How to Fix Roof Condensation

Condensation in roof spaces is a very common problem, with around 1 in 5 properties in the UK affected by it. Condensation on the underside of roofing felt is a typical issue in roofs during winter when temperatures are low. If you have experienced roof condensation and moisture in your loft space, this article will provide helpful solutions on how to fix it.

So whether you’re a homeowner struggling with wet roof insulation or damp patches on ceilings, read on for expert tips to banish condensation for good.

What Causes Condensation in Roof Spaces?

Roof condensation occurs due to temperature differences between the warm air inside your home and cold surfaces in the roof space.

Here are the most common causes of condensation in roof spaces:

Warm Air Rising

As warm air rises, it carries moisture up into the loft space. When this warm, moist air hits the cold roof surfaces like felt underlay or tiles, the moisture condenses.

This process is more pronounced in winter when houses are heated more, producing warmer air inside which then rises up.

Lack of Ventilation

Lack of adequate ventilation prevents moist air escaping the roof space, leading to excess moisture that condenses on cold surfaces.

Older properties often have natural ventilation gaps that allow moisture to escape. But modern sealed, well-insulated houses can suffer condensation unless ventilation is installed.

Insulation Mismatches

Loft insulation is great for energy efficiency but can cause condensation if ventilation is inadequate.

Installing or upgrading insulation without adding ventilation stops warm moist air escaping, causing condensation.

Hot Water Tanks

Hot water cylinders in lofts release heat and moisture, increasing condensation if the loft has poor ventilation.

Everyday Activities

Daily activities like showering, cooking, laundry and even breathing produce moisture that rises up into lofts and condenses.

Key Takeaway: The main causes of loft condensation are warm moist air meeting cold surfaces, lack of ventilation, insulation mismatches, hot water tanks and everyday household activities.

Condensation Problems in Roof Spaces

Condensation may seem harmless at first. But left unchecked, the damp conditions it causes can lead to some serious issues:

  • Rotting roof timbers – Wet or damp timbers are prone to wood rot and decay. This compromises roof structure.
  • Mould growth – Damp conditions encourage mould growth, which is bad for health, especially if you have allergies or asthma.
  • Damage to insulation – Wet insulation becomes less effective and needs replacing sooner.
  • Plaster damage – Staining and erosion of ceiling plaster from dampness. Peeling paintwork.
  • Electrical hazards – Moisture dripping near light fittings or sockets is a fire and electric shock risk.
  • Rusting metalwork – Condensation corrodes and rusts metal roof components like nails and flashings.

So condensation clearly isn’t something to ignore. Next we’ll look at solutions to fix damp lofts for good.

How to Fix Roof Condensation

There are several effective solutions to cure a condensation problem in your roof space:

Improve Loft Ventilation

Increasing roof space ventilation is key to reducing condensation. Warm moist air needs to escape before it can condense.

  • Open loft windows if possible to improve air circulation.
  • Clear any blockages around existing ventilation.
  • Add new ventilation if needed – consider roof vents, eaves vents or tile vents.
  • Make sure any extractor fans vent outside, not into the loft space.

Upgrade Insulation

Improving loft insulation keeps roof surfaces warmer, reducing condensation. But ensure ventilation is adequate too.

  • Top up any gaps in insulation coverage.
  • Upgrade to a thicker insulation if roof space still feels cold.
  • Professional installation prevents gaps that allow warm air to bypass.

Install a Vapour Barrier

Vapour barriers stop warm moist air reaching cold surfaces. They allow water vapour to escape but not enter.

  • Specialist membranes like polyethylene sheet installed under roof felt.
  • Can be retrofitted to existing roofs.
  • Helps insulate roof and prevent interstitial condensation.

Replace Damaged Felt or Tiles

Replace any worn or damaged roofing materials that allow rain ingress leading to dampness.

  • Look for cracks, holes, lifting tiles, worn felt etc.
  • Consider replacing old bitumen felt with breathable roofing membrane.

Improve Loft Hatch Insulation

An uninsulated, poorly sealed loft hatch lets warm air and moisture enter the loft space from below.

  • Insulate hatch with suitable materials – boards or foam.
  • Draught-proof the edges with rubber seals or silicone.

Control Moisture Inside the House

Reducing excess household moisture reaching the loft helps reduce condensation.

  • Cover pans when cooking and turn on extractor fans.
  • Ventilate bathrooms during and after showering, preferably with extractor fans.
  • Avoid indoor clothes drying; use an outdoor clothes line if possible.
  • Ventilate rooms by opening windows for a few minutes each day.

How to Prevent Roof Condensation

Prevention is better than cure when it comes to dealing with roof condensation. Here are some tips:

  • Ensure adequate roof space ventilation from the outset in new builds or renovations.
  • Install a vapour control layer when upgrading insulation to prevent moisture passing into roof space.
  • Maintain ventilation paths – keep eaves, vents and ridges clear of blockages.
  • Reduce household moisture generation through lifestyle changes like venting bathrooms and cooking with pan lids.
  • Install humidity-controlled extractor fans that switch on automatically when moisture levels rise.
  • Insulate and draught-proof the loft hatch to reduce moist air transfer between house and loft.
  • Clean mould growth before it takes hold using dilute bleach or other fungicidal wash.
  • Check condition of roofing materials during annual roof inspections and replace aging felts or broken tiles.


Does a new roof fix condensation?

Not necessarily. Condensation is caused by warm moist air meeting cold surfaces. A new roof still needs proper insulation and ventilation to avoid condensation.

Do roof vents help condensation?

Yes, roof vents are one of the main solutions. Vents allow warm moist air to escape the loft space so moisture doesn’t condense on cold surfaces.

Should insulation touch the roof?

No, good practice is to leave a 50mm gap between insulation and roof to allow ventilation. The insulation should not block natural airflow at the eaves.

Does replacing roof felt help condensation?

It can help. Old bitumen roofing felt can prevent water vapour escaping. New breathable felts allow moisture to escape the roof structure.


Condensation is frustrating but fixing a damp loft is perfectly possible with some simple upgrades.

The main solutions focus on improving airflow through better roof space ventilation, increasing insulation, installing vapour barriers and taking steps to reduce household moisture.

With adequate ventilation and insulation, condensation generally reduces to acceptable levels. But it takes proper maintenance and monitoring to keep it under control long-term.

Prevention is most effective if building ventilation is considered from the outset when renovating or building roof spaces.

With the right improvements, you can get your damp loft back under control, protect your roof structure and insulation and keep your home free of troublesome condensation.