How to Level a Floor in an Old House

Can you fix uneven floors in an old house?

Yes. Almost every uneven floor in an old house can be fixed. Whether it is a half-day job or a structural repair depends on one thing, is the floor sound but sloped, or is the framing underneath failing?

Levelling a floor in an old house comes down to that question. A sound floor that simply sits out of level is corrected with compliant packers or a self-levelling compound. Failed framing underneath is corrected by sistering the joists or dealing with the piers, and that is a different job at a different price.

Across Sydney’s Inner West we work on a lot of Federation cottages, workers’ terraces and post-war brick homes in Five Dock, Haberfield, Leichhardt and Marrickville. Uneven floors are the thing we get asked about most. They are also the thing most often misdiagnosed.

Is It Risky? How to Diagnose Uneven Floors in an Old House

Old houses develop uneven floors for three main reasons, foundation and footing movement, compromised or undersized floor joists, and termite or rot damage. Before you touch a single packer, you need to know which one you have. Fixing the symptom while ignoring a failing footing is dangerous, and your new floor will fail within a year or two.

The three step structural test

1. The marble test. Place a marble or a small ball bearing on the floor in several spots. If it rolls quickly and consistently towards the centre of the room, you likely have a sagging central bearer or joist rather than an isolated dip.

2. The bounce test. Walk across the floor and bounce lightly on the balls of your feet. If it feels spongy, or if glassware in a nearby cabinet rattles, the joists are weakened, undersized or missing support underneath. Bounce and noise often travel together, so it is worth ruling out squeaky and bouncy floorboards as a separate fixing problem before you assume the framing has failed.

3. The subfloor check. Get under the house with a torch. You are looking for damp or standing water, cracked or split joists, rotted bearer ends where they sit on brick piers, piers that have dropped or leaned, and the mud tunnelling that indicates termites. If the piers themselves have dropped, the job is not floor levelling, it is restumping, also called reblocking. That is a structural job with its own pricing and its own tolerances, and it is covered separately below.

CSIRO is blunt about damp subfloors. Its homeowner guide on footing performance notes that where bearers and joists support the flooring, insufficient ventilation creates ideal conditions for condensation, particularly where there is little clearance between the floor and the ground. High subfloor humidity then creates an ideal environment for pests including termites, along with mould. In older Sydney homes, poor subfloor ventilation is the single most common root cause we find.

Do not pack the gap between the bearer and the pier

This is the most common weekend fix for a bouncy floor. Do not do it.

CSIRO warns that where isolated footings rise and fall because of the swell and shrink cycle in clay soils, homeowners are often tempted to cure floor bounce by filling the gap that has opened between bearer and pier with blocking. The danger is that on the next swell part of the cycle, the extra blocking pushes the floor up into an accentuated dome and may also cause local shear failure in the soil. If blocking has to be used at all, CSIRO says it should be a pair of fine wedges, monitored fortnightly.

In other words, the gap is a symptom of ground movement, not a construction fault. Shove a block in there and you have removed the movement tolerance from a house that needs it.

What the results mean

• Any test fails. You are in structural territory. Go to Method 1, and read the section on licensing before you start. If you are also seeing cracking in the walls above, read our guide to the signs of structural damage before you go any further.
• Floor is solid but sloped. The structure is sound and you can treat this cosmetically. Go to Method 2 or Method 3.

One extra check for Sydney homes: if the house was built or renovated before 1990, assume asbestos is present until proven otherwise. Vinyl floor tiles, the backing under lino, and sheeting in wet areas are all common sources. Do not sand, cut or break anything up before you have it tested.

Your next step: complete all three tests before you buy a single material. The diagnosis determines the method, not the other way around.

How to Level a Floor in an Old House: 3 Proven Methods

There are three ways to level a floor. Structural jacking and sistering corrects deep sags caused by failed framing. Packing and re-sheeting corrects a large area that slopes but is structurally sound. Self-levelling compound corrects localised dips within the depth range the product allows.

