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Hey everyone. I have a 1915 cottage home that has 4 termite rotted out floor joist. To my surprise the joist are actual 3"x8"x12' joists. Since they don't make this wood anymore would anyone have an idea of what size joist to replace these with? would I need two double 2x8's and sandwich them together?
 

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retired framer
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Hey everyone. I have a 1915 cottage home that has 4 termite rotted out floor joist. To my surprise the joist are actual 3"x8"x12' joists. Since they don't make this wood anymore would anyone have an idea of what size joist to replace these with? would I need two double 2x8's and sandwich them together?

Do they need to be that size, 2 2x8s will be 3 inches wide but not 8" high.

if you need a full 8" you would cut them out of 2x10s.
How far apart are they?, Do they sit on a beam or wall or??
 

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Solid, full dimension lumber is always stronger than modern nominal size lumber. I can't say if double 2x8 will be enough for you since the variation is a lot about the lumber of your house's time and now.

Sandwiching a plywood makes the "beam" stronger. Maybe even using 3/4" plywood. CDX (exterior sheathing grade therefore made with bracing capacities), rip to 7.25 at the store, glue and nail. 8' section in middle and fill the sides. Any crown up.

If still in doubt, make a worry and guess free triple beam.:smile:
 

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I'm betting they did things differently in 1915 :wink2:

I'd sandwich two 2 x 10's together to replicate what you have. Notch them down to 8" at then ends where they sit on the foundation.

Working through the math of a beam equation you'll see that the height of the "beam" has much more impact on strength than the width. With sistered 2x10's you'll end up with a stronger end product than a single 3x8.

Fasten them together using Headlok fasteners.. here is a link: https://www.homedepot.com/p/FastenMaster-2-7-8-in-HeadLok-12-per-Pack-FMHLGM278-12/202618112
 

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@HenryMac
When you sister them, would it help to also use an adhesive as well as mechanical fastener?

Do you fasten them on each side or just one? What stagger pattern do you use? 2 on top of each other every 12 inches?

BTW, have you ever used ThruLok fasteners?

Dan

P.S. where in Central CO are you?
 

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@HenryMac
When you sister them, would it help to also use an adhesive as well as mechanical fastener?

Do you fasten them on each side or just one? What stagger pattern do you use? 2 on top of each other every 12 inches?

BTW, have you ever used ThruLok fasteners?

Dan

P.S. where in Central CO are you?
3 nails every 16", you only need them to be acting like one, there will never be a force working on one more than the other.
 

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@HenryMac
When you sister them, would it help to also use an adhesive as well as mechanical fastener?
I wouldn't

@HenryMac
Do you fasten them on each side or just one? What stagger pattern do you use? 2 on top of each other every 12 inches?
I would follow UBC guidelines for a built up beam: http://www.mcvicker.com/resguide/page014.htm

20d @ 32" (813 mm)o.c. at top and bottom and staggered, 2-20d at ends.

But instead of nails, I'd use HeadLoks.

@HenryMac
BTW, have you ever used ThruLok fasteners?
No
 
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