Manthorpe G912 Joist Seal 75mm x 100mm - Translucent White Properties Width: 75mm. Block size: 100mm. Height: 225mm. Product information The G912 range is designed to solve theproblems of air leakage associated with built intimber joists. The box is placed over the end ofthe joist and built into the inner leaf of theexternal wall construction. As the timber driesout and shrinks the seal is still maintainedbetween the box and the masonry, thuspreventing air leakage into the cavity. Located around the inner flange is a number ofpush out pockets for the location of restrainingstraps as required. Description Manthorpe Joist Seals solve the problem of air leakage around the timber joist and effectively mount the joist in the wall, eliminating the need for clumsy joist hangers. The joist seal fits over the end of the joist and is built into the block work forming an air tight seal with the masonry ensuring good insulation. During the drying out period the timber floor joist can shrink within the product without compromising the seal, thus complying with Part L of building regulations. Traditionally, joists would be built directly into the block work skin of an external wall. However, robust construction details state that this is no longer acceptable, as shrinkage of joists and mortar allows air leakage to the cavity. One alternative is to use joist hangers “ but these are difficult to fit, slowing down the building process and leading to reports of structural problems such as springy floors and collapse.