joist crack repair question

hoping someone can answer this.
i have a few 2x10 joists that have horizontal cracks.
each joist has only one crack.
they all appear to originate from where the nails went in to secure the joist to the joist hanger.
these joists also have bridging in the center span.
my question is, if these cracks are stable over years and have not grown in length. is it safe to presume they were from the original construction, and not from being stressed ? (ie. heavy loads on top).
the other question is, if the crack originates from the end, where it's resting on the hanger, wouldn't a load on top, tend to compress the crack together ? (since the hanger is providing some resistance from the bottom of the joist).
and thirdly, what does "sistering" the joist actually do ? it would seem to be futile, since the sistered joist, would need to be in a hanger too to support the weight wouldn't it ? (i don't see how just lag bolting another 2x8, 2x10 next to an existing joist is going to help that joist bear any loads that are vertical - since the sister joist isn't resting on anything - just lag bolts - and the forces are still transmitted to the existing joist hanger of the existing joist).
thanks in advance for any responses.
basically i'm wondering if i should worry about those cracks or not - they are stable, and have not changed in size. the joists in question are also sorrounded by doubled up 2x10 joists, 16" away.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well Joe, I think you worry too much. It is very common to run into 2x10's and 12's with splits on the ends, especially douglas fir joists. Not that I like it, but you just have to use them and it has always turned out fine. There are probably several reason the crack doesn't compress together. First, there isn't THAT much weight on any given joist. Second, the joist usually doesn't wind up resting on the bottom of the joist hangar--it shrinks up off of the joist hangar and is actually held by the joist hangar nails working in shear. Sistering can make sense if you are looking for a stiffer floor, for example. I'd guess it is best to have the sister supported on its own (by a ledger or maybe a new double hangar that goes over both joists) However, it may be that the joist hangar on the orginal joist has plenty of capacity.
Are your floors real bouncy? If they are, there is a small chance the splits are something to be concerned about. But if you have no other indications that your floors are underframed, I wouldn't worry about it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

thank you for the replying.
yes, they *are* douglas fir joists.
no , there is absolutely no bounciness at all. the floor is rock solid.
i guess i won't worry about it, but i marked the end of the crack with a pen, just in case (to monitor if it grows). it's been stable for years, so i think you're right. it's probably nothing to worry about.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I would not worry since thay have been in for some time, are dry by now, and your floor is not "bouncy" On the other hand if you want to do sommething about it, I would cut plywood panels the same size as the joist (1/2" or..) support the joist (s) in question with a temporary support, glue and apply pltwood to either side of joist with nails....small. This way you do not add weight, and make the joist like a truss........3/8" will work for lighter weight, and even 1/4. You can staple these and use some good glue and clamps..... jloomis

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.