The Rest of the Story
Once again The Word invites you to travel into the dark realm of
subjects that are sometimes misunderstood by home inspectors. The Word
hopes you will find this trip informative and maybe a little
entertaining.
This month we continue reporting on (as Paul Harvey used to say) the rest of the story.
This is the story about what The Word and his wonderful wife learned
while remodeling our 1980 ranch home in Cary, NC. As inspectors, we
usually just do our thing, collect our fee and move on to the next
inspection. Rarely do we get to see what happens after we leave. The
rest of the story can be interesting and instructive in terms of what we
might want to look for and report, or at least mention, to our clients.
Last
time, we discussed some of the general deficiencies we found in our
home. This time, we’ll get into a couple of the big dollar issues: the
crawlspace and the attic.
“Allergies”
It
seems, sometimes, like The Word’s wonderful wife is allergic to
everything. She is definitely allergic to dust and is probably allergic
to other common contents of attics and crawlspaces. Many clients suffer
from these afflictions.
The Word is allergic to paying utility
bills and to watching (and listening to) his wonderful wife suffer. Many
clients also suffer from these afflictions.
Houses often have
conditions that cause allergic reactions both physical and fiscal. Some
of these conditions, like absent or minimal insulation, are reportable
deficiencies. Other conditions are either concealed (but we know they’re
probably present) or are otherwise out of scope of a home inspection.
Whether you mention these out-of-scope conditions is up to you, but you
may want to consider doing so. Going that extra mile is a great way to
get more referrals from clients (instead of relying on agents).
It’s
amazing how many holes exist between the interior of houses and
unconditioned spaces. These holes can add up to a few square feet at
least. Holes are everywhere. The space around holes for pipes and wires
is usually small, but there are lots of them and they add up. The holes
for tub drains can be huge, often a square foot or more. Holes for HVAC
ducts, vents and chimneys can be huge as well. Remember, too, that the
chimneys and vents themselves can be huge holes. There are also lots of
holes in the walls, especially around penetrations such as windows.
These
holes provide a passageway for conditioned air to enter and leave the
house’s interior. Dust, pollen, mold and water vapor are some of the
common passengers on this air stream, but other and much more dangerous
passengers can also hitch a ride. Radon comes to mind. Vapors given off
by chemicals that people often store in attics and crawlspaces might tag
along. How about bacteria from animals in the crawlspace and attic
(alive and dead), including their wastes? Uncontrolled air movement is
not ideal for several reasons.
A Hole and a Force
Air
movement needs a hole and a force to move it. Holes in most houses are
plentiful. So are forces to move the air. It doesn’t take much force to
move air and when you consider that the holes are open 24/7, a lot of
air can move between the house and unconditioned areas. So what are some
of these forces?
Well, one force is our old friend the stack
effect. The stack effect is a fancy way of saying that warm air wants to
rise. If it were not for the stack effect, chimneys and vents wouldn’t
work. In the winter, the house becomes like a chimney. The air in the
house is warmer, thus less dense, than the air outside the house. This
warmer air wants to rise and will escape through any hole that it can
find. That escaping warm air has to be replaced, and that air is
probably colder outside air drawn in through other holes in the house.
News
Flash: warm air doesn’t always rise! Pressure differences in the house
can cause warm air to move sideways or downwards given the right
conditions.
Blowing in the Wind
Wind is an
interesting force because the air movement between the house’s interior
and exterior will be different depending on wind speed and direction,
and depending on where in the house a hole is located. Wind can increase
the pressure inside the house on the windward side and decrease the
pressure inside the house on the leeward (opposite) side. Thus, air can
flow both from and to the house’s interior at the same moment.
Of
course, the wind effect is not that simple. Wind is also acting on the
ventilated attic and crawlspace. Areas within the attic and crawlspace
can become pressurized and depressurized depending on the amount and
location of the ventilation openings. Pressure conditions in the attic
and crawlspace can enhance or counteract the pressure differences inside
the house and increase or decrease the amount of air movement through
the holes.
We Do It to Ourselves
Just to make things
interesting, let’s throw in the mechanical systems and the fuel-burning
appliances because they usually have an effect on air movement in the
house. Kitchen and bathroom (and any other) exhaust fans will
depressurize the house and draw outside air inside. So will fuel-burning
appliances (including fireplaces) that draw combustion air from inside
the house. The combustion air goes right up the flue or chimney with the
combustion products. The air has to come from somewhere, so it comes
through the holes in our holey house.
