About to pull the trigger on flash and batt. Am I making a mistake?
I’m in CT (climate zone 5.) To be safe, I’m having them put 3 inches of closed cell on walls and on roof slope, then putting R19 unfaced fiberglass on top of the slope.
My roof is slate, only venting is a half moon window, a triangle vent (that can be closed), and a large louvered exhaust fan. It was built in 1938, so there aren’t any plastics or tight sealings up there. current insulation is badly collapsed cellulose fill under the boards.
We don’t have AC — to cool the house down some evenings we’ll open up windows downstairs, and then run the fan. Works great.
1. I’m scared of mold. Does this seem like I’m asking for it? Everyone we’ve talked to (multiple companies) says mold won’t be a problem.
2. How long will this stuff actually last? 50 years? 80? More? We don’t plan on leaving and don’t want our kids (or whomever ends up with this very special house) to have huge, expensive headache on their hands.
3. Is there some point where the insulation gets so old and ineffective suddenly we’d have a mold problem under the batts?
4. Will conditioning the attic make us pay more? My thinking was we’d be able to keep warmth into winter and coolness into summer. Basically a more “neutral” experience than having a very cold attic in winter and an oven above us in summer. Seems a good choice, right?
In closing, any reason we shouldn’t do this? We’d considered doing 2.5 more inches of closed cell instead of batts, but we’d be looking at an additonal $8k, almost a 3rd of the price. its a very large space.
Thanks!
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I'm not entirely clear on where you're planning to insulate. I think you're primarily trying to convert from a vented to a conditioned attic, which means you'd be insulating the underside of the roof sheathing ONLY (an any end walls of the attic), and not the attic floor. If that's the case, the big question is "do you have any mechanicals in the attic?". If you do, then yes, converting to a conditioned attic will probably help you. If this is the case, I would try to do all of the insulation with closed cell spray foam (ccSPF) due to simplicity of installation, but you don't have to do it all with ccSPF. I would try to keep about a 50/50 ratio of ccSPF to "other stufF" to be safe though, and 3" of ccSPF is about R18 or so (higher numbers are a bit optimistic, so it's safer to be conservative and stick with about R6 per inch regardless of what the spray foam manufacturer might claim). You really want to try for R49, which is code minimum, which means a bit over 4" of ccSPF and then around an R23 batt (or go with a bit more spray foam and an R21 batt). More spray foam R value compared to "other stuff" R value results in a safer assembly here.
If you DO NOT have mechanicals in your attic, then I wouldn't use spray foam at all. I would either blow in additional cellulose over the existing layer, or even better, remove whats there now, do a good job of air sealing the attic floor with caulk and canned foam, then blow in at least R49 worth of cellulose. If you have any soffit vents, or have the ability add them, then you should try to add baffles out at the eaves prior to adding additional loose fill insulation. I'm assuming that since you have a slate roof, ridge vents are difficult to add, but gable vents on the ends can work too.
A vented attic with an insulated attic floor is the cheapest and one of the safest attic assemblies out there. You should really only consider converting to a conditioned attic if you have mechanicals up there that you can't easily relocate elsewhere.
Bill
Yes, the attic is what we are doing.
If conditioning we'd JUST be doing the rafters and walls as (you said,) and removing some of the cellulose (some is under tongue and groove flooring, so we'd leave that for sound insulation..
We do like the idea of a climate controlled space for climate-controlled storage and were eventually going to panel to make it usable as, say an art studio.
There isn't enough clearance to do a full R49 fill under the boards, and only one guy was willing to try to blind fill instead of cut holes in flooring. So sealing in a large part of it isn't feasible.
The other thing we were considering was to do a super deck... the real downside is it would raise the floor by 4 whole inches.
Why do you feel conditioned attics are a bad idea? What would be the problems you'd think we'd face?
some points:
1. 3 inches closed + R19 unfaced is the most we can fit in our rafters, some of which are 7.5 inches deep (others are 9). So seems that's as close to 50/50 as we can do?
2. By mechanicals, do you mean stuff like water tanks or HVAC? there's nothing like that. Just some wiring and some pipes. We might add bathroom exhaust fan up there that would exit on the side of the house.
