This article is provided by:
Hallie Myers Bowie of New Leaf Home Design
Ventilation, Insulation, and Gadgets
For those of you who don’t know me, I’m an architect and unlike most architects, I specialize in residential work. The majority of the projects I’ve done in the past 20 years have been home additions and renovations. I’m a certified Green Professional through both the National Association of Home Builders and the National Association of the Remodeling Industry, and I’ve recently had the chance to work on two projects through the US Green Building Council’s LEED system.
Today, I’m going to tell you about the Triangle of Home Energy Use: Ventilation, Insulation, and Gadgets. To help you improve the energy efficiency of your home, I could just give you a list of things you can do. But you won’t remember a list, and it probably wouldn’t be very interesting to read. So my goal is to give you a better understanding of the Building Science behind making a house more efficient. That way you’ll understand your house better, and I think you’ll also better appreciate the value of getting an energy audit, which is a great first step for many remodeling projects.
I want to make clear that I’m not trying to cover everything about “Green” home renovation. The LEED for Homes certification system has (7) categories that it looks at in evaluating how Green a house is. Since I’m focusing on home energy efficiency, I’m going to talk about just two categories: Energy and Efficiency and Indoor Air Quality.
Also, I’m going to focus on basic energy improvements for existing houses. New home construction has a lot wider range of possibilities and I’m guessing most of you aren’t getting ready to build a new house. But a lot of you are living in houses that are already built, and almost all of those houses could be more energy efficient & more comfortable to live in.
There are ways to make existing houses super energy efficient. Houses like these are called “deep energy retrofits”. If you are already planning to replace the siding and roofing, and possibly remove the plaster or drywall on the inside, you can make an existing house extremely energy efficient. However, the return on investment for a project like this is not something most people can justify. But there are sooo many houses out there that could be using so much less energy with just a small investment in upgrades, making some fairly simple improvements to enough houses can have a big impact on our national energy use. And this kind of improvement makes sense from a personal financial standpoint too- especially when you can take advantage of rebates.
Now you might wonder why I have “ventilation” included in the triangle of home energy use at all. And why the heck did I put it first? Most of us would tend to think insulation is the most important thing. Well, there are a number of reasons why you really want to think about the air going in and out of your house even before you start thinking about insulation. For our houses, air can be a good thing, or it can be a bad thing.
Air is bad when it comes in through cracks around the top of the basement wall and under the doors on cold January nights. We can’t control how much air comes in through these cracks, and in fact the laws of physics make it so the colder it gets outside, the faster air moves through them. I don’t know about you, but my feet really notice that cold air. And when my feet get cold, I want to turn up the thermostat, which uses more energy. So sealing up air leaks keeps you from losing energy directly in the heated air that leaves your house, And it keeps you from wanting to set your thermostat higher, because a 68 degree house without drafts feels warmer than a 68 degree house with drafts. But this is just the tip of the iceberg when it comes to the importance of understanding and managing how air moves in your house.
Another thing you should know about air movement is that it affects how well your insulation is going to work. This applies especially to the kind of insulation you are probably most familiar with: the pink fiberglass stuff. Fiberglass insulation works pretty well as long as it doesn’t have air moving through it. It’s designed to work with an air barrier on all six sides. But it usually isn’t installed that way. I’ve read that fiberglass can lose up to 50% of it’s labled R-value because of air movement. Cellulose insulation is not an air barrier either, but when it’s dense packed it does a much better job of slowing air flow than fiberglass.
So we’ve got a couple of good reasons for wanting to limit how much air is moving through random cracks in our houses. But there is more to know about air in your house. Sometimes you’ll hear very experienced and in many ways knowledgeable people say that “a house has to breathe”. I’m not dismissing the concerns of those “house has to breathe” people. They may have seen some pretty nasty situations associated with getting a house “too tight”. They may say you need fresh air for the people in the house, and they may bring up stories of tight houses with mold.
