Hot Bonus Room

Do you have a hot bonus room located over the garage or perhaps one surrounded by a hot attic with little to no insulation? What are the best options for insulating the bonus room without creating a moisture problem? Should you add an additional A/C system to get cooler air to that part of the home? These are some of the topics we will discuss in this article.

Why is My Bonus Room So Hot!

Many times the bonus room and most rooms directly under the attic or surrounded by attic are hot primarily due to lack of air sealing and lack of ventilation. The hot attic is getting hotter as the sun beats down on the shingles. That radiant heat is transferred into the attic and then to the living space through air gaps.

Great Article: How to cool an attic bedroom

Addressing Radiant Heat

Radiant heat can be addressed using a radiant barrier, spray foam, or active attic ventilation. We have found that a combination of all three is typical for most attics. Some attics are difficult to move in or have unique architectural challenges that may require all three options to help reduce radiant heat in the attic.

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Adding More Air Conditioning

We hear this a lot that homeowners have spent money purchasing more tonnage or a high seer HVAC system and are disappointed at the results. Most contractors make suggestions in reverse when it comes to cooling your home. We feel beefing up insulation in the attic, basement, and crawl space should come first. This can include air sealing and a higher R-value of insulation depending on what part of the home is being affected.

Once the home is properly air sealed and insulated, a load calculation can be done by the HVAC contractor. Air sealing the ductwork to make sure the cold air is arriving at its desired destination is also recommended.

Knee Walls Around the Hot Bonus Room

This is another area often fixed incorrectly. If insulation is installed in the knee walls, it is typically batt insulation that does very little to stop air movement. If the knee wall is air sealed and properly insulated in a way to not restrict ventilation, this is the best method to help cool your bonus room.

Mold in the Attic

Most of the time mold and moisture form in the attic from condensation. This in part can be from improper ventilation as well as a super hot attic surrounding really cold ductwork. Leaky ductwork makes this even worse because the duct insulation has little effect on protecting the ducts.

Never install radiant barrier, even if it is perforated, on top of the attic floor. Perforated radiant barriers can still trap moisture and any dust build-up on top of the radiant barrier can make it ineffective over time.

Hiring the Right Attic Insulation Contractor

Let’s face it. Most problems in the attic can be avoided by hiring the right attic insulation contractor. This is rarely the cheapest contractor. We have had to do many redos of attics, basements, and crawl spaces for homeowners that make decisions based on price versus quality. Redoing a project will cost you way more than doing it right the first time.

I hope you found this information helpful in the pursuit of correcting your hot bonus room. We have many videos on fixing hot attics, I will put a link to one below. For others, please check out our YouTube Channel Hot Attic Series.

Also let us know if you have any questions or comments below.

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2 thoughts on “Hot Bonus Room”

  1. Hi, I am going to redo my bonus room, that is above my attached garage, in the spring and have a couple questions.The only access to the bonus room is through a door from my master suite, which is above the garage. Also the bonus room roof is totally separate from the main roof of the house so it does not share any attic space with the main roof. The bonus room is only maybe 7×9′ in the main space of it and then about 4″ high knew walls, and the roof and floor expand as wide as my two car garage that has separate doors, so maybe 20′. The room is all drywalled so until i take it down I wont know how much insulation is behind it and on the floor/garage ceiling. I watched your bonus room insulation video about insulating the space behind the knee wall because i would like to incorporate the space behind the knee wall as usable space if possible to make the room larger. was wondering if you used a radiant barrier on the rafters before you used foam board and spray foam? I was reading that i can use a radiant barrier to keep the heat reflected out of the bonus room, then add an air gap, then insulation, I would use foam board and spray foam like you to keep it in place and seal the edges and seams. Also, there are vents in my soffit but until i take the drywall down i dont know if there is a ridge vent ( dont see anything from outside) to circulate the air. I do know there are no metal type vents in this roof. Can i seal off these soffit vents and possible ridge vent to make the room warmer? I also plan on keeping any existing batt insulation in the floor and then insulate more. But can I use a radiant barrier like prodex in between the joists on the garage ceiling drywall, to keep the heat in the garage, then put in an airgap, then the original insulation, then foam board with spray foam then put down subfloor…Sorry for so many questions.. I have never done this but am very will to learn and try everything myself.. I might hire out the drywall though..
    thank you so much for any help. If you want pics let me know…I am in upstate New York so its very cold here so i wont be starting the work until just after the cold weather breaks.

    1. Hi Angela, I think using the radiant barrier spray foam combination will work but make sure you leave a gap per radiant barrier install recommendations. I would not seal the vents. Sealing the vents could create a moisture problem. We see this a lot on cathedral sealings with inadequate ventilation. I’d recommend you get an insulation company out to give you a second opinion. Doing this project incorrectly yourself will cost you way more than paying someone to do it correctly. Hope that helps.

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