air sealing attic...move plywood?

cindywhitallAugust 20, 2012

(new thread..not part of original decision making topic)

I am going to have my attic air sealed where they will seal all the penetrations to the attic. About 1/4 of the attic has plywood down so we can store stuff. Of course part of it is around the opening where we won't be removing it, which unfortunately is where a few walls meet the attic.

I have been throwing away stuff and plan to move some stuff down while they are working. Is it worth it to do the extra effort (and SWEAT!) to unscrew some planks so they can airseal under them? Hubby doesn't think it's worth it, but I've arranged it so he can do two of them easily.

He thinks we are just as well off just sealing the seams where the plywood (osb) butts each other and not doing under it.

I would have him basically just unscrew the boards but not move them. (I could do it, but what if I do it "wrong"!) Since they will be adding insulation in the parts not used for storage I want to leave them down so they can see where they go. If we move them then they won't know where to blow the insulation. Hopefully they will be willing to lift them and seal under them.

It only came up in one conversation, but they said they would build a little wall (6-8") around the edge of the plywood for the blown insulation.

Would this be better in the home repair forum?

Hopefully you all understand what I mean. I guess the main thing is whether it is good just to seal between the plywood or move it, keeping in mind the extra work to move it. There is batt insulation under it from when the house was built in 1996. It was supposed to r-30 ....


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You are going to have insulation blown on top of your batt insulation? Are you sure you want to do this? It would be a lot neater to lay down a second layer of batt insulation perpendicular to the first. The second layer should not have a paper moisture barrier.

The only place you need to move the plywood is where there is a ceiling fixture, or a area where there may be a chase for pipes or duct work. Otherwise there is nothing to seal.

    Bookmark   August 20, 2012 at 1:59PM
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so 1/4 of the attic area gets no added insulation?
do you realize how this de-rates the overall R-value
of the attic?

we generally take up any storage area,air seal ceiling below, then toenail 2x's
across ceiling joists, insulate and put storage area
back down. added depth allows for added insulation.
then there is no need to build a dam to hold insulation
off storage area.
and you get the full value of the added insulation.

does the company doing the air sealing understand
what they are there to accomplish?

have all junk moved out of attic so they can pick up storage
area, air seal under it. sealing the storage area above
attic floor does nothing for air sealing of ceiling
below existing insulation under the storage area.

I'd make sure to tell them this:
move storage area, air seal underneath.
bath vent fans, supply air penetrations, stove hood venting, plumbing & electrical penetrations. and those cursed recessed lights if you have them.
(after you remove all junk from
attic so they can safely work..and not be moving junk
back and forth)
use 2x's to pick up storage area. use screws to toenail
2x's into existing ceiling joists.
replace decking again with screws and mark any
electrical or plumbing below decking for future

if they do this as a should be a
no-brainer for them.

this is a standard attic air sealing job imo.

will any of the leakage be addressed from inside
the house at the ceiling?
will amount of leakage reduced be verified once
it is completed?

any duct sealing going on?

best of luck.

    Bookmark   August 20, 2012 at 2:42PM
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I can see I should have asked this before....My quotes indicate 944 as the quantity of blown insulation. I assume this to be sq feet. Using the floorplan diagram from the builder when we bought the house my attic should be approx 1200 sq feet (weird because the house is supposed to be 2800). The amount seems right if they measured the part with the wood. I never questioned it when they measured or gave me a price. Luckily there is only 1 bath fan and no stove hood. There are 2 big black tubes that say 8 or R8 on them that I'm pretty sure are return ducts. There is no other ductwork. The 3 recessed lights are accessible, sort of...there is a tray ceiling in the mbr. Next to it is the bathroom with the lights. There are trusses/beams going across for the mbr ceiling, but the bathroom top is BELOW those boards that go across the whole way. Those will be fun to reach! I think all 3 ceiling light fixtures are accessible. One is RIGHT next to the edge of plywood and boy is that insulation dirty underneath!

I love the idea of raising the deck but I am pretty sure it is not part of the quote. I seriously doubt hubby would do it....though maybe he would if it meant there wouldn't be that dam to keep the blown in stuff in.

I thought batts laid crosswise would be good to, but I also read that blown was better as a top layer. I assume blowing it in is cheaper and easier for them to do??

