Add to Existing Attic Insulation?
Here’s the situation – 1920’s Colonial in New England; attic beneath hiproof has some sort of mineral wool insulation between the joists underneath floorboards; ventilation provided by a huge, screened (closable) opening on one end (attic used to have a large floor-mounted fan drawing air out from second floor) and by a “pipe” opening (without squirrel cage) toward the other side.
I’m preparing to have cellulose blown into the walls (no existing wall insulation) and wondering whether to supplement the attic insulation in some way. It can be seen in places between the floorboards or in spots where a few have been removed for electrical work that the mineral wool doesn’t completely fill the space beneath the boards. However, one contractor tells me that there wouldn’t be a sufficient payback for the labor involved in removing and replacing all the floorboards. As I don’t currently use the attic space for storage, he suggested that he add R-19 unfaced FG batts on top of the floorboards (cost of $600). However, given that it can get quite breezy up there given the ventilation, my understanding is that FG batts may be largely ineffective due to convection current losses.
My choices are to (1) leave the attic alone and simply do the walls, (2) bite the bullet and have the floorboards removed and top off the existing mineral wool with cellulose (>$1,000 est.) (how would the density of the added cellulose be controlled?), or (3) add the FG batts on top of the floorboards as proposed.
I’d appreciate any and all opinions on this.
Replies
I don't have a clear picture of the situation. Maybe you can clarify a couple of points:
1. You have a hip roof with openings on opposite sides? So the openings are through the roof itself? Or do you mean you have a gable roof?
2. Sounds like your attic is unconditioned but has a finished floor, is that right? How deep are the joists? Is it a walk-up attic?
Hi Bob,
Thanks for your interest.
Yes, I believe it's a hiproof; it slants down front to back and also side to side. The large screened opening I mentioned is on one side of the house just below the roof line. The ventilating tube does indeed go through the roof; it's positioned closer toward the other side of the house, away from the screened opening.
The attic is what is considered, I believe, unfinished, though it has a planked floor above the joists. It's a walk-up from the second floor. I would estimate the joists to be 8" (I'm not home at the moment to measure.)
If it would be helpful, I could snap and post some photos of the house this weekend.
Pics always help.This ventilation scheme seems a bit micky-mouse if you don't mind me saying. I'd be sure the tube can't get clogged with snow or let water in. That said, venting a hip roof is really hard.If you are decently handy this is not above the homeowner level of difficulty, espectially if you can get to all corners of the attic.I'd like to hear what others say, but if you don't really care about the floor condition you could use a hole saw put some holes in the planks and blow cellulose in there. Similar to how houses are insulated from the outside. You have to be careful not to blow out the ceiling of the second floor but it should work if you are careful.For more insulation you could rip up the entire floor and then you can really add a lot of insulation. You are right though, FG will not do much good with air blowing through it. Though it doesn't sound like the current scheme is going to give you much air flow. You need to think of that too when you add insulation. Finally, before you do anthing go through the attic and seal all penetrations between the conditioned space and the attic with canned foam and caulk. Be careful around the chimney to not create a fire hazard. Not sure what specifically is recommended in that case, so I'll leave it to someone else.You are probably losing a lot of heat from air leaks and the walkup door is probably a big culprit. Take a good look at it and make sure it seals out air when its closed.Be careful where you step and wear a dust mask/respirator.
Thanks, Bob.
I'm likely not describing the tube properly; it is capped and of sufficient diameter so as not to become clogged.
Part of the insulation improvement will include insulating the wall between the walk-up stairs and the heated living area. Also, the door to the walk-up will have a padded layer added to it.
The problem with punching holes in the floorboards is that especially with the insulation already beneath there would be difficulty in getting additional insulation to spread much beyond the perimeter of the hole. Frankly, even removing the floorboards and pouring cellulose on top isn't a great approach. The cellulose density can't be controlled that way without a confined volume to fill. The best (and costliest) approach would likely be to remove the floorboards, remove the exisiting mineral wool, replace the floorboards, and then snake a hose down the empty channel and dump in cellulose to a certain density as the hose is slowly pulled out.
I think I'm talking myself into leaving the attic the way it is....
"Pumping" the cellulose under those attic floor boards is the easiest thing to do. The proper technique will fill the space under the boards. You do not need to remove the mineral wool. But with just an 8 inch fill you won't get the proper R-factor.
If you do nothing you will continue to lose heat into the attic thru the ceiling below. And you will continue to get heat gain into your living space in the summer.
