Would you keep all the windows open with the heat on in your car?

Bet you didn’t know you are heating and cooling a wind tunnel!

Certainly the biggest contributors to moisture in the attic are breakdowns in the building envelope. (Of course I am assuming that water is not getting in from outside the envelope–like a leaking roof) These compromises also make the building less efficient and will empty your wallet more as you attempt to heat and cool your home/tunnel.

air bypasses To understand this problem, it is helpful to think of one’s house like a Tupperware container. Clearly if we leave the lid a little bit ajar (like an attic access that is not weather-stripped), or start drilling holes in the bottom, sides and top, the container will no longer do its job–or at least less efficiently—relative to the number of holes, the size of the holes and where they are located.

Of course, if the holes are so the snake (or whatever else the kid catches) does not die, that is another matter.  It is still important to keep the lid on though.

There are other factors–but let’s keep it simple for today.

We can build the most super-insulated house in the world but if we don’t control air movement in and out of the building our efforts at insulating can be wasted.

One of the most common, obvious, everyday sort of “by-passes” that I see in homes is dampers in fireplaces that are left open. These chimneys will pull conditioned air from the home 24/7–with an occasional pause for atmospheric inversions that can happen. The screen on the fireplace filling up with lint is the first clue that this is happening. Even closed dampers in most cases will not stop this movement entirely.

Eliminating open flame solid fuel appliances altogether is a good idea in the context of building more energy efficient homes.

I have heard people argue that this natural draft is a good way to exchange the air in the home–without a mechanical fan. The truth is that this works–but at much greater cost than running a simple exhaust fan periodically. It is the 24/7 aspect of the chimney that makes it a problem, as it vents conditioned air that we are also paying for. On a windy day the venting might be much more than on a still day. We need “control” over this air exchange if we are truly going to control energy use as well as maintain a healthy indoor environment.

I want to stress that this is a LOT more complicated than I am willing to address here. For example rates of ventilation will not always guarantee good indoor air quality. While outside air is generally of better quality than indoor air, that is not always the case and in some areas of the country, outside air is becoming worse every day. At some point the political aspects of outdoor air quality will be forced to reconcile with the private aspects of indoor air quality. Some will argue that if you want “quality” drinking water you had better be prepared to solid-block-carbon-filter the water where it comes into your home. The same thing is perhaps coming for the air we are bringing into our homes.

Welcome to the 21st Century.

Back to air by-pass issues.

As previously mentioned, the attic access hatch is a common by-pass but the list is almost endless. Here is a partial list of some common breaches: plumbing pipes running through walls and ceilings, can-lights, HVAC equipment/ductwork in attics, crawl space hatches at the interior of the home, wiring holes in top and bottom plates of walls, chimneys, b-vents, improper framing techniques, skylights, pull down stairs, drop ceilings, exhaust fans etc.

“Stack effect” is something else that affects our homes.

Stack effect is relative to temperature/pressure differences. It is relative to the fact that warm air is buoyant. It is further driven by the lowering of pressures inside the home which then allows for air to be pushed into the lower levels of the home (from outdoors and/or crawl spaces). The taller the home, the more pressure differential as the buoyant air moves to the exterior (attic) of the home, bringing with it the moisture in the air. The colder the outdoor environment and the taller the building the more that hot air will be trying to get into the roof structure or outdoors to get to that cold. Perhaps the perfect storm is to have a leaky floor system over a vented crawl space in conjunction with serious breaches in the attic floor.

In this scenario you can think of your poor heating system as attempting to heat a wind tunnel. You will have to be willing to throw a whole bunch of energy at this wind tunnel in order to feel comfortable in your home.

In a very well sealed home there will be less stratification of temperatures and less “driving” of the stack effect–even when doors at the lower level are opened. Opening and closing windows on upper and lower levels in conjunction with each other is a way to manually control stack effect to change the air in the home. This is not rocket science, but can be as expensive as rockets.

At an inspection a while back I had one of the most egregious examples of a home with a functional wind tunnel. The defect was created when part of the forced air heating system was removed. If you could zoom in on this picture, you would be able to see the furnishings in the room below. There were three of these vents into the attic. The missing insulation around the vent is not even consequential in relation to this breach.

Closet vent open to attic

Closet vent open to attic

Sealing these air by-passes, even in older inefficient homes, can drastically reduce heating and cooling costs. Remember , heat tries to get to cold and high pressure moves to areas of lower pressure. So if the attic is really hot in the summer and we are cooling the home we have made the job of the AC unit all the more difficult. Better sealed homes accounts for why the size of heating and cooling systems have halved since the 40’s–remember—back when oil was free?

Sealing and eliminating all kinds of air by-passes is perhaps the most important thing we need to do in making our houses more energy efficient. Insulation alone will not do it and in fact in many cases will only filter the air as the air moves through it. This is especially true of fiberglass insulation–even 18 inches of it. All air by-passes must be found and sealed (or otherwise eliminated) prior to insulating. Choosing types of insulation that are in themselves good air barriers is also recommended.

