![]() In those instances, a shorter joist of the original width is preferred to a longer joist that is not as wide. Sistering joists is a fairly straightforward process but can become laborious if you have to remove many utilities or the joist does not fit against the original due to shrinkage. In particular, the fasteners at either end of the sistered joist, provided they are not bearing, will experience the most force and have more fasteners than the center of the sistered joist. When partially sistering a joist, remember that the way you fasten the joists together is of utmost importance as the fasteners will carry the load to the original joist. Sistering a joist with one end at the point of deflection will not result in any significant reduction in the sag. The further away from the point of deflection you can get the sistered joist, the better. ![]() If space is limited and you need to fix a sagging or damaged joist, you can partially sister a joist, ensuring you get at least 3’ from the damaged area on either end. A non-full sized sister joist will still fix sagging in a joist, which is commonly referred to as deflection. While no specific rule exists for how long a sistered joist should be, a commonly held rule is that a sistered joist ⅔ the length of the original is adequate – only if you cannot run the joist the entire length. Sistered joists do not have to run the length of the original joist. Those joists must be sistered and bear on both ends to a wall or beam. In those cases, a header attaches to joists on either side. This is often found when joists cannot run the length from bearing wall to beam due to stairs. You also must have sistered joists if there is a perpendicular header longer than 4’ attached to the joist. Even if the old joist does not bear to that extent, the new joist must. Homes are meant to be built on single joists at set spacing – sistering only comes into play if the home has been damaged or improper construction techniques were used, which the building code does not cover.Ĭode does dictate that all floor joists should bear a minimum of 3” onto concrete and at least 1.5” onto the wood. The residential building code does not have a section on sistering joists because it is not standard in new residential construction. In those instances, sistering the damaged joist is required. ![]() It is important to repair those joists as they’ve lost some ability to handle a proper load. In those cases, sistering one or several joists after jacking up the old joists to the desired height will fix the sag permanently.Īnd finally, if you can do a visual inspection of your floor joists and find that some are rotten in places, or have soft spots due to moisture damage. They may also be spaced too far apart for the span they support. ![]() Over time, joists can sag due to being undersized or rotten. The other most common reason for sistering a joist is to fix a sagging floor.
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