Work through the diagnosis above before you pick one. The method follows the cause.

Method 1: Sistering the joists (the structural fix)

Sistering means fixing a new joist alongside the failing one so the two act together. It is the standard repair for a joist that has sagged, split or been weakened.

The process:

1. Measure the sagging joist and cut a new length of the same size seasoned hardwood or LVL (engineered laminated timber). Common Australian sizes are 140×45, 190×45 and 240×45. Match or exceed the original.
2. Clear the span and check for services. Old houses often have water pipes, gas lines and wiring strapped to the joists.
3. Set up an adjustable steel prop (an acrow) or a hydraulic bottle jack on a solid bearing plate, with a length of timber spreading the load across the joist. Never jack directly off soft ground or a single brick.
4. Raise the sagging joist slowly towards level.
5. Apply construction adhesive to the face of the existing joist, clamp the new sister into position, and fix the two together with 75mm coach screws or structural bolts in a staggered pattern at roughly 300mm centres.
6. Ensure the new joist bears properly on the bearer or wall plate at both ends. A sister that stops short of the bearing does nothing.

The mistake that costs the most money: jacking too fast. Lift no more than 3mm per day. The whole house has settled around that sag, sometimes for eighty years. Rushing it cracks cornices, splits plaster, jams doors and can crack brickwork above. On a 40mm sag, that is a two week job of quarter turns, not a Saturday afternoon.

The NSW Guide backs this up. Consequential damage caused by restumping works is not treated as defective where the builder has documented evidence that the owner was informed of the nature and likelihood of that damage. Some cracking is an expected outcome of re-levelling an old house, which is exactly why a good builder puts it in writing before starting.

Before you start this in NSW: residential building work valued over $5,000 including GST must be carried out by a licensed builder under a written contract. Structural work affecting the load path is not owner-builder territory unless you hold an owner-builder permit, and if the home is heritage listed or in a conservation area you will also need council consent. Structural work is not a DIY job.

Method 2: The packing technique (the cheapest way to fix a sloped room)

If the framing is sound and the room simply sits out of level, you build the low side up rather than lifting anything. This is packing on top of sound joists to create a flat plane, not packing underneath a bearer where a pier has dropped. Those are opposite jobs with opposite outcomes.

The process:

1. Strip back to the joists or existing subfloor.
2. Find the highest point in the room using a self-levelling cross line laser. Everything else gets built up to match that point.
3. Mark the level line on every joist and snap chalk lines so you can see the plane you are building to.
4. Cut packers from plywood or use engineered plastic packers. Build up each joist to the chalk line, gluing and fixing each packer so nothing can work loose and squeak later. Avoid soft or compressible material.
5. Lay new 19mm structural plywood or particleboard flooring over the packed joists, glued and screwed.

What you need: a self-levelling cross line laser, chalk line, packers, construction adhesive, and flooring screws. This is the most cost effective method for a whole room that leans in one direction, because you are not fighting the structure, you are working with it.

Method 3: Self-levelling compound (for localised dips)

This is the method most homeowners will actually use, and it is the right one for a floor that is structurally sound with a dip or two rather than a whole-room slope.

The process:

1. Measure the deepest point of the dip and check it against the product’s stated depth range. Every bagged compound has a minimum and maximum pour depth, and exceeding it is the most common cause of failure.
2. Confirm the subfloor is sound, dry and firmly fixed down. Compound poured over a bouncy or moving floor will crack, no matter how well it is mixed.
3. Prime the substrate with the manufacturer’s primer and let it dry fully. Unprimed timber and porous concrete draw the water out of the mix and kill the cure.
4. Dam the doorways and any penetrations with a batten or foam strip so the compound cannot run out of the room.
5. Mix with a drill and paddle to a creamy consistency, following the water ratio exactly. Mix only what you can pour inside the stated working time, which is often under fifteen minutes.
6. Pour in closely spaced dollops so they flow into each other, then work it out with a spreader and a spiked roller to release air bubbles.
7. Leave it to cure fully before walking on it or laying a floor covering over it. Curing times vary widely between products, so go by the bag.

