Fun With Insulation

Start by placing baffles in the spaces between the rafters.

Today we've been working since morning trying to properly insulate our bonus room. Even though we are having an unusually cool summer, the bonus room and my office opening off of it are uncomfortably warm. My office is so hot I think it would be uninhabitable during a normal summer.

Jerry did a lot of research and found out the bonus room comfort issue is very common because almost all these rooms are improperly insulated. The typical bonus room is located above a home's garage, flanked by walk-in attics, and with attic space above it. It's easy to see why the room's temperature would be hard to control; you have heat or cold beating down on the roof, penetrating underneath through the garage, and surrounding the exterior walls in the walk-in attics. In our house the problem is compounded by vaulted ceilings on either side of the surrounding rooms, which gather rising hot air, the long, narrow shape of the bonus room, with only two vents at the far end, a giant picture window facing the sunny south side, and our gas water heater located off the room. The water heater is the main culprit in keeping my office so warm. In order to vent the gas thoroughly we can't really seal the attic closet off from the office.

Baffles help stop air from being trapped between the roof and the insulation.

Almost all bonus spaces have insulation against the interior walls on the attic side. The roof and exterior walls are left uninsulated. This type of insulation actually achieves the opposite of the desired result, trapping heat against the interior walls and ceiling and heating them. Jerry showed me a blog about why this happens. It had a lot of math and physics I feel inadequate to relate, but my understanding it that hot or cold air presses in against the insulation and seeps through to the back side of the interior wall. Here it becomes trapped by the insulation in the tiny pocket between the wall and the insulation. In order to fix the problem it is necessary to enlarge the "building envelope". Essentially, you want to move the insulation to the farthest possible point from the interior walls so the air is trapped there before it can reach the interior walls. So, you need to insulate the roof and exterior walls, not the wall separating the attic from the interior.

We used paper-faced insulation on the exterior wall

We started by placing black plastic baffles on the interior roof in the spaces between the rafters. This helps to stop air from seeping in between the insulation and the roof and getting trapped. The baffles are not necessary on the exterior walls. There, we placed paper-faced R-13 fiberglass insulation in between each stud. We wore long sleeves, gloves, hats, safety goggles, and respirators to protect ourselves from the fiberglass.

We used this unfaced insulation on top of the baffles on the roof.

When we finished the exterior walls we placed unfaced R-19 insulation in the spaces between the rafters, on top of the plastic baffles. We used insulation stays, lengths of wire, to hold the insulation in place. After we placed all the insulation, we placed foam board on top of it. The board has foam insulation on one side and foil on the other. Tomorrow we will caulk or tape the seams in the board to further seal the space.

Finally, we sealed the exterior walls and roof with foam insulation board.

Jerry has been monitoring the temperature with an indoor/outdoor thermometer. Last week the walk-in was 30 degrees hotter than the rest of the house and the bonus room was about 10 degrees hotter than the rest of the house. Today, before the foam board was even in place, the attic was only 10 degrees warmer than the rest of the house, and the bonus room only 4 degrees hotter. The next steps will be to place window film over the large, south-facing windows, and also possibly to insulate the upper attic above the bonus ceiling the same as we did the walk-in. My office is typically only a degree or two warmer than the bonus. It is insulated, but unless we replace the gas water heater with an electric one so we can seal the office completely from the attic it will continue to run hot. We plan to see how much having the bonus room cooler helps the office before we decide if we need to do that. We also plan to insulate the walk-in off our son's bedroom the same way, as his room also tends to run hot.

I'm hoping this will make our bonus room much more comfortable for us and our guests. Insulating the walk-in will keep it temperate enough to use as a toy room where the kids can store and go to get their toys, so we can get more use from it. Tomorrow I'll be back to working on my dolls, but I thought you might benefit from our insulation tale!