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Can I Replace Floor Joists Myself?

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    Replacing a floor joist is a major undertaking. If you have no carpentry knowledge, you should hire a professional carpenter to do the project. Replacing a floor joist incorrectly may compromise your home's structural integrity, jeopardising both your safety and its value. If you decide to replace a floor joist on your own, make sure you follow all safety procedures.

    Separating The Floor Joist From The Subfloor

    Find A Replacement Joist That Is The Same Size As Your Floor Joist. 

    Measure the length, width, and height of your current floor joists with a tape measure. Then, locate a replacement floor joist with the same dimensions.

    • Make certain that you purchase the identical type of joist. Buy an I-joist if your floor joist is an I-joist, for example.
    • If you're not sure what sort of joist you have, photograph it from several angles and show it to an employee at your local home improvement store.
    • An I-joist is constructed up of three pieces: a horizontal piece of lumber on top, an identical piece of lumber on the bottom, and a centre web in between, which is typically made of plywood.

    Cut Out The Plywood Web With A Circular Saw If Your Joist Is An I-joist. 

    Detach the web from the top flange with a circular saw (the lumber attached to the subfloor). This will make it easier to remove the top flange away from the subfloor.

    • Wear safety glasses to protect your eyes from flying sawdust and woodchips.
    • Wear a dust mask as well to protect your neck and lungs from the wood particles.
    • After cutting the web away from the top flange, place it somewhere it won't be underfoot.

    Detach The Floor Joist From Any Walls Or Wires. It's Nailed To With A Saw. 

    Cut portions of the floor joist away from the walls with a reciprocating saw. If the saw does not function on its own, pry the joist away with a hammer or crowbar.

    • When using an electric saw, always wear protective eyewear.
    • Before you start cutting wood, make sure you have a wood-cutting blade in your reciprocating saw.

    Pry The Floor Joist From The Subfloor With The Back Of Your Hammer. 

    Begin by using a reciprocating saw to cut away a tiny 1-2 in (2.5-5.1 cm) part of the floor joist. This will result in a weakness. Then pry and cut the floor joist away from the subfloor with pry bars and your reciprocating saw.

    • To help open the gap between the floor joist and the subfloor, use the back end of a hammer or crowbar.
    • When sawing through wood, use a wood-cutting blade, and when sawing through nails, use a metal-cutting blade.
    • This is a challenging task that will require time and effort. Be patient and try out different tools to determine which ones work best for you.
    • Once the joist has been entirely separated from the subfloor, store it somewhere out of the way.

    Installing The New Joist

    can i replace floor joists myself

    Apply Construction Adhesive Along with The Top Of The New Joist. 

    Just before mounting the joist, apply the adhesive. The adhesive should then be applied to the whole length of the joist with a caulking gun.

    • Make sure to apply the glue before installing the joist. When you move the joist into place, the adhesive may dry out if you apply it too soon.

    Move The New Joist Into The Position Of The Joist It's Replacing. 

    Assuming the previous joist was directly on the foundation sill, squeeze one end of the new joist onto it. Then, on the opposite side, slip the other end into place.

    • With a hammer, tap the joist into place.
    • At least one other person will be required to assist you in installing the replacement joist.

    Use A Jack To Raise The Subfloor If The New Joist Won't Fit.

    Use a screw jack, hydraulic jack, or any other form of jack that will accomplish the job. First, place a wood block beneath the jack and another between the top of the jack and the bottom of the subfloor. Then, lift the jack until you can tap the joist back into place.

    • If the jack does not raise the subfloor sufficiently to allow you to slide the floor joist in, use a larger, heavier-duty jack.

    Install Joist Hangers For Added Strength With A Hammer And Nails. 

    Find a metal joist hanger to help support the new joist. Wrap the joist hanger around it. Check that the bottom of the joist is completely supported by the hanger. Then, using 16d galvanised nails, hammer the hanger to the wall. Finally, nail the hanger to the joist.

    • Joist hangers can be found at home improvement stores and lumberyards.
    • Joist hangers are available to support I-joists and ordinary wood joists.

    What You Should Know Replacing Floor Joists

    If a floor joist is in such bad shape that it no longer provides appropriate support for the floor above it, it's time to replace it. However, because rebuilding joists is a large undertaking, it is often advisable to hire a professional to complete the job.

    If you are unsure if the joists should be replaced or fixed, or if there is another foundation issue causing the floor to lose its previously level state, a structural engineer may assist you in making that judgement and calculating the best solution.

    Signs Of Floor Joist Problems

    Walking across your floor is the simplest technique to detect joist problems. According to the International Association of Certified Home Inspectors, a joist could be to blame if you notice the floor in one room sinking or even bowing upward. If you're not sure if the floor dips or bows, place a stone or a small ball on the floor near one corner of the room. If the floor is slanted, the marble should fall to the lower level. If you suspect the floor is higher in one region, place the marble in that area and watch it roll away.

