How-To: Installing a Bathroom Fan

Our first constructive improvement to the house (as opposed the demo) was the install of a bathroom fan. It might seem a bit out of sequence and low-priority, but Sheldon is re-coating the roof on Tuesday, and I wanted to vent the fan out the roof. Although venting out the side wall is an option, its much easier to cut a hole through a wood roof than through a brick wall.

BATHROOM FANS & MOLD

Bathroom fans are important. When moisture collects on surfaces and remains there, it becomes food for mold. If your bathroom doesn't vent but you clean the mildew that builds up, mold may not seem like a problem. But only a portion of the moisture from the bathroom stays in the room; the rest is pushed through the walls into the insulation or wood framing underneath where it causes mold to grow. The idea is to get as much of the moisture as you can out of the house. (The Environmental Protection Agency: "Guide to Mold, Moisture and Your Home".)

While it feeds off the water and surface that it grows on, mold produces Volatile Organic Compounds (VOC's), the group of chemicals that people try to avoid in petroleum-based Paints, Adhesives and Sealants. These VOC's can cause asthma and weaken the immune system. Mold also causes rotting as feeds off wood, drywall, etc.

CHOOSING A BATHROOM FAN:

Sizing-- a good rule of thumb is 1 cfm (cubic foot per minute) per square foot for bathrooms 100 sq. ft. and smaller. For bathrooms larger than that, allot 50 cfm for each fixture (toilet, lav sink, shower).

Noise-- they generally don't sell fans louder than 4 sones. 3 sones is tolerable; 1 sone is very quiet.

Fans get more expensive the larger they get and the quieter they get. Right now Sara's bathroom is less than 50 sf. We might be expanding that, so out of the options, we chose an 80 cfm, 2 sones fan. The fan ran $69.00. To give an idea of how expensive fans can get, a quieter fan [.3 sones] of the same size is $189.00)

INGREDIENTS:

To vent the bathroom, we bought:

1. Broan bathroom fan.
2. 4" 90 degree vent pipe elbow
3. 4" x 3' Vent Pipe section
4. 4" roof cap
5. Tube of flashing cement
6. Self-tapping metal to metal screws
7. Self-adhering foil tape
8. Sheet of galvanized flashing (big enough to cut out a 10"x10" square)*

We had at the house:

9. small pointing trowel
10. silicone caulk
11. caulk gun
12. power drill
13. sawzall
14. white crayon
15. utility knife
16. plumbob
17. roofing nails

*I'm looking at Lowe's website, and they have some great products that would have been really useful, had they been in the store. Such as this skirt flashing. We instead had to buy a big piece of galvanized flashing, cut out a 10"x 10" square, and snip out our own hole (We left two little tabs in the hole, to bend down and fasten to the vent pipe).

HOW TO INSTALL A FAN. AT NIGHT. IN THE RAIN.

We had already ripped out the old bathroom ceiling before starting this project, so our joists and also the bottom of the roof were exposed. If you are installing a fan through and existing ceiling, or have insulation between your ceiling and your roof, TK

1. Applying several parallel beads of silicone caulk to the side of the fan box where is will mount to the ceiling joist, to reduce vibration noise.
2. Screw the fan box into the joist. Make sure you've used a scrap of the future ceiling material to ensure that the bottom of the fan box will be flush with the finished ceiling
3. Attach the vent elbow to the fan box and drop a plumb line from the roof to the top of the elbow to figure out where the vent pipe should penetrate the roof.
4. Sketch out the 4" circle for the vent pipe here.
5. Drill a hole in the center of the circle through the roof decking and roofing material to the outside.


At this point I climbed up on the roof with the crayon, utility knife, sawzall, vent pipe, pre-cut piece of flashing, 4" roof vent cap, flashing cement, caulk gun, trowel, and flashlight. It was starting to rain.


6. On the top of the roof, draw a 4" circle centered on the hole with the white crayon. (I found the hole easily by the light beaming out from the bathroom)
7. Cut out as much roofing material as you can with the utility knife.
8. Use the sawzall to cut out the rest of the circle.

Then Sara came home- it helps to have another person for this next step



9. Drop the vent pipe into the hole and have someone inside the bathroom line the vent up to the elbow.
10. While this person holds the vent and elbow firmly, slide the flashing down around the pipe.
11. Fasten the tabs to the pipe with the HVAC screws, and nail the flashing down to the roof.
12. Fastened the cap on top of the vent pipe
13. Generously apply the flashing cement where the pipe meets the flashing and the flashing meets the roof, making sure to cover the nails.
14. Finished up by wrapping the joints between the fan, elbow and duct pipe above the bathroom with the foil tape.

As uncomfortable as it was kneeling in the rain drooling all over the flashlight (I was holding it in my mouth), the combination of heavy rain and flashlight showed exactly where to build up the roofing cement and where to feather it out with the trowel to direct the flow of water around the pipe. On the roof, in any place that water pools or backs up it will eventually work its way into or under roofing materials.

You can buy a Broan Wall Vent Kit for 16 bucks or a Roof Vent Kit for 20 bucks, roughly half the price of the materials for this project, but the corrugated vent that comes with it lowers the efficiency of the fan, and the connections are loose, which means that fast-moving moist air is spilling out into your attic space, creating the opportunity for mold growth.