old wood building in nj

huangyhg

old wood building in nj
we are performing remodeling work for a one-floor wooden building in new jersey, us built in 1957.
one of the tasks is to evaluate the existing roof capacity for possible additional loading.
the existing roof is 2x10 rafters at 16" oc across two spans of 17' and 15'.  the roof has an 11/16 to 12 slope.
we believe the existing roof may be designed to resist 35 psf ground snow.
our challenge is identify the species and grade of existing wooden rafters.
can anyone give me an educated guess for the most possible species and grade of the existing rafters?  
we might use the lowest design values in the code but it would be nicer we can get a little bit higher value and save some money for our client.
thank you for your help.
actually if you take a small sample of the wood there are several agencies that can tell you species.  contact your local forestry extension or a local university that has a department of forestry.  a quick google gives me
nj forestry dept (732) 833-0325
priscilla hayes, environmental coordinator, cook college/njaes
c/o department of agricultural, food and resource economics
rutgers university--cook college
55 dudley road
new brunswick, nj 08901-8520
tel: (732) 932-9155, ext.233
fax: (732) 932-8887
2x10 roof joists spanning 17 feet will have little or no additonal capacity above the flat roof snow load.  i would strengthen any portion of the roof that has additional load being added.  a common bending value for lumber of that time would be 1250psi for doug fir.  you can increase that by 15% for repetitive and also snow loading.  i would use that value if the framing lumber appears to be #2 or better.

i do not think is a good idea to save some bucks for a client on a structure.they will not value it and your liability will be highly increased.not worth it, that's my take on it.
"i do not think is a good idea to save some bucks for a client on a structure."
i trust this is a response to the specific question asked by the op and not your general design philosophy.