    Feel free to perform the marble test from other room areas, including adjacent rooms, for comparison. Because marble does not roll through thick carpet, this test works best on wood and other hard-surface, smooth flooring. A carpenter's level installed on the floor in several spots helps determine whether the floor is perfectly horizontal in this situation.

    Severe termite infestations, fires, or flooding can all endanger floor joists. If your property has been subjected to such an event, investigate the joists even if the floor above them appears level and unharmed.

    Inspecting Joists For Issues

    A thorough examination of the floor joists can also help you determine which ones need to be replaced. You'll need to access the joists from a crawlspace or an unfinished basement to see them without ripping up the floor.

    Examine the floor joists beneath the sagging or bowing area for signs of damage. Severe water damage, rot, insect damage, twisting, and splintering are all signs that a floor joist needs to be replaced. Furthermore, if the joist was improperly cut or drilled to run wires, pipes, or ducts beneath the floor, the joist may have lost some structural integrity.

    If you are unsure whether the affected joist should be replaced or repaired, have a carpenter with experience in joist projects inspect the situation. The assessment should cost approximately $100.

    If you suspect that several joists are faulty or that there is a foundation concern, consult a structural engineer instead.

    The engineer is qualified to detect potential problems that the untrained eye may miss, such as rotted joists on the inside, weak support beams, or foundation concerns. Expect to pay $300 to $700 for the engineer's evaluation, or $100 to $150 per hour.

    Shoring Up The Floor

    If the floor sags or if the faulty joist spans the entire room, you'll need to reinforce it with a temporary beam and a jack post. A structural engineer may recommend two jack posts spaced equidistant across the span of the sag in specific instances. This provides greater floor support while removing and repairing the problematic joist.

    If you're unsure how to proceed, consult with a professional rather than risking extra structural damage to your home, as cranking up the jack posts too high too quickly can cause cracks and stress on the entire home structure. Furthermore, the floor should be raised no more than 1/4 inch per month to avoid structural issues.

    • Nail two 2x4s together to span many joists, including the damaged one. Nail those to the bottom of the joists spanning the damaged one in the region where the post jack will be installed.
    • Insert a post jack beneath the new 2x4s, on a thick enough wood scrap to support the jack. Follow the manufacturer's guidelines for the size of wood used for the project.
    • To slightly raise the jack's height, turn the nut, lever, or handle in the direction suggested by the manufacturer. Continue carefully rotating it to raise its height until it can't be wiggled free. Increase the height by no more than 1/4 inch to slightly lift the drooping floor.
    • Continue the practise of raising the floor by 1/4 inch or less each month until it is level. After it has been levelled, the problematic joist can be replaced.

    Replacing A Joist

    Floor joist replacement is best left to a professional, especially if the joists are inaccessible from a basement or crawlspace. This means that portions of the floor and subfloor must be removed in order to gain access to each troublesome joist.

    On the other hand, if you can readily see and access the joist from the basement and believe you can handle the removal and replacement yourself, equip yourself with a decent work light and enough of eye protection.

    Keep a spare box of reciprocating saw blades on available, as cutting through nails might cause the blade to break. Before cutting off the old joist, make sure you measure it from end to end. It should be about 12 inches longer than the room it spans, although it might be just a few inches longer. The new joist should be the same size as the previous one, so it sits atop the beams or foundation walls in the same way.

    • Using a crowbar or other pry bar, pry the broken joist off the subfloor, pounding wedges of wood between the subfloor and joist to make your work simpler.
    • After loosening a section of the joist, weaken it by cutting it vertically with a reciprocating saw. Working your way across the joist span, pry it loose from the subfloor. When required, use the reciprocating saw to cut through nails. Remove old joist sections until they are fully removed from the project area.
    • On the top side of the new joist, dab a bead of construction adhesive.
    • Enlist the assistance of a friend to help you slide the new joist into position.
    • Place a bottle jack alongside one end of the joist and a woodblock atop it between the jack and the subfloor. Raise the jack and subfloor just enough to tap the joist into place.
    • Tap the joist into position. At either end, fasten it to the supporting wall or beam.
    • Lower the jack and remove the scrap block of wood.

    How Difficult Is It To Replace Floor Joists

    Dry rot and termites are two elements that can compromise the structural integrity of your foundation joists; if you observe this compromise and the joist is still intact, you can replace it with construction adhesive and lag bolts.

    When a joist's structural support is fully eliminated, it must be removed and rebuilt. If you're wondering how tough it is to replace floor joists, the only person who can answer that question is the person doing the work.

    If you're curious about how tough it is to replace floor joists, keep reading.

    Shoring up the floor, identifying the replacement joist, detaching and prying the old joist, and installing the new joist are all steps in replacing the floor joist. Replacing a floor joist necessitates the use of safety equipment, some carpentry skill, and the ability to operate in a restricted location.

    How To Tell If You Have Joist Problems

    There are several indicators of a joist problem, but simply walking across the floor is the simplest. If you see one region of the floor sinking or even bowing upward when walking across it, you may have a joint problem.

