Floor Joist & Subfloor Repair in St. Louis, MO

Floor Joist & Subfloor Repair in St. Louis addresses one of the most common structural problems in our older housing stock. St. Louis brick homes, from the Victorian mansions of Lafayette Square to the two-family flats of South City and the brick bungalows on The Hill, were built with wood framing that sits directly above grade or in damp basements. The combination of our humid continental climate, freeze-thaw winters, spring flooding from the Mississippi watershed, and the relentless moisture that comes with aging foundations creates ideal conditions for wood rot, soft joists, and sagging subfloors. When a floor feels bouncy, soft underfoot, or visibly dips, the cause is almost always compromised floor joists or subfloor sheathing. We repair or replace those members, level the floor, and restore the structural integrity that your home depends on. For a free estimate, call (314) 338-6837.

Why Floor Joist and Subfloor Damage Matters in St. Louis Older Homes

Floor joists and subfloor are the first line of defense against moisture and gravity. In St. Louis homes built before 1960, these members were typically milled from Douglas fir or oak and sit in direct contact with rim joists and sill plates that often rest on limestone or brick foundations without modern moisture barriers. Water seeping from basement walls, condensation from summer humidity, and standing water after heavy rains penetrate the wood from below. Once rot begins, it spreads along the grain and across members, weakening the entire floor system. A soft spot that seems minor today becomes a structural liability within years, affecting not just comfort but the integrity of walls and finishes above.

Soft or spongy wood in joists or subfloor indicates active rot and requires replacement or reinforcement to prevent further collapse.
Bouncy or uneven floors signal that joists have lost strength and need sistering, jacking, and leveling before new subfloor and finishes go down.
Termite damage (identified from a professional pest inspection) requires removal of the affected wood and replacement with pressure-treated or naturally rot-resistant stock.
Water staining, black mold growth, or a musty smell in crawlspaces and basements warn that moisture control and joist repair need to happen together.
Sagging or tilting floors in corner rooms often point to failed sill plates or rim joists that need to be sistered or replaced in sections.

Addressing these problems early keeps repair costs manageable and prevents damage from spreading to beams, walls, and finishes above.

Local context: St. Louis sits in a humid continental zone with an average annual rainfall of 40 inches and spring thunderstorm activity that can saturate basements and crawlspaces. Freeze-thaw cycles in winter expand cracks in foundation mortar and allow capillary moisture to rise into wood framing. Homeowners in Soulard, Tower Grove, and Benton Park often discover joist rot during basement finishing or after a heavy rain reveals soft spots in the floor above. Early detection and repair prevent expensive structural failure later.

For more information on wood damage and repair options, see our wood rot and dry rot repair service page.

How We Repair and Replace Floor Joists and Subfloor in St. Louis Homes

Our process begins with a careful inspection to identify which members are damaged, how far the rot has spread, and whether repair or replacement is the right answer. We document the damage, assess moisture sources, and explain what needs to happen. If joists are sound but the subfloor is compromised, we replace just the subfloor sheathing. If joists show rot or weakness, we either sister new lumber alongside the damaged member or remove and replace the joist entirely. We then jack and level the floor before installing new subfloor, ensuring a solid, flat surface for finishes to follow.

We inspect all accessible joists, rim joists, and sill plates with a moisture meter and probe to identify soft wood and assess the extent of rot.
We remove damaged subfloor sheathing and set aside any flooring or finishes that can be salvaged and reinstalled after the structural work is complete.
We sister new joists alongside compromised members using full-length bolting and nailing, or we remove and replace the joist if rot is too extensive.
We install pressure-treated rim joists and sill plates in areas exposed to moisture, and we use naturally rot-resistant species like redwood or Douglas fir for interior joists where appropriate.
We jack the floor level using temporary posts and beams, then install new subfloor sheathing and fasten it securely to all joists.
We address moisture sources, such as improving drainage, venting crawlspaces, or sealing foundation cracks, to prevent recurrence.

The result is a solid, level floor that will support finishes and the home's structure for decades to come.

