Is It Possible To Over Insulate A Home? Will My Property Get Damp, Mould or Condensation After Fitting Insulation?

Millions of homeowners have taken advantage of the government’s green energy schemes and installed new or additional wall and loft insulation.

But is it possible to over insulate a property and if so, what are the repercussions?

Insulation is the material often placed above the ceiling in the loft or between the outer walls of a home in the cavity. In some homes, it’s placed on the inside wall, as an extra barrier.

There are many advantages to installing insulation:

  • reduced heating bills
  • doing your bit for the environment
  • it’s a good selling point should you place your home on the market

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How Insulation Works

In the winter months, the air inside the home is warmer than that outside. Insulation creates a barrier that slows down the transfer of warm air from inside the home to outside.

This means your boiler doesn’t have to stay on so long and you’ll save money.

In general, the thicker the insulation, the warmer the home will be.

During the summer, the opposite happens; the warm air outside is kept out by the insulation and the home stays cooler.

The Relationship Between Insulation and Ventilation

In the summer, most homes in the UK never experience any issues with insulation or ventilation. The air outside is roughly the same temperature as that inside and the occupants often open windows to allow fresh air into the property.

In the winter, the situation is different, the air outside is much cooler and we often keep our windows closed. Too much insulation and a lack of ventilation can lead to issues that will be discussed on this page.

The relationship between insulation and ventilation is very much a balancing act;

Too little insulation and too much ventilation and your home will be inefficient and your heating bills will be higher than they should be.

Too much insulation and a lack of ventilation and your home may experience issues such as stuffy, stale and unpleasant air along with related problems such as condensation, mould and damp.

The balance is a delicate one and will vary from home to home.

Government Recommendations

The government recommends that homeowners in modern homes constructed with two walls and a cavity should have loft insulation to a depth of 250mm to 270mm.

Cavity wall insulation is also recommended.

Many buildings constructed prior to 1920 were built differently; the walls, ceiling and floors were designed to breathe.

Insulating these older buildings is more likely to lead to all sorts of problems as the balance between insulation and ventilation is disrupted.

If you live in a building constructed prior to 1920, do watch the excellent video below which is from Peter Ward at Heritage House where you’ll see the importance of wall ventilation:

Below is a video from The Restoration Couple, another example of how important breathability is in older period homes:

Is It Possible to Over Insulate a Home?

For older homes constructed from breathable materials such as hydraulic lime and soft bricks, the answer is YES.

Symptoms are:

  • damp walls and floors
  • condensation, especially in the winter
  • crumbling plaster and walls
  • bad or foul air in the home
  • coughing, wheezing and breathing problems, those with pre-existing conditions are at particular at risk.

The risk of over insulation to a modern property is less obvious, while such homes are built from non-breathable materials such as concrete and cement, they do (or should) have vents on the windows and extractor fans in the kitchens and bathrooms.

Still, if too much insulation is fitted and other steps are taken, such as replacing old drafty windows with modern airtight double glazing, it is certainly possible your home will experience issues related to a lack of ventilation.

Soaked wall from wet cavity insulation

Damp caused by soaked cavity wall insulation.

Solutions For Over Insulated Homes

If you live in a period property it’s essential that you receive advice from an expert who understands the importance of breathability.

Any work to such homes should be carried out using original materials wherever possible.

If you’ve had modern wall, ceiling or floor insulation fitted to a period property and are experiencing problems with damp, mould or condensation, you’ll probably need to remove the offending material and replace it with something more breathable.

The usual culprits are:

  • Cement-based products instead of lime (brick pointing, mortar repairs etc).
  • Gypsum plasterboard instead of breathable lime plaster.
  • Synthetic insulation instead of sheep wool insulation (this page lists the benefits of sheep’s wool).
  • Plastic non-breathable paints and coatings instead of dyes.

For modern homes, the solutions are often quicker, easier and cheaper:

If you suspect that insulation is causing an issue with your modern home, consider either of the options below (or all of them):

Remove the Offending Insulation

This is a common practice for cavity wall insulation that’s getting wet from rainwater penetrating the outer wall.

Many cavity wall insulation products have been miss-sold and weren’t appropriate for the property.

Window Trickle Vents

If you upgrade your windows to double or even triple glazing, you’d better make sure they are fitted with window trickle vents like the ones shown below.

This is even more vital if you also upgrade your cavity or loft insulation at the same time, as many homeowners do.

Window vents, trickle vents

Window trickle air vent. These prevent a build-up of bad air and condensation and should ideally be fitted in every home, especially in the bedrooms.

Passive Air Vents

A passive air vent system will help to circulate air throughout the entire upper floor of a typical home.

These products are an excellent way to solve condensation and related mould and damp problems.

Here is a photo:

Air vent system to reduce condensation

Positive Input vent (PIV) system. Read reviews on Amazon

Below is just one of the hundreds of positive reviews you’ll find on Amazon:

I have had the drimaster in for a year. Condensation and damp problem resolved immediately. 

By Lesley on 04 November 2016

Loft Vents

If you’re experiencing condensation in the loft space, these vents are cheap and easy to install:

Underfloor Vents

If you have a suspended floating floor on the ground level (not a concrete floor) then it’s essential that any wall vents aren’t blocked, if required, extra vents can be fitted to allow the void under the floor to breathe.

Blocked floor vent. Image source

Ventilation though a cavity wall

Underfloor vent

Excellent Related Articles

Below is a list of articles and websites with advice should you be experiencing issues after installing insulation or are concerned about possible problems:

This Daily Mail article from 2017 claims that up to 1.5 million homes have been blighted by botched cavity wall insulation.

The consumer advice company Which? discusses the risks associated with cavity wall insulation into walls in exposed locations that experience wind-driven rain that can soak into the insulation and cause damp problems. Read their guide here.

Jeff Howell has written several informative pieces on the subject of cavity wall insulation and associated damp problems. This Telegraph article is a good place to start.

For a more in-depth look at insulation and dampness, head over to Heritage House and this great article.

A quick search on Google will reveal that there are hundreds of companies specialising in the removal of cavity and loft insulation. None of these services would be offered if there wasn’t a huge nationwide problem with insulation causing damp problems. Some firms even offer both installation and removal services!


While many millions of homes have had their insulation upgraded without any issues, for some, the work has resulted in damp problems that have caused many thousands of pounds worth of damage.

For modern homes constructed after 1920 and with a cavity, you can usually resolve such problems by:

  • make sure the exterior wall is in good condition and rainwater isn’t penetrating into the cavity and soaking the insulation.
  • remove the insulation if you can’t prevent rainwater from soaking it.
  • maintaining the correct balance between insulation and ventilation, remember that an airtight home is not a healthy environment. Window and passive vents can help tip the balance in your favour.
  • make sure any insulation is consistent, any bare patches may get cold and this is where condensation and damp spots may appear.

For period buildings that are constructed with breathable materials:

  • always get expert advice from someone who understands the importance of breathability in period buildings.
  • any insulation must be breathable. If you’re confused by this statement, read this for an explanation of how insulation can also be breathable.
  • plasterboard should be lime-based and not gypsum.
  • mortar repairs must be with lime and not waterproof cement.
  • non-breathable coatings, sealants and paints should be avoided, and breathable dyes should be used where possible.
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