As we have said several times before, converting your garage into more living space is a great, cost-effective way to add more room to your home. The main challenge is making that cold, damp garage into a warm and inviting house room. One Critical aspect of this transformation is insulation.

Garages are not designed to be lived in. They have a singular purpose; they house your car. And your car doesn’t care if your garage is cold and damp, but you do.

Before you even think about buying supplies, check your local building codes. There are probably standards that must be met when converting a garage into a living space. Also, get the recommended R-value for the floor, ceiling and walls. The R-value refers to the ability of the insulation to resist heat loss.

Ceilings and Walls Examine the ceiling and walls for any signs of cracks that may let moisture into your garage. You will need to repair these openings before any other steps are taken. This can be done with spray foam.

Use fibreglass batt insulation and make sure it fits tightly between the wall framing and ceiling joists. Do not overstuff the cavity with insulation. If you used face insulation, the vapour barrier should be toward the heat side or facing you. Staple the flanges to the studs about every 8 inches.

Floor First, make sure the concrete floor is level and free of moisture.

There are a couple of options for insulating the garage floor: You can cover the floor with rigid foam insulation or install wood sleepers on the garage floor and install rigid foam panels between the sleepers.

Use a vapour barrier. Use six-millimetre polyethylene (plastic sheeting). Cover the entire slab and extend it up the side of the walls 4 to 6 inches. Overlap the seam about 8 inches and use insulation tape to seal the seams. If you are not using sleepers, position the foam board over the plastic sheeting and leave a ¼-inch crack around the borders. Use insulation tape to seal the joints.

Use insect- and decay-resistant 1-by-4 or 2-by-4 stock for the sleepers. Place sleepers around the perimeter of the garage. Leave a ¼-inch space between the sleepers and the walls. Fill out the remainder of the area; if you are using 1-by-4s, place the boards 12 inches in the centre. 

Place 2-by-4 sleeper stock 16 inches on centre. Use a powder-actuated nailer to secure the sleepers to the concrete slab. If you use 2-by-4 sleepers, the result will be a much stronger floor.

The rigid foam insulation should be the same thickness as the sleepers. Fit the foam between the sleepers, but leave a ¼-inch space around the perimeter. Only use compression-grade rigid foam insulation panels.

FAQs About Garage Renovation

How Much Does It Cost To Insulate A Garage?

The options for insulating are to treat the internal or external surface. The advantages of external insulation are that it retains more of the floor space and, most importantly, provides weather-proofing to the wall. 

Starting price for insulation materials will be around $350 for sufficient polystyrene and fixings for a single garage, plus installation costs which will be significant. That will provide 50mm polystyrene, which will need to be clad or rendered to provide a waterproof finish. 

While there is potential for the skilled DIYer to take on the project, it is not simple and probably best left to the professionals. In which case, budget $100/m2 for the finished project.  

Do I Need To Insulate A Garage?

The method and amount of insulation will vary with the intended use for the garage. If it is to be used for a garage conversion idea such as a utility room or home gym, say, it will need less insolation than if it is to be used as a living space or a bedroom. In the first case, the 50mm insulation discussed above would be adequate. 

If it is to be used for accommodation, it would be wise to increase to at least 70mm Kingspan or Celotex or 100mm polystyrene. 

It is not uncommon for the garage to be repurposed, at least in part, as a plant room to accommodate a boiler or heat pump and hot water cylinder, perhaps with solar panel control gear. 

In this case, insulation is not necessary. However, consideration might be given to pipe runs from and around the garage to ensure they are not in the way if there is a change of mind and the garage is to be used as accommodation. 

Is Insulating A Garage Worth It?

If the garage is being converted to accommodation space, there is no option. It will be necessary to comply with building regulations and be sufficiently comfortable to live in. 

In financial terms, the questions of ‘payback’ or ‘return on investment’ do not occur. The project is extending the living space and will therefore add to the heating bill. Insulating the garage will minimise that and improve the thermal comfort of the garage and any adjacent rooms, but it will not reduce the overall heating bill.

What Insulation Do I Need For The Garage?

Fibreglass is the most commonly used type of insulation in garages (just as it’s the most popular type in homes). It’s sold in precut batts and long blankets that fit between wall studs and ceiling joists.

What Is The Cheapest Way To Insulate A Garage?

Fibreglass roll insulation is the cheapest and easiest type to install, provided that your garage’s interior walls have not been constructed. Unroll the insulation between the wall studs with the vapour barrier facing the inside of the garage.

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Insulate The Walls, Ceiling And Floor

Insulating a garage is not a complicated process, often easier than insulating the house. Still, to get it right, you need to know how the garage is constructed and the reason for insulating it.

