Sign In to join the community | Help

can anyone tell me what a sisters joint is?

Can anyone tell me what a sisters joint is ? I have dry rout  on the ends A frames I tried to nail new facie board on them  they will not stay

Not what you were looking for ? Try posting a question
Posted 2011-08-30T01:26:02+0000  by tweetybird tweetybird

Good Day Tweety!


Sister Joists are the common solution to reinforce joists that are damaged or sagging.


If you think of the analogy of a skater who discovers they are on thin ice, they are told to lie down and spread their weight out over a larger area to prevent breaking the ice.


This same idea applies to sistering.


Using the same type material (lumber) as the damaged joist is most common, although metal plates and other similar material have been used for this function.


You may also consider "sandwiching" the damaged joist with two pieces of reinforcement ... one on either side.


Different systems are used to suspend the sister while positioning. I have found an extra pair of hands, metal joist hangers, and a hydraulic lift make it easy to move sisters into an exact position. Others will create a temporary hanger from scrap wood and attach one or both ends ... then attach the sister.


When attaching sisters, I like to use several large washers on a heavy bolt, drill pilot holes, insert bolts, and tighten to secure the "load sharing" sister(s).


Keep in mind that your support system may have sagged due to the damage. So be prepared to lift the joist back into a level position before you drill your pilot holes. This will ensure that the load is shared across the entire surface.


I like hydraulic lifts for this function as well.


Like the analogy of spreading the skater's weight out, your sister joists will ideally be as long as the original joists to spread the load out further. In practice, you may see sisters that simply bridge small gaps. But for best results, spread the load as far out as is reasonably possible.


This is a common DIY repair that will increase the life of your deck/floor for many years.


See your local Store Associate and they can walk you to the different departments for supplies.

Posted 2011-08-30T11:40:27+0000  by Pat_HD_ATL

Hi Pat,


I think I need to do this repair on the outside edge of my deck.


Are the bolts you mentioned like carriage bolts?


Do you recommend a particular size?



Posted 2011-09-01T21:28:04+0000  by ELV

Sistering beams involves overlapping boards. The longer the overlap, the stronger the connection. It is commonly used to repair a joist in a deck or when your span is longer than the joists you have. The connection can be done with deck screws, lags or carriage bolts. You can do a search on a pattern that should be used for your application. The city I'm in allowed me to sister my 20' joists with a screw pattern that alternated about every 6-8" from what I remember (see attached picture)

Sistered Beams.jpg

Posted 2011-09-03T15:33:46+0000  by Paul

Hi Elv!


Thanks for the Call Out!


On a recent deck repair (similar to your description) I used 1/2-inch galvanized carriage bolts as well as several increasing size washers on each end of the bolt.


The galvanized bolts are impacted less by the weather, so the repair will commonly outlast the deck.


Several increasing size washers were used because this helps spread the load out further resulting in less fatigue or failure of the wood where the bolts pass through ... when using a carriage bolt two additional washers per end is typically enough.


This repair should add years to the life of your deck!

Posted 2011-09-06T18:11:01+0000  by Pat_HD_ATL
Not what you were looking for ? Try posting a question