You could pump under the attic floor as above, and than dump more cells on top.
For attic acess make a "cat walk" down the middle. Make your own open web supports a foot high and then screw some 1/2 ply on top. Then blow the loose cells under it.
If you want storage space make a large platform the same way. Pump the cells below.
I've not found an insulation contractor who told me it was possible to "pump" cellulose over the mineral wool with any degree of effectiveness. Apparently, the cellulose would not spread out much from point of ingress. There would have to be a "ton" of holes drilled in the floorboards to fill in the uneven volume above the mineral wool. And it turns out that the joists are only 6" high. So we're talking about an R-value of 21-22 tops even if the entire volume were filled with cellulose. It doesn't seem sensible to me to just dump additional cellulose above the floorboards. For one, it would be a mess to access any of the 2nd-floor wiring after that.
I don't get what you mean about "controlling density" of the blown cellulose. In my experience, cellulose is simply blown in to an attic, period.
If you don't need the attic for storage, I agree with the approach of adding a cat walk, if needed, then blowing in cellulose. I think I'd pull the old floor boards and blow in at least a foot of cellulose. I have about 28" of cellulose in my attic.
No matter what route you go, do seal up the surfaces between living space and attic. That should help considerably.
I still don't understand what you are saying about the screened opening. If it's below the roof and above the living space that would be unusual. Sounds like your house is balloon framed. Is that correct?Life and suffering are inseparable.
Hey, I am in a somewhat similar situation (except I have three smaller "attic" areas, as the upstairs (1.5 story 1920 Minnesota bungalow) is finished.
There is some blown in insluation under the floor boards. In order to be able to use the attic area for storage, I was thinking about puting down some foam board and then plywood over that to walk on (sort of like Andys basement finishing article several months ago).
What do you guys think of that?
Erik
How would the foam board seal down to the existing insulation? If there is an air space above the existing insulation and below the foam you add, I'd think there would be a tendency for the heat to roll around the edges of the foam and render it not very effective. You could mostly get around that if the foam was sealed so no air could flow around. But then you could wind up with moisture trapped under the foam.
I'll be interested to see what others think about your idea.Life and suffering are inseparable.
I also do not think your foam and plywood is a good idea, for same reasons.
Build a deck platform on top. Blow cells under the original attic floor and then more under the new platform.
Insofar as cellulose density, the stuff seems like it would compact if blown into a confined space under some pressure. The amount of cellulose in a given volume should be controlled in order to gain some expected insulation value. Intuitively, it seems reasonable to not compact it fully nor to let it fluff up without limit.
I misstated the situation about the screened opening. On one of the four sloping sections of the roof is a structure that juts out to the side which appears to be solely there for the purpose of ventilation. This structure has a large screened opening on one side.
I think you guys are right that the best approach for the attic in terms of adding effective insulation would be to remove the existing floorboards, build up the height of the joists, fill the volume with cellulose and cover with plywood. However, I see a significant cost in doing that without a reasonable payback period. Plus, access to the 2nd floor wiring would be made much more difficult. Attic space whether I use it now or not would be lost. The walls of the roof slope in making the added structure somewhat difficult to design at the perimeter.
I was considering the offer from the contractor to have him lug enough rolls of R-19 FG batts up there to unroll over the the entire area of the floorboards. I thought that the batts could relatively easily be pulled away in selected areas for access or storage. But now I'm unconvinced of the effectiveness of that approach because of convection current losses of FG batts.
Pull some of the boards up, shove a 2" tube into the bay as far as you can and start blowing. You can dense pack it, maybe not completely but surely better than what you have now.
Something like this will be as effective as the effort put into it, fiberglass will be a complete waste of time and money.
You now have less than 6" of loose fill with more than likely some areas with zero or very little insulation. Do what you can to pack it with cells and it should make a hell of a difference.
Joe H
Thanks, Joe. I will pursue your suggestion with the contractor. It sounds to me that you're advocating at least a partially closed channel such that the cellulose becomes packed to some degree as it's blown in. That makes sense to me. Now it's a question as to how easily a tube can be inserted given the existing mineral wool. I plan to inspect the existing fill better by looking through the gaps between the floorboards throughout the attic floor. I believe that the only areas with little to no existing fill are those where some boards have already been pulled up for some electrical work and the mineral wool was pushed aside. If the undisturbed areas appear to be largely filled, I think I'll leave much of the attic alone.
