Anyone have any suggestions?

If the ductwork is in the attic, consider going to a sem conditioned attic by spraying foam on the underside of the roof deck. But, it's all or nothing. Either ventilate properly with proper vented soffits and ridge vents or eliminate it entirely.

If we do the "semi-conditioned", we put the foam in and then is there just no air circulation in the attic at all? I don't really understand how using the foam works but would like to understand it better.

Thanks!

Cost effective option = suck out insulation, install vent baffles, ensure soffits allow ventilation, close up gables, put in new insulation. Air comes in the soffit and goes out the ridge vent.

You should be able to see if the soffits allow venting from the outside. Another way is to turn off your light in the attic and if you dont see daylight near the soffits then they dont allow air in.

hi lucas_tx_gw, there is so much on this subject , bottom line yes, close or seal up gable vents. like vithdude said make sure soffit is venting properly. the insulation installer should know how and where the new blown insulation should be. the insulation should stop short of the soffit and allow air flow into the attic and out ridge vent.

Thanks Gene. The issue with both gables and ridge vent is that the air just gets sucked in the gables instead of the soffits, is that it?

sorry lucas for not getting back sooner. yes that's basically it.

hey,
no baffles under foam.
this is a detail of a foam sealed unvented attic.

here in La. 90% of homes have ductwork in the attic.
100% of homes have oversized holes in the sheetrock
ceiling that are not air sealed.
by removing the insulation from the attic floor
& moving both the insulation & the air barrier to
the roofline, the ducts are now in a semi conditioned
space. any holes in sheetrock ceiling/attic floor
no longer suck attic air into the house.

R-6 ductwork (code minimum here in La.) in an attic
surrounded by 130+ degree air is a stupid thing to do.
this is one solution that solves that & the air leakage
from the attic into the conditioned space below.

one can seal each opening in the attic floor/ceiling
of living space.
but ductwork in hot attic is still an
issue. put high efficiency equipment in a vented
attic in a hot humid climate & equipment, supply
plenum & ducts will condensate.

best of luck.

Thanks for all the replies. So energy rater, what temperature do these attics stay in the summer?

in our climate within 10-15 degrees of ambient.
although most say within 10-15 degrees of
conditioned space/
it works out to about the same here.

It probably would be here as well since inside is 70s and outside is 90-100. Definitely something to consider.
So the only air exchange is the accidental exchange through the attic ceiling? I'm still just working on getting my head wrapped around that.

To put it simply, when the insulation is in the attic floor, modern ridge and eave vents are not sized to move enough air to cool the air of a hot attic. Even if it was, too much of the heat is from infra-red radiation from the roof that does not heat the attic air until it strikes the attic floor. Increasing the air flow through the attic brings hot humid air into the attic and pulls conditioned air from the house into it as well. Its a ventilation concept from the time when houses were not insulated or air-conditioned.

A common solution is to insulate the rafters either with batts with vent baffles behind it or with sprayed foam with no venting behind it (sealed attic). That and perhaps some kind of radiant barrier will lower the temperature of the air in the attic and lower your air conditioning bill.

"So the only air exchange is the accidental exchange through the attic
ceiling? I'm still just working on getting my head wrapped around that."

I hear you!
and yes,
the only air exchange to the attic through the
ceiling (into the living space) is accidental exchange.

you still have air exchanges in your living
spaces, just not so much to/from the attic.

even with a vented attic, you don't want to
share attic air with conditioned space air.

the holes that allow this exchange
need to be sealed, or move the air & thermal
barrier to the roofline.

best of luck

Thanks I appreciate your patience. I understand that right now my ceiling is exchanging air with my attic (without my permission :-) I just struggle with the fact that if we seal the attic, that's the only air ever going in or out of the attic. Seems like it would get quite musty. Do people sometimes actually go so far as to put vents from the HVAC into the attic to prevent that?

If the HVAC equipment or its ducts are in the attic the air leakage will adequately ventilate and dry the space.

If you seal the attic I recommend using full coverage of Grace Ice & Water Shield as roofing underlayment.

"Do people sometimes actually go so far as to put vents from the HVAC into the attic to prevent that?"

yes they do.however these are houses where the ceiling plane is tight
so that there is a lack of exchange between the two spaces.
that degree of tightness is something that is planned, it doesn't
occur in regular stick build.

also ducts leak. in creating this unvented sealed attic
you are covering the issues left behind by hvac & building
trades. average duct leakage is 30%. this leakage
tempers the attic air. the thermal bypasses & holes
in the attic floor into the house that allow temp
transfer are now filled with this tempered air, lessening
the heat/temp transfers.

