Attic insulation ventilation question

8 years ago

We recently purchased and subsequently remodeled a home built in the 1950's in Orinda, California. The roof, while not flat, has a very low pitch to it, leaving little space in the attic for insulation. At the peak, there is probably 24 inches of space between the roof and the ceiling, becoming less as you move towards the outer walls. We've had a pretty cold winter here in the Bay Area, and we're finding that this house doesn't retain heat very well at all, especially in the bedrooms.

As part of the remodel, our contract did have insulation blown into the attic, but since the house has been so cold, we had another insulation company come out to reassess. His opinion was that not enough insulation was blown into the attic, and the house would benefit from another 6-8 inches of insulation. However, this would leave very little space in the "attic" for ventilation (which our contractor was quick to point out).

My question is, is ventilation something I should be concerned with? If so, how much space should we leave for ventilation? Thanks in advance for your help.

Comments (6)

mike_home
8 years ago
An unconditioned attic needs to be ventilated. How is the attic ventilated now? What type of insulation is currently there and how many inches?
energy_rater_la
8 years ago
install baffles at soffits. insulation should not touch roof decking.

insulation does little to stop air leakage from attic into

house.

have you done any air sealing?

where is hvac system & ductwork located?
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maucelil
Original Author
8 years ago
@mike_home: attic is ventilated with fan. There is about 6" of sprayed cellulose insulation. There is another 12" or so of clearance before the roof deck. Roof is about 17 years old, tar and gravel.
maucelil
Original Author
8 years ago
@energy_rater_la: regarding the baffles at the soffits, can you help me understand what these are and how they would help? Insulation not touching roof deck. Have not done any air sealing - what is typical? HVAC is an electric furnace. All ductwork run under the house in crawl space. Registers located on floor in front of window (in each room). Thanks.
mike_home
8 years ago
Is the attic fan installed in the roof deck or in the gable end of the house?

The fan is exhausting the air. Where are the air intakes? If you add more insulation then you don't want to block any air intakes.

Is the insulation open or closed cell? That will determine the current R rating. Is the contractor proposing another 6-8 inches of spray foam insulation?
energy_rater_la
8 years ago
no foam mike_home, contractor is proposing blown insulation either fg or cellulose, only OP knows.

just google baffles for attic ventilation OP. lots of pics there.baffles are installed on roof at eaves to do two things.

one is to keep insulation at low point of eaves/soffits from

clogging up air flow.

the other is to establish a pathway for air to enter attic

at soffit/eaves.

attic ventilation that works is one of these three methods.

all are stand alone, not strategies to be mixed.

gable end vents. soffit/eaves may or may not

have vents cut into them.

soffit/eaves vents with ridge vent at peak of roof.

or lastly soffit/eaves vents with passive vents installed

on roof.

the idea is to take air from soffits & vent from gable end,

ridge vent or passive vents.

google attic ventilation for more detailed info.

prior to adding insulation minimal air sealing

of air barrier (ceiling of living space) from living space

to attic is done. for example recessed lights (Insulation contact not

IC air tight recessed lights) would be addressed prior to insulation.

much harder to dig out each area to be air sealed with newly

installed insulation.

fortunately, you can do a lot of air sealing from inside the living

space.

making as tight of an air barrier between living & attic spaces

is one of the first steps to efficiency (and better air quality that goes

along with it).

it is easier to heat/cool a house with minimal air leakage.

first area to air seal is house to attic. then floor to crawlspace

(now that we have that info) once the air sealing is completed...then

insulate. (3" closed cell foam installed on underside of floor,

installed from under the house)

if you have 8, 12 or 20+ inches of insulation & there is air moving

through it...then it isn't performing. keep in mind that there is a diminishing

return for more inches of insulation. the first 6" of insulation does most

of the thermal barrier work, added insulation above this 6" saves you

less & less $$ in utility costs. meeting code minimums is the least you

can do. here in La. R0-30 is code, but people often have R-38.

not a big jump in price, and not a big savings in utility costs.

you make your own call on what to be installed.

are you willing to do any work? (ie caulking etc)

whats your location?

best of luck

Attic insulation ventilation question

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mike_home

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Attic insulation ventilation question

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mike_home

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