thanks for the honeywell link sniffdog I'm kinda late for the discusstion, but wanted to contribute. I'm all about the build tight ventilate right. But..unless you actually test for tightness of building envelope the question is if you will need fresh air or not. Lots of homes are not tight enough to require fresh air. And contrary to the install on the link provided by sniffdog..I wouldn't run my fresh air supply along the roof line. Too hot in my climate. The temp of the air in august would be too high for most central systems to dehumidify and cool. For the program I work with any home with less than .35 air changes per hour requires mechanical ventilation. There is even a ventilation standard..ASHRAE 62.2 to determine how much (how many CFM cubic feet per minute) of air is to be added to the home. But first you have to test the house with a blower door to determine if the .35 ach has been met. If in fact the house is tight enough to require fresh air. then you want to carefully choose your location that the fresh air will be drawn from. clean it..measure it and condition it before it enters the living space of the home. I usually install a 12x12" filter back grill under a porch this allows you to filter the air, and the location is where air is cooler, as opposed to attic. an insulated sealed duct to the return side of the central system is added, this runs along the floor of the attic. At the return air plenum a barometric damper is installed, set to cfm as determined by number of occupants and ashrae 62.2 the damper opens for instance when stove vent is in use and both bath fans are in use. as the fans turn off..the damper closes. These fans are to vent the humidity out of the living space. less humidity allows for RH levels to even out for better iaq and a healthy house. When the house is not calling for air ( fresh air required to keep house from going into a negative pressure) the damper remains closed. by putting the fresh air to the return side of the system, it is dehumidified before entering the house. the idea is to keep the house under a slight positive pressure so that it is not sucking through unsealed holes. This is just the way that has evolved for me over the years to address this situation. Keep in mind that these homes were tested and amount of fresh air...and need for this added air..was verified and not just based on home owner or builder assuming that the structure was actually tight enough to require fresh air. skuttle 216 is one example of a barometric damper. install the set up described above..set the weight on the damper..and forget about it..except for changing the filter in the 12x12 fbg. keep in mind that mine is a hot humid climate best of luck.

As Hendricus has already pointed out, they make a metal "pipe flshing" that is about 20"x2" with a hole in the center and a rubber boot that seals around the pipe. It is installed so that the shingles on the row above the pipe fit over the metal and the metal will fit over the shingles on the row even with the pipe and the row below the pipe to insure water on the roof will flow over the roof opening without a leak. You need not worry about it because any reputable roofer is fully aware of how to properly install flashing around vents and they will automatically include them in your bid.

Try 'flat roof solutions.' EPDM joints are made with seam tape (uncured EPDM that comes in a roll and sticks by itself). You will need toluene to clean the surface before using the seam tape. Other solvents can damage the EPDM, but toluene is available in quart cans at a paint store. Be careful with the seam tape. It sticks to everything, including the tool you are goping to use to cut a piece off the roll.

Sombreuill: Thanks makes sense, I have a company coming out to quote on brushing and fixing a couple of areas where the birds pulled out the thatch. I will ask them how to seal it as the company who did the job originally walked away before finishing. It is now 8 years and it needs maintenance every 5-10 years. I wanted to replace it with a tile roof but it is very cool in summer and warm in winter inside the cottage. I also have a loft in the roof which if I were to cover it with tiles it would be too hot.