I am sorry you are thinking about your attic, if you weren’t planning on thinking about it, and you now are, I am doubly sorry.
I will start by stating that ideally attic spaces would be completely controlled spaces, for example, Attics can actually have:
– Comfortable temperature and humidity year round- Excellent Lighting throughout with logically placed illuminated switches
– Excellent accessibility with no tripping hazards or or head-bangers
– No bugs and functional shelving for storage
– and provide easy access to wires, pipes, ducts, etc
The above photo shows an example of a pretty good attic. The only thing that could be better would be even more lighting and a window on each side. You can notice an orange ring at the top of the gable end wall. This is where the Powered Attic Ventilator Fan used to be. During the installation of the foam we were running that fan, and we continued to run it for several days while the foam cured, and the smell was exhausted. You can see in the picture a large circular white stain(by the purple storage bin) where a mushroom of foam was sprayed so that it could be later be scraped up, trimmed, and used to plug the PAV hole. If ever needed, this plug can be popped out, the home can be ventilated, and then the plug can be replaced/re-sealed with can-foam. Along with the addition of a sealed crawlspace this home’s energy bills were reduced by almost 50%. There are times during the year where one of this home’s HVAC systems can be left OFF while the other heats or cools the whole home. In other words, the capacity of the 2 HVAC systems is greatly over-sized given the work we’ve done. This whole project was over $12,000 and included removal of all of the old insulation, various floor and ceiling air-sealing details, and upgrades to the bathroom ventilation systems.
If this expense is not in your budget, or your attic is never going to be “this useful”, your best bet might be traditional attic weatherization with proper attic ventilation. Attics under low-pitch roofs, or attics full of trusses make spray-foam less rewarding than folks with huge, wide-open volumes. What do you stand to gain if you “gain complete control” of your attic space(s)? If you think you need to do something about the (hostile)conditions in your attic, then there are lots of different strategies for passive ventilation and a few different ways to incorporate “active ventilation”.
If you have not completed Attic Air-Sealing, Insulation, Crawlspace Air-Sealing, Crawlspace Insulation, or duct-sealing/replacement, then those scopes of work are likely to provide you more benefit per dollar spent than any project narrowly focused on Attic Ventilation.