We recently bought a 123 year old house. The attic had been finished with a master and ensuite about 10 years ago. About a week after moving in the attic shower was leaking and the bedroom ceiling below it fell. A plumber came out and sealed the leak in the shower. Since we had a giant hole in the ceiling revealing the plaster and lath, I decided to have the entire ceiling and old insulation removed. This revealed that the attic was built on 2×6’s with occasional 2x4s sistered to help level the floor above. The 2×6’s are old and is true 2″ x 6″ lumber. The bedroom underneath with the exposed ceiling is 14ft x 13-16ft.
My question. I’m concerned that the attic is supported by 2×6’s every 16″ on center. This is our first single-family home, and my experience with these sorts of things is nearly non-existent. Since the ceiling is exposed, should I sister 2x6s end-to-end with the current 2×6’s, should I add 2×6’s in between the current 2x6s, do nothing?
I would love to do whatever possible that does not require demo’ing the bathroom above. It’s awesome and one of the reasons why we bought the house.
Any advice would be appreciated.
Replies
If the floor is bouncy sister the existing 2x6 with another. No need for ones in between because the 3/4” osb can handle the 16” between each joist just fine
Does it need more 2x6s to increase the load capacity?
Only if the floor is bouncy. The poster mentioned a bathroom above. Is the tile cracked? Is the floor bouncy? Drywall or plaster cracking? If not it’s ok. If you want to make it stronger sister it. Or even better make a mini box beam. Run a 2x6 to the other side of each wall stud and block between the old and new so the sistered floor joist connects to the wall stud.
You should consult a structural engineer as the maximum allowed span for 2x6 joists, 16 o.c. is about 9 -10 ft. depending on the type of wood. The 2x4's to "level" the floor above are not adequate. Sistering 2x6's will not solve the problem
With current 6" framing height, at best, you can achieve a doubling of floor stiffness and strength, by completing the sistering as better-than added 2x6. Place longest-possible 2x3s below the leveling 2x4s. Shim between the 2x4 and 2x3 if you wish, to make a flat and level new ceiling plane. The new plane might be with 6 1/2" beam height. Make the beam height 7 1/2" OR MORE, by adding 2x4s instead of 2x3s. Prefer 2x4s for availability in the full length of the room. Then bridge the 2x4s and 2x3s with rips of quality 3/4" plywood as composite-beam webs. Bond the plywood to the sistering 2xs with great density of 3" deck screws.
See continuity with my practice of Strong Attic Floors, shared in several blog posts. Search: " energyconservationhowto + strong attic floors". Include the quotes in your search. There are only two results, for my search with Google. The first is a post with title Strong Attic Floors, concisely describing the method. The second is my post of the method at InspectionNews.
At the concise blog post, pick Label: Strong Attic Floors, to find all related posts.
At the Inspection News post, read on to comments of salty old home inspectors, who know only sistering. One, detecting that I live in Oregon, suggests meanly and wrongly that I am a pothead.
In preparation to join this conversation, I offered this statement of modesty in my credentials, to Fine Homebuilding editors:
Please know that sistering is an inefficient and questionably way to add strength. The sistered material, not coupled to supporting walls, is significant added weight, and may just add to over-stress of original materials. I practice the construction of grand box beams that are not much in need of explanation, as sensible. A beam is strengthened as the cube of beam height and only at best times-two with sistering. An attic floor is freely thickened with advantages in protective covering of insulation, wiring, plumbing, HVAC and more. Thickened times two, strength in increased times-eight. There are rules to be applied in the nature of mandatory connecting webs and of fastener dimensions and placement-density. The pinning can be with bolting and washers for maximum security. I have in the past been a licensed Professional Engineer but can't serve as a portable author of the method. My alma mater, Oregon State University, BSME 1966, in several prospective departments, has not stepped forward in my service.
Find important confirmation of public interest in the problem, in writing by a respected United States Senator:
US Senator Jon Tester, (D) - MT
In his book Grounded, pp 116 - 117:
For many years before I got involved in politics, I used to solve math problems in my head during the long days of driving back and forth on farm equipment. As the powerful combine engine rumbled under me, I’d give myself long multiplication and division problems to figure out without paper or a calculator. How many square feet in a square mile? (27,878,400.) How many square feet in an acre? (43,560) How many acres in a football field? (l.32.) So how many square feet are in a football field? 67,600.) I solved problems just to see if I could, and I did because I had the time and mental capacity to do it. And then I moved on to more practical problems. When a wooden stringer above my butcher shop started to sag, I had to figure out how to replace it. For years that stringer, a sixteen- foot piece of thick wood in the attic, held up the weight of hanging sides of beef, and it Finally started to show its age. But the only way to get a new piece of wood into the attic was through a small vent in the side of the shop. If I slid a new sixteen-foot stringer into the vent, I wouldn’t be able to swing it into place in the attic, because there were too many trusses in the way. I finally figured out that the only way to replace the stringer required pushing two twelve—foot boards through the vent and using wood glue and bolts to groove them together in- side the attic. It’s not like putting a man on the moon, but I finally solved the problem while operating a combine. Thirty years later, that stringer is still holding strong.
