According to Japanese Building Standard Law, 2-hour fireproof floor slabs and walls are needed to construct over 4-story buildings. To develop the 2-hour fireproof CLT structures, small furnace fire tests and actual-size fireproof tests were conducted for CLT specimens cladded with some refractory materials. Small furnace fire tests were conducted to demonstrate the fire resistant properties of CLT cladded with calcium silicate boards, gypsum boards, and these combinations. Actual-size 2-hour fireproof tests were conducted for the cladded CLT floor slabs combined with a steel beam. From these tests, the following were indicated; CLT cladded with calcium silicate board （JIS A 5430 Calcium silicate board Type3, 0.5TK） 15mm （outer） and gypsum boards （JIS A 6901 GB-F） 45mm （inner） had adequate 2-hour fireproof performance. Heat conduction of screws to fix the outer claddings did not cause charring of CLT when claddings had adequate 2-hour fireproof performance.Further thermal insulation on steel member subjects or some artifice around the CLT-steel joint region should be done if CLT and steel members used together.

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Didecyl dimethyl ammonium chloride（DDAC）is one of most widely used quaternary ammonium compounds as active ingredient of wood preservatives for pressure treatment. In Japan, its retention amount in treated wood is regulated in Japanese Agricultural Standard（JAS）for Sawn Lumber. According to the quantitative determination method of DDAC in the JAS, DDAC extracted from treated wood with hydrochloric acid-ethanol under reflux prior to analytical determination. Then, the extraction solution is filtered by vacuum filtration and the residual wood is washed by ethanol. The combined filtrate and washing are transferred into a volumetric flask and diluted to the volume with ethanol. These operations are time consuming. To optimize extraction method, ultrasound assisted extraction with hydrochloric acid-ethanol（3：97, v/v）, formic acid-ethanol（3：100, v/v）or formic acid-methanol（3：100, v/v）were investigated to extraction of DDAC from treated wood. Consequently, ultrasound assisted extraction with formic acid-methanol showed the maximum recovery rate of DDAC from treated wood. The recovery is the same as that obtained by the JAS method. Furthermore, filtration with syringe filter could be applied after ultrasonic assisted extraction, instead of vacuum filtration. The quantitative determination of DDAC in same treated wood sample was carried out by 5 different laboratories using the ultrasound assisted extraction and syringe filter filtration. Consequently, it was found that the results from different laboratories are almost the same.

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