What Type of Contractor Can fix Uneven Joists and Flatten Them Out the for the Installation of New Subfloor?

Updated November 24, 2020
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Question by Guest_9076799: What type of contractor can fix uneven joists and flatten them out the for the installation of new subfloor?

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Answered by JP: I pulled up a combination of carpet, linoleum attached to 1/4" lauan plywood, and poor condition hardwood on my first floor in order to have laminate installed throughout.

The installer came out and showed me that the subfloor was not flat enough to put down the laminate and had dips and rises off by more than an inch in places. I've pulled up the 5/8" T&G subfloor in one of the rooms and it's a real mess underneath - you'd have to see it to believe it.

I need a contractor/carpenter that can sister a few of the low joists to bring them up and plane down high spots on others. Also, since the subfloor was cut out, I need blocking installed to provide nailing ledges for the new subfloor.

I had a 'home improvement/handyman' come out and he looked at my like I had two heads, shrugged his shoulders, and told me it was way out of his league.

Please excuse the delay in my response to your question! My recommendation would be to search Angie's List under the "carpentry - unfinished" category. This category is set up to provide ratings and reviews on companies and contractors that specialize in or have experience with carpentry projects such as framing and structural wood repairs. Another option would be to search under the "remodeling - general" or "builders - home" categories, but these categories are a little more broad in scope.

I can provide information based on Angie's List ratings and reviews for companies in the "carpentry - unfinished" category in your area. If you'd like to see that, please let me know by submitting a new answer as a response in line with this Q&A. You can also contact a neighborhood specialist at 1-888-888-5478 or memberservices@angi.com. Good luck with your project!

Source: www.angi.com?CID=ANS

Answered by LCD: From your description, especially being up to an inch out of level, you definitely need a full-fledged carpenter to level the joists, possibly remove and replace the worst ones, and install a new subfloor before you can think about a finish floor installation. Your first thought, though, should be what caused this - was it extremely poor initial construction, do you have house settlement issues, lack of tiedowns and cross-bracing between joists, or water infiltration or condensation causing warping ? If those are the cause, you need to fix that first, otherwise it may happen again and ruin your new floor.

Answered by TLD:  I have done a lot of repairs of this nature, and even several repairs of repairs. As the handyman indicated it can be a very complicated repair. floor joists should not be that much out from eachother even on 100+ year old homes or even 100+ 2 story homes with 10ft. ceilings on each story, with a basement. Like someone said earlier, the cause is what you need to find out, the problem could be bigger than you can see in the one room. problems like this can easily be affecting adjcent rooms, walls, and because of the walls, even the roof!!!! hopfully yours isn't that bad. But what I wanted to add was it may seem to be cheaper to sister a board to the low ones and cut/plain down the higher ones this is a very bad idea from a structure point of view. What appears to be the high ones are the ones that are more than likely where they all are suppose to be, and even if they really are to high, plaining them down will weaken them badly!! On 'sistering' all this does is postpone the true fix of replacing the joist, and if needed adding peir and beam support if needed. Think of it like this: If you have a board that is 8 ft. long, supported on each end that sags in the middle, because for some reason it is not as strong as a new board, and you nail or screw and glue another board say 5 ft. long in the middle of the 8 ft. to make the middle even with the ends, all the weight is still only supported by the 8 ft board. You have not strengthen the board or floor at all!!! Something has happened at the ends of the joists where they are supported, or look along the entire length of the joist for a crack. If you can grab the bottom of the joist with your hand push and pull on it and if a peice breaks off you need to replace the entire board for the floor to hold up like it should. I've even had half the floor joist come up with the subfloor. just nailing more lumber to them will not last.

Answered by LCD: One comment on the sistering thing - the other commenter made a good point that sistering has limited uses - a bit more detail on where it IS productively used:

1) if the entire joist has failed or split through, then any "sister" fastened to it would need to be full-length and bear the full load, and the nailed or bolted-together old damaged one would then just act as a nailing strip for the overlying sheathing (because the new one would not be at standard spacing for sheet underlayment). This is commonly done, rather than replacing the damaged one (unless the old one is rotted so the rot could spread), so the overlying flooring does not have to be removed to allow for nailing the underlayment (plywood/OSB) into the new joist if it were put in the place of the old one. Allows for repair totally from underneath.

