Your Guide To Solid And Internal Wall Insulation

Find the right insulation option and internal wall insulation installers with Insulation Advisor.

Save £100's on Your Energy Bills
Make your home more energy efficient
Reduce your carbon footprint
Free no obligation quote
0% VAT Payable on Home Insulation
Improve indoor comfort & air quality

How it works

Enter Your Details

Provide a few basic details to get started

Book Your Free Survey

We visit your home to assess suitability for solar

No Obligation Quote

We provide your highly competitive free quote

Your insulation is installed

Start enjoying the savings with your new insulation

Insulation is an excellent way to both reduce your carbon footprint and save money on your heating bills. You can insulate your roof, loft, floors, and walls, but wall insulation is one of the most effective types of insulation for improving thermal efficiency. In fact, the Energy Saving Trust estimates that installing wall insulation can save you up to £620 per year off your energy bills – based on energy bill prices as of October 2023.

Your home will either have cavity walls or solid walls, and the type of walls it has determines how you’ll insulate them. In this guide, we’ll explore solid walls, and how insulating them with internal wall insulation is one of the best options for this type of wall.

What are Solid Walls?

Solid walls are walls with no gap (known as a cavity) in the middle of them. Older homes are much more likely to have solid walls, so if your home was built before the 1920s, there’s a high chance its walls are solid.

If your home was built after the 1920s, it will probably have cavity walls which can be filled with cavity wall insulation to improve their thermal efficiency. As the name suggests, cavity walls have a space (a cavity) inside the wall. These walls were built to encourage ventilation around the home in a way that keeps dampness and mould at bay.

If you’re unsure if you have solid or cavity walls, with solid walls, the bricks have alternating patterns, and each brick might be a slightly different size or length from the last one. In cavity walls, the bricks usually have an even pattern and are all laid lengthways.

Cavity walls are also thicker since they require space for the cavity. If you’re unable to tell just by looking at your wall whether it’s a cavity wall or a solid wall, hire a professional to take a look.

What is Solid Wall Insulation?

Insulating a solid wall is different from the techniques used to insulate a cavity wall. With a cavity wall, you fill the gap in the wall with insulation material. With a solid wall, there’s no such gap to insulate, so instead, you’ll need to insulate the wall either externally or internally.

Internal vs External Wall Insulation

Both internal and external solid wall insulation involve applying installation materials to your wall. The difference between external and internal insulation determines whether the insulation is installed on the inside (internal walls) or the outside (external walls).

While both have their pros and cons, an obvious advantage of external vs internal wall insulation is that it doesn’t take up extra space inside your home, nor is it overly disruptive to install. Yet internal may be the best option for your home based on its location and proximity to neighbouring properties, etc.

Types of Insulation for Internal Walls

There are two main options if you want to install internal wall insulation – rigid insulation boards or a stud wall. Stud wall insulation will take up more space internally than rigid insulation boards as it is thicker. However, a stud wall does have advantages in that it is sturdy enough to be able to accommodate heavy wall fittings such as radiators or kitchen units. If the surface of the wall you’re insulating is uneven, you’ll need to level it with a layer of plaster or render before fitting rigid insulation boards, so a stud wall could be the easier option.

A stud wall involves installing a metal or wooden stud work frame to the wall and packing it with mineral wool fibre. You can plaster over the stud wall if you want to decorate it.

Mineral wool insulation isn’t as efficient as rigid insulation boards, so the filling should be at least 120mm thick, meaning it takes up more space in your rooms. If you want to double up the effectiveness of the stud wall, you can cover it with insulation boards to minimise heat loss and improve the thermal efficiency.

Rigid insulation boards are made of insulated plasterboard, which is then fitted to the inside of your walls. The insulation itself tends to be made from a form of foamed plastic.

Rigid insulation boards should be between 60mm and 100mm thick, but the thickness required will depend on the material used.

To install insulation boards, fix them directly onto the wall using plaster or adhesive. The boards will have to be held in place using extra fixings, and the installer will then seal the joints between the boards to prevent air from escaping.

The Pros and Cons of Internal Wall Insulation

Here are the main advantages and disadvantages of this type of insulation.

Pros of internal wall insulation

While it’s not the cheapest form of insulation, internal is significantly cheaper to install than external insulation. You can expect to pay around £8,500 for internal, while external insulation will set you back an average of £12,000.

Internal insulation is one of the most effective ways to make your home more thermally efficient, mostly because of how much heat is lost through your walls. Increasing your thermal efficiency brings other benefits, such as reducing your carbon footprint and lowering the cost of your energy bills.

The more energy efficient your home is, the less often you’ll have to switch on your heating or air conditioning. Not only will this save you money on energy bills, but you’ll also use fewer fossil fuels in your home, making it more planet-friendly.

