prioritizing energy savings - spray foam vs. wood stove

[twd000]

A question....did the OP want to sprayfoam the attic floor to get better airsealing, under the existing insulation, and then up the insulation to R-50 as needed (and keep the attic vented) OR to sprayfoam the roofline sealing the attic?

The former, not the latter.

The furnace and air handler are in the basement. The duct work servicing the 2nd floor bedrooms runs through the attic

 

[woodgeek]

The former, not the latter.

The furnace and air handler are in the basement. The duct work servicing the 2nd floor bedrooms runs through the attic

Thanks for the clarification. In practice, sprayfoaming the entire attic floor is overkill and too expensive, unless the ceiling below is something super leaky like planks. If its drywall, you only need to seal the top plates. Less insulation to move = less labor = cheaper. Whether your outfit seals the cracks there with sprayfoam or caulk is IMO up to them. I used caulk DIY.

If the ducts are well sealed (not leaky), then just bury them under the other insulation. Done.

 

[semipro]

Info on attic air-sealing
http://www.finehomebuilding.com/pages/how-to-air-seal-attic/

 

[St. Coemgen]

Improving your insulation can help you reduce costs on both heating in the winter, and cooling in the summer. That is, improving insulation is a full 12 month investment that helps all year long.

If one really has to choose only one option or the other, if one can improve their insulation (including properly controlling the general air movement into or out of their house) that is usually the option one should select first.

 

[OhioBurner©]

The reason people always harp about attic insulation is because it's accessible.

A lot of folks favor doing insulation first, and yeah attic insulation is #1. My house is very poorly insulated and leaky. It's pretty much a lost cause. And probably 80% of my house has no attic, only the master bedroom and bathroom have attic space overhead and its real tight in there with my low pitch ceiling. Rest of my house is all cathedral, and over half of that is only around 3" thick with fiberglass and I am sure some of it is wet since the metal roof either condenses or leaks in spots. And I am not about to tear down nice tongue-n-groove or even just drywall to get to it. One room, which had no insulation between the ceiling and roof, I did tear down last year since it was one of the few remaining rooms that were very old plaster. But the rest of the more recently refinished rooms I'm pretty stuck with thin FG. I'd be better off trying to move to a new house than insulate and air seal this one.

 

[semipro]

A lot of folks favor doing insulation first, and yeah attic insulation is #1. My house is very poorly insulated and leaky. It's pretty much a lost cause. And probably 80% of my house has no attic, only the master bedroom and bathroom have attic space overhead and its real tight in there with my low pitch ceiling. Rest of my house is all cathedral, and over half of that is only around 3" thick with fiberglass and I am sure some of it is wet since the metal roof either condenses or leaks in spots. And I am not about to tear down nice tongue-n-groove or even just drywall to get to it. One room, which had no insulation between the ceiling and roof, I did tear down last year since it was one of the few remaining rooms that were very old plaster. But the rest of the more recently refinished rooms I'm pretty stuck with thin FG. I'd be better off trying to move to a new house than insulate and air seal this one.

You may want to consider an insulated, unvented roof conversion. http://www.finehomebuilding.com/des...-details/an-unvented-superinsulated-roof.aspx

 

[OhioBurner©]

You may want to consider an insulated, unvented roof conversion. http://www.finehomebuilding.com/des...-details/an-unvented-superinsulated-roof.aspx

For the part I remodeled (the old plaster room) I did that. There is no feasible way to ventilate (and insulate) a roof that has only 3" thick trusses with the ceiling/walls attached underneath. And the metal roof was brand new when we moved in I have no intentions of ripping it off for any other major remodel. It was ventilated only in that it is very leaky and not weather tight. At the ridge and down by the eaves there were gaps here and there you could see daylight through. No sheathing either btw. I filled the truss bays with 3.5" thick foam board and another 1.5" layer on the underside though I am only 2/3 done with that. I'm not sure if the newer side is really vented or not, as it is cathedral again, except over the bedroom/bathroom. There is a vent on the gable end but I think it is just decoration. There is some venting under the eves but it is a fake gambrel roof and the part of the eaves is actually part of the wall and not sure if it actually goes up into the small attic space over the bedroom. I don't see any ridge vents or any other way for air to escape.

 

[cableman]

I just completed 2 attics in the house we just moved to, once it got cold i knew i had to do something.
1st i fixed and ran any wiring i needed to. Started great stuffing anything that was an air leak to the living space, ended up buying the pro gun and man that thing is so much better. I ended up sealing all top plates, wire holes, ac ducts and air handler.
After that i installed raft-r-mate in every bay cause the old insulation had blocked the air flow to the soffits. Picked up 32 rolls of r30 and rolled it opposite the beams in both attics. Close to r50 now!
I also great stuffed my basement sills.
My exterior outlets were drafty too, i pulled them all and siliconed the wire entry into the box then caulked the sheetrock around each box.
What a difference and how the house doesnt cool down as fast. I can only imagine how much someone would have charged me!