3. we do have a gable vent on one side, and a large window on the other. Along with our fan. All can be closed, of course. So does that mean we have both vented and unvented?
If you want to convert to living space, that's a different concern. The usual questions that come up are just related to insulation, so it didn't occur to me that you might want to use the attic for additional living space, which would be a "finished" attic. If you want to do that, then you would need to insulate the roof and not the floor.
1- You can insulate over the rafters. If you use ccSFP and 3.5" deep mineral wool batts (which are the size made for 2x4 walls), you'd get R39 between the rafters. If you then put 1.5" polyiso over the rafters, you'd be up to R49 total. You could go with 1" plyiso for about R45, but the 1" polyiso would be continous insulation, so better overall performance than you might expect since it wouldn't have issues with thermal bridging. You could then drywall right over that (or use T+G). You would want to tape the seams and use detail the polyiso (or drywall) as an air barrier here, and I'd use vapor permeable polyiso (not foil faced).
2- "Mechanicals" would mean water heaters or HVAC equipment. This stuff is sometimes installed in the attic, and that's a common reason to need to convert an attic to conditioned space. Wiring doesn't matter, and vent pipes don't matter. You shouldn't have any water supply lines up there since they'd be exposed to freezing. A bathroom exhaust fan isn't a problem, either, but be sure you use insulated ducting for the vent.
3- I would call this a "vented attic" since you have vents. The vents would typically be open to allow for airflow through the attic. Since you want to eventually use the attic for living space, an art studio, you'll need to insulate the roof and end walls. You'll want to do a good job air sealing as you insulate too for maximum efficiency.
Bill
Thanks, this is super helpful.
So you're saying 3" of CC and 3.5" mineral wool batt, instead of using unfaced R19 fiberglass? We were looking at R39 with that too.
Would using mineral wool remove the need to spray ignition barrier paint on the CC?
I'd think we'd do this in stages, live with R39 for a few years and when we're ready to finish panelling it, add the 1" unfaced polyiso and T+G, and probably a few light sconces.
Is there anything we should be scared of here? How long does CC actually last, before it has to be torn out and redone?
Could the water and air proofing it provides create moisture issues or problems elsewhere in the house? I assume in case of issues we could install a dehumidifier up there, or even just pop open the attic window and vent and run the fan to get air moving... Thankfully our slate guy loves the idea!
Properly installed (no gaps) mineral wool will take care of the required fire protection for the spray foam.
SPF lasts a long, long time. I wouldn't worry about it "getting old" or "wearing out". It won't cause any vapor issues, but it will make it less likely thaat you'll quickly find any roof leaks. I don't really count that against it though, since you should be checking your roof periodically anyway and fixing things before they get so bad that anything might start leaking.
Bill
We need more information about how the attic is accessed. Is there a pull-down hatch? Stairs? If it's a pull down hatch, you could insulate more cheaply by upgrading the air-tightness of that hatch and then putting insulation at the floor. (on top of the boards), as Bill says.
What does your local code say about fire and this set up? Some locales require a fire retardant layer below closed cell foam -- rock wool or slightly thicker drywall.
thanks. regarding access, its a pull down stair. It doesn't seem reasonable to air seal this, such as with a cover on top or similar (the stairs slide up and across the floor when it's closed. The super deck guy wasn't a fan.
For spray foam, we'd be having it painted with ignition retardant paint to make it compliant
I can't imagine pull down stairs and no windows would meet code for living space.
oh worth mentioning, we have a kneeling attic as well attached to the 2nd floor office. We do use that for storage. There's no reasonable way to insulate that floor. The walls however have cellulose bats built in.
Would closed cell on the rafters in that area make sense?
"...We don’t have AC — to cool the house down some evenings we’ll open up windows downstairs, and then run the fan. Works great...."
Can you expand on this?
Do you mean a window fan or are you talking about the current fan in the attic?
If you mean the existing attic fan (ie fan which pulls air from the living space below into the attic or out through the attic) then you should just air seal the second floor ceiling and re-insulate the attic floor.
yes, its an attic fan. The plan was to foam on all sides of its enclosure, which just leaves the access door, which could either be bagged when not in use or a thick piece of insulation board could be attached to the door (or a bag placed over the entrance when not in use.
