How to Seal Attic Before Insulating

thebigadJuly 13, 2012

In a previous post, I received a lot of help (from energy rater la) on figuring out how to seal attic openings before laying out insulation. Like many, I thought insulating would seal the attic - not the case.

While most of my questions were answered in the previous post, I thought I would post under a new post so that somebody in my position could easily get an answer as well, and keep the conversation going under this post. Below are some questions I still have from the previous post. If they get answered in the previous post, I'll post them here.

Question: If I have an IC can light, can I just spray foam around where the housing meets the attic floor and then cover it with insulation?

Question: If I have a non-IC can light, I understand that I need to cover it with an airtight box and spray foam that box to the attic floor. What if the non-IC can light is near the very edge of the roof. How do I cover it up so that (A) it is airtight and (B) I can throw insulation on it?

Question: I have a brick chimney that I need to seal around. My fireplace is natural gas and not often used. Do I still need to put metal flashing at a 2 in. distance all around the chimney or can I just spray fireblock foam around the base of the chimney and then dump insulation around it?


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question 1..No.
the IC light still lets attic air into the house.
build the box.and use cfl's.

question 2..if it is too close to the may just have to let it suck air into the house. Unless you can
build the box with angled sides and top leaving side of box
closest to eaves open. you can only do what you can do.
you can look inside the can from inside and get model number
and brand name and buy an ICAT insert. about $15 and
loads of fun to install. but if its just one can light..
it would be worth it IMO

I would NEVER put foam next to a can light.
foam shrinks and does not air seal as well
as folks seem to think. its easy..but testing
with blower door shows that after a couple of years
that foam does NOT seal air tight.

question 3..fireplace..I generally use ductboard..another fire rated material if gaps are large. sheetrock is a cheaper although harder to work with material.
nail in place, caulk to attic floor & use fire rated
caulk to seal next to brick.

best of luck.

    Bookmark   July 13, 2012 at 7:51PM
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I am learning this right now as I did a bunch of foaming a few years ago and now I need to go back cause of leaks and use a caulk that will stretch for expansion and contraction. Regular caulk would work but I really prefer this new stuff that has a lot more ability to stretch. There are places that foam is wonderful but it isn't always the best option.

    Bookmark   July 15, 2012 at 5:09PM
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    Bookmark   July 16, 2012 at 9:35AM
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what new stuff countryboymo?
I use dap's Alex 25 year caulk for just about
hvac caulk (gray & clear) in attic only.
both have a strong smell.

when foam is approved by acca..and tested
after a few years maybe I'll recommend it.
until then....

best of luck OP.

    Bookmark   July 16, 2012 at 10:54AM
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I have more insulation board to put up on the back of two knee walls in the attic that are part of the living room area along with more attic sealing.

I have used a couple 'stretchy' caulks in the basement and used big stretch on two problem joints that have a lot of expansion and contraction and where regular caulk was holding on the edges but was tearing in the middle which is not an adhesion issue. I removed that and replaced it with big stretch and wow it seemed to have glued very well to the siding seams but still is really flexible. There are other products with these properties and more out on the shelf every day. I almost forgot about a problem area I had with a bad design on the deck and the interior door that rain and snow was being blown in and ruined some hardwood. I put in a better quality door and also incorporated a piece of stainless for flashing that will block anything from getting under the door and sealed it with a similar product on the inside.

Here is a link that might be useful: Big Stretch Caulk

    Bookmark   July 16, 2012 at 11:51PM
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you should check the weatherstripping section
for backer rods. foam tube different sizes
I usually get 5/8" & 1/2" just about $4 a bag.
old product, been around a long time.
you can trim the rods but still want a tight fit
push it in with a butter knife or flat screwdriver.
then caulk both sides of backer rod to area to be sealed.

works great!
if you have single glass wood framed windows,
you just use the backer rods without caulk to seal the

if the gap to be sealed is over 1/4" wide you have
to caulk ..let dry..and recaulk. backer rods solves
those issues, although I go back and closely inspect
to make sure it is totally sealed.

you can use it in a lot of places.

always nice to trade info with you!
take care.

    Bookmark   July 17, 2012 at 8:09AM
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Question: I don't look forward to building about 15 boxes for all the recessed lights I have. I read before that you could retrofit a large styrofoam ice cooler instead. Is this a good idea? Any chance that the foam would melt? If that is a concern, are the other materials (foamboard) fire retardant?