    If you are unsure whether the floor dips or bows, lay a marble or a tiny ball at one corner of the room; if the floor dips, the ball should roll to the lower area; if the floor bows, place the ball in the suspected high position and see if it rolls away.

    Carry out this test from various places of the room, including adjacent rooms, to ensure that the results are correct.

    This test works well on certain floor surfaces, such as wood and smooth flooring, although the ball or marble may struggle to move through dense carpet.

    In this scenario, a carpenter's level set can be used to place on the floor in various spots to help determine whether the floor is fully flat.

    A weakened joist can be caused by a variety of factors, including severe termite infestations, fires, or flooding.

    If you have recently encountered such a circumstance, investigate the joists even if there appears to be no problem and the floor above them appears level and undamaged.

    Inspecting Your Joists For Issues

    Take a close look at the floor joist to see if it needs to be replaced or repaired. You may need to access the joists through a crawl space or an unfinished basement to inspect them without ripping up the floor.

    Look for any signs of deterioration in the floor joists beneath the region where you noticed the drooping or bowing of the floor. Severe water damage, insect infestation, decay, bending, and splintering are all signs that a floor joist needs to be replaced.

    A floor joist can also lose structural integrity if it is cut or drilled incorrectly to instal wires, pipes, or ducts beneath the floor.

    If you can decide if you need to replace or repair the afflicted joist, you can consult with a carpenter who has experience with joist jobs and have them inspect the condition. The assessment could cost you anywhere from $100 to $200.

    If you suspect that the problem is caused by several joists or that there is a problem with the foundation, you can engage a structural engineer instead. They will be able to detect difficulties that you would miss, such as rotted joists, weak support beams, or foundation problems.

    You should expect to pay between $300 and $700 for the assessment, or between $100 and $150 per hour for an engineer's advice.

    Shoring Up The Floor

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    If the floor sags or the issue joist spans the entire room, a temporary remedy can be accomplished by strengthening the floor with a temporary beam and a jack post.

    If you engaged a structural engineer, they might recommend two jack posts spaced evenly across the span of the sag. This will provide the floor extra support before you remove or replace the faulty joist.

    Assume you have no technical knowledge on how to resolve this. In such scenario, you should call a professional rather than attempting to repair it yourself, which could result in additional structural damage to your home because cranking up the jack posts too high too quickly could produce cracks and stress on the entire home structure.

    To minimise structural difficulties, you should not raise your floor more than 1/4 inch per month on average.

    If you have carpentry skills, you can go ahead and make a temporary repair to the joist. Using a nail, including the damaged one, connect two 2x4s long enough to span numerous joists.

    Attach them to the bottom of the joists spanning the damaged one in the region where the post jack will be installed.

    Insert a post jack underneath the new 2x4s, which should be positioned on top of a heavy wood scrap large enough to support the jack. The wood used in this project should be handled according to the manufacturer's instructions.

    The manufacturer normally indicates that turning the jack's handle in the right direction will slightly raise the jack's height. Then, slowly turn it to increase its height until it is wiggled free.

    As previously indicated, you should not raise the height more than 1/4 inch to slightly lift the sagging floor.

    You can repeat this process every month, increasing the floor by 1/4 inch or less until it is level. Once it's level, you can proceed to replace the problematic joist.


    Replacing floor joists can be a difficult and time-consuming task. If you're up for the job, though, follow these procedures to replace your existing joists with new ones. Don't damage any walls or other structures because they may need to be repaired before you continue. If you are doubtful about anything, seek assistance, and make sure there is no electrical wiring running beneath your subfloor or joist area before taking things up! After removing the old joist, use braces (or similar) for support while putting the new beam underneath it all; this will prevent future concerns such as sagging flooring.

    Frequently Asked Questions About Floor Joists

    Dry rot and termites can compromise the structural integrity of foundation joists. In cases where a joist is intact, it's possible to sister a new joist alongside construction adhesive and lag bolts. However, when a joist loses structural support, it has to be removed and replaced.

    Sistering a floor joist is the best way to fix a rotten or broken floor joist. Sistering a floor joist involves joining a new joist with an old joist to restore structural strength to the floor structure. If your flooring is sagging, it's time to make some repairs.

    Labour Costs to Repair Floor Joists

    Projects tend to take anywhere from 5 to 24 hours.

    Telltale Signs of Damaged Floor Joists

    1. Moist, rotting wood.
    2. Skewed or unlevel door and window frames.
    3. Sagging, sloping, or uneven upstairs floors.
    4. Tilting or sinking crawl space supports.
    5. Cracks in the interior drywall.

    Floor joist replacement costs $12,500 on average, typically between $5,000 and $20,000. You might pay as little as $2,000, while the largest and most complex jobs cost up to $30,000. Expect to pay anywhere from $100 to $2,000 per joist depending on the extent of the damage and its accessibility to your contractor.

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