Absolutely! The Retract-A-Gate Safety Child & Pet gate has been extensively tested in wet rainy seasons and hot dry summers.
The Retract-A-Gate safety gate has also been tested outside during a full northern USA winter with flawless results. With that said, it is recommended that you bring the Retract-A-Gate inside during freezing temperatures (simply unsnap the safety gate from the brackets). Anything, including Retract-A-Gate, which is left outside will have a reduced life compared to only indoor use; but you can feel confident that the retractable safety gate will stand up well to outdoor use.
One thing to be aware of is that some fading or degradation due to extended sun exposure is possible. Because of this, we recommend bringing the Retract-A-Gate indoors when not in use.
Installing on a Trex or composite deck?
If installing outside to a Trex or composite deck, the posts will normally have a 4x4 wooden post inside them. In this application we would recommend pre-drilling your holes and using stainless steel screws the same size as the ones we provide (#6 flat head). Stainless steel will hold up much better when in contact with the treated wood posts that are normally on the inside of the Trex.
You can also attach the wall brackets to your house siding if there is solid wood underneath.