Powered attic ventilation
fans will usually depressurize the attic and draw air from the house.
These ventilation fans are usually installed without accounting for
existing ventilation openings and are often installed in an attempt to
improve perceived ventilation inadequacies. If the attic ventilation is
indeed inadequate, power ventilation won’t make more outside air
magically appear. The power ventilation fan may, instead, pull air from
the house through the many holes between the house’s interior and the
attic.
A forced-air HVAC system can pressurize or depressurize
areas within the house. A leaky return air system can pressurize the
house because more air is being supplied than is being withdrawn.
Conversely, a leaky supply air system can depressurize the house because
more air is being withdrawn than is being supplied.
A bedroom,
or any room with a door, can be pressurized by the HVAC system if there
is no return duct or relief opening to relieve the pressure from the
supply duct. The pressure can force air through the holes into
unconditioned spaces.
Tightening the Ship
So far, we
have lots of holes in houses and lots of ways to move air and its
contents through them. Losing conditioned air is an energy- efficiency
bummer, but energy efficiency is only part of the story. Because the air
probably contains moisture from occupant activity (cooking, bathing and
just breathing) it can create moisture problems in the unconditioned
areas. This moisture may condense on the cooler surfaces, damaging
materials and providing the moisture that fungus needs to grow. If
condensation occurs somewhere near the insulation, the insulation will
get wet and will tend to retain the moisture against nearby materials
for a longer time. Wet insulation is close to worthless as an insulating
material so we have the potential for a triple whammy of energy
inefficiency, damaged materials and fungal growth.
So do we agree
that air movement between conditioned and unconditioned space is not
good for many reasons? If so, what can be done to stop this air
movement?
The first improvement is to find and seal as many holes
between conditioned and unconditioned space as possible. Hole sealing
can be quite cost effective and, since it requires little training, is
something that many homeowners can do themselves. Hole sealing is
something you may wish to suggest to help improve the house’s energy
efficiency and reduce air movement and the stuff that rides along with
the air.
The second improvement is significantly more costly and
complicated than hole sealing, but it can have a much greater impact on
the house. Bringing the attic and crawlspace within the house’s thermal
envelope by sealing and insulating their perimeters can be a good choice
for many clients, especially those buying houses on crawlspace
foundations. The cost and difficulty of these retrofits should not be
underestimated. Part of the cost, of course, is cleaning up the mess
caused by years of air and moisture infiltration into these spaces.
Figure 1
The Word’s Attic
The
Word elected not to seal his attic. There are no appliances or ducts in
the attic, thus the cost benefit of sealing the attic didn’t seem
favorable. The Word did, however, have the dirty, compressed, uneven,
marginally effective loose-fill fiberglass insulation removed. In its
place, a layer of open cell foam was sprayed to air-seal the attic from
the house’s interior. The remaining insulation requirement was achieved
using loose fill cellulose. A baffle was installed around the attic
access opening to keep the insulation in place, and the opening was
insulated and weatherstripped.
This is about as good as it gets
in terms of an energy-efficient attic. The Word could have added a
radiant barrier in the rafters to reduce some radiant heat gain, but
given the tree-cover on the lot, that seemed to be overkill.
Crawlspace Sealing 101
Sealing
the crawlspace, however, was a no-brainer. In The Word’s opinion,
crawlspaces should be sealed unless there is some overwhelming reason
not to. There are just too many problems that can occur in a ventilated
crawlspace. So in case a client asks, or in case you want to seal your
own crawlspace, here are the basic steps for doing so.
Before you
start, do your homework. If there’s a fuel-fired appliance in the
crawlspace, that appliance may need to be changed to a direct-vent type
that obtains its combustion air from outside the crawlspace. These types
of problems can greatly change the cost of crawlspace sealing.
- Get a permit if required by your jurisdiction.
- Correct any exterior foundation grading and drainage deficiencies,
including gutter problems. This is always a good idea and especially so
when sealing a crawlspace. You don’t need water problems after spending
all that money to seal a crawlspace. - Correct any water
infiltration or drainage issues in the crawlspace. Crawlspace dirt
floors should slope toward one or more points where water can drain out.
