Part one of my summer reno project dressed up concrete, with a bit of insulation for frills. I called it unsexy renovations, but the climax did spew paint all over the basement, leading to a modest, post-exertion haze of satisfaction. Part two of the basement remediation has a less aesthetic outcome but is more exciting because it involves tools. And calculated carpentry.
A: Cracked Joist. Weak joists need support. Electricians, plumbers and ‘finishing the basement’ enthusiasts have not been kind to them. They have holes, are notched, checked1 and the bearing2 was poor for a few.
This particular joist bears on the header for the stair opening from the first floor to basement. It had the classic wrong things done to it, with a hole drilled for [I don’t know what, because it isn’t there any more], which could have caused the crack. This crack isn’t all the way through the joist (yet) so it’s not critical, but seems to me the best time to repair it is now, before it goes further. Also, there a gap between the header and this joist, through which I can see five sturdy nails. Not ideal.
I decided to sister the joist. This means attaching a new piece of lumber, of the same dimensions as the old one, to strengthen it. Some might question whether it’s necessary, because the crack isn’t all the way through, especially because of the renown strength of the old growth wood in the house’s structure. I figure there is no harm in sistering, even if it isn’t absolutely necessary.
To execute, all I needed was a little more than 8 feet of 2″x8″. True 2″x8″, if I’m going to match what’s there, but a nominal piece of lumber (1.6″ x 7.25″) would be easier and cheaper to find and install. And a joist hanger big enough for 2 2×8’s, at least one of which is really that big. Turns out there’s a hanger of the right dimensions made for engineered trusses, so I used one of those. And the right kind of screws to attach the joist hanger. And adhesive and screws to attach the sister to the original joist.
In prep work, I find I need to remove a bunch of nails sticking out from the subfloor above. Don’t want to press up on them, because there are ceramic tiles above that don’t need pushing on or the grout/tile may crack. Also tricky because the ideal tool, a sawzall, won’t fit in the space and this needs more precision than I can get with such a tool. Instead, I found a good pair of bullnose end-cutters (pliers) that snipped the nails off flush with the underside of the subfloor.
To clear a space for the new sister, some unused plumbing needed to go.
There was an ABS drain pipe and some copper lines running along the joist. Sawed, glued and capped the ABS.
The copper was trickier, mostly because it was tied into the plumbing for the rest of the house. This meant that if I didn’t get a good seal on the cut off pipes, it would either leak constantly or interfere with the main water supply. No margin for error. Cutting the pipes was easy with a specialized tool, called ‘a pipecutter’. Smoothing the cut with a sharp edge (I used an old chisel) and abrasive pad is suggested as a critical step. Then I capped with ‘shark-bite‘ end caps which made a sound seal.
So far, we’re living happily ever after, with the modified joist hanger (even with one the correct width, it needed cutting and drilling to adapt) attached with 1 1/2″ Simpson SD Connector screws.
The original joist and its sister were joined with construction adhesive, and #10 3 1/8 #RSS screws every 12″.
The relationship is working fine. The floor above, at the base of the stairs, has stopped creaking.
B.Floors rattle.
Textbook says floor joists should be cross-braced. The idea is to join each joist to the ones on either side to create a floor system that draws on the strength of all its components. Much of the cross bracing was removed from the main floor joists (visible in the unfinished basement). No one is around to answer why. It looks to me some of it was to install heating/cooling ducts3, some turning a central joist into a beam, others to install basement lighting.
The benefits of cross-bracing joists are less wobbly floors and less chance of sagging floors under heavy loads. This is technically cosmetic, although gives me an uncomfortable feeling when I walk across the floor and the china rattles. Most people might ensure the strength of the floor before setting up a pool table or grand piano in their home. Fewer people think about ordinary household items, that tend to be heavy, like full china cabinets, book shelves or weight sets. Still fewer people would appreciate that where heavy items are placed on a floor system can lead to concentrated loads on the structure.
But I digress. The point is that cross bracing joists is a good thing. So, I put a bunch of cross braces back into my basement ceiling/main floor.
The interesting thing about this task was knowing the angle the braces needed to be cut. I wonder how the carpenter did it in 1927? First, I measured one of the original cross braces. The angle was about 70 degrees. Then I found an app where I input the span of the joist (from 14 to 17″) and the height – I went with 6 1/2″, leaving 3/4″ top and bottom. Miraculously, these dimensions turn out the same angle I measured on existing braces. Gotta love it when new and old knowledge agree.
Anyway, the rest was just a bunch of cutting and getting dirt in my mouth and eyes as I held the braces above my head, levelled them and screwed them into the old joists. I drilled pilot holes, because I am concerned about splitting wood4. I used construction screws. Screws are for when you don’t want things to pull apart, which is exactly the idea with cross bracing – making the floor one by joining all the joists together in a network. Nails are stronger, especially the sturdy ones I can see in the structure of my old house. They are good to resist shear (mostly downward) forces. If the force on the joint is apart, you want screws, if the force on the joint is up or down, you want nails.
A detail I didn’t appreciate until I saw it on YouTube (sorry to whoever posted it that I can’t mention you – I’m trying to remember to keep track of where the good advice comes from), – braces should be ‘head to head, toe to toe.’ Meaning, the bearing on one side of the joist should be the same on the other. Intuitively this makes sense. Think about picking up a book between the palms of your hands. You put them directly opposite each other, otherwise the book skitters sideways.
The physics of cross-bracing is exciting, if you like that sort of thing.
1 Checking in wood is random splits that do not weaken the structural integrity of the wood beam or joist. This is different from cracks, that go all the way through a piece of wood and therefore relate to structural instability.
2 Bearing means the contact between structural pieces of wood (or whatever). In other words, the contact. If something is being held up by something else, there needs to be the right amount of contact. As an analogy, your hand might easily lift a 5 kilogram weight, but not if the only contact it makes is through your little finger.
3 IMHO, another good reason to leave hot water heat systems intact. Forced air ducts take up so much room and mess up existing structures.
4 As I watch videos about modern construction techniques, I wonder about firing a zillion nails into pieces of wood. Each fastener burrows in, disrupting the structure a little. But I don’t see a lot of concern about putting too many nails into wood. Shouldn’t there be?