Spray Foam or Blow-in insulation for unfinished attic

[Bitey_Barkface]

We just purchased a 70 year old house and got a good price because it needs some work done, one of those things being the attic. Out home inspector noted "staining" on the rafters in the attic, noting that it could possibly be mold and that we needed to vent the space properly, he also noted that out insulation was light. Long story short, we've gotten 5 quotes from insulation/ventilation companies and it seems we're being told something different by each one.

Here's what we know:
"R" rating is currently 25, the standard is 50
There is currently blown in cellulose in the attic
There is a ridge vent, but I guess it's not working
There are soffits, but again, they are either plugged or not made properly
The roof is sloped comes down into the walls (I think that makes sense?)
There is one sealed window in the attic
We're in a cold climate (Halifax, NS)
The attic will remain unfinished and we won't be using it for storage. It's too small to stand in


Here's what we're being told:

1. Suck out the insulation in the slopes, leave the rest (so we don't have to pay for removal) and spray-foam the slopes and the ceiling of the attic using ClassicPlus 3/4 lb light density spray foam, moving the envelope of the house and creating a new room. This would not require any additional venting and the spray-foam is also a vapor barrier and will prevent any potential mold growth.

2. Blow in cellulose to R50 and install true vents at the soffits, if they're functional, otherwise no true vents

3. Blow in cellulose to R50 and put in two gable vents for ventilation

We were leaning toward the spray-foam, but upon research it seems it's easy to reach a point of diminishing returns and it's a lot more expensive than anything else.

Any insight on this would be helpful. My head is spinning.

[Telecaster]

There should be soffit baffles that keeps the blown in insulation away from the soffit vents.  Sounds like maybe they never installed in baffles, which is why the vents aren't working properly.  But it is important that the attic is vented properly when the job is done.


Based one what you've said, I'm leaning towards at least some spray-foam. But there is one thing, I'm not understanding/needs to be decided.  You need to decide where the thermal barrier will be.  If the attic is unheated and used except for storage, then the thermal barrier should be below the attic.  Does that make sense?  So not the roof, because you don't want to heat that space.  So the thermal barrier should be right above the highest occupied space in the house (which is where the blown in insulation is now, if I understand you correctly).

The advantage of closed cell foam is that is creates a vapor barrier which physically prevents warm air from escaping the house.  That is a good thing.  Older houses often don't have a vapor barrier of any type installed.   But R-50 of foam would be really expensive and the only advantage would be that it gives you the attic space, which you don't want.   Based on what I know, I would suck out the cellulose and spray on a layer (a couple inches) of closed cell foam on the layer where the cellulose is now.    The blow cellulose back on top (reusing the stuff you sucked out) up to R-50.    Cellulose on top of foam is completely legit.  People do it all the time.      That way you get the vapor barrier, plus the full R-50 insulation. 





 

[Fishindude]

Easier / cheaper fix.
Leave the insulation in place and add another 6" or so of blown in over the top of it.
Repair or replace the ridge vents, then install some gable end vents for additional air inflow and ventilation.

Yes the ideal set up is vented soffits for air to come in, with a ridge vent for hot air to go out, but it's not always economically practical.

[zolotiyeruki]

For attics, there are three issues that need to be addressed: 1) vapor barrier, 2) air barrier, and 3) insulation.  #1 and #2 can be handled together--typically with a poly barrier just behind your ceiling drywall, or with kraft-faced batts.  I'm betting that in a 70-year-old house, you have neither.

If the blown-in insulation is the only insulation in your attic*, then this is what I'd suggest:
1) vacuum out the old insulation **
2) install soffit vent things that go between the rafters and keep the insulation away from the underside of the roof decking, so there's a path for the air to vent through the attic
3) put down a poly vapor barrier across the whole attic, and make sure it's sealed everywhere***
4) blow in a boatload of insulation, including the old stuff (you can reuse it)

Are you willing/able to DIY some of this work?

