Replacing rotted joists, true 3″x8″ rough cut, 15+ feet long, 100 years old. This was great wood, and it was a crime to let it get wet and rot.
Original joists were set into deep pockets in the bricks as the structure was being built, and I want to set the new joists into the same pockets. I plan to use sistered 2x8s, glued together in place, so I can put the ends in the pockets. This involves some cutting. I know not to put any cuts in the middle third of the new joist, and not to put any cuts right near the end(s), but is there a “best” place for them?
Obviously, I’m not a structural engineer.
How about two 2x8s, 12 foot long, one in each pocket, and two 2x8s, about 4 foot each, extending from each 12′ to the opposite pocket? All glued up, clamped, nuts and bolts at the cuts.
Over-engineered enough to install a large hot tub above it? Or am I kidding myself that sistering 2x8s in this fashion nearly doubles the load carrying capacity?
Replies
Sounds good to me. Glue them up with urethane glue.
If you want to go all the way you could use 2x10s and notch them slightly on the bottom corners. This would give you the full 8-inch height. OTOH, it might be better to have the height a little short and shim them on the ends with some sort of non-absorbant shim (plastic, tropical hardwood, etc), so they don't absorb moisture from the brick.
Hello, How high above the ground is this porch area? What happened to it, why so much water damage?
Remember the joists were that length for a "cantilever" effect supporting things together. Blindly bolting and gluing material together and notching the ends at will is not the way to go.
The keyways must also be water damaged and structural assessment is warranted in this instance. Save yourself some money and find out what it will take to support what you want and where you want it with some consulting. Try to find a impartial assessment.
No best place for notching and boring imho but if you really have a need of some type your right, the joist is divided into 3rds. Solid wood and TJI type could be the only types that should need any at all. (Although I have seen webbing cut out of floor truss's before. Bad practice.) Notching of solid wood at ends are max 1/4" of depth and I think that is only for the leveling of a floor seeing as the timbers were strong back then but generally not cut to the standards of what they are today. Notch factors for safety reasons should be max at the top of a joist 1/6th the depth Holes must be min 2" from top or bottom, max size1/3 depth.
TJI TYPE JOIST'S ARE MUCH DIFFERENT! Big holes in middle. Interior only.
Hello, How high above the ground is this porch area? What happened to it, why so much water damage?
It's not a porch. The beams extend from one brick wall to another. The house was neglected and the roof leaked -- but only over the back third of the townhouse.
This is a townhouse from an era when a townhouse was where you stayed when in town. Most of these people also had country estates or beach houses. These are mansions, not what we call a townhouse today.
Remember the joists were that length for a "cantilever" effect supporting things together. Blindly bolting and gluing material together and notching the ends at will is not the way to go.
The original beams appear to be old growth wood. They are incredibly heavy, and sistering two 2x8s won't begin to replace what was lost -- but it'll more than meet current floor loads. The only "support" that the beams provided appears to be compression of the brick walls, as the beams extend all the way through each wall.
I know what a cantilever is, but I do not see how it applies to my situation. Perhaps I was misunderstood. Or perhaps I misunderstand you.
The keyways must also be water damaged and structural assessment is warranted in this instance. Save yourself some money and find out what it will take to support what you want and where you want it with some consulting. Try to find a impartial assessment.
The brick walls are quite dry and stable. And no damage to the plaster, embossed wallpaper, or paint below. But I'll check them for deterioration.
No best place for notching and boring imho but if you really have a need of some type your right, the joist is divided into 3rds. Solid wood and TJI type could be the only types that should need any at all. (Although I have seen webbing cut out of floor truss's before. Bad practice.) Notching of solid wood at ends are max 1/4" of depth and I think that is only for the leveling of a floor seeing as the timbers were strong back then but generally not cut to the standards of what they are today. Notch factors for safety reasons should be max at the top of a joist 1/6th the depth Holes must be min 2" from top or bottom, max size1/3 depth.
Of we go to 2x10, we may have to trim them a bit at the ends, but 2x8 should support the hot tub and be easier to level with shims. And with more than 12 feet of room between the floor and the bottom of the new beams, we should be able to run everything above the ceiling without any holes thru the joists.
Thanks!
I vote that you just go ahead with your idea. If you leave the floor in place it will be next to impossible to get a single beam into the pockets. The important part of this built up beam is not really the joint but the length of the boards where they overlap. This length should be as long as possible and should be well fastened. I would simple use 10d nails 3" oc, but other combinations of nails, bolts and glue would also work well. Don't be afraid to overdo it. If you have any concerns about strength, use 2x10's. The added depth will more than make up for the lower grade of the replacement wood. If I had any concerns about future moisture I would use treated lumber.
It probably would be a good idea to add a piece of, say, 3/4" plywood across the joints, since the actual joint locations will be the weakest part.
If you use good glue, a few dozen nails (16-20d, and clinch the ends where they protrude), and 3 bolts each side of each joint, the boards ain't coming apart. Your biggest worry is to not "over fasten" it and weaken the lumber, so make sure all the fasteners are staggered.
The biggest question is simply whether doubled 2x8s are sufficient here. 16' is a long span for 2x8s.