Related question: The house has a heated "sunroom" off to one side - that is, the commonly-seen one story room on older Colonials that has lots of windows. It has a flat rubber roof on top. One contractor didn't mention doing anything with this sunroom roof (let's assume it's not insulated now). Another guy said he would blow in cellulose either through holes in the eaves or, if that's obstructed, through holes in the ceiling (which I would then have to patch). Given the amount of window area in the room (regardless of the window quality), would I stand to gain much in heat loss reduction by the insulating of the roof in this room?
See Fred Lugano's article, Insulating with Cellulose in FHB 130. I think that if you head over to the main FHB site, you can buy a pdf download of it for a few bucks. It should answer most of your questions.
The subject house in that article, btw, is mine. I've been living with the cellulose for five years now, and my only complaint is that we don't hear cars coming down the driveway. Andy Engel
Senior editor, Fine Woodworking magazine
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Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
Cellulose Sounds of Silence!
The first thing I noticed when I had cells put in my walls and attic - just how quiet every room became.
I have attached a picture of the house from the rear to show the sunroom I mentioned. One of the storm windows is off. (I'm planning to replace the old windows with Marvin double-glazed casements. Its roof is copper-flashed with a rubber top surface.
Re 6" attic joists: Mike Smith has mentioned laying down a second set of attic floor joists, perpendicular to the originals and on top of them, to give more depth for cells.Or insulate the roof deck. You've probably got 2x6 rafters though, which is where I'm stuck....
I have a similar situation in my Victorian. Having pulled up some attic floor boards for electrical work, the mineral wool is dense in places and thin to non-existent in others. I have thought the only way to reinsilate would be to pull up the floor and spend a very dirty respirator donned weekend pulling and vacuuming out the old wool. I can not imagine in my house, that trying to blow in cellulose to the existing wool would fill the voids. I would guess that you could add to the existing wool after pulling up the boards, if you did not get rid of the old. One problem point for me is that the floor board ends are under the plate. I had considered sawing them off a foot or so from the perimeter and screwing them down.
You can neck down the end of the cellulose blower with a piece of plastic pipe. I've seen it as small as 1 inch, but 2 in. is more typical. Insert the pipe all the way, blow until the hose starts to plug, pull it back, repeat as needed.Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
Definitely try to blow under the boards. For the future, if you can, map out the wiring before blowing.
The previous post by Andy Engel is the way it may be done. Floor boards are lifted every 5-10 feet, depending on ease of accessing all spaces to be insulated by the end of the pipe/hose. The cavities are filled until the material flow stops and the hose is pulled 1-2 feet. Be careful of blowing pressures (a professional installer will know his equipment).
Cellulose fiber has a nice quality of also adding to the airtightness of wall/ceiling cavities. I've measured 2 two-storey houses with a fan door before blowing the walls with cellulose- air leakage reductions of 34 & 39% by adding cellulose. In fact with densities higher that to prevent settling, some funded weatherization programs are using the cellulose as an intended air sealing tool.
Another quality of cellulose- it's R value is pretty well near constant (3.8-4.0) in densities from 1.6 to 3.2 lbs/cu ft
Bear in mind that the channels under the floorboards already are partially filled with mineral wool. It's not possible to run a hose into the channels at this point. And without pulling the boards up, it's hard to say to what extent the channels are filled. Ideally, the boards should be pulled up, the mineral wool removed, the boards reinstalled, and then a hose could be snaked into the empty channels to pack them with cellulose to the desired density. Not cost-effective, though.
At this point, I suppose the boards should be pulled up in sections, the cellulose blown over the top, and boards reinstalled. No control of fill density this way, however.