Which product. Cement-based compounds handle moisture better than gypsum-based ones, which matters in an old Sydney subfloor. Check the bag against your floor covering too, because most flooring manufacturers specify a substrate tolerance and will not warrant an installation over a surface that does not meet it.

What if your floor is a concrete slab?

Plenty of post-war Sydney homes are slab-on-ground rather than bearer and joist, and the approach changes completely.

On a slab, high spots are ground down with an angle grinder or a hire floor grinder fitted with a diamond wheel, and low spots are filled with self-levelling compound as in Method 3. There is no sistering, no packing and no jacking, because there are no joists to work with.

The important distinction is what caused it. A slab that is out of level because of a poor pour is a surface problem and the grinding and filling approach fixes it. A slab that has curved, dished or domed has moved, and that is a footing and foundation question governed by soil reactivity, not a flooring one. If you are seeing slab movement alongside cracking in the walls, stop and get it assessed before you spend money on the surface.

How Level Does an Old Floor Actually Need to Be?

NSW has a published benchmark, and it allows more deviation in an existing house than in a new build.

The NSW Guide to Standards and Tolerances treats floors as defective at the following thresholds.

Both tolerances apply within the first 24 months. For a new floor, overall deviation across the entire building footprint should also not exceed 20mm.

What that tells you is simple. The standard itself accepts your old house will never be as flat as a new one. If you are re-levelling a Federation cottage and someone promises you a laser-flat result across every room, they are either inexperienced or about to cause a lot of cracking getting there. A finished result inside 15mm across any room and 8mm over any 2 metres is a properly executed job by the NSW benchmark.

The Guide also sets a limit that catches out most DIY attempts. Packing to stumps or piers under bearers is defective if it:

• is not made of durable, non-compressible material such as engineered plastic packers
• does not provide the minimum bearing area required by AS 1684
• exceeds a total thickness of 20mm

Roofing shingles and soft timber offcuts, which appear in a lot of overseas guides, do not meet that. If the gap needs more than 20mm, the pier needs attention, not more packing.

One caveat on all of the above. The Guide is an advisory document rather than a regulated standard, and it states that legislation, the National Construction Code and your building contract take precedence over it. It is the benchmark used to resolve disputes, not a law in itself.

What Is the Cheapest Way to Level a Floor? Homemade Alternatives

The most affordable approach is to pack out large sloping areas at joist level, and to mix your own sand and cement levelling screed for localised dips rather than buying premixed commercial compound by the bag.

Homemade floor leveller mix

Ingredients: 1 part general purpose cement, 3 parts fine washed sand, and liquid acrylic bonding agent diluted per the manufacturer’s directions, used in place of most of the mixing water.

Method: mix the sand and cement thoroughly dry in a bucket or barrow. Add the bonding agent slowly while mixing with a drill and paddle until it reaches a thick pancake batter consistency. Mix only what you can place in twenty minutes.

Application: prime the substrate with diluted bonding agent first so the existing floor does not draw moisture out of the mix. Pour into the dip and feather the edges out with a steel trowel.

Be honest about the limits. A site mixed sand and cement screed is not the same product as a commercial self-levelling compound. It will not self level, it needs to be worked by hand, it is not suitable for feather edging down to nothing, and most flooring manufacturers will not warrant a floating floor or tile installation over an unbranded mix. If you are levelling under an expensive floor covering, buy the bagged product. On a laundry, a garage step or under carpet, the homemade mix is fine.

Try this now: measure the depth of your dip with a straight edge and a tape. Under 6mm and you do not need a wet mix at all. Layered underlay will take it up for a few dollars.

