There are many approaches. My recommendation is to stain the decking and beams with a light colored semi-transparent stain, keep both beams and exposed decking ceiling materials a harmonious, light color. I'm not a fan of dark decking/ceilings or dark beams, which shout for attention, create a visual contrast with the rest of the house, and tend to lower the ceiling, making the space seem smaller.

Here's some ideas:

My buddy is contactor and he recommended using only Sherwin Williams for good quality. I found a nice selection there of semi transparent stains. I also just got a post card 2 days ago that they are having a 30% off sale. You should check it out.

I chose this one to stain my friend's porch. It is called Clasic Barn Red.

Keep the beams natural. I'd use either a water based sealer like Bona natural, or an oil based sealer such as Messmers oil.

I would never make any part of a ceiling dark. A water borne clear acrylic finish will help prevent the fir from darkening. I would only stain fir if it had lumberyard marks or stains that could not be removed and I would have tried hard to remove them before installing them. Before stain use a good wood conditioner to help prevent uneven staining. There's a big risk here so always make a sample and get the owner's approval of it in writing. Put the sample in your safe deposit box with the owner's initials on it.

I failed to mention that the one I chose is water based. It makes for easy clean up and no annoying odors if used indoors.

The existing part of the house is long and narrow. Here is a pic of the narrowest part and what it used to look like.

All of the paneling have been removed. We also removed the short wall you see on the right, the built-in, and the walls behind the built-in. Now it is one open space, stretching around 52' before hitting a wall. The two tall windows on the left will be part of the addition and have been pushed out 10'. Approximately starting where the old sliders are will be a 20'x8' slider. The new beams will run across from right to left and the T&G will run the same way as the old ceiling paneling. Greatly appreciate any and all advice! Thanks

The picture below has some elements of what we are looking for: the gray floor and the wood ceiling. However, I think we would want a much lighter shade for the wood ceiling. What is the natural sealed douglas fir color or would we be happier with a semi-transparent stain as mentioned above? From the images suggested above, it looks like the beams and the decking should not have the same stain or shade. Thanks!

If it was my house I'd make the beams and the decking/ceiling the same color: a light colored semi-transparent stain harmonious with floor and other major interior finishes, probably using Olympic Stain, which has a large range of colors.

Virgil, thanks for the advice. Should the windows and doors have the same stain or something darker or lighter?

Well...if you plan to paint your walls (gyp board or other paintable materials), then I would paint all interior trim around doors, windows, base, cove, etc. My general approach is to keep trim a lighter, harmonious color than the painted wall color(s). If the walls are stained, I'd use the same stain for trim.

I am using vg fir for all of my doors and trim. I am using Danish oil, natural, knowing it will darken some over time. It's a very easy finish to apply and gives a nice matte finish.

Virgil, we plan to have drywall throughout the house. Might do paneling for some accent walls. Some of the windows and doors will be vertical grain douglas fir. I was asking if the windows and doors should get the same stain as the ceiling. I suppose the trim should be done in a similar fashion as well.

seabornman, leaving the fir natural is definitely an option we want to consider, but I am not sure what is the actual natural color. I have been trying to find some pictures online, but there seems to be quite a bit of variation. If we did the semi transparent stain on the ceiling as Virgil suggested, I am assuming the natural finish on the windows and doors will be lighter.

The design problem when using painted gyp board walls, and stained wood trim and doors is that the materials are so dissimilar that they tend to visually fight one another for dominance and importance. In other words, there's a strong visual contrast between the two different materials.

That's why I typically recommend painted trim and doors when using painted walls and stained doors and trim when using stained walls.

I have been poring over the photos on Houzz. Trying to get sense of the colors people use. It is difficult to decide which look makes the most sense.

Here the window, trim, and ceiling seem to be in the same shade.

Here the ceiling is darker and windows and doors are lighter.

This is suppose to be clear sealed douglas fir with painted windows and doors.

This house has similar shape to mine. Looks like the similar colors are used for windows, doors, and ceiling.

All of the photos above have the beams and decking finished in a natural color of one shade or another. With such a dominant wood tone in the space, having matching trim for doors and windows, and doors, is consistent and makes sense.

If you change the finish of the beams and decking, however, then the schemes above will look very different and fragmented.

The beams and decking are perhaps the key for the rest of the interior finishes. But it also depends on the style of architecture.

I know this thread is a month old, but what did you end up choosing? Did you go with an oil or water based coating? We also have fir beams and are trying to figure out what to do with them.