* our attic (only 10 years old) has kraft-faced batts, then several inches of blown-in fiberglass.
** you could also rake all the insulation to one side, put poly on the now-clean side, then rake all the insulation back onto the poly, exposing the other side, and put poly down on the 2nd side
*** an alternative:  get a thin (2" or something like that) layer of spray foam, to ensure that all gaps and penetrations are sealed

[Rural]

We have R60 of spray foam on our roof deck, and I can tell you it's fairly wonderful in terms of making the house quiet, draft-free, and stable in temperature. We did it when we built, though, so the cost was almost certainly reduced, and the the trouble definitely was. We have foam in all the exterior walls, too, so the sound dampening is really amplified.


When we had ours done, we were told that spray foam on the top of the ceiling is not recommended at all, but I don't recall why. You might ask/ look it up if you're looking into it.


R60 is ten inches of foam, by the way; R50 is ~8 (6 to 6.5 per inch).


The cost is more, no doubt. You'd also need to close off vents up there if you do the roof deck, obviously, and you should do the gable end walls.

[Spork]

I love our foam.  We're open cell ... we're pretty far south and that seems common here.

And, yes, ours is done at the roof line, not at the ceiling below.  It makes for a really nice, comfortable attic that is good for storing things without melting them in the summer.  There is need to insulate plumbing/venting.

One thing I also notice is how clean the attic stays.  A vented attic pulls in all sorts of dust as convection moves through it.  Ours still looks like new construction.

[Rural]

Ours is closed cell (and the R values I mentioned above are for closed cell), even though we're also in the south. Our house is earth sheltered and open cell is not recommended below grade. If it meets your needs, though, open cell costs less.

[Rollin]

2.5-3.0" of closed cell on mine, under the roof, and on the top of the ceiling AND roof of the garage (plus I have an insulated garage door). We are in a cooling area (FLA) and my A/C is in the attic. The attic area dropped from avg. high of 130 F to 93F max in summer. Now my unit and duct work is in 93F worse case and will significantly increase the life of the unit. My bills have gone from over $400 (highest month) to no more than $250 - average $183/month (did other things like go to LEDs and variable speed pool pump, plus I have solar water heater - had that before foam). It seals the area too, no outside ventilation. Not needed because it is now "conditioned." Someone earlier said why heat/cool that area? I am not doing anything to heat it on purpose, but actually capturing the cool air that made it into the attic and would have gone through the vents. I left the blown in place so that ells me what was being lost to the out of doors.

Cooler temp areas are probably similar, but not sure.

Expensive, but I think once you factor in lower power bills and longer life of your HVAC, plus your comfort it is well worth it. ROI is longer, but once its done its done - no more coming back to refill loose. Besides, the loose stuff allows a lot of air flow and eventually compacts - loosing its R value.

[Jeremy E.]

http://www.mrmoneymustache.com/2014/05/01/beating-the-stock-market-with-diy-insulation/
Some of this info could be helpful

[Bitey_Barkface]

Wow, so much to think about! But you fine folks have armed me with a lot more info then I had before. Thank you all kindly.

We're leaning toward the spray foam, especially since the quote isn't astronomical (the attic isn't large), but now I know the right questions to bombard the contractor with. :)

[bacchi]

Open cell spray foam can cause rot from condensation.

http://www.greenbuildingadvisor.com/blogs/dept/musings/open-cell-spray-foam-and-damp-roof-sheathing

http://buildingscience.com/documents/insights/bsi-077-cool-hand-luke-meets-attics

[Rollin]

Open cell spray foam can cause rot from condensation.

http://www.greenbuildingadvisor.com/blogs/dept/musings/open-cell-spray-foam-and-damp-roof-sheathing

http://buildingscience.com/documents/insights/bsi-077-cool-hand-luke-meets-attics

I did not have this in my earlier post, as I don't know what the differences are for in the south vs. the north. However, ours (closed cell) also offers a 99% water penetration barrier. So, if a hurricane rips off our shingles, the house is very unlikely to get water damage. Additionally, and not of minor significance, the foam holds the roof on better than a roof built to Miami-Dade standards. I watched a video where a Miami-Dade section of roof destructed with ~ 700 pounds, whereby the foam section (with NO nails whatsoever, only foam underneath) had the machine go to ~2,700 pounds before the steel eye hooks exploded - that is the roof section stayed intact!