How you know it worked: the cured surface lays flush under a 1.2 metre spirit level with no rocking and no gaps, and it dries without crazing or cracking. Across the room, you are aiming to land inside 15mm in any room and 8mm over any 2 metres.

How much does it cost to level floors in an old house?

Floor levelling in Sydney is priced three different ways depending on which job you are actually buying. Cosmetic levelling is priced per square metre. Restumping or reblocking is priced per pier. Structural jacking and sistering is priced per job, because the variable is access rather than area.

What moves the price the most:

• Subfloor access and clearance. A crawl space you can sit up in is a different job to one where a bloke is on his back in 400mm of clearance. This is the single biggest cost variable on an old house and it is why nobody can quote a Federation cottage over the phone.
• Number of piers affected. Restumping is priced per pier, so a single dropped pier and a whole perimeter are very different numbers.
• Whether the flooring is lifted and relaid. Pulling up original hardwood, storing it, and relaying it without damaging the boards adds significant labour compared with sheeting over the top.
• Extent of rot or termite damage. Timber that has to be replaced is scope you cannot see until the floor is open.
• Asbestos. Any pre-1990 floor covering that has to come up may need licensed removal, which is a separate cost and a separate contractor.
• Heritage listing. Approvals and compliance add time before anyone picks up a tool. This is routine on the heritage restoration in Sydney’s Inner West work we do.

The indicative DIY and professional ranges are in the table below. Jonathan Homes quotes floor levelling as a fixed price after a subfloor inspection, so you know the number before the floor comes up rather than after.

Should I Level the Floor Myself or Hire a Professional?

You can safely level a floor yourself if the problem is cosmetic, meaning dips under 25mm with no bounce and no sign of rot or termites. You should engage a licensed builder if the slope exceeds 50mm over 3 metres, if the floor moves underfoot, or if any footing, pier or bearer work is required.

Cost ranges above are indicative market figures only and will vary with access, materials and the extent of the damage.

Quick decision path

• Is the floor bouncy, damp or showing rot or termite damage? Call a licensed builder.
• Is the floor solid but dipping in one area? Self-levelling compound.
• Is the whole room solid but slanted? Packing and re-sheeting.

Does an Uneven Floor Devalue an Old House?

Severely uneven floors can reduce a property’s value, because buyers and building inspectors treat them as a possible structural red flag and price in the unknown. Minor sloping in a house over seventy years old is widely accepted as historical settling and rarely affects a sale.

Inspectors look for one thing. Has the movement stopped? A gently sloping hallway in a 1920s Haberfield bungalow with sound joists and good subfloor ventilation reads as character. A spongy floor with fresh cracking above it reads as an unresolved problem, and that is what gets flagged in a pre-purchase inspection report.

If you are selling, fix anything spongy and anything sitting well outside 15mm across a room. Leave minor cosmetic dips alone or resolve them cheaply with underlay when you next replace the floor covering.

Getting It Right in an Older Sydney Home

Levelling a floor in an old house is rarely just a floor job. In the houses we open up, it almost always comes back to subfloor ventilation, drainage around the house, or a bearer that has been sitting on damp brick for decades. Fix the floor without fixing the cause and you will be back under the house in three years.

If your floors are moving, sloping or feeling spongy, get it properly diagnosed before you spend money on flooring. Call Jonathan on 0414 595 933 for a free consultation.

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References

1. NSW Fair Trading / Building Commission NSW, NSW Guide to Standards and Tolerances 2017, clauses 4.4, 15.8, 18.2 and 18.3. https://www.nsw.gov.au/housing-and-construction/building-or-renovating-a-home/after/safety-and-standards/guide-standards-and-tolerances
2. CSIRO, Foundation Maintenance and Footing Performance: Preventing soil-related building movement, Building Technology Resources, 2024. https://research.csiro.au/infratech/wp-content/uploads/sites/38/2024/12/2979_FoundationMaintenanceandFootingPerformance_WCAG.pdf