Hot Bonus Rooms & How to Fix Them

Services for Real Estate Pros with Energeyes Inc.

Last week we discussed the common problem of the uncomfortable bonus room and reviewed several reasons why it gets so hot. (To see last post click HERE) By popular demand, I am posting again to answer the question of, "what can be done about it". I will give the solutions to the four problems identified last time, namely "Attic Air Currents", "Attic Heat Buildup", "Attic Access Doors", and "Heat Rises".

1. Sealed Insulation: Because fiberglass insulation is porous it MUST be sealed on all six sides to perform at its maximum. When you look into most bonus room attics you will see that the insulation on the wall is exposed on the back, the insulation between the ceilings is exposed on the ends, and the insulation between the floor and the garage is exposed as well. If this is the case, air currents which are caused by the force of warm air rising, will be constantly moving across and through the fiberglass insulation greatly reducing its effectiveness. To solve this problem a proper air barrier needs to be installed to block these air currents. First, install a sheathing material such as a thin ply wood or dry wall over the back of your exposed knee-wall insulation. Make sure to seal each of the joints with an expandable foam or calk to create a proper air barrier. If you want to the very best results you can use a foam insulation board as your air barrier which will also add additional R-value to your wall assembly. Second, use the same sheathing material and cut pieces to fit in the cavities between the two floors and the floor joists. You can cut them a little small so they fit easily and use expandable foam to seal around the crack. Third, the final project is to finish making your insulation air tight by installing a card board stop over the exposed ends of your ceiling insulation. If you look at this insulation you should see a styrofoam baffle between the top of the insulation and the decking on your roof. This is to allow hot attic air to flow to the peak of the roof between the insulation and the roof decking and exit out your ridge vents. When installing your card board stop you need to make sure that it goes between the insulation and the styrofoam baffle and then folds over the end of the insulation. The goal of this stop is to block air currents from flowing through the insulation and direct them to flow through the space between the baffle and the roof as intended. Once you have finished these three steps your insulation will be able to function as designed and perform at is best.

2. Radiant Barrier: The best way to combat attic heat buildup if you have a properly vented attic is with a radiant barrier. This product was developed by NASA and reflects radiant heat. Radiant heat is the heat you feel when you step into direct sun light. When the sun hits your roof it heats is up, and it intern, begins radiating heat into your attic. By installing a radiant barrier across the air barrier covering your knee-walls it will reflect that radiant heat away from your bonus room. You can also install it on the underside of your roof rafters, as a second line of defense, to block heat from entering your attic. Properly installed radiant barrier combined with properly sealed insulation makes the best barricade against the summer heat.

3. Attic Door Insulation: If your attic doors are not insulated at all or if they are covered with some old fiberglass insulation, it is high time to properly insulate them. The best option is to use a foam boar product around 2" inches thick which will give you an approximate R-13 insulation level. You can also attach some of the radiant barrier to the back of these doors to reflect the attic heat.

4. Air Sealing: Although there is nothing that I can recommend to reverse the reality of heat rising, there are solutions to help limit its affect. Air sealing your home is the key. In order to understand how to properly air seal your home, you must remember that hot air rises and that for every cubic foot of air that escapes from your home one is replaced. These two realities mean that when warm air in your house rises to the highest point in the home and escapes through a crack or hole into your attic it is replaced by warm outside air from somewhere lower in your house like a plumbing penetration in your crawlspace. As this action occurs hour after hour it draws more warm air into your house and makes your AC system struggle to keep up. To stop this problem begin sealing all the penetrations you can in your attic and then begin sealing any other air leaks lower down in your home. When air sealing always remember "top down" because if you can stop an air leak in your attic it will block air that is trying to escape as well as keeping that air from creating a negative pressure on your house and drawing in warm air from somewhere else.

Hot bonus rooms are a hassle, but they don't need to get the better of you. These fairly simple solutions can revolutionize the comfort of your bonus room and make it a place that you actually enjoy spending time on these hot summer days. I know my explanations may be a bit confusing if you don't have a construction background so feel free to ask me any questions. If you don't feel like spending the time in your cramped hot bonus room attic to install these improvements, give us a call, and we can do it for you. Visit us at 


Comments (10)

Jeremy Wrenn
Winslow Homes - Youngsville, NC
C.O.O., Winslow Homes

Awesome, Phillip!  Great follow up to the previous article.  I suggested it for feature, and am going to re-blog it as well.

Good info!