Summary, assuming that we will or cannot raise the deck then we SHOULD move any wood covering something that needs sealing. No pipes in the area to worry about. I will work hard to take out as much as I can and unscrew the planks so they can access the area.

energy_rater, I'm not sure who is doing the actual sealing. We contracted with an hvac company for the air sealing as part of a complete project w/ sealing, hvac, hot water etc. I don't know if they sub out the sealing or not but they did do an energy audit. SO, it may not be a no-brainer as much as a "lets do what we can get away with". The state does not seem to REQUIRE blower door tests, though the one company that did do it, and was going to do an "after" also wrote for the same amount of footage and was the one who told me about building the "dam."

Apparently me research fell short as I didnt consider this until it's too late to change it (without probably paying more) I will look into it though.

What about putting that foam board insulation under decking? could that be done without adding 2 x 4's? Cost per sheet? (4 x 8)

    Bookmark   August 20, 2012 at 4:46PM
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I assume you have a pull down stair attic? What are they doing about sealing and installing the stair opening?

The blown in layer is less labor intensive and will fill in areas that are irregular in shape. It does have some advantages over a fiberglass batt. There are Youtube videos available showing how it is installed. I personally don't care for it especially since you plan to store items in your attic.

I would imagine your HVAC contractor has sub-contracted this work to an insulation company.

    Bookmark   August 20, 2012 at 5:18PM
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They are building some kind of hatch cover. I did see how that is often done on youtube with the solid insulation and building a box. I had often thought about that flimsy stair backing, but never considered building a cover for it.

Not fun working up there, so I'm happy to pay someone to do it!

We don't store anything of much importance up there and what is stored is in boxes or plastic tubs. Christmas stuff, carpet remnants (for patching stains....used a small piece once in all these years and jus threw tons away) off season clothes but those are in vac seal bags and double bagged. I hope it isn't messy, but we aren't up there much...mainly at Christmas and after Christmas. We have a basement too, also filled with junk we probably don't need.

The tray ceiling in MBA has sloped sides going up to the top part of the ceiling. Batts over batts might not do as well there.

It really was eye opening to see the dirt on the back of the insulation around the ceiling fan box. Most people have no idea, I didn't, of how much air leaks in and out. That room does heat up in summer with south windows and I bet that opening doesn't help.

    Bookmark   August 20, 2012 at 5:40PM
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putting foam sheathing doesn't do anything
but insulate the storage area flooring.

it is a waste of time money and effort.

in adding foam sheathing you are adding a vapor
on top of the batts/blown insulation.

batts actually work better on slopes
because it is the uniformity of the insulation.
as you will see, the blown will vary in depth
in this area.

it would behove you to get up into the attic before
they finish and take a look. ask the R-value per
inch of whatever blown insulation they are installing.
figure out how many inches need to be in place to
achieve this quoted R-value. take a yardstick or
some form of measurement and measure the depth
of the install in several areas.
or ask them to do it while you shine a light
to see if the depth is reached. any low spots
should be filled. blown settles so depth should
be a few inches over quoted inches. types of
insulation have different qualities so some
compacts (settles) more than others.

if they are using cellulose..the air sealing is
more important than ever.cellulose has a fine
dust that will enter thru the smallest of areas.
the bath fan for instance has openings in the housing.
the cut where it fits thru ceiling is oversized.
this cut should be sealed with mastic tape.
back draft damper should be properly installed
and vented out of insulation..perferably out
of attic.

the sloped ceiling is another place that will de-rate the
overall R-value of the install. as are each
recessed light (1 unsealed IC light = 1 sq ft of
uninsulated attic space) you can see by the
dirt on the batts how leaky the can lights are.

if they don't address them from in the attic
you may be able to install an ICAT insert
and trim from inside the house. expect to
pay $15 for insert, plus trim.
you will need to brand name and model number
of the recessed light. once you retrofit them
use cfl's for more savings.

if the attic is 1200 sq ft, and bid is for 944 sq ft,
then 256 sq ft is the storage... I guess.

I don't know what your starting out R-value is
or what they plan to install. but as an energy rater
(note rater not auditor) we have to deduct for
areas like sloped ceilings, recessed cans, storage
areas and all areas that have less insulation than

the attic staircase when not properly
sealed and insulated derates the insulation install,
and air leakage from this and recessed cans further
are also penalties.

I'm learning that these are some of the many differences
between raters and auditors..and when utilities are
involved in providing work for auditors and incentives
the quality of the audit/rating is in question.
if some company is paying a portion of your fee,
you are not unbiased and working 100% for the

I've found hvac companies to be bad at sealing
their own work..

best of luck.

    Bookmark   August 21, 2012 at 10:12AM
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