Finding your thread pretty interesting as I've got almost the exact same situation (35 Colonial 6" wooden floor already down almost no useful insulation under it, 12 miles north of Boston). Not sure what is under the floor boards although I suspect based on what I can see I've got fiberglass (although not sure what you're calling mineral wool I may have the same).I'm certainly no expert but here is my plan; I'm going to pull the floor boards in at least in a few areas, particularly around any drain vent pipes. Tough because I have so much crap stored up there already. Seal those with foam. If I can get away with it I'll pull some of the boards near the center, see if I can drag out the junk insulation beneath the edges in there. I'll then put a hose under the other boards and try to get compressed cellulose in there. Once that is done I'll build a second 6-8" floor onto of the existing perpendicular to the first probably 2 foot centers with 3/4" Plywood or OSB on top then more cellulose compacted under that. Is the second floor worth it, don't know but its better than what is there now. I'll probably leave a 2' walkway down the center that isn't raised. I'll lose the insulation value in this area but it will make everything a bit easier regarding door access (mine is a walk up), and still having enough height to stand in the center of the roof. The roof isn't high enough to make the room useable so insulating the roof itself with foam doesn't seem worth it (although if oil prices keep going like they are ?)My questions still are venting in the attic. Right now it has almost none other than the two little windows at the ends. I'd like to put in soffit vents (don't know how this is done yet) and vent (with the pink baffles (don't know the actual name)that attach to the under side of the roof itself) those into the attic and eventually add a ridge vent when the roof is replaced which should be relatively soon. Until the ridge vent I'll probably put some type of solar fans (no operating costs) in the two windows to move the air out.Not sure this will all work but its a plan, I just need the time to do it. I've got to have a look for the article Andy mentioned as well.Tom
Edited 10/9/2005 12:54 pm ET by Ribs
you might want to think more about foam. cost to heat wont stop going up
I would consider avoiding the whole debate of raising the floor, etc. simply by insulating with spray-in foam between the rafters. This makes your attic a part of the conditioned space, removes the need for the ventilating ducts, and should significantly cut down on the stack effect in your home sucking the warm air out of the space below.
This may be more expensive in the short term, but if the attic is accessible, you've just increased the amount of livable space. Put windows in and you've got an office space, playroom, whatever, in the making.
It is a shame your stuck on cellulose. the task at hand could be done with foam and you wouldn't need to add anything. I looked at your pic and I foam the roof deck on that style roof all the time and don't need to add anything . unless it is a 2x4 roof then I add 2x2 to get the right thickness of foam. I'm in and out in 1 to 2 days and the only thing that changes is the usability of the attic. and the cost is not much different then cellulose.
good luck, and sorry for muddying up things
The problem I see with foam is that its pretty much permanent. You are more or less banking on insulation technology not advancing again. You spray the roof and then suppose 2 yrs down the road someone comes up with an insulation that's R20/inch. Then what? Maybe that's not a problem if you've already got sufficent insulation, but if you are only putting in 6" of foam - that's not sufficient for the next 20 years as heating costs increase.Cellulose has the nice benefit of being removable for replacement by better future insulation, for additions/builing changes, and for repairs.Though, as purely a short term game, I agree, spray foam wins. In the long term, I'm not convinced its the best idea.
with energy prices skyrocketing foam man probably has the right ideabut a few reflections on your situation and this thread in no particular order
hope your "2nd story wiring" is romex and not knob & tube -
insulation qualities on knob & tube wiring sometimes do not
provide for covering w/ cellulose insulation*fire hazard
you seem to be fixated on the density issue - seems to me you should
be given over to the idea this attic should be insulated and
that's that / no walking over it & get your electrical right now I'm a layman in this regard ( insulation ) but from what I read from many of the so called experts on this site and others their opinions leave much to be desired - you are probably much better off with the 28" of fluffed Loft that hasbeen has than a dense pack of whatever inches - in dry snow I'll take my bulbous goose down parka over your miracle fiber anytimeanyway other than providingsome strapping engineering to your ceiling structure you hardly need those floor boards and you're not giving enough credit ( nor is your contractor ) to the filling capabilities of the cellulose pump/blower - duct tape and an easy 90 degree abs plumbing fitting will get you almost anywhere
I'm losing it here. Not sure what Foam Man is referring to - the sunroom insulation (above the ceiling) or the second-floor attic. I wouldn't consider foam for anything other than above the sunroom ceiling (see below).
(Wiring is Romex, BTW.)
I am not considering insulating the attic rafters; the attic is not going to be a heated space while I'm the owner of the house. The question is how/whether/to what extent to add to the existing mineral wool insulation under the attic floorboards. I've decided to preserve the floorboard area for storage and I will not consider building a raised structure above the boards to fill in with cellulose.
Contractor says he cannot snake in a hose above the mineral wool, so boards have to be removed wherever I want cellulose added. Further, there's not a reasonable payback period to pull up all the floorboards to top off the mineral wool. (Est. added cost: $900) It appears (viewing between the floorboard cracks) that there's maybe 4-5 inches average height of existing mineral wool (some places more, some less). Maybe I'll pull up a few additional boards in areas that seem to be particularly deficient in mineral wool height. (Some boards are already off due to earlier electrical work.)
