How we reach these goals is by controlling moisture and radon from the ground, “conditioning the space”, with insulation and air-sealing, and then providing for all the other important health, safety, and code issues that go along with a sealed crawlspace.
This is considered “best practice” in the energy efficiency industry, and this is how it happens:
First, the client or our team removes any stored items from the crawlspace, and cleans out organic debris that would rot or provide food for mold.
If a client has issues with standing water periodically (or wants one in place for the next flood), we can install either a basic sump pump hole, or a larger system with a perimeter French drain, or a more advanced unit with a battery backup. We only use the highest quality 1/3 hp cast iron Zoeller sump pump, check valve and real plumbing to a logical location in our system design. These systems are built to last, but should be inspected and tested periodically to insure everything is a good shape.
Next, we lay down our cross-linked polyethylene vapor barrier, seal all seams, and up about a foot onto the foundation wall and glue things in place with a generous amount of low VOC (i.e. healthier) modified hybrid polyurethane sealant that is permanently flexible so if things settle, the barrier will stay in place.
Our vapor barrier is well suited to crawlspaces that don’t have heavy traffic. If there is heavy traffic, we put down a pond liner or the client can put down carpet remnants on top of the vapor barrier in higher traffic areas to protect the vapor barrier. This is the same system we install for our advanced, energy efficient radon systems, but we first lay down the perforated pipe under the vapor barrier to allow the Energy Star rated radon fan to effectively create more even suction on the whole crawlspace with the minimum amount of power consumption.
Warning: I digress into building science here, but worth a read if you want to learn more about the subtle building science of your crawlspace. On the walls of the crawlspace we seal the rim joist and sill plate (the top foot of the crawlspace wall that is made out of wood) with spray foam to reduce the air leakage at this “achilles heel” portion of your home.
It is important to note that above grade (above the dirt level), your home is designed to breathe moisture to the outside. Below grade, your foundation walls need to be able to breathe to the inside because moisture in your below grade concrete will not go towards a higher concentration of moisture (i.e. the surrounding soil after a rain), and it should not be trapped in your foundation wall.
We have clients in beautiful 100 year old homes in Boulder who have rubble foundations (porous foundations of stacked stone) and they get a bid from a contractor for closed cell foam on the interior of these walls. They are told that it will make the wall stronger, seal and insulate at the same time. This is likely true in the short term, but I am worried about the next 100 years for the home.
These homes have done well in terms of durability for the last 100 years, but are energy hogs, and can have bad interior air quality because of moisture in the crawlspace. Most older homes do not have proper exterior French drains, or grading of the soil keeps moisture from seeping into these crawlspaces, so closed-cell foam that would then trap the moisture in the walls (remember, foundation walls below the level of the dirt won’t dry to the outside) and when the temperature drops, it freezes the water in the rubble foundation, and you can guess what the result might be over the years. You won’t be able to access the walls to address the problem because it is very difficult to remove closed-cell foam.
Because of the problems listed above, we like to seal the rim joist with foam only, and then install a foil-faced silver rip-stop covered R-19 formaldehyde free, partially recycled content continuous piece of fiberglass batt that is encapsulated on all six sides to reduce air-infiltration. We then spray foam all the edges of the insulation AGAIN to insure all the edges are fully sealed. It takes twice as long, but performs twice as well with this method, and stays in place much better than only ram-setting the insulation to the wall without the foam.
If you notice any fiberglass in your home that has dark, dirty spots, this is an indication of air leakage where the insulation is just acting like a filter and not actually insulating. I like to use the analogy that insulation is like a sweater or fleece. If you go skiing or cycling, you’ll quickly realize the benefit of a Gore Tex shell to stop the wind. The same is true in your home, and encapsulating the insulation on all 6 sides is just as important if you want to be comfortable and also save energy.
If your crawlspace access is from outside the home, we cut and install a rigid foam hatch plug to continue the “thermal envelope” of this space, and keep the cold air out. This, in conjunction with the wood cover most people have to keep the rain and raccoons out, works very well.
Finally some very important health, safety, and code issues we need to cover. If you have an “open combustion” furnace or hot water heater in the crawlspace, or a furnace closet on the main floor with a grill in the floor that draws combustion air from the crawl space, we need to duct this to the exterior of the crawlspace using one of the former crawlspace vents.
If your furnace or hot water heater have a metal flue, they need this treatment. If they both have two white PVC pipes coming off of the unit and connect to the outside of the home, then they are “sealed combustion” making them safer and much more energy efficient. If we simply ignore any open combustion appliances it will cut off the air they require for the burning process, which can cause them to not draft properly (allow the exhaust to go up the flue) or create more carbon monoxide, which can get you sick, or even die from this invisible and odorless gas.
When we are insulating and air-sealing a home, we always do a “test in” before our work, and a “test out” after the work that includes using a blower door to see how tight your home is, and running a full CAZ test and analysis. This includes making sure your combustion appliances (furnace, hot water heater, and stove etc.) are not creating too much carbon monoxide and that they are properly drafting to get the exhaust out of the home.
Part of this is simulating “worst case” where we run any fans that suck air out of your home (bath fans, clothes dryer, range hood fan, etc.), putting your furnace and hot water heater under negative pressure and making them more likely to backdraft. By testing your home under this worst-case scenario, it insures that in regular day-to-day use you are more likely to be safe. Most homes pass this test, but every month or so we find a home that fails, and in some cases have a life-threatening carbon monoxide problem that can be corrected by Eco Handyman, or our heating and cooling partner.
If you have any questions, or would like a consultation, please don’t hesitate tocontact us.