I just requested Testors book from our library to figure out the post above.
I apologize for leaning upon Jon Tester's credibility. His challenge is an example of the problem of an under-size beam, but not of my solution. I think it is two-piece sistering. Two twelve foot pieces with eight foot overlap in the sixteen foot space. Lots of bolts and glue. I don’t understand the constraints. Perhaps a better solution in creating a taller beam, is possible..
Now offer a specific solution of the original post: Employing the AWC Span Calculator, judge that the ceiling framing should be 2x10. (https://awc.org/calculators/span-options-calculator-for-wood-joists-and-rafters/)
Build-down such framing , with the attached suggestion of arrangement:
That of the graphic allows fussing the ceiling level. More likely you will choose quicker assembly 9.5” tall, without the 2x gap for shimming.
Are you suggesting that I need not get the book to understand your post ? I enjoy Testers discussions I’ve seen on tv.
Just got the notice its in, I think I’ll take a look.
Got the book. Went to 116 and 117 and I see the story of driving the farm feilds and figuring about things to the max. Admirable.
I initially thought you farmed and spent a bit of time politically.
Sorry.
For those who won't link to my blog energyconservationhowto, here are attachments giving examples of my everyday use of Strong Attic Floor methods, placing attic ladders. The examples are from one job, an interesting challenge of placing a ladder diagonal to found attic flooring. The ladder frame itself as a unit, bears upon surrounding walls. Cut floor joists are supported by the super-strong ladder frame. Attic plywood flooring, well screwed to the framing, completes the box beam assembly.
I thicken the floor in a box beam array, building upward. Attic volume commandeered was needed for proper floor insulation, best protected by the flooring crucial to the added floor strength. The offered solution in this conversation builds downward in volume that will not be missed in an old home with high ceilings. Knock off the window capitals maybe, and the room appearance changes little. Learn to use the contained volume for good purposes as in new/ better HVAC duct pathways and lighting/ wiring chases.
If you were framing the floor today following the IRC span tables you could span 11'-10" with Dfir 2x6s with a dead load of 10psf and a live load of 30psf (bedrooms/bathrooms). As you note the joists are full 2 in. x 6 in. so you'd get a span bump for that. Plus due to the age I'd guess that the lumber is old growth which is stronger than the lumber we get today - another span bump.
My guess is that the joists are adequate just as they are. You may notice a little deflection in the floor as you walk across it - and that's natural. It doesn't mean the floor is in danger of collapse.
If you want to stiffen the floor and ensure the joists aren't overspanned according to today's standards you can add one additional 2x6 joist alongside each existing joist. Since the new joists would be shorter in depth than the existing joists it will be pretty easy to roll they upright once you lift them on top of the top plates.
You'll have to cut the new joists shorter than the original joist length by the width of one top plate - that way one end can be pushed over one plate and out to the exterior wall sheathing while the other end clears the inside edge of the opposite wall plate. When you shift the joists back over the opposite wall there should be enough joist bearing on each plate of at least 1-1/2 in. which is the minimum the code is looking for.
I would raise the joists up to the underside of the sheathing and shim between the bottom of the joists and the top plate at each end. Apply construction adhesive to the side of the joists that will sister against the existing joists and nail or screw them tight together. The adhesive will help reduce the chance for squeeking .
If the joist density at new-construction had been doubled, 6 1/2" spacing between joists , the floor would be twice as stiff and strong. Sistering new 2x6s can't directly carry any load. If they don't carry load, they have very indeterminate benefit depending on nailing, while adding a bit to the weight carried by original true 2x6s. Sistering is dumb. Benefits can't be computed.
What good is any rationalized "span bump"? Safety is in affordable over-design measures. Want a large visible factor of safety. My solution which may readily increase strength by times-three with modest taking of space-below, is not to be dismissed. We really need that here. A sixteen foot span might be carrying the weight of a filled bathtub at midspan. Real 2x10 strength is needed unless we know more about forever usage of that bathroom above.
Why can't "Sistering new 2x6s can't directly carry any load" ?
A double beam can span greater lengths than a single ply beam of the same size and a triple ply beam can span greater lengths than a double.
By adding additional joists in a given floor area the load carried by each joist is reduced resulting in greater individual joist span since each joist has less load on it.
Where sixteen foot spans demand 2x10, the strength multiple is 1.5/2 * cube of (9.25/6). The multiple is 2.7. Again, if the structure had been built with more old growth real 2x6, a multiple of 2.0 would come with 6 1/2" between joists. A sistering new crummy 2x6 aiding only through nail attachment might give a multiple of 1.5, something substantially less than 2. No one can calculate the number.
