Does pressure-treated lumber have the same design values as lumber that is not pressure-treated?
AF&PA's National Design Specification® (NDS®) for Wood Construction (2001 and later), outlines the following for pressure-preservative treated lumber (similar provisions are provided for structural glued laminated timber):
"4.3.13 Pressure-Preservative Treatment
Reference design values apply to sawn lumber pressure treated by an approved process and preservative. Load factors greater than 1.6 shall not apply to structural members pressure-treated with water-borne preservatives."
For structural sawn lumber incised to increase penetration of preservatives, the NDS outlines the following:
"4.3.8 Incising Factor, C_i
Reference design values shall be multiplied by the following incising factor, C_i, when dimension lumber is incised to parallel to grain a maximum depth of 0.4", a maximum length of 3/8", and a density of incisions up to 1100/ft^2. Incising factors shall be determined by test or by calculation using reduced section properties for incising patterns exceeding these limits.
Table 4.3.8 Incising Factors, C_i
__________________________
Design Value-----------------------C_i
E, E_min------------------------------0.95
F_b, F_t, F_c, F_v----------------------0.80
F_c⊥-----------------------------------1.00
__________________________"
The wet service factor, C_M, applies to dimension lumber (including those preservatively treated). According to NDS section 4.3.3:
"Reference design values for structural sawn lumber are based on the moisture service conditions specified in 4.1.4. (19% or less for lumber). When the moisture content of the structural members in use differs from these moisture service conditions, reference design values shall be multiplied by the wet service factors, C_M"
Similar provisions are provided for other structural wood products.
"4.3.13 Pressure-Preservative Treatment
Reference design values apply to sawn lumber pressure treated by an approved process and preservative. Load factors greater than 1.6 shall not apply to structural members pressure-treated with water-borne preservatives."
For structural sawn lumber incised to increase penetration of preservatives, the NDS outlines the following:
"4.3.8 Incising Factor, C_i
Reference design values shall be multiplied by the following incising factor, C_i, when dimension lumber is incised to parallel to grain a maximum depth of 0.4", a maximum length of 3/8", and a density of incisions up to 1100/ft^2. Incising factors shall be determined by test or by calculation using reduced section properties for incising patterns exceeding these limits.
Table 4.3.8 Incising Factors, C_i
__________________________
Design Value-----------------------C_i
E, E_min------------------------------0.95
F_b, F_t, F_c, F_v----------------------0.80
F_c⊥-----------------------------------1.00
__________________________"
The wet service factor, C_M, applies to dimension lumber (including those preservatively treated). According to NDS section 4.3.3:
"Reference design values for structural sawn lumber are based on the moisture service conditions specified in 4.1.4. (19% or less for lumber). When the moisture content of the structural members in use differs from these moisture service conditions, reference design values shall be multiplied by the wet service factors, C_M"
Similar provisions are provided for other structural wood products.