Jul 02, 2011 07:10 AM
Phillip Bradrick
Energeyes Inc. - Raleigh, NC

Thanks Jeremy!  

Jul 02, 2011 07:27 AM
Jeremy Wrenn
Winslow Homes - Youngsville, NC
C.O.O., Winslow Homes

Phillip, as customer of mine commented, "I used a radiant barrier paint in my bonus room made about a 3 degree difference in the summer."

Do you have any experience with that product?

Jul 02, 2011 09:15 AM
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC


Great article.

I am curious why would not also recommend cellulose insulation. One of the main reason for the vapor barrier with fiberglass is just as you state as how fiberglass performs.  All insulatiors are based on the ability of the insulator to minimize the heat transfer. One of the best heat insulators is air, which cellulose insulation does a much superior job of trapping than fiberglass thus reducing the transfer of heat.  So with no air movement there is no heat transfer and thus the reduced need to have a vapor barrier.

I really would like to see the industry stray away from fiberglass.



Jul 02, 2011 02:50 PM
Phillip Bradrick
Energeyes Inc. - Raleigh, NC


The radiant barrier paint products only block 60-70% of radiant heat compared to the foil product we install which blocks 97% of radiant heat.  If the customer you mentioned had the radiant barrier paint applied to their roof deck but didn't do anything the improve the performance of their bonus room insulation it is not surprising that they only saw a 3 degree drop in temperature.  You really have to address all of these issues at once to get a significant improvement in the comfort of a bonus room.

Jul 11, 2011 02:42 AM
Phillip Bradrick
Energeyes Inc. - Raleigh, NC


Thanks for your comments. You are correct that a dense-packed celulouse insulation product performs better than fiberglass insulation, but the expense for doing a small bonus room insulation job of this kind is fairly high. Once fiberglass insulation is sealed on all six sides its performance is dramaticaly improved and when you combine that with a radiant barrier product it is enough to deal with the average discomfort of the bonus room. If someone is doing a remodel job or building a new home and can choose what insulation to use it definitely worth looking at dense-packed cellulose or a foam insulation product for the best performance of this space.


Thanks for checking in!

Jul 11, 2011 02:56 AM
Dan Edward Phillips
Dan Edward Phillips - Eureka, CA
Realtor and Broker/Owner

Good Morning Philip, an excellent post to educate home owners before they remodel a bonus room or have a contractor remodel it. 

Welcome to Active Rain!  Your input will be appreciated.

Jul 24, 2011 04:01 AM

Hi Phillip - Very good article and explanation. I realize this is an old post but wonder if you can provide info. I am familiar with the other elements you cover but have never heard or seen/heard the installing a card board stop over the exposed ends of your ceiling insulation. Do you have a picture or link to a site that shows exactly how this and the styrofoam baffle are installed? Does the baffle get air sealed with caulk or tape to the air barrier on the back of the knee wall? Thanks

Nov 16, 2015 10:48 AM
Phillip Bradrick


Thanks for your comment. There are a couple of approaches that can be used to seal off the ends of the batt insulation in the vaulted ceiling area. The easiest is tucking a piece of house wrap around the end of the bat and using a can of spray foam to seal around the edges. You can also cut a piece of ridged foam board to cover the majority of the cavity and seal the edges with foam. The only thing you will want to watch out for using a ridged material is that in some cases the pressure of the foam expanding and partially crush the styrofoam baffle. I don't have any pictures of this currently but hopefully this explanation helps to clarify the process.

Nov 16, 2015 09:54 PM

Thanks Phillip for your reply. That makes sense and the house-wrap seems easier.

Related to this house wrap technique:
1. How far in from the edge of the knee wall should I cover the 2 ft sloped "vault"section? Is it advisable to cover air barrier over the whole vault section since it isn't tight against the roof air channel there is a 4-5 ft clearance from the vault & bonus room flat ceiling to to the roof deck)?

2. should I also cover the edge that transitions from the vault to the flat ceiling, and if so how far from the corner edge should I take the house wrap over r-30 batts on the flat ceiling?

3. For proper air sealing, do I need to caulk or foam the drywall seams from knee wall to vault transition (like you do along the baseboard/ wall framing base), or is the interior drywall tape, paint and the house wrap over top edge enough to properly air seal? I do not detect a draft/air leak from the interior, although an obvious temp difference since insulation doesn't wrap over these seam corner connections.

Thanks for your time.

Nov 17, 2015 04:00 AM