I don’t know what the calculation factor is but I can tell you that a doubled joist is stronger than a single one, just like a doubled header is stronger than a single ply header. On top of that if Mike Guertin says so it’s definitely true. He’s one of the most knowledgeable carpenters out there.
this response may be a little pedantic.
if you nail or bolt a piece of wood to an existing joist, then you are fastening to the joist, not to the floor sheathing. say you cranked up the new piece flush with the top of the adjacent joist [which is probably sagging]. typically this piece gets fastened to the existing joist, but is rarely screwed to the floor above. As soon as MC of the new member goes down to EMC, then this new piece loses contact with the sheathing above and thus isn't carrying load directly. the load transfer is from the existing joist, through the shear-loaded fasteners to the new stiffening member. i believe i've seen specs where the new sistering member has 1/2" clearance at the top, accounting for inconsistencies with the existing system. however, real world there is no difference.
I don’t understand the constraints. Perhaps a better solution in creating a taller beam, is possible..
This seems to be repeat of my words, hopeful of a response. I think it would be fun if Senator Tester joined this very important conversation. I have posted mention of this at the Senator's web site.
Hello Tiny,
My name is Mark Petersen. I'm a Tech Editor here at Fine Homebuilding. Would you be okay if I run your question, and the answer provided here by Mike Guertin, in the magazine's "Ask The Expert department?" If yes, I would love to get the original hi-res photos to run with the copy. Could you please email them to me at [email protected] I would also need your real name (or alias if you prefer:) and the city where you live. I think this topic will be helpful to a lot of folks in our audience. Thanks Tiny!
Mark,
Good thing you aren’t going to print this whole encounter.
Mark,
Would you please get one of the site managers to knock it off with the annoying pop-up ad that appears with every damn page change?
Once is quite enough.
Thanks
This should be fixed! Pls let us know if not!
Sorry for the delay.
Seems to be working!
Thanks!
consider sistering sheet metal C joists to the existing wood joists.https://www.bmp-group.com/docs/default-source/literature/c-joist-span-tables-and-detailsb7dd4bcfd1de6413ac21ff00002d9a3e.pdf?sfvrsn=81032fe2_0
Just my two cents but it would be helpful to clarify if the house is balloon framed or not. If it is there is no top plate the floor joist is nailed to the side of the stud. If you sister the joist, the sister will run into the stud and has no bearing. It will make the original joist stiffer but if you slide the sister over and attach it into the side of the stud and block the space between the two joists every 2’ you create a mini box beam that in my opinion is stronger because there is bearing for both the original joist and the sister.
I’d be curious what the engineers and an expert framer like Mike Guertin says about this. Is this box beam assembly stronger because it has better bearing into the wall studs, or is glueing and screwing two floor joists together providing less deflection even though the new sister joist has no bearing?
Consider framing type especially if it is balloon framing. When sistering slide the sister over and attach it to the stud's side and block between joists every 2 feet. This creates a mini box beam for added strength. Expert opinion like Mike Guertin's, can clarify if this beats gluing and screwing two joists together even without sister bearing..
That's good, To strengthen your attic support without impacting the bathroom above I recommend consulting a structural engineer or an experienced contractor.
To strengthen your attic support without impacting the bathroom above I recommend consulting a structural engineer or an experienced contractor.
I will build a list here, of related conversations at this Forum.
This is found by Google search "reinforce a wood beam by making it taller," hoping to find more of my approach, posted October :
https://www.finehomebuilding.com/projec, t-guides/framing/how-to-reinforce-2x6-ceiling-joists-to-handle-heavy-loads
The same words search directly at Fine Homebuilding adds this conversation:
https://www.finehomebuilding.com/forum/4-ply-2x12-beam-sag
Here is another related conversation:
https://www.finehomebuilding.com/forum/how-to-reinforce-2x4-attic-floor-joists-2
In a new posting at Fine Homebuilding, The Story of Habitable Attics, https://www.finehomebuilding.com/2023/09/13/the-story-of-habitable-attics https://www.finehomebuilding.com/2023/09/13/the-story-of-habitable-attics?oly_enc_id=6122E5655590G8K, a sistering 2x12 is the only solution offered as fix of inadequate 2x6 floor framing. Span length isn't enumerated. Handling a bunch of very long 2x12 is beyond reason. The span sister must be one-piece and notching for obstructions is forbidden.
I am certain there are more conversations in this. I will be back to add them here.
That's good
I just learned at Wikipedia, what a master ensuite is. So, Tiny, your wonderful new home has a master bedroom integral with this attic bathroom. The 2x6 framing under that bedroom, surely, is also inadequate. Then, gut other broad ceilings below and build-down as 2x10, as I offer. In the painless 4" sacrifice of room volumes below, find many opportunities for modern amenities. Serviceably improve lighting, ventilation, HVAC ad more. The build-down might leave quite a bit of accessible space at the periphery.