Example from the field: A 1920s brick bungalow in Creve Coeur had a sagging kitchen floor and soft joists along the basement wall. We sistered new Douglas fir joists to the damaged members, jacked the floor level, removed and replaced the rim joist and sill plate with pressure-treated lumber, and installed new subfloor. The homeowner then had the flooring refinished and the kitchen cabinets reset. Total time in-house: 5 working days. The floor is now solid and level.

Learn more about our structural carpentry approach on our framing and structural carpentry page.

Approach	Description	Best for
Sistering	Installing a new joist alongside a damaged one, bolting and nailing the two members together to share the load.	Joists with moderate rot or settling that are still structurally sound enough to be reinforced.
Full Joist Replacement	Removing a joist that is severely rotted or structurally compromised and installing a new joist of the same dimension and grade.	Joists with extensive rot, termite damage, or failure that cannot safely carry load even with reinforcement.
Subfloor Replacement	Removing damaged subfloor sheathing and installing new plywood or OSB fastened securely to all supporting joists.	Soft, rotted, or water-damaged subfloor where the joists themselves are still sound.
Jacking and Leveling	Using temporary posts, beams, and hydraulic jacks to lift a sagging floor back to level or near-level before structural repairs and new subfloor are installed.	Floors that have settled or sagged due to joist settlement, rot, or inadequate support, when returning to level is feasible.
Rim Joist and Sill Plate Repair	Replacing sections of rim joists or sill plates that are rotted or damaged, using pressure-treated lumber to resist future moisture damage.	Perimeter joists and plates that sit in contact with foundation walls and are exposed to capillary moisture and condensation.

Floor Joist and Subfloor Repair Cost in St. Louis: What to Expect

The cost of floor joist and subfloor repair in St. Louis ranges from $1,800 for small, localized subfloor replacement to $8,000 or more for extensive joist replacement, jacking, and moisture remediation across a large area. The primary factors that affect cost are the number and length of joists that need sistering or replacement, the size of the subfloor area being replaced, whether the floor needs to be jacked level, and the accessibility of the work. A single sistered joist with new subfloor in a small room costs less than replacing multiple joists across an entire first floor or basement rim. Moisture control work, such as improving drainage or venting crawlspaces, may add to the scope. We recommend getting 2 to 3 estimates from local contractors so you can compare approaches and pricing. See our full pricing guide for more detail on how we structure estimates.

Factors that move cost upward include the extent of rot (repair versus replacement), the number of joists affected, access difficulty (tight crawlspaces or finished basements require more labor), and the need to jack and level the floor. Pressure-treated lumber and rot-resistant species cost more than standard framing stock but last longer in damp conditions. If termite damage is involved, the work is documented from your pest inspection report, and we replace the damaged wood with appropriate stock. Permits are often required for structural work that alters load-bearing members, and the St. Louis Building Division should be consulted before work begins.

Hiring a Carpenter for Floor Joist and Subfloor Repair Near Me: What to Look For

When you are looking for a contractor to handle floor joist and subfloor repair near St. Louis, focus on three things: experience with structural carpentry in older homes, willingness to explain the damage and the repair method clearly, and full insurance coverage. A good contractor will tell you whether a joist can be repaired or needs replacement, and why. They will walk you through the process, discuss moisture control, and explain what permits may be needed. Ask for references from recent projects in similar St. Louis homes, particularly in neighborhoods like Lafayette Square, Soulard, or Tower Grove where older brick construction is common. Check that the contractor is fully insured and ask to see proof of coverage. If the work involves altering a load-bearing wall or removing a beam, confirm that a licensed structural engineer has reviewed the design and that the St. Louis Building Division has issued a permit. For free estimates and to discuss your specific floor problem, call (314) 338-6837 or visit our contact page.

Verify that the contractor carries liability insurance and worker's compensation insurance, and ask for a certificate of insurance before work begins.
Request references from at least two recent joist or subfloor repair projects in St. Louis, and follow up with those homeowners about the quality of work and the contractor's professionalism.
Confirm that the contractor understands the difference between repair and replacement, and that they will explain why each joist or section of subfloor is being addressed the way it is.
Ask whether permits are needed for the scope of work and whether the contractor will handle permit applications and inspections or if that is the homeowner's responsibility.
Get a written estimate that breaks down labor, materials, and any additional costs such as jacking, moisture work, or travel, so there are no surprises when the invoice arrives.