By Charles Buell, Real Estate Inspections in Seattle

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Two wrongs still don’t make it right.

Two wrongs still don’t make it right.

As you can see in the picture, the cut truss (wrong #1) is pointing right at the whole house fan (wrong #2).

While whole house fans may have been a good idea, once upon a time in some climates, they have virtually no place in modern energy efficient construction. In northern climates they are of particular concern as they are typically NOT adequately insulated and sealed against heat loss in the winter. When they are not insulated and sealed, the natural stack-effect of the home will pull warm air into the attic more or less around the clock.

The idea of these units is to flush the warm daytime air from the home at night, and then pull in the cool night air to cool the home off. Not a bad idea really. While this principle works in older poorly insulated homes, in modern well insulated homes they should not be necessary. Merely opening a few windows on opposite sides’ f the home should achieve the same result.

If the home is overheating during the day, one should look to the causes of that overheating and fixing the overheating as opposed to installing a system that should not be necessary. If one’s home is overheating and one considers it “well insulated,” I would argue that one should perhaps re-think one’s definition of “well insulated” or that perhaps there are other factors contributing to the overheating.  A good question to ask might be, “what are the air sealing abilities of the insulation?”  Not all insulation is created equal.

As a side note, I can pretty easily argue that even newly constructed homes in areas of the country with high cooling needs are NOT adequately insulated to appreciably reduce energy costs. Code requirements for energy conservation are “minimum” standards, and make no distinction between the air sealing characteristics of the various kinds of insulation.

If installed properly, and if used properly, and if maintained properly in the off season, these fans can help reduce air conditioning costs, improve comfort and improve air quality. Please note that this statement includes a lot of “ifs” and their installation can more often result in increased heating costs in the off season.

Another issue that arises from these fans is that if they are not sized properly (and they rarely are) they are capable of drawing more air into the attic than the attic space can get rid of. This can result in pressurizing the attic and minimizing the effectiveness of the fan—oversized or not. Regardless, even if additional venting is installed to compensate, there will then be compromised and possibly inadequate venting of the roof structure for that part of the year when the fan is merely wasting energy. It might be possible to balance these differences, but the reality is that often the different requirements for the different functions are simply not taken into account—or, worse yet, not even possible to take into account. More often than not, when I see them installed in the Northwest, they seem to be installed on the insistence of someone that has moved here from a climate where they worked or were possibly even necessary.

For the installation above, someone is now going to have to incur the cost of removing the fan and repairing the damaged truss. These costs will now need to be added to the increased energy costs created by the installation in the first place

By Charles Buell, Real Estate Inspections in Seattle

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Is your insulation doing what you think it is doing?

I do not want to tackle the huge ugly topic of whether fiberglass insulation should be used at all–as it frequently is in attics.

For today, I just want to talk about one obvious issue with fiberglass insulation that prevents it from performing as expected.

The short version of what is wrong with fiberglass insulation is that it is not an air barrier, therefor, if it is not encapsulated and air sealed on all six sides its performance suffers. In an attic, at most, only five sides is likely to be sealed leaving the entire top not sealed.

This post is about the sides, which can and must be air sealed. The vented sides are typically not adequately air sealed, especially along the eaves. Insulation baffles, designed to keep insulation out of the lower roof venting and to allow for air flow into the attic, rarely gets adequately sealed.

Soffit vent that allows air flow into the attic

Because the baffle/top plate connection is not air sealed, and because fiberglass insulation represents very little resistance to air flow, air pushes its way into the attic right through the insulation. As it does this, it either cools the ceiling in the area, or warms the ceiling in the area depending on the season and/or side of the house.

In the winter and/or the north side of the home, the air will tend to make the ceiling cooler in the area of the vent. In the summer, especially on the sun side, the air will tend to warm the ceiling in the area of the vent. This will increase both heating and cooling loads of the home.

This next picture shows what that area looks like at the interior ceiling with Infrared camera on the South side of the home. Warm air is moving through the insulation and warming the ceiling.

In the same house on the North side we can see how the ceiling area near the vent, as indicated by infrared camera, is “cooler.” In the actual picture we can see the fungal growth present because this vent happens to be in the area of the bathroom. The moisture in the bathroom condenses on the cooler surface creating a perfect environment for mold growth.

The only real repair for this condition is to pull back the insulation and properly air seal the gaps where the insulation baffle and the house framing meet.

Spray foams are good for sealing the areas where the baffle makes contact with the framing as indicated in the circle in the picture above. Of course, in a perfect world, we would not use fiberglass insulation at all, and instead use types of insulation that are much better at stopping the flow of air. Cellulose fiber insulation can do a much better job at this.

 

Charles Buell, Real Estate Inspections in Seattle