I have a REI Half Dome + that I bought about 12 years ago. I use it a couple of times a year for short camping trips and have rarely needed the rainfly. On a recent raft trip we set up the rainfly as it looked like rain that night. Sure enough it started raining about 11:30 and poured all night. Water came through the rainfly almost immediately and from all sections of the rainfly. Water was dripping throughout the tent. The next morning we had a couple of gallons of water on the floor as the bathtub floor was water tight. I should have turned the tent upside down and slept under it.
The rainfly still looks good, no holes, rips or scrapes. Do these rainflies just deteriorate over time and loose their water repellent quality or what? Puzzled Fireplug
Many (most) camping tents used PU (polyurethane) coatings and a DWR (Durable Water Resistant) coating to waterproof the fly which is generally made of nylon or polyester. DWR's wear off and PU breaks down over time such that it will wet out. This may be particularly problematic with nylon since it also absorbs water. So it is not unusual for an older tent fly to leak particularly if it has not been stored in ideal conditions...generally clean, cool and dry.
You can sometimes rejuvenate a tent fly by washing it (this can reactivate any remaining DWR to some extent), or by reapplying a DWR on the outside, and/or re-coating the inside with some suitable product. Sometimes it is necessary to re-seam-seal the tent fly with seam sealer either first removing any long runs of loose seam seal tape or sticking or small runs back down depending or just applying along the seam if it is not taped. While this is much cheaper than buying a new $300 tent it is quite a bit of work that can have unsatisfactory results and I might look a new tents before deciding to take it on.
Before doing any of that you should convince yourself that the water you saw was not condensation. In the right conditions condensation can form on the inside of a fly and cause considerable wetness. It does not sound like that was the case here except that the area of leakage was non specific. If it was me I would test the tent on a warm dry day with a hose and see if the leaks reproduce.
Thank you, OldGuyot,
Your explanation was clear and understandable. The tent has been stored clean and dry and in a garage or basement, so it didn't get too warm. I guess it deteriorated as you explained. I wish REI and other tent manufactures made this disclosure or made it more prevalent in their advertisements and disclosures. Knowing the age of the tent, I would have tested the rain fly before our trip.
Do you know of any tent brands that use better rain fly materials?
Appreciate your knowledge, Fireplug
Not so much about the brand as the material although personally I like Big Agnes tents. MSR have a reputation for making durable tents. They don't always get it right but premium brands tend to use premium materials. I had my BA Gen 1 Copper Spur UL2 over 10 years and although I used it lightly it is still working fine. It was stored in the house and I did touch up the seam tape. I currently use a Tiger Wall UL2. These are both Sil Nylon tents. I also have a Sil Polyester Luna Sol trekking pole tent.
I would say that sil nylon or sil polyester are the more durable (long lived) fabrics although I don't have any data to back that up so take my opinion with a grain of salt. Silicone is UV resistant and since it is slippery and flexible it is resistant to light abrasion but its soft so can be damaged by hard abrasion . It mold resistant even if slightly wet when stored (but I wouldn't test it). Nylon is strong and can be made in very light weaves but tends to sag in the rain so only works well for light weight smaller tents. Polyester is innately water resistant but due to its weaker fibers is only available in heavier weaves. Since it doesn't sag in the rain it great of larger tents.
Most silicone coated tents have an interior PU coating and this construction is sometimes called Sil/PU. Big Agnes uses this in many of their smaller backpacking tents. The PU coating is partly to allow them to be more easily seam sealed since silicone is harder to seam seal because not much sticks to it and partly since PU can carry the required flame retardants. The PU layer may degrade over time but since it is an interior coating it probably won't affect the waterproofness except for the seams which may need some attention as was the case for me.
As far as I know silicone coated tents don't need a DWR treatment.
Since the fire regulations were changed earlier this year (2021) I would expect to see more Sil/Sil Nylon and Polyester tents since the change means fire retardants won't be necessary on smaller tents to meet the new fire standard or so I understand. My Luna Solo is Sil/Sll Polyester.
Tents made of Dyneema are also hardy and light weight (don't need DWR or Fire retardants) but Dyneema is expensive and may or may not age well. There have been reports of de-lamination and pitting although possibly these were just isolated cases. It is hard to say because Dyneema hasn't been used as a tent fabric for that long. It was originally developed as a sail cloth.
@Fireplug After my tents are a couple of years old, I typically apply a can of silicone spray sealant onto the rainfly about once a year. Nothing fancy, just a spray can you can typically pick up at walmart or some other big box store. I've found that the sealer from Kiwi works well.