Is white pine strong enough for roof ?

I am designing my roof for a 15' x20' pumice cob house. I was contemplating reciprocal roof (yes J I am a newbie DYIer) I am planing on a copper sheet roof (yes it will have expansion joints), with insulation Pumice or pumice cob.. (worried about the weight). I have read the book RECIPROCAL FRAME ARCHITECTURE it has great load/span information, but not about specific types of wood. I was thinking of using 5" hard wood saplings, but I also have access to a lot of crowded white pines on the edge of our property They were planted in the 60's supposed to be a christmas tree farm sponsored by the state.. but the state supplied the wrong trees. so the 1 acre lot was never harvested as christmas trees and allowed to grow very crowded, and now that they are reaching maturity they are getting to the point when wind blows them down, they pose a threat to our neighbors driveway. We have to thin them, and allow other things to grow there. I have heard that the knots all over white pine makes them too weak for heavy structure. I read somewhere on Permies about a resource for strength of different timber, but I can't find it, and I think I recollect that it was for vertical strength. If I use the white pine as sawn beams and rafters will I get cracking and load failure? Should I stick with the saplings ? If so, how long do I have to dry them after debarking them? or can I use them right away? Thanks for any and all info..
And J I am one determined woman, don't bother telling me not to attempt it. I plan on learning tons, and this as all of life, is an experiment... which means I will throughly enjoy it, which is the reason I am doing this crazy endeavor.

What size are the white pine trees and what is your climate? i.e. do you have to worry about snow? I don't have an answer for you, but perhaps with more info JayC. (or others) will.

Hi Brad,
Thanks for answering!
The trees diameter's are about 2' some thinner some thicker, there about 35' tall (I'm guestamating) It's the middle of the night and I just got home from a really tough shift at work or I would head out there and measure them, or I would if it wasn't raining and no moon. I have many excuses. I do look at them every day so I am pretty sure at my guesses.They have grown slowly because they are tightly packed in there I am hoping that it will have made their rings smaller so they will be stronger than your average white pine, most of them are rod straight there was no room for them to bend.
I live in upstate Ny which is huge and varies in its climate. I am zone 5, in the "southern tier" south of Ithaca NY, and just above the northern Penn. border. The native forests are Oak/ maple predominant. Our winters used to get more snow, fun snow, but the last 2 winters have been cruel -5 to -20 at night for extended periods, and icy snow, that makes crusts so winter hiking is a B****, unless you have great snow shoes. You know the kind when you take a step you are supported, then the next step you crash through a layer.. makes for hard walking. So yes, I have to worry about snow loads and possibly ice on top of that.. That is why I am contemplating a metal roof, (slides off) and the fact that I will be collecting rain water from the roof made me want copper so I will already starting my antimicrobial system with the surface collection....
I hope that answers the questions that need answering, if not ask me again, I love spouting off on my building ideas that are this spring finally starting. I will be breaking ground as soon as the rain /snow they have predicted stops. I am so excited!

Hi Suzanne,

I am so happy to read about a determined woman that's going to plow right into a difficult build. Yes, you can do it and yes those 2' diameter white pines will be great!

Since I have never built a reciprocal roof and I know he'll be on here soon, I am going to let Jay answer your questions there. I however used to be a "roofer to the stars" and a lot of that work was custom copper roofing and flashings, so I can walk you through any design you may have. I am wondering if you are going to seam all four sides of the "copper shingles" or go with a clipped and capped standing seam? Unless you have access to a 10' break, I would go with the shingle style. You can build one of these with a 4' harbor freight break and hand tools. If you're going to use copper, then you won't want caulk. Check around at the antique and thrift stores and you may be able to find an old fashioned soldering iron. You heat these up in a fire and solder all lap joints, for a roof that will not need any service 'til after your gone.

We all love visual aids, photos and drawings to help everyone to be on the same page as you are.

All Blessings,
Bill

Bill,
Short answer I was going with the shingles, thanks for the soddering info. I will not have time until Thursday, to post anything more detailed, or pictures... 3- 12 hour shift ahead of me...I'll post more on Thursday. Thanks for your help! And encouragement !

Hey! EVERYONE!!!,
I found a calculator for timber!!!
http://www.nicomaparklumber.com/beam-calculator.html
you use the info from this page to calculate the load and what you are using it for!!!
yea!
http://www.forestryforum.com/members/donp/Fblist.htm
I think we could use this!
And Bill I will post a true answer to you later today hopefully with pictures!
regards