Well since one side is painted already... I would just stick with that to keep it consistent. If it's in bad condition though, you could powerwash it off and apply what you want.

I don't know of any completely non-toxic products to use... but as an aside from that... my experience sealing my privacy fence and pergola/deck... you want to go with a semi-transparent stain of some sort. The stain absorbs the UV rays to some extent vs a clear coat. Clear coats will be more for water and wear resistance... which doesn't last too long.

The best part is that with a semi-transparent stain, you can just reapply on top of the old product. This is unlike a paint where you will have to remove all loose material before reapplying. My fence is up to 8 years with the original coat. It probably should have been reapplied 2 years back, but it still looks decent enough. You don't get cracking/chipping like paint... it just color fades. You own results will be dependent upon how much sun your fence gets.

Try and hunt down product reviews though for anything you go with. Many clear coat products are almost useless.

Thanks for the info.

A contractor I talked to yesterday that has worked on a few houses in this development says the dealers paint is only paint and does not have any sealing. I think I will double check with the dealer.

What style of fence is it? picket? paddock style (flat boards)?

I believe most "sealers" need to be reapplied every year or two in order to keep it repelling water. Regardless though... with or without the sealer component.... the paint will eventually start to flake off and chip. You can stay on top of it by sanding/scrapping it and adding new coats as needed... or just let it go and apply a new finish overall.

It's like this one.

http://sierrafencetx.com/wp-content/uploads/2012/10/2-rail-fence-with-treated-pine-posts.jpg

Linseed oil

Ahh linseed would be natural alternative... But many now are augmented to make them a better product.. Unless you get the pure stuff. And it offers no uv protection which causes the most damage to wood. at least that fence would allow you to do a different finish on the inside without it clashing with the outside....as in ... If the painted it brown... You could get a brown semi transparent stain.... Or they do have fancier transparent sealers with some uv protection... Though they can be more $$$$

I'm less concerned about $. More concerned about

- environmental friendliness

- protection offered, both quality and duration

- Ease of touching up at the end of above duration

Well there has to be some low VOC versions of exterior stains/sealers out there now. There are a lot of for interior paints now. Just go for something that has the longest UV protection.

For my two cents worth.

Re: linseed oil-do not leave rags etc laying around it does spontaneously catch fire. Will not if open to the air as on your fence.

Far more expensive and durable is TUNG OIL it is hard to find pure tung oil but it is available.

I would thin either tung oil or linseed oil with 25-50% solvent-mineral spirits so that it soaks in 2-3 coats should do it and you will need to re-coat it every year. You slop it on with an old towel and then wipe of the excess or it will get tacky. The used rags can be placed in a coffee can filled with water.

Re: UV protection

I don't think any of the coatings offer much UV protection except paint. Good quality UV resistant marine varnish is available but it is far too expensive for this use. Frankly a wooden fence rots due to water infiltration. Unless it has all been pressure treated, depending on its quality and where you live, it will last only about 10 years. I expect if the builder only painted one side it was an inexpensive quality fence.