I have a rotted joist in my floor that I can access through my basement, but is above several pipes. I could squeeze a 1x10 through the gaps but can't get a 2x10 to fit. So wondering if I got two 1x10 to fit, then affixed them together, would that have the same strength that a single 2x10 would have?
In theory, yes. But do consider the type of wood. Look online to compare the strength of various species of wood before you go this route. The reason for caution here is that there are strong woods that you would typically find good quality 2x framing members cut from. On the other hand the typical wide boards (1x material) that you see are cut from much softer and less strong types of wood.
Another thing to consider is the portion of the log that 2x beams and 1x boards are cut from. Study the wood's grain pattern on the end of the beams/boards before committing.
If your length is not longer than the lengths that you can get in plywood you may want to consider composing a beam out of lengths of plywood that you sandwich together in place. With enough layers you may even be able to stagger butt joints in the lengths of the plywood strips to achieve longer lengths. Glue bonding with fasteners to draw the strips together would be essential for this type of sandwiching.
It’s probably stronger if same grade...(whether they are fastened together or not,) because: 1) same cross-sectional area, 2) same area from same distance from neutral axis, and 3) more surface area seen during grading.
1) Strength of beam is based on several factors, one of which is cross-sectional area. If they match, they are the same strength.
2) Extreme Fiber in Bending: Because the two 1x10’s have the same surface area as the single 2x10 from the neutral axis, it’s the same strength.
3) Lumber is graded on what is seen and not seen by the grader. More surface area of small pieces of lumber can be seen in small pieces of lumber than larger pieces of lumber, so the grader is more certain of the quality of the wood and therefore has a higher grade strength. That is to say, the grader can’t see the inside of a large piece, so there’s a safety factor in the grading (and thus structural design) that reduces its strength.
Strength has nothing to do with how to fasten the two pieces of lumber together.
I’d fasten them together with minimal number of fasteners, because they’ll tend to “buckle” under extreme loading before the wider lumber.
However, if you’re fastening sheathing to the top, you’ll need to be more careful to fasten directly into the skinnier 1x10’s.
Yes, but it will be much weaker. Here. Get some sheets of paper. Kids' construction paper would be best, but any will do. Take 2 sheets at a time and do these things:
- one pair, do nothing
- one pair, draw dots on a 2” (50mm) grid and staple the paper everywhere there are dots.
- one pair, mix up a 1/4 teaspoon of Elmer's or any wood glue thinned with water, and brush it lightly across one sheet and lay the other on it. Press them together and let them dry.
Now see which one is the stiffest. The unaltered paper will flop like a noodle. The stapled paper will be stiffer, but the staples will "work", enlarging their holes and reducing stiffness. The glue-laminate will in hands down.
A great glue to use is West System epoxy with bonding filler added to it - not too much, a lot of the epoxy will soak into the wood and it won't take the filler with it. The wood will be pretty well-finished just by virtue of being the finer one-by stock; if not, a thin pass through a planer would not be uncalled for.
It might also pay to "triple" it.