    Bookmark   July 17, 2012 at 10:24AM
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The coolers work awesome except some foams and caulks eat styrofoam so some testing needs to take place before you head into the attic. If you have to deal with codes and an inspector ask his opinion first. There are covers available that can be caulked in place and are treated so they won't burn and aren't quite as easy to find, are more of a pain to work with and to some are expensive if you have a dozen to do. One other option is a 'sealed' trim that goes on the inside. I think these are great if installed and caulked in place so they truly are sealed but then painting can be a challenge later. They come with a flakey stick on gasket which is still much better than a cheap trim but still is far from perfect without caulk.

I have purchased the trims from Ebay much cheaper than home depot or lowes and I did use caulk and caulked the tiny slots in the top of the trim and at the ring to sheetrock contact area.

Doing the rings inside the house still does not spare you from sealing the wires and pipes that enter into the attic which are huge leaks also.

Most people blow off the recessed light sealing and they can be the largest hole into your attic and cause the most comfort/allergy issues. I have 14 and on an energy audit we tested the cfm or cubic feet per minute of air at each vent and register and also tested each recessed light on a day with light wind. I had an average leakage of 5 cfm from each light which doesn't seem like much until you do the math per hour and per day.

70cfm per minute for 14 lights
4,200 cfm per hour
100,800 cfm per day.

I don't even remember the numbers when we fanned the doors but they went all over the place negative and positive which pulls nice clean air out of your attic and cellulose fibers or fiberglass fibers in for the owner to live in.

I highly recommend paying someone to shoot your house inside and out with a thermal imaging camera before you jump in too far so you can develop a game plan. I also highly recommend a blower door test with the thermal camera and cfm testing ducts and such. I had less than 150cfm total of actual return air going through my registers on a 1200cfm system because I was sucking air out of the attic and basement for return air. I would have never known the severity of the issue without the test.

Get the testing done and pay for it get photos of the results. I would pay for the testing and any other services I would wait on until you digest the information and figure the best way to attack the issues. I hope I get to read your findings and what approach you decide on.

You are on track to keep money in your wallet and be more comfortable in the process.

    Bookmark   July 18, 2012 at 12:13AM
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Apart from all the other useful info, don`t forget to seal the tops of the walls where plumbing or electrical come and go. Here in BC spray foam is allowed for that, and to me it has a great advantage since it tends to `mushroom`at the top and bottom, sealing it better and adding a little more insulation. I don`t think caulking has anywhere near a comparable r-value.

    Bookmark   July 19, 2012 at 2:57AM
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but caulk has more expansion and contraction than foam.
it isn't about the r-value, of what seals the hole but the air seal of the hole.
over time in extreme attic heat caulk holds the seal.

as foams are mixed on site for unvented attic applications,there is more human error.
wrong mix, wrong temp, wet roofing materials, cold roof

while you don't read about these issues on foam
websites, you do see them in the field.
what is where inspections and testing of these
applications show the other side of the sales
& promotional information.
we talk about it on sites like this..but it
isn't readily available for the public.

the trade off for all the detailed air sealing
is so the insulation will perform on the attic floor.

the other side of the equation is to forgo
air sealing at attic floor and foam insulate
the roofline.

this moves the air and thermal barrier to the
roofline, making leakage sites at
attic floor less of an issue.

one is the detail and lesser cost..sweat equity
the other is the fix all unvented attic
to compensate for lack of better building practices
@ 3x the cost.

once the air leakage is minimized then the sizing
of the hvac becomes critical. too much and you
oversize and don't remove humidity. too little
and comfort is an issue. IMO the insulation companies
and hvac companies need to come together and do
better jobs of load clacs and accepting responsibility
for their installs.

foam has been around for a while, but caulk and mastic
are specific proven sealants. to is the
combination of the right materials that seal effectively
now and for years to come.

to me if you air seal the house, mastic seal ducts
then half of the problem is solved. sizing hvac
not rule of thumb wag sizing and you have several
benefits. comfort, efficiency, better indoor air quality
and lowered utility bills that continues to
off set costs long term.

best of luck.

    Bookmark   July 19, 2012 at 11:11AM
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Is there a caulk brand/model you recommend to use up in the attic to seal around stuff?

    Bookmark   July 23, 2012 at 9:34AM
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