If an integral garage is making the bedroom above it (or the lounge beside it) cold, what you want to do is insulate the house from the garage, as you’re not particularly looking to keep the garage warm but rather to prevent it from affecting the comfort in adjacent rooms.

 However, if it is an integral or detached garage conversion that is being insulated to provide more living space, it will want the same level of insulation as the house itself. 

Here’s what you need to know about the process. 

Garage Walls

Garage walls are typically single-skin brick or block, which presents the problem of rainwater penetration as single skin masonry is not great at keeping rainwater out. Usually, in the uninsulated garage, any moisture penetrating the wall will mostly be evaporated away and not be an issue. 

Installing insulation will prevent air movement on the wall, and moisture penetrating the wall does become a problem. If the internal surface of the wall is damp, then its cause – poor brickwork or pointing, cracks in the render, failed gutters and the like – needs dealing with before any insulation is installed. 

The options for insulating are to treat the internal or external surface. The advantages of external wall insulation are that it retains more of the floor space and, most importantly, provides weather-proofing to the wall. 

However, internal wall insulation is more likely as it is usually simpler and cheaper. There are three ways to do it. 

Fix The Insulation Directly To The Wall

Kingspan and Celotex offer products specifically designed for this method, with insulation bonded to plasterboard and with a vapour barrier. If the wall’s surface is in good condition, this is a relatively inexpensive and quick method of insulating. 

The boards are glued directly to the wall (using a specific adhesive), together with mechanical fixings (screws). The boards themselves are quite expensive, at £9/m2 for Tektherm polystyrene to £19/m2 for Celotex PL4040, but this is offset by the speed of installation. 

Fix Battens To The Wall Which Can Carry The Insulation

This provides a gap between the wall and the insulation, ensuring that any moisture penetrating the wall cannot reach the insulation. 

This is also a good method where the wall is particularly uneven. The cost will be broadly the same as with the first method as it will use the same materials, plus the cost of battens. 

Construct A New Stud Wall Inside The Existing Wall

This is generally only done when the existing wall is particularly subject to rainwater penetration as it is the most expensive option and no more effective. The stud wall will generally be 100mm thick and need a 40mm ventilated cavity between it and the wall meaning that it will significantly intrude on floor space.

Apply Insulating Plaster Directly To The Internal Wall

This is most useful on stone walls, where breathability is important and would involve natural insulation, either hemp or cork-lime mix (the hemp or cork providing the insulation) or layers of lime plaster sandwiching a cork or wood fibre insulation.

This option will not get the low U-value – typically around 0.5W/m2, which is about the same as 50mm polystyrene will do – but it achieves all that the other options provide at broadly the same cost, provides a solid fixing for pictures, cupboards, etc., and is breathable, deals with moisture penetration.

The objective is to keep rooms above or adjacent to the garage warm. The only wall that needs insulating is the party wall with that room. That wall will be a cavity wall and require the cavity to be filled with insulation first. 

There is no potential for this to cause any moisture penetration problems as the external surface of the wall is not exposed to the elements. The option exists to add more insulation to the external surface, but this is largely unnecessary as the wall is sheltered and the cavity fill is sufficient.

Integral garages often have cavity walls, and where it is being converted to habitable space, then cavity-fill is an option. This wall can be insulated internally, but external insulation would only be effective if the cavity is also filled.

Insulate The Roof/Ceiling

Insulating a roof or ceiling will follow the same rules as insulating a similar area in the house. In the case of the flat roof, it may be necessary to drop an existing ceiling and install insulation between the joists.

 In the case of a pitched roof, installing insulation between rafters ensures a ventilation gap between the insulation and the underside of the roof covering. In both cases, rigid foam insulation is likely easiest to install and most effective.

Plasterboards can be reinstalled to provide a ceiling if desired, or the joists or rafters battened across to hold the insulation in place. Cost and U-value will be broadly the same as for the walls.

Insulate A Garage Floor

It is safe to assume that the floor is uninsulated and solid concrete, laid on hardcore. Getting the garage to habitable standards means doing something with the floor, if only to comply with building regulations. Still, it isn’t easy to justify the cost of excavating the floor and relaying the concrete merely to install insulation. A more practical option will be to place insulation on top of the floor, and how thick that is will be affected by the ceiling height.

 The optimum insulation thickness would be 100mm of rigid foam insulation, giving a U-value of 0.22W/m2K. The minimum ceiling height in habitable rooms would be 2.1m. It may be that there is insufficient ceiling height for 100mm of insulation or that it presents problems elsewhere — at door thresholds and the like. In which case, install what is practically possible. Even insulating a floor with 10mm insulation will make the floor feel warmer if it does not do much to improve the U-value.  

Insulate A Garage Door 

If the garage is to be a habitable space, then it makes more sense to remove the door and infill the opening with an insulated timber frame or masonry wall. 

