Don’t waste your money insulating these spots – experts reveal the solutions to try instead that'll keep damp and mould at bay

If your home is feeling a chilly despite having your heating on, or you have inexplicably high energy bills, then it might be that you need to address your home's insulation. But while improving what you have or replacing it altogether can help, getting it wrong can lead to condensation, damp and mould — and nobody wants that!

When it comes to how to insulate your home, correct installation is key. This not only means you need to choose the right type of insulation, but it also needs to be laid or applied in the right way, and only installed in the right place.

While there are areas you should never insulate for a variety of reasons, there are some that you should specifically avoid due to the risk of causing damp or mould.

1. Areas with existing damp issues

This might seem obvious, but if you want to avoid damp and mould, it's vital you address any existing moisture issues before you even think about upgrading your insulation situation. 'Any damp problems must be addressed before insulation is added,' says property and construction expert Thomas Goodman from MyJobQuote. 'Unless a moisture barrier is added first, damp will penetrate the insulation and lead to mould growth and ineffective insulation.'

The ingress of moisture can cause your insulation to fail, meaning it doesn't last as long as it should.

Tackling this should also be a key concern if you are trying to insulate a basement, as the subterranean nature of the space poses its own set of unique moisture challenges.

'Installing insulation directly over damp ground without first applying a moisture or vapour barrier can trap moisture, leading to mould growth, and even structural damage,' explains Michael Chichester, Head of Lender Technical at e.surv.

'This is especially true in unventilated or poorly ventilated spaces such as basements. To mitigate these risks, it is generally more effective to install a vapour barrier over the ground surface first, followed by insulation applied to the underside of the floor above. This approach helps maintain airflow in the void, prevents moisture ingress, and supports long-term thermal performance.'

2. On solid walls (without a damp proof course)

If you live in an older house that has solid rather than cavity walls, or a timber frame structure, you need to be very careful before applying insulation to the walls.

'Breathability is key, particularly in solid-walled or timber-framed buildings,' explains Michael. 'Many modern insulation materials (e.g. PIR boards, EPS) are non-breathable and therefore trap moisture, causing interstitial condensation, rotting timbers, and damaged finishes. Within older properties with brick or stone walls, breathable materials like wood fibre or lime plaster are far safer and more effective.'

3. Under suspended floorboards

If you live in an older property with suspended floors, you might be dealing with draughts that are making your home feel cold. But stuffing the gap with insulation isn't the answer, as this can block essential ventilation, leading to issues of damp and mould.

'Ventilation is needed to prevent warm and moist air becoming trapped and leading to condensation,' says Thomas. 'The insulation itself may become damp and this reduces its effectiveness.'

4. Over non-IC recessed lights

Spotlights that are recessed into the ceiling are hugely popular, but combining these with insulation can pose a serious fire hazard. But not having adequate insulation can also mean that you run the risk of condensation forming, which can lead to damp if not resolved. So what can you do?

The best way is to make sure your spotlights are IC (Insulation Contact) rated - which means they can come into direct contact with insulation without posing a fire hazard.

Alternatively (or additionally), using a fire retardant downlight cover, like the Loft Lid from Loft Leg (£48.99 for a pack of 8 at B&Q), acts as a protective barrier between the light and the insulation.

5. In an unventilated loft

Lofts and attics should be well ventilated to prevent moisture from building up, which can cause problems of condensation, damp and mould as well as structural issues. You also need adequate ventilation in order for your insulation to work most effectively.

'Insulation in the loft will help to reduce heat loss and save money on energy bills,' says Thomas. 'However, if the roof space is not adequately ventilated, the warm air that naturally rises from within your home will cool, can cause condensation and ultimately, damp.'

Inadvertently blocking any vents, or taking insulation to the edge of the roof space can interrupt the flow of air across the space.

6. Around flues and chimneys

'Chimneys are another common pitfall,' reveals Michael. 'Even disused flues often help manage moisture levels in a property. Blocking them up without ventilation can cause damp patches, mould, and even structural damage through freeze-thaw cycles. For active chimneys, getting insulation too close to the flue can pose a fire risk so clearances and fire-safe materials are essential.'

If you're concerned about draughts coming from the fireplace, a specialist draught excluder, like a Chimney Sheep, from £21 on Amazon, for when it's not in use can help.

7. Where you already have adequate insulation

When it comes to insulation, it's definitely not a case of more is more. In fact, too much insulation can hamper ventilation and trap moisture in your insulation, which is a big no-no.

This is another reason it's important to use a professional to address your insulation needs. They will not only be able to identify any areas where your insulation is lacking, and be able to safely remove old insulation, but also make sure that insulation isn't added where it isn't needed.

They will also be able to give you ideas of other solutions you can try to keep your home warm, like window film kits or thermal curtains.

FAQs

What can you do in areas you shouldn't insulate?

If the thought of not adding insulation in these spots is leaving you cold, the good news is there are plenty of other solutions you can try that will keep you warm throughout winter.

Thomas Goodman shares his expert tips, from instant fixes to more involved renovation work:

• fitting good quality double or triple glazing
• using a chimney draught excluder to minimise cold air from blowing in and causing cold spots, which can lead to condensation
• hanging thermal curtains
• using draught excluders on external doors
• fill gaps around pipes, electrical outlets, etc.
• regularly service your boiler and central heating system
• open curtains on sunny days to take advantage of solar gain
• put down rugs on wooden or tiled floors
• insulate pipes and hot water cylinders.

What should you do before updating your insulation?

'Before installing insulation, it’s essential to understand how the building performs, where the risks are, and what materials are most compatible,' says Michael. 'Ultimately, what works for a modern cavity-walled property could be entirely wrong for a 19th-century terrace. depends on the age, construction and condition of your home there’s no one-size-fits-all solution.'

What happens if you over-insulate a house?

Adding too much insulation to your home is not a sure-fire way to lower your heating bills as much as possible. In fact, rather than making your home even more comfortably warm, it can cause moisture to become trapped which can lead to condensation, damp and mould. Unresolved, these can wreak havoc with the structural elements of your home — something which is very costly to fix.

This moisture can also degrade your insulation, meaning it stops being effective and needs replacing way earlier than planned.

When assessing your insulation, make sure there aren't any areas you should have insulated but didn't.