How to insulate a basement – the best materials for walls, ceilings, and floors

Basement insulation will make yours a comfortable part of your home, and save you money, too

kitchen diner and living space in a basement extension to a Victorian home with a golden retriever
(Image credit: Simon Maxwell)

Basement insulation can make yours a space that’s comfortable to use as well as dry – qualities you won’t want it to miss out on. And, of course, the basement is one of the areas of your home that should be well insulated if the whole home is to be as energy efficient as possible. 

Knowing how to insulate a basement can also have financial benefits. ‘A properly insulated basement can save you money on heating,’ says the US Department of Energy’s Office of Energy Efficiency & Renewable Energy.

Your basement ideas might include turning it into a home office, extra living space, guest bedroom and bathroom, or it might simply be a laundry room or storage space, but whatever your plans, basement insulation is a must and here are the details.

Basement insulation: walls, ceilings, and floors

If yours is a new basement construction, insulation can be added to the exterior of its walls. For reasons of practicality in an existing home, insulate interior walls. Bear in mind that even if you want to know how to finish a basement on a budget, wall insulation should be part of your plans.

You can also insulate the ceiling of a basement, but note that the Department of Energy does recommend that basement wall insulation is preferable to ceiling insulation.

Similarly, while insulating the basement floor isn’t as crucial as insulating the basement walls, it can be worthwhile. 

How to insulate a basement wall

Knowing how to insulate a basement wall is therefore key to any basement insulation project, and your number one priority.

Building codes will specify the R-value which is required for your home. The R-value tells you the insulating material’s resistance to conductive heat flow – the higher the R-value is, the better insulator it is. 

The Department of Energy says that almost any insulation type can be used, and its R-value guide offers recommendations for different regions.

Options for basement wall insulation include blanket insulation, foam board, loose-fill insulation and spray foam insulation, the Department of Energy says.

Interior insulation does reduce the space inside the basement, and be aware, too, that many types of insulation require a fire-rated covering, the department says.

How to insulate a basement ceiling

Another basement insulation option is insulation for the ceiling. If the basement is a completely unheated space, adding ceiling insulation in the form of batts or blankets will keep the living space above warmer. Be aware that if there are water pipes, these should be insulated because the basement will be colder than before.

However, if yours is a heated basement either because you want to use it as living space or because of the heating system, stick to insulating the basement walls to keep the heat in the space.

How to insulate a basement floor

To insulate a basement floor, you can use foam board. Also on offer are modular flooring systems that can go over the concrete slab without subflooring and which create a thermal break, or those that are subfloor and insulation in one.

The latter are preferable if the ceiling height of your basement is limited, and may be necessary in order to adhere to the height requirement of building codes. 

Consider a radiant heating option on the subfloor afterwards and before installing basement flooring for comfortable, even heat. 

What type of insulation is best for basements?

The best basement insulation for walls is probably spray foam insulation which will keep moisture out, stop cold air getting in, and has high R-values. Bear in mind that this is the most expensive insulation solution and it must be correctly installed to stop air leaks.

Easier to install if you are DIYing is foam board. If you do opt for foam board, bear in mind that it’s important that joints are properly taped, and that they are cut accurately. 

How do I insulate my concrete basement?

‘When it comes to converting a basement into a living space, one of the top things you want to do is to frame up your walls against the concrete in order to hold insulation,’ says Abel Gonzales of Brunson Construction. ‘This is because the concrete and ground get cold easily and that will make the living space cold.’

Concrete contains moisture so it’s vital to use basement insulation that will prevent the movement of this moisture and stop mold growing. Opt for foam insulation, which can either be in the form of spray foam or foam board.

Insulate a concrete floor before you lay flooring, using either a special product that combines insulation and subfloor, or with foam board insulation. If you use the latter, you can lay then pressure-treated sleepers followed by the subfloor.

Is insulating a basement worth it?

Whatever you plan to do with yours from finding basement bedroom ideas, using it as extra living space, or simply employing it for storage, insulating a basement is worth it.

Home energy efficiency requires proper insulation from the roof to the foundation, according to the Department of Energy, and the basement is no exception to the rule. An uninsulated basement loses heat, which means larger utility bills, and that’s a result no one welcomes – especially when managing basement remodeling costs in the first place.

Sarah Warwick
Sarah Warwick

Sarah is a freelance journalist and editor writing for websites, national newspapers, and magazines. She’s spent most of her journalistic career specialising in homes – long enough to see fridges become smart, decorating fashions embrace both minimalism and maximalism, and interiors that blur the indoor/outdoor link become a must-have. She loves testing the latest home appliances, revealing the trends in furnishings and fittings for every room, and investigating the benefits, costs and practicalities of home improvement. It's no big surprise that she likes to put what she writes about into practice, and is a serial house revamper. For Realhomes.com, Sarah reviews coffee machines and vacuum cleaners, taking them through their paces at home to give us an honest, real life review and comparison of every model.

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