[Rural]

Open cell spray foam can cause rot from condensation.

http://www.greenbuildingadvisor.com/blogs/dept/musings/open-cell-spray-foam-and-damp-roof-sheathing

http://buildingscience.com/documents/insights/bsi-077-cool-hand-luke-meets-attics

 Huh. Looks from your second link like the only real concern about condensation is from ducts or sprinkler systems. We could probably have gone with open cell in our attic, since we have neither ducts nor sprinklers. In the walls, now, we did well to go with closed cell since we have actual water pipes there, plus the whole below grade thing.  Of course, it probably would've cost us more to do two different spraying events than it would've saved us to go with the cheaper foam in the attic…

[sisto]

I agree with what fishindude said. I had similar situation at my house. I didn't do blow in, but I bought rolls of fiberglass insulation without the moisture barrier and put them on top of the blown in. That made a huge difference and did not cost much at all and completely DIY job.

[gruopp]

Hey Bitey,

One thing you REALLY need to consider is if you have any sort of older combustion heating system in the house, i.e.  Natural Gas furnace or a boiler that runs from fuel oil.

In this case, you shouldn't get spray foam because typically after foaming a roof, there isn't enough air leakage to allow the Carbon monoxide created by fuel combustion out of the house,

If you have a high efficiency  furnace, sometimes call 90%+ or seal combustion furnace, than you don't have to worry about the leaking CO because it has its own air intake and output piping, in which case you should not hesitate to go with foam over any other type of setup.

Sounds like you're in a cold climate, so you should get closed cell foam.  The installer can recommend how thick to go for your climate zone.

Some folks mentioned worrying about condensation. This is only an issue if 2 conditions occur
1.) There is moisture present in the interior air of your home. ex: from bathrooms and kitchens that aren't vented properly
2.) The insulation is thin enough that the cold exterior air can drop the interior air temperature low enough to turn the humidity into water droplets

So if you have the proper heating system, thick enough insulation, and adequate venting, than you'll be in good shape,

Homes are systems, and when you change one thing, you have to consider a bunch of other stuff too! Good luck with the decision!

[RichMoose]

I'll add my 2 cents here. I see a couple viable options here so I'll kind of break it down:

A) Remove all existing cellulose; repair ridge vent and soffit vents (you need both for proper ventilation); repair any potential roof leaks, replacing shingles if needed; hire a contractor to "butter-in" a 2-3" layer of closed cell spray foam onto the ceiling wrapped around the bottom chord of your trusses/ceiling joists making sure that the foam doesn't block the updraft from the soffit vents; blow in the new cellulose yourself on top making sure you use attic rafter vents at the soffit line to allow airflow. I would consider this to be a reasonably cost-effective and very efficient method of combining moisture protection, increased airflow, huge insulation factors, and reduced condensation issues during those cold, humid East Coast winters.

B) Pull all cellulose to one side of attic; lay down a good 6m poly vapour barrier taping all joints etc; shovel cellulose on top and lay down vapour barrier on the other side of the attic; spread old cellulose evenly across attic (important because the older cellulose will be compacted from age and handling reducing its effectiveness); repair ridge vent and soffit vents; repair any potential roof leaks; blow in the new cellulose yourself on top making sure you use attic rafter vents at the soffit line to allow airflow. This will be more cost effective with insulation performance that's similar to option A but not quite as great from an air-sealing and moisture protection perspective.

Some things to consider! Now would be a great time to add any ceiling fixtures and upgrade to copper wiring. Also, don't spray down a thick layer of closed cell insulation - it's a royal pain if you ever want to make alterations up there in the future. Don't spray foam the underside of the roof and blown in cellulose on the ceiling. This has the potential to create condensation problems as any moisture in the attic space won't be able to vent up past the spray foam.