Many people who live in listed properties or conservation areas might find that their planning permission application for external wall insulation is rejected. Fortunately, internal wall insulation doesn’t involve making changes to your property’s exterior, so you shouldn’t have to get permission from your local authority to make it happen.

Cons of internal wall insulation

One of the biggest disadvantages of internal insulation is that it takes up space inside your home. If your rooms are large, this might not matter so much, but in smaller rooms, internal insulation can take up valuable space where furniture should go.

If you want internal wall insulation but want to take up as little space as possible, consider installing rigid insulation boards instead of a stud wall.

Internal wall insulation can be disruptive to install, since it takes place inside the rooms of your home. You’ll have to move furniture out of the way and remove items from the wall, and the rooms in question can be out of use for a day or so. Work room by room over a few days to avoid too much of your property being out of bounds.
While internal wall insulation will certainly make a difference to your property’s thermal efficiency, it’s not quite as effective as external insulation. It is, however, much cheaper to install, so you might see a quicker return on investment with the internal solution than the external alternative.

Is Internal Wall Insulation Worth Installing?

Internal insulation is an effective type of insulation that reduces heat loss from walls – one of the parts of our homes that loses the most heat. Internal wall insulation isn’t, however, the cheapest way of insulating your home.

If budget is a factor, and your home doesn’t have any insulation already, you might want to consider insulating your loft, instead, with a material that’s DIY-friendly. Remember, you’ll really only need to consider internal or external wall insulation if your walls are solid.

If you have cavity walls, you can install insulation in the gap between the two sides that make up your walls, instead.

Can I Insulate Just Some of My Walls Internally?

While only insulating particular rooms in your home to shave costs is tempting, it’s not necessarily the best idea.

When you insulate the inside of the building, you raise the internal temperature and the amount of moisture that’s in the air as a result. That air then has to condensate, and it’s much more likely to condense on the cold parts of your property – in other words, the areas you haven’t insulated.

While you might want to keep costs to a minimum and so consider insulating only parts of your home, it could cost you in the long term, especially if it translates into damp and mould.

Does Internal Wall Insulation Make Your Home More Soundproof?

While internal insulation can reduce the noise that comes from outside or adjoining properties, it doesn’t have as significant an effect as you might imagine.

If noise is a serious issue for your home, consider investing in soundproofing, instead, rather than hoping for soundproofing as a side effect of insulation.

How Much Does Internal Wall Insulation Cost?

According to the Energy Saving Trust, internal wall insulation costs around £8,500. This cost is based on a typical 3-bedroom, semi-detached house in the UK, so if your home is smaller, you can expect to pay less. Larger detached homes with more rooms will cost more.

How much you pay for labour costs if you choose to have your internal wall insulation installed will depend in part on which area of the country you’re in. You’ll pay more for internal insulation if you’re in London and the Southeast, for example, than in the Northeast.

The good news is, insulation usually pays for itself multiple times over during its lifespan. Most home insulation will last the length of your home, and you can expect to get a return on investment during this time.

With Insulation Advisor, you can find the best possible deals with local installers that are ready to get started ASAP, meaning the typical costs of internal wall insulation may be less than if you compared installers yourself.

Does Internal Wall Insulation Cause Damp?

Internal wall insulation doesn’t automatically cause dampness, but there are a few things to be aware of before installing it, especially if your home is especially prone to dampness.

To explore the connection between internal insulation, we need to understand how damp occurs.

The dew point is the point when air meets a certain temperature that causes the moisture to condense. Internal insulation keeps the wall at the external temperature, drawing the dew point towards the internal surface.

If the dew point occurs too close to the internal surface of the existing wall, this can cause moisture which is absorbed by the insulation and appears as damp patches on the plasterboard surface.

The good news is that installing internal wall insulation doesn’t make damp an inevitability. To prevent damp, you’ll need to install a vapour control layer, which should significantly reduce the risk.

How to Prepare for Internal Wall Insulation

Installers may charge an hourly rate for their labour costs, so you’ll want to make sure internal insulation can be installed as quickly and efficiently as possible.

To prepare your home for internal wall insulation, move as much furniture out of the way of your walls as possible. If you’re having insulation fitted across your whole property at once, you might benefit from putting your belongings in storage temporarily.

Installing internal insulation can cause some mess, too, so lay down mats to catch any dust and debris around the areas of installation.

How to Find an Internal Wall Insulation Installer

Internal insulation is best fitted by a professional installer. It’s only suitable for DIY installation by those who have experience working on very similar projects.

Insulation Advisor can put you in touch with trusted installers who can advise you on the right insulation for your home. Whether it’s internal wall insulation, or you could benefit from some other insulation, we’ll help you find a local installer that can satisfy your insulation needs.

On This Page
Get Your Insulation Quote

Recent Articles