2) if the problem is a crack or split in one part of the beam (wherever it occurs) partial length sistering can work to "bandaid" that spot and properly done, with proper type and spacing of fasteners, can make the old joist or beam about as good as the undamaged part. Obviously, the more serious and long the damaged area, the longer the "sister" has to be - typically extending at least 1.5-2 times teh beam depth and sometimes on larger members as much as 5-6 feet (each way) past the damaged area, so sometimes the "development length" of the repair (how much "good" wood it has to tie into to transfer the load to and from the repair piece and around the damaged area correctly) can sometimes result in a near or total length sister or replacement.

3) another place where a type of sistering is useful though more commonly called a levelling firring job or subfloor nailing cleat, if the sagging beam/joist does not matter on the underlying level (like in an unfinished basement),, and is structurally sound. Commonly it is done using 2x3 or 2x4 or similar sized strip material (or sometimes metal angle brackets), to level out a naturally sagged but structurally sound floor by jacking/hammering the subfloor (but not the joist) up to desired elevation by first cutting through the fasteners down into the joist that hold the subfloor sheathing down, jacking/wedging the sheathing into desired elevation so it is suitably level, then putting in cleats or firring strips in contact with and glued/screwed to both the sheathing and to the sides of the joist, supporting the subfloor on those cleats which are then supported by the beam or joist - like putting little crutches under the subfloor sheathing. It is necessary to be careful doing this, that it is properly fastened to avoid creaks and bouncing (so usually construction adhesive glued AND screwed at close interval), and also to use correct length screws so they do not penetrate into the overlying flooring.

On the sagging issue - an old floor (typically over 50-75 years old to get this dramatic if there are not structural issues) can sag several inches in a normal household span and still be within design criteria. For instance, if the design standard for that floor is L/120 sag (much of which might be from creep, not deflection under load), that means a joist 16 feet long (a common 1/2 house-width joist length, with floor joists supported by foundation wall on one end and mid-house beam at the other) is some 185 inches long free span typically. An L/120 sag criteria would allow just over 1-1/2 inch sag and still be within normal criteria. A long full-house width joist or beam spanning say 24-30 feet (mostly in older houses) would be allowed a long-term sag of about 2-1/2 to 3 inches.

4) also sistering is used in cases where the original member was undersized or not the right structural grade, or the load is being increased (think hot tub, jacuzzi, water bed, major storage or book cases (especially if not along the wall), room-center real stone fireplace, etc) over the original design load. Then additional strenght can be provided by sistering full-length (usually) joists on one or both sides of the existing members.

Different building codes, different types of woods, and different construction years have different allowable sag limitations - some L/120, some L/240 (more common in modern houses), some L/360 depending on use of the building and other factors, but it is not unusual to see 2-4 inches of sag in older wood-framed houses, and I have seen as much as 12 inches in very old buildings with heavy (2-3 inch thick) hardwood flooring, just from long-term creep of the wood under little more than the dead load of the construction materials and normal household furnishings. A sag is not necessarily "bad" structurally (even though it may be aesthetically unacceptable) if it is not caused by rot, insect damage, cracking support members, or foundation failure.

Bear in mind that to correct sagging the sag has to be taken out (and sometimes over-corrected for to account for post-repair dead load sag and the "memory" of the old member wanting to revert to the sagged position) BEFORE the sister is fastened to the old member, so some professional judgement is called for in doing this. Also, for some limited types of repairs metal plates or pieces of plywood may be used instead of wood - especially for end-bearing cracking, some types of splitting (especially on laminated beams), cases where added moment capacity is needed in the center of a beam, sometimes over mid-span supporting posts, and for cases where an unallowed penetration by an electrician, plumber or especially HVAC worker damaged the member locally by removing material that is too excessive or the wrong place in the member.

Obviously, for structural as opposed to long-term sag repair, a Civil/Structural Engineer needs to evaluate the situation and design the fix - both to get it right, to be able to get a building permit in most areas, and to provide bidders and the successful bidding contractor with the details of what they are supposed to do.

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