A local carpenter who has worked on St. Louis brick homes understands the specific challenges of our climate, our building stock, and our moisture issues. That knowledge is worth the investment in the right contractor.

Floor Joist & Subfloor Repair in St. Louis: Pricing Guide

Service	Price	Details
Single joist sistering with subfloor patch	Starting at $1,800	One joist reinforced with sistering, new subfloor in that bay, jacking and leveling included, up to 100 sq ft
Multiple joist replacement and subfloor	Starting at $4,500	Two to four joists fully replaced, new subfloor across the affected area, jacking, leveling, and pressure-treated rim joist work
Extensive floor system repair with moisture control	Starting at $7,000	Multiple joists and rim joists replaced, large subfloor area, jacking and leveling, drainage or ventilation work to address moisture source
Crawlspace or basement access challenges	On estimate	Tight spaces, finished ceilings, or complex layouts require on-site inspection to assess labor and staging before pricing
Travel and site preparation	Included	No additional mileage or travel fee within St. Louis and surrounding service areas; site prep and debris removal included in estimate
Free estimate	No obligation	Call (314) 338-6837 for same-day or next-day appointment; we document damage and explain repair options before you commit

Indicative pricing, the exact cost depends on square footage, finish, and site access. Free personalized estimate within 24h at (314) 338-6837.

Floor Joist & Subfloor Repair: service areas

📍 St. Louis 📍 Clayton 📍 University City 📍 Webster Groves 📍 Kirkwood 📍 Ladue 📍 Maplewood 📍 Richmond Heights 📍 Creve Coeur 📍 Chesterfield 📍 Ballwin 📍 Florissant 📍 Hazelwood 📍 Affton 📍 Crestwood 📍 Sunset Hills 📍 Ferguson 📍 St. Charles 📍 Wentzville

Frequently asked questions: Floor Joist & Subfloor Repair in St. Louis

How much does floor joist and subfloor repair cost in St. Louis?

Floor joist and subfloor repair in St. Louis typically starts at $1,800 for small subfloor patches and single joist sistering, and ranges up to $7,000 or more for extensive joist replacement, jacking, and moisture control work. The primary cost drivers are the number of joists needing repair or replacement, the square footage of subfloor being replaced, whether the floor needs jacking to level, and the accessibility of the work area. Pressure-treated lumber and rot-resistant species add to material cost but provide better longevity in damp conditions. We recommend getting 2 to 3 estimates from local contractors to compare approaches and pricing.

What causes soft and bouncy floors in St. Louis older homes?

Soft and bouncy floors in St. Louis brick homes are caused by rot, settling, or damage to floor joists and subfloor sheathing. The humid continental climate, freeze-thaw winters, and moisture seeping from foundations create ideal conditions for wood rot to develop. Capillary moisture rises through limestone and brick foundations into wood framing that lacks modern moisture barriers. Termite damage, water staining from basement floods, and condensation from summer humidity all contribute. Once rot begins, it spreads along the grain, weakening the joist and causing it to sag or deflect under load. The result is a floor that feels soft underfoot and may visibly dip in the center of the span.

Can floor joists be repaired or do they always need to be replaced?

Floor joists can often be repaired by sistering a new joist alongside the damaged one if the rot is moderate and the remaining wood is structurally sound. Sistering involves bolting and nailing a new joist to the existing damaged joist so they share the load together. However, if the rot is extensive, the wood is spongy or crumbling, or the joist has lost more than half its depth, full replacement is the only safe option. We assess each joist individually during inspection and explain why repair or replacement is appropriate for that member. Sistering costs less than replacement and keeps the original framing in place, but it is only viable when enough sound wood remains to bond the new joist securely.

How long does floor joist and subfloor repair typically take?

A typical floor joist and subfloor repair in a St. Louis home takes 3 to 7 working days depending on scope. A single sistered joist with subfloor patch in one room may take 2 to 3 days. Replacing multiple joists across a larger area, jacking the floor level, and installing new subfloor across the entire first floor can take 5 to 7 days or more. Access and working conditions affect the timeline. Crawlspaces with low headroom or finished basements where the floor cannot be accessed from below take longer. We schedule the work around your schedule and provide a realistic timeline during the estimate.

