I am going to re-roof my house I need trust struts added, there are none in a 24' span and the roof sages in spots. 2X4s run from exterior wall to exterior wall and from exterior wall to the roof peak and no center W supports.
What is the best way to add the W supports with out sagging the ceilings inside the house?
No way to tell you without actually seeing the job. It appears you will have to "jack" the roof up before you can do anyting. IF the roof is sagging, that means "something" had to move outward to absorb the settling, and removing the sag, may cause some damage if things cannot return to their original location. Possibly "stringers" between the rafters going to the peak will stabilize things.
This is one of those situations where you really do have to be there to see. And, it probably would be worth paying a structural engineer to give you an opinion. I did that, and he only charged me an hour's labor to do some calculations and give me an opinion after looking over the situation. Now, if he'd had to draw plans and get it certified and passed by the building department, it would have been a lot more, but just to give me some expert advice, it was realtively cheap.
This is the first house I have seen that doesn't have the W web built into the trusses. House built in the mid 60s, 24' wide.
The bottom chord is still level and the top chord is sagged by the weight of the sheeting, shingles and time.
What I am thinking is run a 6" wood I beam about 8' off center of peak on both sides the full length of the house and build the W web off that to keep the bottom chord from sagging.
Would a 4"X4" or some thing on that order work as well?
quote; This is the first house I have seen that doesn't have the W web built into the trusses.
You haven't seen many houses in that case. There are hundreds of thousands of roofs built like that when they did not use manufactured trusses. Usually, they installed collars/crosspieces on some of the rafters, creating a triangle, to keep them from sagging.
Ya! In Tn. There isn't much for code enforcement.
A structural engineer could tell you how to fix it. It may be that that once in 100-year snowfall overloaded the roof, and something's failed, or it was never up to code in the first place. Most people don't have enough knowledge to calculate and evaluate what's there with what's needed, and guessing is throwing money at it, and that may not fix it.
I think the main thing is that a 2X4 isn't meant to span 14'
If your house has a 2x4 stick built roof the lumber is way undersized. As a rule stick built roofs do not have trusses, so the homes you have lived in previously must have used manufactured roof trusses that are set in place using a crane. I hear what you are saying about wanting to use what is there and build your own trusses, but I would not do that without having an engineer draw up exactly where to place the bracing. The strength in the 2x4 trusses comes from where the bracing is placed. Randomly placing bracing will yield poor results for the time and money spent.
Also this will not fix your sagging roof issue, just stop it. As others have suggested its probably well worth having an engineer look at your situation BEFORE spending any money.