As the utilization and consumption of lignocellulosic biomass grows, so too will the need for an adequate supply of feedstock. To meet these needs novel waste feedstock materials will need to be utilized. Exploitation of these novel feedstocks will require information both on the effects of solvent extraction on the subsequent analysis of potential novel feedstocks and how accurate current methodologies are in determining the composition of novel lignocellulosic feedstocks, particularly the carbohydrate and lignin fractions. In this study the effects of solvent extraction on novel feedstocks including, tree foliage, tree bark and spent mushroom compost, with 95% ethanol, water and both sequentially, were investigated. Chemical analyses were carried out to determine the moisture content, ash, extractives, post-hydrolysis sugars, Klason lignin (KL) and acid-soluble lignin (ASL) within the selected feedstocks. The effect of extraction was most pronounced for Klason lignin with a strong correlation between higher Klason lignin determinations and greater amounts of non-removed extractives in the cases of tree foliage and bark. Increased Klason lignin values are reported to result from the condensation of non-removed extractives during hydrolysis, hence the lower Klason lignin determinations following extraction are considered more accurate. In addition, total sugar determinations were lower following extractions, due to the solubility of non-cell wall carbohydrates; thus, the determinations following extraction are more accurate representations of structural cell-wall polysaccharides such as cellulose. Such determinations will assist in determining the best way to utilize these novel feedstocks.