Do I need a permit for floor joist and subfloor repair in St. Louis?

Permits are commonly required for structural work such as replacing or altering floor joists, especially if the work affects load-bearing rim joists or sill plates. The St. Louis Building Division should be consulted before work begins to determine whether a permit is required for your specific scope. Small subfloor patches that do not affect structural members may not require a permit, but it is always wise to ask. We are familiar with St. Louis permitting requirements and can advise you on what is needed. If a permit is required, we handle the application and coordinate with the building inspector for final approval.

What is the difference between wood rot and termite damage in floor joists?

Wood rot is fungal decay that develops in wood exposed to moisture and poor ventilation. It causes the wood to soften, lose strength, and eventually crumble. Termite damage is caused by insects that tunnel through wood, leaving galleries and weakening the structure. Both result in soft, compromised joists that need to be repaired or replaced. The treatment differs: wood rot repair involves removing the damaged wood and addressing the moisture source; termite damage repair involves removing the damaged wood based on a professional pest inspection report and replacing it with pressure-treated or naturally rot-resistant lumber. We do not perform pest treatment or termite control, but we repair and replace the wood damage that the pest inspection identifies.

What is the best time of year for floor joist and subfloor repair in St. Louis?

Spring and early fall are the best times for floor joist and subfloor repair in St. Louis. Spring work allows homeowners to address damage discovered during winter thaws and heavy rains before summer humidity intensifies moisture problems. Early fall provides stable weather and lower humidity before the freeze-thaw season begins. Summer heat and humidity can make crawlspace and basement work uncomfortable, and winter freeze-thaw cycles can complicate concrete work if rim joists are being set on foundation walls. The most urgent repairs are those where active rot is spreading or the floor is noticeably sagging, which should not wait for the ideal season. Call (314) 338-6837 to schedule an inspection and discuss timing.

Can you help document floor joist damage for an insurance claim?

Yes, we can help document damage to floor joists and subfloor for your insurance claim. We photograph and describe the damage in detail, explain the cause (water damage, settling, rot), and provide a written repair estimate. We can also provide receipts and documentation of the work performed if the claim is approved and we complete the repairs. However, we cannot guarantee that your claim will be approved or that the damage will be covered by your policy. Insurance coverage varies by policy and insurer. We recommend contacting your insurance agent before work begins to understand what is covered and what your deductible is.

Do you handle emergency floor joist and subfloor repair in St. Louis?

Yes, we handle emergency calls for floor joist and subfloor damage. If a floor has suddenly become soft, bouncy, or visibly sagging, or if you discover water damage after a basement flood, call us at (314) 338-6837. We respond to emergency calls within 24 hours and can often schedule an inspection the same day or next morning. If the damage is severe and poses a safety risk, we can discuss temporary shoring or jacking to stabilize the floor while we plan the permanent repair. Emergency work may have scheduling premiums, but safety comes first.

Are you fully insured for floor joist and subfloor repair in St. Louis?

Yes, we are fully insured for floor joist and subfloor repair work in St. Louis. We carry liability insurance and worker's compensation insurance to protect you and our crew. We hold a City of St. Louis Construction Industry Contractor License and have been in business since 2016. We can provide a certificate of insurance upon request before work begins. Insurance and licensing give you recourse if anything goes wrong and ensure that our crew is trained and accountable.

What happens if I ignore soft or bouncy floors in my St. Louis home?

Ignoring soft or bouncy floors allows the damage to spread and worsen over time. If the underlying cause is wood rot, the rot will continue to consume the joist and subfloor, spreading to adjacent members and eventually compromising the entire floor system. A floor that sags or bounces puts stress on walls, finishes, and structural members above, potentially causing cracks in drywall, plaster, or brick. The longer you wait, the more expensive the repair becomes because more wood needs to be replaced and more of the home is affected. In extreme cases, a severely weakened floor can fail suddenly, creating a safety hazard. Early detection and repair keep costs down and protect your home's structural integrity.