When the attic is finished, there would be an interior wall, with closet space on either side of the fan, and a thick door that could be opened to reveal the fan.
The end result would basically be like a built in wall fan behind a small square "front door."
Another question... at what point does conditioning an attic force someone to increase the square footage of their house on paper, and have a bigger tax burden? Is it up to us whether we declare it "finished?"
If we stop short of code (R49) does that prevent that? How about not panelling the entire area (half of the attic is accessed behind a chimney and we wouldn't be panelling anything back there, pure storage)
Ideally your plans are approved by local building department and the additional square footage is added to the property. You don't need to get the building dept involved if you're upgrading existing insulation in an attic. Buiding out living space is a different story.
Typically homeowners don't want to go through the expense or risk the rejection by the building department so they renovate on the down low hoping not to get caught.
I am sorry there is no free lunch, you don’t get a climate-controlled storage space for free!
The fact is if the attic is heated and cooled you are paying for the energy required to make it so.
If you decide to move the insulation to the roof line and gables walls you will need to buy insulation to cover about twice as many square feet as the attic floor. Remember every one of those square feet is leaking energy and you just doubled your leaking area. Moving the insulation to the roof line all but forces you to use spray foam insulation. Spray foam insulation is the most expensive way to buy an R of insulation and most people will not spend the money required to even install the code minimum R38. For 10% of the cost of spray foam any fool can flood their attic floor with r60 cellulose using the free blower from the Home Depot.
Your current plan of sealing the vents insulating the roof without removing the old insulation and not conditioning the attic. Is a game of Russian roulette with mold and rot. No one can predict what the temp and humidity of the air in your attic will be but we can be pretty sure some times the dew point of the air in the attic will get above the surface temp of your spray foam. How often will it happen is unknowable? How much water will collect is unknowable? Will the water evaporate before mold and rot set in is unknowable? Leaving the old insulation in place now works against your efforts to keep the attic climate controlled.
Seems to me for less money you could build a storage deck above your new R60 cellulose insulation.
I can only think of one thing that was stored in my attic that was retrieved and used in the last 20 years. My mother’s basement is full of junk that came out of a relatives attic over 50 years ago one day I will throw it all away.
Walta
It seems to me Walta makes many good points. I've said that before on this particular subject.
To clarify, the choices are:
1) CONDITIONED: rafters with 3" closed cell and batts up to R38, eventually up to R48 with polyiso and wood panelling. That would be conditioned since it's in equilibrium with the rest of the house, no? The old insulation everywhere but under central part of the floor (it's currently about 2 inches deep, its the original stuff from 1938) would be removed.
The vent, window, and window fan would not be permanently sealed. The area will primarily be storage for now, but could be used as an art studio.
2) UNCONDITIONED: a combo of added cellulose and a superdeck over areas that can't be reblown without tearing up the floor, along with sealing around chimneys, etc. (I believe that gets to R60). Attic will be unconditioned, vents will be open all the time as the are now. The access ladder won't be able to be super decked or sealed particularly well as it slides across the the floor when stowed.
Does that affect your answer? Thanks.
Currently, we're probably at an R6 for our attic insulation.
the other thing... doesn't installing a decent dehumidifier up there solve any issues of potential condensation? Its worked very well in our basement, which has unexcavated sections and an exposed sump pool... sometimes it's more comfortable down there than on the first story.
Worth noting we closed the window, the fan, and the vent from fall to spring to see what would happen and there was only some very slight mold growth on some rafters... and that was on uninsulated roof deck...
Not an expert, but I think you are probably to need a dehumidifier to mitigate risk. Your climate zone doesn't allow vapor diffusion ports, and you have no AC.
A regular big box dehumidifier might not be sufficient, however. To get a better handle on things, you should install a wireless humistat (or several) in the attic and keep an eye on conditions over time.
cool... I was looking at ones with added pumps that can drain out of the house automatically. I'm not running upstairs to dump out buckets.