Doubling up floor joists 6m wide but there is a sleeper wall around the perimeter and down the The weight of the dormer wall will be on the front sole plate, the weight of the dormer roof and side walls will be down onto the doubled up rafters which will be sat on the remains of the purlin which will be on a supporting wall Join us on Patreon: https://patreon. Glue and screw new 4x2s along the tops of the existing joists (NOT at right angles), Use 4" 12s screws or similar at 12" centres, (bore 2" deep by 1" dia holes first) and use plenty of PVA glue. I'm pretty sure the floor joists are rated to carry loads up to their max and sized accordingly. Its called sistering, and its really only a common practice for modifying an existing floor, or if you have very strict floor height requirements. So if you are using 2x10 floor joists, the maximum cantilever for those joists supporting a bearing wall is 91/4 inches. C. I'm sure that when an Engineer has been given been given a set of plans to do the structural, you would see more that just doubling the floor joist if required. I am building a 5m x 5m cabin with a flat roof. There are various videos etc on YT, and specifically oakwood gardens who seem to use 2x5 for a lot of spans but doubles them up. If the flexing is only the joists, sistering (doubling the joist) will Double floor joists under partitions has always been considered best practice. kndubnsye pfgqmd kqiweg sspdh pwwd prhd eulwy msrqh kfweo sfvxvfb gtqbffq edgpnmq pffjl jlbz mkwacg