Why Is the Room Above the Garage So Hot? (5 Effective Ways to Cool It!)

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Why Are Rooms Above Garages Hot?

Do you have a room above your garage that you are not able to use during summer because it gets too hot. There does not seem to be any problem in the other rooms on the same floor. So why is the room above the garage hotter than others?

A room above the garage gets hot because the warm air in the garage is lighter and rises up. If the garage ceiling is poorly insulated or there are leaks then the heat infiltrates into the room above.

A garage is more exposed to the elements than possibly any other room in your house. Typically two, sometimes three sides of an attached garage are exposed to the elements. It is worse for a detached garage. All sides are exposed!

The garage door is the biggest culprit when it comes to heat gain (or loss) by a garage. It is large enough to take up most of one wall. 

More often than not a garage door is made from steel or aluminum, both of which are good conductors of heat. 

The garage door opens several times in the day. It lets in a huge amount of hot air every time it opens.

Why Room Above Garage is Hot?

Heat is transmitted through conduction, convection and radiation. A garage door, that is not insulated, does a great job of each, unfortunately!

Hot air is lighter than cold air and moves up. You know that because you have seen hot air balloons go up in the sky. In a similar manner the hot air moves up and lingers around the drywall garage ceiling.

This heat can be transmitted to the room above by conduction if the garage ceiling is not insulated or through convection if there are air leaks.

GMS Intro
GMS Intro

How Can I Cool Down My Room Above My Garage?

Conceptually heat flow is quite similar to water flow. Heat flows from an area with high temperature to an area with low temperature just like water flows from high ground to low ground.

Think of your home as a water reservoir. When temperatures outside are high, heat flows in and accumulates within the house. HVAC is the way to get the heat out and keep every room in your house at a comfortable temperature.

However, you can not duct your home HVAC to your garage. It is against the building code!

But you can adopt some or all of the ways that I am giving below to make the room above your garage less hot.

1. Improve Insulation Above the Garage Ceiling

The insulation between the garage ceiling and the floor of the room above may not be sufficient or may have become less effective with the passage of time.

The least destructive way of increasing the insulation in that space is to use “Injection Foam Insulation”. Injection Foam Insulation is injected into a closed cavity (the joist bay). Holes are drilled into the ceiling drywall and the foam is injected, under pressure, till every available space is filled up.

The entire process is not messy. The holes drilled into the drywall are small and can easily be patched and painted over. Of course injection foam insulation can only be done by experienced contractors who have the expertise and the equipment.

Injection foam not only insulates but also seals all air gaps. The heat and even the sound from the garage will not be able to get into the room above.

2. Improve Insulation in the Knee Wall

The insulation in the knee wall is usually totally ignored after construction. Like anything else it degrades over the years. Poor or inadequate insulation in the knee wall will make the room above the garage hot.

313 CAD 2-4 Knee wall inside conditioned space 5-01014 GBA 1-31-12 0 US Department of Energy, Public domain, via Wikimedia Commons

The best way is to pull out the old insulation and replace it with new fiberglass insulation rolls such as Owens Corning R-13 Faced Insulation Roll. To beef up the insulation you can fill up the void space in the knee wall attic with cellulose.

3. Improve Airflow to Room Above Garage

The room above the garage gets cooled, like any other room in the house by air ducts from the HVAC system. Quite often the problem may be that the airflow into this room is not enough. What about the return-air vent? Is it in working condition and open?

All the work on improving the insulation will make the room above the garage less hot, but it may still not be comfortably cool, without tweaking the airflow from the HVAC system.

4. Make your Garage Cooler

It stands to reason that if your garage is cooler, then the room above the garage would not be so hot. A lot of the heat entering your garage is through the garage door. And a lot of it is radiant heat if your garage faces the sun most of the day.

It takes very little money and effort to insulate the garage door for hot climates. In hot climates, the focus has to be on blocking as much of the solar radiation as possible. This is achieved by sandwiching a layer of air entrapping material between reflective films.

There are two brands which are very popular and get good reviews; REACH and REFLECTIX. Take your pick.

Reach Barrier (3009) Garage Door Insulation Kit, available on Amazon, works well in hot climates.

Reflectix (BP24050) Bubble Pack Insulation, available on Amazon, comes as a roll rather than a Kit.

For more information check out my earlier post, The Best Garage Door Insulation For Hot Climates (Helpful Advice!).

5. Add Natural Ventilation

A cool way to ventilate a garage that is unconditioned is to add vents at the right places to create natural ventilation.

Strategically placed garage wall vents can get the air circulation going naturally. 

A few vents on the higher end of the garage wall (nearer to the roof) or preferably garage roof vents, will let the hot air garage out. A few vents in the wall, just a couple of inches above the floor will pull in the cooler outside air to compensate.

The vents in the wall will not only to set up air circulation within the garage but also to cool the garage during warm weather.

Garage Wall Vents are the easiest and the cheapest (actually totally free!) way to cool a garage.

Find out more at Why Have Garage Wall Vents? (7 Important Reasons You Need To Know!).


The room above the garage gets hot as warm air in the garage moves up and either infiltrates the room or heats it by conduction in case the insulation is not good.

You can take one or preferably all of the following five ways to cool down the room:

  1. Improve Insulation Above the Garage Ceiling
  2. Improve Insulation in the Knee Wall
  3. Improve Airflow from HVAC to Room Above Garage
  4. Make your Garage Cooler by Insulating the Door
  5. Add Natural Ventilation in the Garage using Vents

There is an initial investment cost but there is absolutely no maintenance or running cost. All of the five ways are passive and have no running costs.

Thank you very much for reading the post. I do hope you found it informative and useful.

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