If it is to be retained as vehicle access, and insulation is still needed, then specific materials are available, like ThermaWrap, Superfoil, or Weather Stop. These are all glued to the inside of the door – either self-adhesive or with adhesive pads – and are a simple DIY job, costing around $60 for a single garage door. 

In addition, it would be wise to install draught-proofing and Weather Stop (amongst others) and provide sealing strips, which are again a DIY job and cost around $50. Even if the rest of the garage is not to be insulated, then treating the garage door in this way will make the garage a warmer, more welcoming space at minimum cost.  

Garage Conversion Insulation Requirements

Garage conversion insulation regulations determine how much insulation you need on the walls, floor, and ceiling of the garage. Insulation is measured in U-values. The U-values determine how much heat is lost through the walls of your space. U-values are calculated Watts-Per-Metre-Square-Kelvin (W/m2K).

To comply with building regs for garage conversion insulation, the U-value targets are:

  • 0.18 W/m2K for a flat roof
  • 0.28 W/m2K for the walls
  • 0.22 W/m2K for the floor

The garage conversion minimum floor insulation depends on the material that you use. The most common form of insulation is polystyrene, which would need to be 100mm thick.

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5 Types Of Insulation For Your Garage

Insulating a garage makes sense if you’re planning to heat the space. When it comes to choosing materials, you can use the same types of insulation used on the rest of the house, but some are better than others, depending on whether the garage is finished. You also want to look at insulating the garage door, which has different installation requirements than walls or ceilings. 

Here are five types of insulation for your garage.

Fibreglass Insulation

Fibreglass is the most commonly used type of insulation in garages (just as it’s the most popular type in homes). It’s sold in precut batts and long blankets that fit between wall studs and ceiling joists. You can also get loose-fill fibreglass, which is suitable for blowing into a garage attic space above a finished ceiling.

If the walls and ceiling will remain open (not covered with drywall or plywood), it’s a good idea to use paper-faced or encapsulated fibreglass batts that are wrapped in a plastic film. These will give the walls a slightly more finished look, and you won’t have the itchy fibres of the insulation exposed and ready to catch dust at all times.

Cellulose Insulation

Cellulose is loose-fill insulation that is growing in popularity. Made primarily from recycled newspapers and treated with a fire retardant, cellulose is usually blown into wall and ceiling cavities with a special blowing machine that also aerates the cellulose and fluffs it up. Blowers can be rented at many tool rental stores, and home centres will sometimes loan you a free one if you buy your cellulose from them.

Because it’s loose-fill, cellulose is suitable only for finished garage walls and ceilings. If the garage is already finished (but uninsulated), you can install cellulose by cutting strategic holes in the wall material, spraying the insulating into the cavities between framing members, and then patching the holes.

Rigid Foam Insulation

Rigid foam comes in 4-by 8-foot sheets and 1/2-inch to 4-inch thicknesses. The most common materials include expanded polystyrene (similar to Styrofoam), extruded polystyrene, and polyisocyanurate. Rigid foam offers a high R-value per inch of thickness and can be cut to fit almost any space. It’s a good choice for thin walls and insulating garage doors.

Spray Foam Insulation

Spray foam (beyond the low-expanding canned product) is excellent for R-value and air sealing. As a high-end material typically used for energy-efficient construction, spray foam may be overkill for most garage projects. But it might make sense if you’re converting the garage to a living space.

Garage Door Insulation

Don’t insulate your garage walls and ceiling without insulating the big garage door, too. You can buy insulation kits for standard metal garage doors, or you can cut pieces of rigid foam insulation or Reflectix sheets to fit each door panel/section. 

Remember that the structural metal ribbing of garage doors is an excellent conductor of heat, and this typically doesn’t get insulated. As a result, the overall thermal performance of the door will be well below the rated performance of the insulation itself.

Air sealing is particularly important with garage doors. Create a seal along the sides and top of the door with special garage door trim with an integrated weather-seal strip. Seal along the bottom of the door with a new rubber gasket, or “bottom seal.” It’s available in different sizes to cover small or large gaps between the door and the garage floor.

Garage Insulation Basics

It pays to insulate your garage if you’re adding a garage heater, whether on a permanent or as-needed basis. If you’re not adding heat, there’s little point in insulating. It’s a popular misconception that insulation adds warmth. 

In reality, insulation merely slows heat transfer through the insulated barrier (wall, ceiling, or floor), which is good for hot and cold climates.

Some say that insulating an unheated garage attached to the house may offer an additional thermal buffer between the exterior of the home and the outdoors. 

But no state requires the entirety of the garage to be insulated as part of an energy-efficiency mandate.2 It’s also unlikely that this minimum improvement in energy transfer will offset the costs of adding extensive insulation. The walls that are shared with the house, however, should always be insulated to their maximum value.

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