need advice:type of wood to use, sunroom ceiling?

[TFF]

I have a sunroom that projects out much like a giant bay window. The ceiling glass panes (5) are angled about 30 degrees and have wood runners between each pane. The runners are dual 2x4x5' and stacked and angled at same 30 degrees. The upper runner has an undercut rabbet for sun screens to slide in via the rabbet . I am having all five of the large ceiling glass panes replaced as the dual pane windows have lost seal. They are 30 years old. While doing this I want to replace the ORIGINAL dual stacked wood runners. Surprising to me is the integrity of the wood has held up. I am not exactly sure what they are but since the wood panel members on the entire structure are cedar (not spanish) I suspect the runners on top are cedar as well.They have been power washed and repainted several times over the decades and no real visible rot (but I have not gotten on a ladder and poked the boards). I prefer to paint the new runners again, but not really necessary if that affects your answer. So what do you suggest I use as the type of wood for the runners?
As for sunlight, the sunroom faces west and gets about 5 hours direct sun (fall, winter) and about 7 to 8 hours direct sun spring, summer. Winters average in the high 20's but can at times get into the teens. Summer is hot humid in Maryland and can get to 100 degrees at times. When it does snow and ice forms on the angled ceiling, it tends to melt quickly from the solar rays even if the temp is below 32.
Next question is what screw type should l I use to hold them? Stainless steel? thread type?

[br549]

It sounds like an interesting design and problem, but I am having trouble picturing it in plan or section. Could you please provide pictures of the existing structure, and sketches, even if just drawn by hand, of the "runners", which sound like rafters between the glass panes. And, how much, and what parts of the wood, will be exposed to weather?

[Hobbyman2]

locust is very resistant to decay it has a pinkish color . as to the screws,, anything from the marine environment , cedar would be a good selection ,Teak if it is in your budget , if the existing cedar structure has lased 30 years that's not bad . my .02

[RFGuy]

If you can post a picture, it may help us to get a better idea. From the sounds of it, you will be painting this, correct? If so, then you could really use any wood here. Anything from pine, douglas fir, etc. all the way up to hardwoods could be used. It really is up to you. Since you will be painting it, I wouldn't put an expensive hardwood there though. Just make sure you design it in such a way that rain runs off and seal every possible connection point, otherwise water will get in and rot the wood. Without a picture, I can't know the design of this window for sure, but if possible you might want to consider adding some kind of air gap or insulation between the inside and outside. You are replacing the windows with dual plane which will help, but if you have solid wood runners going from inside to outside encasing the windows, you will get thermal conduction through the wood. A simple air gap between inside and outside wood members could give a welcome extra bit of insulation to the overall window opening. Just a thought...

[TFF]

The 5' runners are the stiles for the screens. There is no need for a rail top or bottom. They sit on top of the window frame stiles that hold the window panes in. They slide in and out via the common rabbet in both stiles. They are permanently exposed to weather.

[TFF]

RFGuy, you raise really good points that I had not considered. I should not assume once the screen stiles are pulled up that there is no underlying problem. I will be prepared for that conversation with the window company who will do the install.

The construction of the large cedar sun room enclosure has stood up well over 30 years. All the cedar has been treated, painted several times during its life. Approx measurements are 10'W x 8'H front, 5'W sides, 30 degree angled top. The full height of the top runs from 8' front up to 10' where it connects to house (approx 30 degree angle).