I realize that you are dealing with the abstract, whereas
I have done so many of these homes that it is factual to me.
same with duct leakage testing.
if you had a blower door test & had the time to actually
feel the leakage sites (rather than just having a number
for leakage amount) then it would be much easier
for you to understand.

here is one of my favorite building science articles.
note the related articles listed on right of link for your
educational purposes. note the location of the tests in
the article.
(welcome to my world grasshopper...)

http://www.buildingscience.com/documents/insights/bsi-077-cool-hand-luke-meets-attics

enjoy!

give it a read & post back with your thoughts.
now that we are having this discussion.

When using open cell foam, some thing seem to indicate that condensation on the sheathing can be an issue. Have you seen that or how do you prevent it?

I just won a $5.00 bet! I told my colleague that of all of
the info in the article, that would be the one thing that would
be the next topic of this thread. LOL!
read under picture 2;
"I was worried that moisture from dew and rain would wick into the overlaps of asphalt shingles and be driven inwards by solar radiation and lead to increased moisture contents in roof sheathing—especially in unvented roof assemblies—turned out I was wrong."

under picture 3:
"turned out that there was no measurable
effect of roofing underlayment permeability on inward moisture drive
through the roofing assembly."

lucas - we live near Houston, and DH and I DIYed our radiant barrier back in 1999. Nerdy me charted before/after attic temps and avg kWh usage during the hottest summer months. We experienced a 10-15 degree drop in attic temp after the radiant barrier went in, and our avg kWh usage (mostly from A/C) dropped ~ 25-30% overall.

Energy, I did see that in this article they did not think rain was driven in but I think there are other articles out there that do indicate this could be a problem.

In your mind that's not an issue?

Javiwa,

You did a radiant barrier but left the attic vented is that correct?

Our house was built w/o a ridge vents (!), and we were told in '99 that was the best method of cooling the attic. We didn't have the funds at the time to have ridge vents installed, so we opted for the cheaper, DIY fix. About five years ago, we had roof repairs done, so had the ridge vents (and a few extra soffits) installed at that time -- ridge vents plus soffits now.

I have a radiant barrier also.
no ducts/equipment in attic,
both are inside living space.
attic has gable end vents only.
my air barrier at the ceiling plane
is near perfect.

my house has full sun on roof.

at best my rb install saved me 15%,
10% us more accurate.
it did drop attic temps about 10-15 degrees
as stated above.
the air sealing & not putting the hvac
equip/ductwork in the still 130 degree
attic provided double the rb amount easily.

did you chart the temps & do any air
sealing work?

in the software I use for modeling houses & measuring
the upgrades in efficiency, radiant barriers
show about a 10% improvement & savings.

and OP, no in my mind & experience there is
no issue with your concern for our climate.
but something to think about if your water
heater is in the attic & is electric
is a heat pump water heater. it will
add dehumidification to the attic.
standards for electric water heaters are
making a big change.
it is something to think about.
(if you foam insulate the roofline)

best of luck.

energy - I don't believe our attic space ever got as hot as 130 (topped off at ~120 on a 98/99 degree afternoon, measured at 4 p.m.). It's a two-story home and, at the time, street/yard trees weren't tall enough to provide any cooling shade, so full sun. All of our AC equipment, ductwork and water heater were installed in the attic (it's NOT been fun replacing the water heater twice over the years!). We haven't done any air sealing, and the temps for the 5-7 years were taken off my energy bill summaries; recent 2-3 years summer temps have been taken off the energy company's online summary (very handy!).

Of course, I'm going by memory, but I don't believe our family implemented any extra steps to keep the cooling bill down in recent years (that would account for the higher decrease). If it matters, radiant barrier was the spray/roll on paint.

Thanks all. We actually have two attic spaces due to an addition. The main one has only ductwork in it which is the flexible insulated kind but for the addition they did put the HVAC in the attic. All electric, no hot water heater thank goodness.

Start with the most important issue and its not the temperature of the attic. If the HVAC equipment and/or ducts are in the attic, you are losing a great deal of conditioned air to the attic space due to leaks and older minimum code insulation and you need to put an end to that waste. You also need to avoid bringing large amounts of hot/humid or cold air into the attic. That is never effective because so much of the heat in an attic is from infra-red radiation from the bottom of the roof deck that passes through air without being cooled.

The modern solution is to insulate between the roof rafters and, if you like, add a ventilation space between the insulation and the roof deck so air that enters at the eaves can exit from the ridge and slowly dry the roof deck. Or , alternatively, you can seal the attic - its your choice.

The attic space would then be partially conditioned by the HVAC air leaks and thin insulation which will keep it at a moderate temperature, dry and not musty and will reduce the heat and cooling losses from the house below. This is how new houses are built.

We just completed construction of a new beach home on the Florida panhandle. 3250 SF. I paid an extra $2,500 to spray open cell foam on the roof deck, gable and knee walls.

During hot and humid days, the attic is about 10 degrees warmer than the house and it is nice and dry. Money very well spent.

Thanks Jack. That attic then is sealed? "Semi-conditioned" space?