Find an interesting example of this box beam construction that enabled beautiful placement of an attic ladder diagonal to attic floor framing:
http://energyconservationhowto.blogspot.com/2023/09/an-attic-ladder-installed-diagonal-to.html
I get what you are saying but building down doesn’t work. If it has modern framing there is only 5.5” between the top plate and the bottom of the subfloor for the attic. How would you get a 9.25” beam in 5.5” of space? If you notch it it’s only as strong as a 2x6. If it’s balloon framed as I suspect there is a 1x4 that in notched into the wall studs that supports the floor joists. To install a 2x10 you would have to cut this out which takes away support for the existing floor joists. It also weakens the stud and you would be attaching the 2x10 right at the notch further weakening it with your fasteners. In my opinion this makes the whole assembly weaker not stronger.
I have revised the posting you address, to clarify my proposal. Added graphics now show my intent in relation to the balloon framing details you provide. Others might come up with better ways to make good use of the volume surrendered at high ceilings.
I’m not trying to knock your idea. Balloon framing is almost exclusively what I deal with and it’s tricky. Just trying to give my 2 cents to the conversation. I’ve thought about adding taller joists myself and then when tore out all the plaster and lath I did a lot of head scratching trying to figure out how to make it work. Just trying to save someone else the trouble. I enjoy seeing other people’s approaches and ideas. Best, Primitive
I don't find building up difficult at all. Building down will be no different. In fact, I have an excellent building-down example. A bathtub drain often interferes with floor framing, as here with a dangerous carve-out of a 2x8 floor beam. See my blog post titled Strong Attic Floors, http://energyconservationhowto.blogspot.com/2012/11/strong-attic-floors.html. Call the fix a box beam. Don't we all know and trust, box beams? Adding beam height is such an obvious solution.
Not sure if you have moved ahead with sistering, as suggested by Mike G, but if you have issues with that method or want additional peace of mind, you can attached 2x4s horizontally to the underside of your joists LIBERALLY Glued and Screwed in place. In effect you are creating a site made I joist between the upper subfloor and the lower 2x. I have a large span kitchen floor that was bouncy before I tiled. Used the method above and have had nary a cracked tile even with 20+ people trouncing around the kithen during parties...and yes my kitchen is THAT big....its over 20' in each direction and holds a 10' table for 12.
This method works only in new construction, then with wasteful thickness in a site-built I-beam. 2x flanges in an I-beam are fine, and enable the bonding you describe. You can't screw into the edge of an OSB web. With 2x on-flat webs, I would use many deep-penetrating screws.
As a repair where only one flange can be applied, the existing flooring or whatever likely can not bear loads in tension or compression. The existing "flange" only adds strength in resisting failure as a roll-over. Beam strength is increased only as the combined beam height, cubed. That is times-2.6 if bonding 2x on-flat, to upright 2x6. If span tables call for 2x10 and found framing is ordinary 2x6, the wanted strength multiple is (9.25/5.5) cubed, that is times-eight.
Please see in my build-up example of a notched 2x8 under a bathtub, that the notch is not at all repaired with an added 2x flange bonded beneath. The repair does nothing.
I am by far not an expert but have had to deal with very old uneven cut rafters and joists. With a similar span I decided to do a full sister on rafters (I replaced all the joists) but to add strength I scarf joined the sisters. Used in shipbuilding a scarf joint allows for longer spans but also retains between 65% and 90% of the total strength of a single board depending on the length of the scarf.
You can put in the scarfs with or without wedges depending on how much strength you want.
If you want to add strength and support, sister and for the full-length and scarf so that it is easier to get the entire length in over each supporting wall. I used a full length piece of lumber and then was able to make the scarf match by cutting both sides at the same time.
Also, if you want to address any uneven ceiling in finishing before sheetrock fir it down and level.
Insulation and sheetrock coming next week.
Gave me some extra piece of mind in addition to the sister on the overall length, in my case it is snow loads.
To understand scarfing, Google "Used in shipbuilding a scarf joint allows for longer spans but also retains between 65% and 90% of the total strength of a single board depending on the length of the scarf."
Find an education at Forestry Forum.
A beam may be lengthened while preserving strength as a single-piece beam. Do the extension where stresses are least, near end support. So that is how a sister can be fit in with real doubling of strength. Times 2.0. With this, realize the strength multiple for most sistering is less than 2.0. There are standards for sistering. And if doubling the strength isn’t enough, another solution must be found.
Would you please get one of the site managers to knock it off with the annoying pop-up ad that appears with every damn page change?
We’ve tried but with the change in ownership and the retiring of our known friends in places of power………..