Now, if you are working on the energy efficiency of an older house, you should know that these stories are generally about new construction. If a house is built leaky, it’s almost impossible to get it air sealed so much that you need to add extra mechanical ventilation for fresh air, and you are also less likely to have indoor humidity build up to where it creates problems. So it just doesn’t make sense to spend time worring about getting an existing house too tight. But it’s important to understand the principles so you can make informed decisions.
The “too tight” house problems I’m talking about are ones where the warm humid air inside the house ends up making the walls or roofs wet. These problems are all about air movement and energy loss. A story I heard just the other day is an example of the problems you can have when you don’t have a continuous air barrier on the warm side of your insulation. The house involved was just a few years old, and was pretty well air sealed. So far so good. And because it was built to a more recent building code, it had insulation on the basement walls. They had decided to use a kind of batt insulation that has a plastic facing on the inside. The paper facing you often see on fiberglass insulation is flammable, so you need to cover it with drywall. The plastic faced insulation can be left exposed. So they fastened these blankets of insulation at the top of the block wall, just under the wooden rim joists that run around the outside of the floor framing. And then they stuffed some fiberglass insulation up into the rim joists so they would be insulated too.
The fiberglass did keep the house from losing some energy through the rim joists by conduction. However, this made the inside surface of the rim joists cold. But – pop quiz time- does fiberglass stop air movement? ___ No. So the warm, moist air inside the house moved through the insulation and eventually it found the cold wood of the rim joists. When moist air hits a cold surface what do you get? Just like on a drink with ice cubes, you get condensation. In this case, there was enough condensation so the water started running down the wall, behind the plastic faced insulation blankets. The plastic then made it hard for the wet insulation to dry out, even when the wall got warmer. As a result, the insulation got really moldy.
Houses generally didn’t have these problems before the energy crisis of the ‘70’s. That’s because the house was so leaky that the constant winter influx of cold, dry air kept the relative humidity in the house really low; and there wasn’t any insulation keeping any part of the house cold enough to create condensation. So the system worked. The only problem was that we had to use a whole lot of fuel to keep the house warm, and even then there were cold drafts everywhere.
But it was a system that took into account all of the conditions in the house, even if it did so by accident. As we started making our houses more energy efficient, we have discovered ways we need to adapt the systems in our houses to adjust for the presence of insulation and air sealing.
One of the places we’ve adapted our building systems is in the attic. How many of you have had your roof shingles replaced at some point? How many had a ridge vent done as part of that roofing replacement? The ridge vent, and the eave vents that should be installed with them, provide air movement to prevent mold. The building code started requiring ridge vents sometime after we started getting serious about attic insulation. Without insulation, attics stayed warm enough so there wasn’t too much condensation. But with more insulation, the underside of the roof sheathing was colder than it used to be, and we started to get condensation from the warm moist air escaping through the ceiling. So building officials realized we needed to provide more air movement to help dry out the wood surfaces and prevent mold problems. Having intake vents down low, and exhaust vents in the ridge provides that air movement, and keeps an insulated attic dry.
Unheated Attics with Flat Ceilings
So now I’m going to move on to insulation. First of all, more is generally good. And since warm air rises, the best place for the most insulation is in your attic. If you had insulation added more than a few years ago, you could probably benefit from adding more. The minimum thickness of cellulose or batt insulation required by code for attics is now about 11 inches, GoodCents energy auditors recommend over 14, and a really efficient house would have about 18 inches. In a ranch house like mine, that means that the insulation is a lot thicker than the depth of the ceiling joists, so you can’t put a floor over the insulation and store Christmas decorations in the attic. But it’s nice and easy to add a lot of insulation in this kind of attic. Blown in insulation, either fiberglass or loose fill cellulose, will work, and this is a pretty good do it yourself project. My preference is for cellulose because it reduces air movement better and has more recycled content.
