Home insulation: where, how and why you should insulate a house

The right home insulation will make your home warmer in winter, cooler in summer, and reduce energy bills.

Insulation types: all the materials from sheeps wool to rigid boards
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(Image credit: Thermafleece)

Maximizing home insulation makes your home a more comfortable place to be. It will get rid of cold drafts and ensure rooms are warmer in the cooler months of the year. But it will also help keep rooms cooler when it’s hot outside.

And the benefits don’t stop there. Get your home insulation right and you’ll reduce what you spend on heating and cooling annually, plus do your part to use less energy. 

There are many areas of your home that will benefit from insulation – or from boosting what’s already there – and attic insulation is a great place to start your project. But windows, doors, walls and floors can also be improved when you insulate a house using the best materials and installation approach.

What is the best type of insulation for a home?

There are many different home insulation types available. ‘Choosing the right one is dependent on where in your home insulation is required, and the location’s recommended R-value for types of insulation,’ says Leonard Ang, CEO, iPropertyManagement

‘The most common type of insulation is fiberglass and blanket types, as they are easy to install, relatively cheap, and can go in walls, ceilings, and floors.’

Home insulation types:

Blanket insulation, which comes in rolls or batts. It can be made from materials such as fiberglass, mineral wool and natural fibers.

Foam boards, which come in different types such as polyisocyanurate, polystyrene, and polyurethane. 

Spray foam insulation, which expands to fill gaps.

Blown-in and loose fill insulation, which may be cellulose, fiberglass or mineral wool. It can be used in cavity walls or loft floors, for example.

Rigid fibrous or fiber insulation is made from fiberglass or mineral wool. It’s used in ducts in unconditioned spaces.

Wondering what is the most efficient insulation for a house? Different types of home insulation have different R-values. The R-value is a material’s thermal resistance and the higher the value, the greater its insulating effectiveness. 

But what’s also vital is the thickness of insulation and you can achieve effective insulation for a particular area of your home with different materials so long as you use the required thickness. In other words, you might want to use a greater depth of a lower cost insulation unless there’s a space restriction.

Is home insulation expensive?

Some types of home insulation are relatively inexpensive in themselves plus they can be fitted on a DIY basis, reducing the cost to insulate a house still further. Others cost more and some must be installed by professional contractors which will also result in a higher bill. Bear in mind that the overall cost will also depend on your home’s existing insulation as well as how it was built.

‘The cost of insulation is between $1,500 and $6,500 depending on the choice of the materials,’ says Lionel Scharly, strategic construction advisor at Real Estate Bees.

How much money will home insulation save you?

The US Environmental Protection Agency (EPA) estimates that air sealing a home and adding insulation in the attic, floors over crawl spaces, and accessible basement rim joists can save an average of 15 per cent on heating and cooling costs, or an average of 11 per cent of total energy costs. 

‘The most cost effective way to insulate is to get a contractor to do a full assessment of your house and provide you with a quotation that details your cost savings over time due to insulation,’ recommends engineer Mogale Modisane of ToolsGaloreHQ.

You can also check out the US Department of Energy’s energy saver calculator to estimate costs and payback.

Insulating your home against drafts

Unless your home is very new, you will almost certainly lose some heat through air leakage around doors and windows, gaps in the flooring, or through the chimney. 

Windows and doors can be improved with caulk and weatherstripping. If windows are single pane versions, add storm windows. If gaps around a window are large, use foam sealant.

Be aware that doors and windows in historic homes may need particular maintenance.

Fireplace chimneys with air leaks need these sealed using fire-resistant materials. Consider also an inflatable chimney balloon for the fireplace flue when it is not in use to seal it.

Baseboard gaps can be filled with foam sealant if they are large.

Plumbing, electrical wiring and ducting coming through the walls, floors, and ceilings may also suffer from air leaks, which should be caulked and sealed.

Insulating your attic

Attic easy to access and has no damp problems? You can DIY. Calling in a professional’s also possible. Attic damp? Sort this out first.

1. Insulating between boards
If the loft joists are regular, you can use rolls or batts. Lay the first layer between the joists, and the next at right angles to cover the joists. 

For old buildings, permeable insulation is effective.

2. Loose fill and blown-in insulation
This is usually less expensive to install than batt insulation and gives better coverage if properly installed, according to the US Department of Energy. You can rent a machine in order to install it, or pour it in. You can also call in a professional contractor to insulate the attic this way.

3. Spray foam and foamed-in-place insulation
This can be used for unfinished attic floors.

4. Radiant barrier
If you live in a hot or warm climate, the Department of Energy recommends considering installing a radiant barrier which will reduce heat gain in summer, and reduce cooling costs.

The typical cost of installing attic insulation is between $1,500 and $3,500, according to online home services company HomeAdvisor.  

Insulate exterior walls

Blown-in insulation can be used to insulate the exterior walls of your home. During a remodel where wall cavities will be open two-part spray foam or wet spray cellulose insulation are possibilities, according to the Department of Energy.

If they’re not going to be open, it suggests the option of injectable spray foam insulation.

Cavity wall insulation costs about $1 to $2 per square foot on average, according to HomeAdvisor

Insulate an internal wall

Walls can be insulated internally by fitting batts of insulation between the wall studs. Fiberglass versions are inexpensive, but care should be taken when fitting them; wear a mask, goggles, and protective clothing. 

‘While fiberglass offers several advantages over other types of insulation, it does have the disadvantage of sagging over time, necessitating the need to replace it regularly,’ says David Sheppard, founder/home improvement contractorHVAC Judge.

Fiberglass batt and roll costs on average between $0.30 and $1.50 per square foot, according to HomeAdvisor.

Insulate the floors

The US Department of Energy recommends insulating floors above cold spaces like vented crawl spaces and unheated garages as well as slab floors built directly on to the ground. Bear in mind also that floors in old homes often allow the escape of heat and good floor insulation can help prevent this. 

Which floor insulation you use will depend on the type of floor concerned, whether it’s suspended timber, solid and made from brick, stone or tile, or concrete. Fiberglass or mineral wool, foam boards, or spray foam might be used for floors.

Insulating a crawl space or floor costs between $1 and $5 per square foot, according to HomeAdvisor.

Insulate ductwork

Ducts in an unconditioned space should be sealed and insulated, according to the Department of Energy. 

‘Ducts carry hot or cold air through the walls and ceilings of your home,’ says Lester Mclaughlin, VP of Operations at Blue National HVAC. ‘Sometimes they’re installed in drafty spaces without climate control, like your attic. If your ducts are poorly sealed or uninsulated, you’re likely losing heated or cooled air and wasting money and energy.

‘All insulations have what’s called an R-value, which is a measure of the resistance to air and temperature flow a material provides. I recommend using insulation with an R-value of 6 or higher.’

Minor duct repairs can be made on a DIY basis, and seams and joints sealed with duct mastic, providing gaps are not over one-quarter inch in size.

Bear in mind, however, that ducts in unconditioned spaces should be sealed and insulated by professionals, says the Department of Energy. 

What is the cheapest way to insulate an old house?

The cheapest way to insulate an old house is to address any air leaks. ‘Reducing the amount of air that leaks in and out of your home is a cost-effective way to cut heating and cooling costs, improve durability, increase comfort, and create a healthier indoor environment,’ says the Department of Energy.

Caulking – for cracks and openings around door and window frames, for example –and weatherstripping – where components move – are quick fixes, and offer speedy returns on investment, frequently in a year or less, the department says.

Carpet with an insulating pad underneath can also be a low cost solution as can curtains in heavy fabrics with an insulating lining.

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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