For the sunroom, the approach will likely be to put in holes through the ceiling, pump in cellulose and patch. Could consider foam, though cost will likely be much higher, especially considering that it would be a small job for a contractor. Advantage of foam, as I understand it, is a higher R-value and resistance to moisture ingress (sunroom has a rubber roof and no ventilation). However, not expecting much water vapor in the sunroom. Further, if I could be convinced that moisture would inevitably collect in the cellulose, I could paint the ceiling with some sort of water-proof primer. Any thoughts on this?
So here's what is being planned: Pump all house walls (including sunroom) with cellulose (no wall insulation at all currently). Insulate attic walk-up door, stairway (beneath steps), and exposed inside wall of stairway. Add cellulose to sunroom ceiling (as described above). Add cellulose above existing mineral wool in the attic in select areas. Estimated cost is roughly $2,700 before 20% rebate from the gas company.
If any more pictures of the house (inside or out ) would help, please advise.
Edited 10/12/2005 6:08 pm ET by marcwd
Contractor says he cannot snake in a hose above the mineral wool, so boards have to be removed wherever I want cellulose added.
A pipe on the end of the hose can be shoved past/through/over the mineral wool. If you're going to pump the cavity full, the wool is going to be crushed anyway. Pushing a pipe through it won't make any difference.
I'll agree that pushing a hose doesn't much work, but a pipe does. Sounds like maybe your guy isn't much interested in doing it?
Joe H
Joe,
Perhaps a pipe would work; I don't know. I suppose the pipe would have to be half the length of the joists and be inserted somehow in the middle of the attic floor and be pushed out down the channels toward the ends of the attic.
I don't think that the contractors (I've had two look at the attic) aren't interested in doing the job. But both have said that the floorboards would all have to be removed because of the existing insulation. The payback period for such work would be lengthy.
Thank you.
Dude, take this in the right way. You coulda been done already. And your cellulose contractor sounds lame if he cannot snake and pump under the floor boards.
If you only insulate in 'select areas' you wasted time/money. The heat will find the other non-insulated areas to escape.
Get out a circular saw. Set the blade depth to a cat's hair short of the thickness of those attic floor boards. Rip down each joist bay twice to open a channel as wide as the cellulose guy's hose. Pump in the cellulose. Should NOT take $900 worth of labor to do that. You could do it yourself, right?
This is better than only doing spots. Even better would be to make the storage platform on part of the area nearest to the attic entrance. You won't be using the whole attic for storage will you? Blow loose cells all over the attic floor and under the platform. Be done. Be warm. Save on heating costs.
Phil,
I appreciate your reply. It's not that the contractors can't snake and pump under floorboards, it's just that they tell me it can't be done if the channels are already partially filled. The boards would have to be pulled.
As far as cutting out a slot over each joist channel, well, that is interesting. But wouldn't I be left with an attic floor having all these slots cut in it end to end? And, yes, I suppose I could built a storage platform up there and then hose the floor down with cellulose. But if I ever needed to clear any portion of the floor for electrical work or more space or to do any work in the attic, it would seem that I'd have a hell of a mess to work in.
Edited 10/14/2005 6:16 pm ET by marcwd
So use Phil's idea of cutting slots, then rip some OSB 8" wide and cover them when finished. A few DW screws will hold them in place.
Dense pack cells will crush rock wool or FG, I think your installer has never tried it.
Can't shove a pipe through that stuff? Try it yourself with a piece of 2" pipe of any sort.
Joe H
Joe is right, sounds like this insulation guy never tried it. It is done all the time. It is done on drywalled walls from inside and from outside, with existing fiberglass already in there. The cells just push and condense the existing stuff. It is also done on cathedral ceilings with f-glass already there. The installer goes up on the roof, rips a slot along the ridge and slides a pvc pipe down each bay, pumping the cells in there.
Believe us!!!! It can be done and you will be all the better off to do it completely and the right way. A little effort now gives a future of savings.
The cost of the foam was outrageously more expensive then the cellulose (maybe because I could do that on my own). I also can't just come up with 5 grand as easy as 1 or two this winter and another 1 or two next winter when/if I add a second layer to the decking. When I got the cost to do my house I figured out how long it would take to recoup my money (based on a 50% savings (which I think is highly unlikely)) and energy cost at 2.50 gallon it was going to take 15 years to recoup my money, that's a pretty lousy return.
I also tend to agree with the post that in a few years there may be better alternatives.
Edited 10/12/2005 1:37 pm ET by Ribs