Capes, Third Floor Rooms, and Cathedral ceilings
But not all houses have flat ceilings and empty attics between the heated space and the unheated world. Lots of the houses in Akron have living spaces on the top floors with sloping ceilings. It’s a lot harder to get insulation into these roofs. Even if you are prepared to tear off the plaster or drywall on the inside, chances are that the rafters are only 6 or 8 inches deep. If you have enough head height, you might be able to fur the ceiling down for more insulation. But here is the most important thing, and we are back to talking about air again. All you people with rooms on the third floor, or Cape Cod houses with bedrooms upstairs, or cathedral ceilings- are you listening? DO NOT fill the entire depth of your attic rafters with fiberglass insulation. If you are using a spray foam insulation, or rigid insulation where you are taping the joints very carefully, you can fill the whole space, because these products are also air barriers, so no moist air will be able to get up where it can cause mischief. But for cellulose or fiberglass, you need a 1” air space between the insulation and the underside of the roof sheathing. You also need to make sure that air space is connected to eave vents at the bottom and a ridge vent at the top of every rafter bay. What will happen if you don’t leave this air space? Warm moist air will find places to go through the ceiling, will get cold enough to condense inside the insulation, there won’t be enough air movement to dry it back out, and you will have mold. Eventually your roof sheathing will rot away. If you are really motivated to add insulation to a roof like this, there are things you can do, but we’ll need to look at your specific situation to come up with a solution.
After you have done as much as practical to air seal and insulate your attic, you may want to look at your walls. The first step here is finding out what is in the walls already. If they are completely empty, you can get right to work. If they are insulated, you need to find out how much insulation they have and what kind of shape it’s in. An auditor’s infrared camera can help with this, and you may want to open up a small area to look in the walls too. If the studs are completely filled with insulation, you probably won’t want to do any more. If they have old insulation that’s just 2” thick, some foam or dense-pack cellulose installation companies will be willing to add more insulation without removing the existing insulation.
A quick note here about cellulose. Cellulose can be installed in two ways: loose fill or dense fill. Years ago, loose fill was common, and it started getting a bad reputation for settling. Dense fill will not have settling problems. It does require trained professional installation though. The machines you can rent for DIY use only do loose fill. Also, cellulose is treated so it’s not flammable, and if you have enough water in your walls to get it wet, you have bigger problems you need to deal with.
If you are going to be replacing the siding, you have the opportunity to add some rigid insulation on the exterior. This has the advantage of getting you more insulation than you can fit inside your stud walls, and also adding a thermal break between the studs and the cold outside air. Because rigid insulation is not vapor permeable, you want to pay attention to thickness and how it affects where water vapor wants to condense. If you have 2×6 walls, you’ll want at least 1 ½” of rigid insulation to keep the walls warm enough to avoid condensation. 2×4 walls will keep the dew point further to the outside, so you can have as little as 1” of rigid insulation then.
The third part of the Triangle of Energy Use is Appliances and other Gadgets.
There may be other experts out there who could talk for hours about these, but I have just two simple rules for you here:
- Don’t use what you don’t need, and
- Buy efficient appliances and electronics.
Buying efficient appliances is the easiest. When you go out to buy something new, look for the Energy Star label. Be aware that the cheapest furnace is also the one that is going to cost the most to run every month.
Not using what you don’t need is trickier. In following up on energy use in super-efficient new homes, they have found that some houses use more energy than their designers expected. This is because occupant behavior is just as important as design. When you have a house full of 60” televisions running 12 hours a day, or a programmable thermostat that is programmed to heat the house to 75 degrees all day, every day, or people who leave the windows open in the middle of winter, it’s going to affect the amount of energy a house uses. So paying attention to the choices you are making is key here.
Now you know that Ventilation, Insulation, and Gadgets are the triangle that affects energy use in your home, and especially how important it is to pay attention to how air is moving in your house, and how much humidity it’s carrying.
I have an Energy Saving Tips list has some suggestions on behaviors you can adjust for energy savings, and I have other articles on Energy Audits. If you would like me to email you either of these, or if you’d like to sign up for my newsletter, please contact me.