner in which people use them i.e. the person using the structure cannot be guaranteed to be receiving that much protection at all times.

For example if a tent was positioned so that the sun was streaming in through the open entrance onto the occupant, that person would be receiving little or no protection from the structure. The position of the occupant in the shade structure is very important and the further back the occupants are from the opening the greater the protection.

Labelling for these products should make it clear that the UPF rating is for the material only and not the overall protection provided by the shade structure as this can vary depending on the manner in which it is used. For many types of shade structures it is also appropriate to state that they do not provide protection against reflected or scattered solar ultraviolet radiation, as is required in the labelling of sun protective headwear.

Two factors to consider when evaluating the effectiveness of a shade structure for UVR protection are how protective the materials are that it is made of, and how much coverage does it provide to the user. The effectiveness of the material can be determined by testing it to determine its UPF rating. The coverage, or how much sunlight it prevents from reaching the user depends on the positioning of the structure with respect to the sun. Generally shade structures of larger area offer more protection than smaller ones.