I don't think that you have to worry about "overfastening". I once thought that was a problem myself. Then we built some trusses in place using 8x8's with 2 layers of 3/4" plywood on each side of the truss as gussets for the joints. The engineer had specified 60d nails on 2" centers. We predrilled these nails. Before we took the job (It was in a church attic as a support for a future bell tower, still unbuilt after 20 years) we tested this out on a small piece of 8x8 fir. Rather than weakening the block the nails made it just about indestructible. We proceeded to nail approximately 6000 of these nails with a sledge hammer.
I'm not an engineer, but I think you should consult one.
If I understand correctly, you want to span 15' with 4 pieces bolted together, none of which span completely between the bearing points. You say that you will bolt at the joints... I think (once again, I'm an armchair engineer) that you will need more than just a few bolts at the joints to handle the tensile and compressive loads. I'm sure this can be done, but I would definetely want some pro advice.
Another thing to remember is that you are replacing 3x8 old growth lumber with 3x7-1/4" new lumber. I'm guessing that you will lose bearing capability. Once again, I think the person to ask would be a professional engineer.
BTW- where are you?
Jon Blakemore
If I can find a structural engineer that'll field questions, I will certainly ask him or her about the replacement beams. I guess I'll have to save up a few questions, to make it worth my money.
And I am painfully aware that I'm losing strength by replacing these wonderful old beams, but they're in rough shape, and I don't know where I'd get comparable old growth beams or how to put them in.
Open to suggestions.
How bout a picture? So I read the thread and here's what I'm thinkin, Where are you at? It sounds like lots of work so that doesn't seem to be a big problem. How bout sourcing the replacements from a mill to match. Then mine the beam pockets to allow new to be slipped in place/ full length with no splices. then replace the removed brick to restore the structural bearing points. Also the need to calculate the loading on the brick and how much surface you need at ends of joist. Say if the original sat on 2 courses of brick-8" on each end and you could take off 4" on each end to slip them in and create a larger bearing plate to make up for the shorter joist?
The way you can get joists of comparable strength today is to find a mill that deals in B.C. Fir (Douglas Fir) and order custom cut 3x8s rough sawn and not planed. I have exactly the same joists in my house, except they are 20 feet long; they were milled from new wood for the rebuild in 1995. I also put in 4x8 and 6x8 beams 30 feet long at the same time, from the same mill. No problems.
To put them in, you'll have to open up the joist pockets on the outside of one wall so you can slide the joists into place. You can either slide it in completely from the outside with a crane, or manhandle them from inside so that you slide one end through the wall far enough to clear the other end to approach the pocket on the intact wall, then slide it back until it seats. I would suggest going with the second method; a 15-foot-long 3x8 isn't that heavy and a couple or three people will probably have less trouble handling them in a tight place than would a crane operator. (If getting them inside the house is a problem, you might have the crane send them in through a window--a much bigger target--then take over with method #2.)
When all the joists are in place, re-brick the outside of the joist pockets and away you go. That's the nice thing about brick--it's modular....
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
With no masonry experience, is "re-bricking" above the new joist DIY or contract work? Laying brick never seemed that complicated, but if there are tricks to doing it well, I don't know the tricks.
Rough and finish carpentry, sheetrock, etc, but no masonry experience.
Bricks,... all you need to know is to keep them straight, level, and true, use the right motar and chip off all the old before restacking the brick back as it was..
It should be relatively simple to keep everything level and straight from the short amount a brick pocket will contain..
If there is a trick it's in making the motar the correct consistancy.. Think of real stiff mashed potato's
I think you should check with the builing inspector. He will be ulitmatly responsible for giving you the OK. Could save you from doing the work twice.
I also saw a This Old House episode where they replaced beams in brick. Silva did a "Fireman's Cut" on the end. This was to stop the beam from falling on a firemans head. No more details.You get out of life what you put into it......minus taxes.
Marv
Fifeman's cut is used to prevent the WALL from falling on the firemen. See, joists set into masonry pockets tend to rotate when having structural failure, the fulcrum being the wall edge. This rotation causes the end inside the pocket to behave as a lever and therefore lift the wall above. By champhering off the upper corner of the beam you can prevent this from happening.
F.
thanks frankie.You get out of life what you put into it......minus taxes.
Marv
Thanks from me, too. You taught me something tonight. It was worth dragging my aching carcass outta bed this morning, LOL!
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Use a 'fat' mortar; one with lime added. Makes it sticky. You can also use concrete glue like For the small amount you'll need you'll be okay with a quality pre-mix product. Follow the instructions on the bag scrupulously, then realize that it's like your grandmother trying to tell you how the bread dough should feel when you've got 'enough' flour in it....
Practice with a few dozen bricks before hand. Build a little something or other, let the mortar dry, then try to knock it apart. If you have to work hard, you win. If not, hire a mason for that part of the job. A speciality subcontracted out is no shame. But watch the pro while he's there. Think of paying him for two things: 1, the job. 2, the lessons. Give a nice tip if he goes along with the gag....
