Bitumen subfloor - Is it damp?
- JDN Property Services
- Aug 1
- 2 min read
Updated: Aug 19
Bitumen Subfloors – Strange Smells & Mistaken Damp: What You Need to Know
By JDN Property Services Ltd
At JDN Property Services, we’ve recently had a spike in calls from concerned homeowners reporting a strange, musty smell coming from their floors – often accompanied by fears of dampness or water ingress. In many of these cases, the culprit has been the same: bitumen subfloor coatings.
So, let’s break down what’s going on…
What Is a Bitumen Subfloor?
Bitumen is a tar-like substance that was commonly used in older properties as an adhesive or damp-proof coating, particularly below floors. It was considered a good moisture barrier in its day – and in many cases, it still performs well. However, like most materials, it’s not without its quirks.
Why Is It Smelling?
The recent heat and humidity in Central Scotland has caused temperature fluctuations within homes, particularly under floors and in void spaces. When bitumen warms up, it softens slightly and emits a distinct, oily or musty smell. This is entirely normal – and although it can be unpleasant, it is not a sign of dampness or decay.
Think of it like asphalt on a hot day – bitumen reacts in a similar way.
Why It Gets Mistaken for Damp
The smell can travel up through floorboards or around skirting boards, especially in older homes with timber floors or floor vents. When this happens, it's easy to assume that moisture or rot is to blame.
We’ve also found that some rooms may have hygroscopic salts (salts that draw moisture from the air) on walls or around corners of the subfloor. While these don’t always mean there’s a live damp issue, they can add to the concern.
What We’ve Been Finding
During recent subfloor inspections, our team accessed voids via floor hatches or cupboards and found dry conditions overall, with no damp readings or visible signs of moisture – just that tell-tale bitumen smell. In some instances, salts were noted below the damp-proof course (DPC), which is not uncommon in older properties, and not a cause for alarm if dry.
What Can Be Done?
If the smell is particularly bothersome, there are a few options:
Ventilation improvements – Increasing subfloor ventilation can help disperse odours more quickly.
Subfloor encapsulation – In some cases, laying a new damp-proof membrane and recapping the subfloor with a thin concrete screed may help, but this involves more invasive work and is typically not essential.
Monitoring & reassurance – A professional survey can help rule out damp and provide peace of mind.
🧰 Need Advice?
If you're worried about strange smells or potential damp in your property, give our friendly team a call. We’ll carry out a professional inspection and give you straight answers – no scare tactics, just honest advice backed by over 20 years’ experience.
📞 01698 609001