Sub-5 oz long sleeve baselayer shirt for 3 season hiking

5.75 ounces in large, and quite warm to me. I have the same basic layering system as you, and I love this North Face garment as my second layer over my t-shirt. I use it around town as well. Here is a link (mine is in black):

http://www.rei.com/product/873516/the-north-face-light-zip-neck-top-mens-2013-closeout

The non-zip version comes in at 5.2 ounces in a large, but I much prefer the .5 ounce penalty for the flexibility of the 1/4 zip.

Good luck in your search!

The Arcteryx Phase SL Zip Neck LS Men's is listed at 4.4 ounces. It's expensive though.

GoLite has a number of options in the 5-ounce range:
http://www.golite.com/mens/shirts-tops/running-hiking

Most of the tops from the mainstream athletic manufacturers (Nike, Adidas etc.) are quite heavy, but they may have a few light ones. I should take my scale to the sporting goods store some day.

I wear this and love it. I think a medium weighs in at 5.8 oz, but maybe someone has the figure at hand. I wear a small myself but haven't weighed it. I do think Underarmour has a lot going for it. For one thing you can find it for relatively cheap. The Rab Meco has good odor control though which is important to me at least.

it depends on where you hike.

Me and my son both have worn UA base 1.0 in low humidity in NM, even in 90F+ temps. In the same top at 70F in the humid SE Appalachians, I got too hot and switched to a SS shirt. The Base 2.0 is definitely too thick for any hiking, my base 2.0 in L is about 6oz,my base 1.0 in L is 3.95 oz and could shorten the length a few inches and save maybe a few tenths. These are powerstretch fleece type garments.

The phase sl likely is too light for 3 season hiking, especially if you're worried about warmth. I have an SL and use it year round as a baselayer because it wicks so well (great evap cooler in the summer under a nylon collared shirt). The phase ar would be more applicable, but above the 5oz mark. As it stands I don't think too many LS will be warm and under 5oz. Maybe some very thin merino but that runs into price/durability issues.

I think someone here spoke highly of Craft shirts:
http://shop.craftsports.us/men.html?cat=62

Unfortunately, Craft doesn't list the weights.

I'm a huge fan of Craft baselayers.

My ~2010 Pro Zero Extreme (long sleeve, size small) weighs 110 grams or 3.9oz. I can't find anything better for working hard in cold temps. It's warm, breathes super well, and dries incredibly quickly. Make sure to get a snug (next-to-skin) fit for best performance.

This is the current version: http://shop.craftsports.us/active-extreme-crewneck-mens-31790.html

Perhaps a vest?

Luke's ultralight makes a pretty good one, if I recall.

I know this is an oldddd thread but I would like to throw this out there. For a super light long sleeve shirt check out the Patagonia Fore Runner long sleeves. The Fall 2014 version in size small weighs just 3.7 ounces and the fit is awesome since it's made for trail/ultra running. Conversely, a short sleeve Fore Runner I have from Spring 2013 line weighs 3.6 oz. The newer (not newest) long sleeve version weighs just one tenth of an ounce heavier. These shirts are awesome. I've bought two long sleeve and the one short sleeve all for half price. It's really easy to find these shirts on sale. Definitely worth trying. They have the polygiene treatment and UPF 20 to boot.

Outdoor Research MEN’S ECHO L/S DUO TEE 3.8oz in Large UPF 15

Outdoor Research MEN’S ECHO TEE 3.1oz in Large

Outdoor Research MEN’S ECHO L/S ZIP TEE 4.3oz in large

my go to tops!

My Patagonia Cap 2 (long sleeve crew) weighs in at 5.1 ounces. It is a "Slim Fit" which is close to form fitting but with enough room that I can layer it over Icebreaker wool short sleeve.

It wicks moisture pretty well, dries extremely quickly and has an anti-stink treatment. It is also on sale right now:

http://www.patagonia.com/us/product/mens-capilene-2-baselayer-lightweight-crew?p=44815-1

On the minus side, the thumb loops leave something to be desired.

I went through this same issue last year and settled on the OR Echo Duo l/s, great shirt. Might be a little too lightweight for true 3-season. I also have an Echo Duo s/s that I can layer with it — the two together weigh under 7 oz (size M).

I've seen the OR Echos and would have gotten a few of those but could never find one on sale. But the thing I like about the Pata shirts is the fit. I'm 6' and 137 lbs after a good meal, but I'm not a weasely, scrawny skinny, and I have pretty broad shoulders for someone of my stature. A "swimmers physique" if you will. So finding shirts that fit is tough. I need a small "girth" but a longer torso, arms and broader shoulder cut. Basically a Small/Tall. And the Pata shirts have a longer cut torso and arms. Still pretty tight in the shoulders but much better. Most size small long sleeve shirts are too short in the arms for me and that's my bigger issue. But this one works well for me. So if you have a similar build this one may work for you. Not as light as the OR shirts but dang light.

And the Pata shirts are power dry without the power dry label. Same weave and everything. Different weave on the inside from the outside, optimized for wicking and evaportationrespectively.

But only buy them if they're on sale. and try to get the newer ones.

Arcteryx motus long sleeve weighs 4 oz. I used it on the pct and it's an awesome shirt.

I bought one of these from costco for 12 bucks. weighs 4.7 oz for a size medium and seems to keep me really warm when worn so far. Seems like a great budget item if i do say so myself. Here is a link to the same one:

http://www1.macys.com/shop/product/32-degrees-heat-by-weatherproof-thermal-long-sleeve-crew?ID=1031709