A damp floor usually comes from one of three things: a solid floor with no effective damp proof membrane (DPM), a leaking pipe under or within the floor, or a suspended timber floor that is not properly ventilated underneath. Modern floor coverings such as laminate, vinyl and rubber-backed carpet can trap that moisture and grow mould beneath. We identify which it is, then repair the floor with a membrane, a leak fix, timber repairs or better underfloor ventilation as the case needs.
Solid floor or timber floor?
The first question is what kind of floor you have, because the causes and fixes differ.
| Solid floor | Suspended timber floor | |
|---|---|---|
| What it is | Concrete, quarry tiles or similar laid on the ground | Floorboards on joists with a void underneath |
| Common in | Kitchens and back extensions of older houses; many post-war homes | Front rooms of Victorian and Edwardian terraces; many older houses throughout |
| Usual damp causes | No DPM or a failed one, leaking pipes in the slab, damp from walls | Poor ventilation under the floor, leaks, damp walls touching joist ends, high ground levels |
| Typical signs | Lifting or loose tiles, white salts, damp patches, mould under coverings | Musty smell, soft or springy boards, mould on skirting, fungal growth |
| Typical repairs | Surface membrane, or lifting and relaying with a new DPM; leak repair | Restoring underfloor ventilation, leak repair, replacing decayed timber |
Damp solid floors
Many older solid floors were laid straight onto the ground with no membrane at all. Quarry tiles and old concrete let moisture pass through slowly and evaporate into the room, which was manageable when floors were left bare or covered with rugs. Put laminate, vinyl, rubber-backed carpet or a tightly fitted floor on top and that moisture is trapped. It condenses under the covering and mould and odour follow. People often first notice it when lifting a floor during a refurbishment.
Repairs range from a surface-applied damp proof membrane over a sound floor to breaking out and relaying the floor with a new membrane and, where appropriate, insulation. The choice depends on the floor’s condition, the room’s height and door thresholds, and how the DPM will connect with any damp protection in the walls. Where a wall also has low-level damp, the two need to be considered together; our rising damp treatment page covers the wall side.
Older floor tiles, particularly small square vinyl or thermoplastic tiles and their black adhesive, can contain asbestos. Do not break up or sand old floor tiles before they have been tested. We do not disturb suspected asbestos; a licensed specialist needs to test it first.
Damp timber floors
A suspended timber floor stays healthy as long as air moves freely through the void beneath it. If that airflow is reduced, humidity under the floor rises, timber moisture content climbs and the joists and boards can start to decay. Wet rot is the most common result; dry rot is less common but more serious. Signs include a musty smell, boards that feel soft or bouncy, mould on the underside of carpets or on skirting boards, and in bad cases visible fungus.
Common causes include blocked or too few ventilation openings, raised ground or path levels outside, debris in the void, a leaking pipe under the boards, and damp walls in contact with joist ends. We lift boards where needed to look underneath, take readings and check the timbers. Repairs may involve restoring ventilation under the floor, fixing leaks, isolating timbers from damp masonry and cutting out and replacing decayed sections. See our wet rot repair page for more on timber decay.
Leaks: the cause people miss
A surprising number of damp floors are caused by plumbing: a weeping joint under a kitchen sink, a heating pipe buried in a concrete floor, a leaking washing machine hose, or a shower tray seal. Leaks tend to show as a patch that stays damp regardless of the weather and may spread slowly. We look for this before recommending membranes, because no membrane will deal with a leak. Where a leak is confirmed, it is repaired, the floor is allowed to dry and damaged materials are replaced.
How we approach a damp floor
- Ask and look. When did you notice it, does it change with the weather or seasons, what is the floor covering, has anything been changed recently?
- Measure. We take moisture readings, bearing in mind that meters give relative readings on masonry and can be confused by salts. We look at the pattern, not just a number.
- Look underneath. On timber floors we lift a board or two where practical. On solid floors we check edges, coverings and services.
- Check outside. Ground and path levels, downpipes, gullies and anything blocking ventilation openings.
- Explain and quote. We tell you what is causing it and give a written quote for the repair.
Floors in Liverpool homes
In terraces across areas such as Kirkdale and Bootle, a common pattern is a suspended timber floor in the front room with a solid floor in the back kitchen or extension. Each half of the house can have a different floor problem. In inter-war and post-war homes, solid floors are more common, often under several layers of later coverings. Where there is a cellar below, as in many Victorian houses, floor damp is often linked to the cellar; our cellar damp proofing page covers that. Homes in St Helens show a similar mix of Victorian terraces and inter-war houses.
What affects the cost?
We quote once we know the cause. The main factors are the floor type and area, whether coverings need lifting and replacing, whether the solid floor can take a surface membrane or needs relaying, the amount of timber to replace, leak repairs, access to the void, and any work needed on adjacent walls or plaster. Our damp and mould cost guide explains these factors in general terms.
Damp floors are one part of the damp and mould repairs in Liverpool we carry out. If you are not sure whether the problem is in the floor, the walls or both, a local damp specialist can look at the whole picture before you spend money on the wrong fix.
Floor damp, lifting or smelling musty?
Call 07777 659786 or leave your details. Tell us what the floor is, what covering is on it and when the damp shows, and we will call you back to arrange a visit.
Frequently asked questions
Why is there mould under my laminate floor?
Usually the floor underneath is releasing moisture that the laminate traps. Older solid floors often have no damp proof membrane, and a plastic underlay or laminate stops the moisture evaporating, so it condenses and mould grows. A leaking pipe can do the same. The fix is to deal with the moisture source before relaying a floor covering.
How do I know if my floor has a damp proof membrane?
You often cannot tell by looking. Floors laid in older houses commonly have none. Clues that a membrane is missing or failed include damp patches, lifting tiles, white salts and mould under coverings. We can assess the floor and, where needed, check at the edges or where services pass through.
Can damp come up through a concrete floor?
Yes. Concrete is porous, and without a membrane ground moisture can pass slowly through it. On a bare floor it may evaporate unnoticed, but under impermeable coverings it builds up. Leaking pipes laid within the concrete are another common cause of damp patches on solid floors.
Why do my floorboards feel soft?
Soft or springy boards often mean the timber, or the joists beneath, have been wet for a long time and have started to decay. This is commonly linked to poor ventilation under the floor, a leak or damp walls. It should be checked promptly, as decayed timber can weaken the floor. We inspect underneath and advise on repairs.
Can I put a new floor down over a damp floor?
It is best not to until the cause is dealt with. Covering a damp floor usually traps the moisture and makes things worse, and many flooring products need the subfloor to be dry before fitting. Fix leaks or install a suitable membrane first, then check the floor is dry before laying the new covering.