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Brick as normal. Shim joist into place. Keep shim bearing dimension as small as possible. Now fill in the space between the joist and the brick with non-shrink grout. This is not the same as the grout used for tiling. It will be available at most masonry suppliers.
You can use screw-jacks instead of shims but then you will need 2 screw-jacks per joist per day/ night.
F.
I've done something similar in the past. I sistered 2x10's on a pair of horses, 12d nails and subfloor adhesive. I had a 14'-0" span that sat on rubble walls with a brick facing. I found that I could install the joists easily by removing top layer of brick and then place joist. Brick was replaced afterwards. Not sure if this would work in your case, though I guess it might. If this would work I would go to 2x10's ,cut notches.
I suppose you know you may have to shim the joists after the first heating season unless you you engineered joists.Engineeed joists are deeper so you may have to remove some masonry.
mike
Be sure to leave some air space around the ends in the pockets.
"Beams" are now required to have air space so they won't rot where the go into the pockets.
Without knowing the joist spacing, one cannot say if your plan is sufficent, but I'm fairly certain (i) you're not doubling the load carrying capacity (at least without also gluing them togrther and (ii) bear in mind that a 15' span for select 2x8 douglas fir joists 12" OC will only buy you 40lb/sq ft dead load - put that hot tub on top and I'd be wondering how long before it becomes a sunken hot tub {G}
You could also have a welder fabricate some hangers--tabs that insert into the beam pockets and stirrups to hang the new joists. That way you could use joists that span the distance between the interior faces of the brick, without fooling around splicing the joists, and without worrying about trying to isolate the wood from the brick.
Yeah, that's a pretty good idea. The hangers could have a drop on them so you could use 2x10s. Would likely be quite a bit more expensive, though, depending on where you live and who you can get to make them.
If that's the case, then why not just attach a ledger underneath the beam pockets on each side and skip the hangers altogether? perhaps put some type of bridging between the joists against the end walls to hold them upright and solid....
A lot depends on the stability of the brickwork. Attaching a ledger might compromise it, or it might be difficult to attach the ledger.
Let me toss another issue into things.. I suspect that the joists rotted because they were set into the pocket formed in the bricks..
The reason is that all masonary will wick up moisture from the ground, any wood set onto that moisture will tend to rot, if you do reuse those pockets, make certain the wood is permanetly seprated from the masonary. you could do it with copper or if you only want things to last a short time aluminum..
Instead of TGI's I'd have a local sawmill cut me some white oak joists.. you can get them to match the size and white oak is a natural decay resistant wood that is incredibly strong..
I pay 80 cents per board foot for white oak.. if you need 3x8's then then it would cost you $24 for each joist
I know that rough white oak beams are available. I've seen 84 Lumber trucks with a load of them. They're used to line trenches and such for sewer work.
If I went with rough sawn white oak beams -- or douglas fir -- how long would I have to let them dry before I put down the underlayment for the floors? A 3x8 must take a while, but they'd shrink some (giving them some breathing room in the pockets). We'd like to move the owners in sometime later this year.
I have to assume that white oak is at least as strong as old growth pine.
Most houses are built with frairly green wood, either SD19 or KD 19 (that means it has 19 percent moisture when it arrives on site.. Depending on the season the tree is cut it may have between 20 and 40% moisture while it's growing..
While it is true that dried wood gains strength, they rate wood according to it's relatively green condition since that's the way most houses are built..
Put the timbers in place when you get them, they are plenty strong and will dry slightly while shrinking a bit.
If you wait and dry them out you will have slightly tighter nailing/screwing contact but at the cost of a great deal of risk regarding twisting, bowing, warping..
It will take about 5 to 7 years in your house for them to completely dry out!
Old growth Oak/ Pine etc. is still possible.
My house is built with a lot of Old growth white Oak, it was growing before this country declared it's independance, (I counted growth rings) growing on the side of a hill where it was too difficult to harvest untill recently..
Thus you do not need to eliminate the possibility of old growth. You'll just have to be very carefull and work with a logger.
By the way The UBC or any book does not give any better load capacity based on old growth.. (too hard to police) If you get a tree that is grown on the north side of a hill it will be a lot tighter ring count than one grown on the south side.. However they rate a tree based on it's specific gravity and tight growth rings affect that.. For example, Swampy white has a low rating of 9,900 PSI with a high rating of 17,700 PSI the differance in specific gravity is the higher rating has .67 specific gravity while the lowest rating has .60 specific gravity..
Enough trivia about wood, here are the numbers regarding strength (in the only direct that is affected)...
there are 16 varieties of pine recognized and it varied from a max loading of rupture at 4900 PSI for sugar pine to jackpines max of 9000 psi
Now they may have what are called western white woods and there the strength varies evan more..
White oak varies from a low of 7200 PSI for the bottom rating of Bur oak to a max of 17,700 PSI for swampy white (live oak is considered a seperate species)
Thanks to everyone for their input. I learned a lot!
I'm moving to sistered 2x10s, scarf jointed, with fireman's cut.
If I can track down rough oak beams for a reasonable price, I'll try removing the bricks and placing one end into a pocket, dropping the other end into its pocket, then re-bricking.
Still wish I knew as much about wood as FDAMPIER5 does.