If the points are to sump pumps, so be it. Make sure the sump pump is
accessible after the crawlspace is sealed. - Wait for a while,
if necessary, to let a wet crawlspace dry some before proceeding. You’ll
be sealing in whatever moisture is on the ground and in the crawlspace
walls so, ideally, things should be as dry as practical. - Remove any old insulation. It won’t be useful in the new system and
having everything visible helps you find and correct any problems that
may exist. - Clean up the crawlspace floor. Sharp objects can punch holes in your vapor retarder.
- Seal all the holes you can find between the crawlspace and the
house’s interior. Even though the crawlspace will become
semi-conditioned space, you still want to control if and where air flows
between the crawlspace and the house’s interior. - Clean up any fungal growth in the crawlspace. You don’t want any fungus, alive or dead, entering the house.
- Seal existing crawlspace ventilation openings.
- Cover the crawlspace floor with a thick, reinforced vapor
retarder. You can get by with 6 mil poly, but it’s better to use a much
thicker, reinforced material. Ten mil is what The Word used. Even
thicker is better but more expensive. Run the vapor retarder at least 6
inches up all crawlspace walls and columns and seal the vapor retarder
to the walls and columns. If you’re using spray foam insulation, that
will handle the sealing. Overlap and seal all seams in the vapor
retarder. - Insulate the crawlspace walls including the band.
The Word used closed cell foam. It’s both an air and water barrier and
does a good job of getting into areas that are hard to reach and
completely seal by other methods. The amount of insulation depends on
your climate zone. Figure 1 shows the foam being applied. Remember to
leave a gap in the wall so you can see the wood-eating critter tubes. - Apply an ignition barrier on any foam insulation used, if
required. Check the manufacturer’s ignition barrier requirements
carefully. Ignition barriers aren’t inexpensive and a big fight might
ensue if a barrier is required and it’s not in the insulation
contractor’s bid. - Provide ventilation to the crawlspace. The
Word chose the conditioned air method which involves supplying
conditioned air at 1 cubic foot per minute per 50 square feet of
crawlspace area. The International Residential Code also specifies
providing a return duct or transfer grill into the house, but this is
not allowed in North Carolina. - Weatherstrip and insulate the
crawlspace access door (assuming, of course, that it’s an exterior
access door). It’s now an exterior door, so treat it as such. - If you’re in a Radon-prone area, consider having the house tested
before sealing the crawlspace. A Radon mitigation system is less
expensive to install before sealing the crawlspace.
Here are a
couple other nice-to-haves. Put an extra layer of vapor retarder on the
path to any equipment in the crawlspace that requires service, such as
an air handler or a water heater. The vapor retarder is most likely to
tear on these paths. Have the contractor leave some extra vapor retarder
and sealing tape for vapor retarder repairs. Repairs will be needed at
some point.
Danger, Danger Will Robinson!
Air sealing houses
is good, but air sealing can cause problems. People need some “fresh
air” from the outside. If air sealing causes the air changes per hour,
as measured by a standard blower door test, to fall below five,
mechanical ventilation may need to be added.
The more serious
problem can occur when air sealing is performed on houses where
combustion air for fuel-burning systems is drawn from inside the house.
This means fireplaces and fuel-burning stoves as well as fuel-burning
furnaces, boilers and water heaters. Air sealing these houses can kill
the occupants if inadequate combustion air creates a carbon monoxide
problem or if the systems were malfunctioning and the effects were not
apparent because the home was so leaky.
A qualified person (e.
g., BPI certified) should perform a blower-door test on all houses that
have been extensively air sealed and should perform a combustion safety
test on houses containing fuel-burning systems. If the tests indicate
problems, appropriate remediation should be performed. At a minimum,
carbon monoxide alarms should be installed in all houses with combustion
appliances or with an attached garage.
The Bottom Line
They
don’t build houses like they used to. That’s true. In terms of air
sealing and insulation, they build them better now. It’s both possible
and useful to consider upgrading attics and crawlspaces to modern
standards. The Word is glad he did.
Memo to crawlspace
monsters: The Word does not
reside on Mt. Olympus (just at its base) and
welcomes
other viewpoints. Send your lightning bolts or emails to Bruce@DreamHomeConsultants.com. The thoughts contained herein are those
of The Word. They are not ASHI standards or policies.
Bruce Barker operates Dream Home Consultants. He
has been building and inspecting homes since 1987.
He is the author of “Everybody’s Building Code” and currently serves as chair of the ASHI Standards Committee.
To read more of Barker’s articles, go to
www.dreamhomeconsultants.com.
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