 

[woodgeek]

I can only imagine how much someone would have charged me!

About $2-3k for materials and $2-4k for labor

 

[cableman]

Wow, cost me 700 or so

 

[Seasoned Oak]

60 MBTU for the season sounds about right even low for NH 70MBTU was average last time i checked. So if your already fairly well insulated i cant see huge savings there. Around here propane heat is about the most expensive heat there is. ID go with a different heat source. My house is poorly insulated but my heat source is so cheap it doesnt matter much. Check into the cheapest fuel by cost per million BTUs . Could be pellets. All this is subjective of course results may vary.
Heating cost this winter season for me is roughly
Space heating $600
Water heating $300
Electric $1800 for 3000 Sf house, family of 6.

 

[iron]

i'm curious about the concept of sealing along top plates where they meet the ceiling drywall. i, like others, have a low pitched roof and access to those tight corners would be downright painful.

so, my question is: what exactly are you sealing here? is it just a product of wall penetrations you're trying to mitigate (outlet boxes, picture nail holes, etc)? if so, couldn't you just spray foam locally those areas? then, seal the easier-to-get-to spots in the attic (ceiling lights, interior walls, plumbing pipes, etc)?

 

[woodgeek]

i'm curious about the concept of sealing along top plates where they meet the ceiling drywall. i, like others, have a low pitched roof and access to those tight corners would be downright painful.

so, my question is: what exactly are you sealing here? is it just a product of wall penetrations you're trying to mitigate (outlet boxes, picture nail holes, etc)? if so, couldn't you just spray foam locally those areas? then, seal the easier-to-get-to spots in the attic (ceiling lights, interior walls, plumbing pipes, etc)?

Drywallers are taught to leave a 1/8 to 1/4" gap between the drywall and plate. Times the length of the gap, this results in an area that is an order of magnitude larger than the wiring and other penetrations. In my house, this worked out out to several square feet (!) of opening.

As for the low pitch, the pros always have a 'little guy' designated this job.

 

[iron]

sure, but the corners are taped and mudded? where is the air leak coming from?

 

[cableman]

I didnt get my outer top plates just the wire hole there, atleast insulation is in those walls. Sealing the outlets up helped the outer walls. As far as the inner top plates go, i could see straight down the wall when i lifted the insulation! Then there was the shotty ac duct work install, i had an inch gap on 2 sides of the return vent, and many other areas needing attention

 

[woodgeek]

sure, but the corners are taped and mudded? where is the air leak coming from?

The corners are taped and mudded, and the cavity space has free exchange to the attic. That cavity space connects to the space under the floors, through hardwood floors into the interior, as well as exterior wall cavities, the attached garage, etc.

When I got my house, the dryer exhaust dumped into the attached garage. All that moisture flowed into the framing cavity of the house, thence directly into the attic space and condensed onto the underside of the sheathing.

 

[iron]

sorry, i must be missing something.

drywall is either nailed/screwed to the studs. it runs from floor to ceiling save for some gaps at both ends (one is taped and mudded, the other has a floor next to it with base trim (usually). i just don't see how heated air from the inside of the house makes it into the stud cavities unless it's through outlet openings or some other wall penetration. the air is not going through the floors unless there's a utility going through. exterior air might get in depending on sheathing, but that goes straight to the attic and seems like it would help cycle air through there akin to soffit vents.

perhaps i'm just trying to convince myself not to crawl into tight, painful positions....

 

[Where2]

sure, but the corners are taped and mudded? where is the air leak coming from?

If there is a wire going through the top plate, there's probably also an outlet box in that wall cavity between the studs. The old steel boxes resemble swiss cheese with lots of holes in them providing plenty of ingress of fresh air to replace that which goes up and out the top plate. (new plastic boxes are somewhat better, but still not perfect) Further contributing to this air migration path is the gap at the floor between the flooring and the wall materials. When I started dissecting the walls of my house at 45.8°N, which had un-taped drywall seams behind the 1970's paneling, it was quite evident where the air had been flowing through the paneling and drywall following the path of least resistance. The house had previously used a wood stove for supplemental heat, which obviously didn't always have the best ventilation capability. Sure, there was foil faced pink fiberglass in the stud bays, but this house is built on a ridge and the wind last night made +18°F feel like -1°F. None of the seams in the foil are taped, so air moved where it was easiest to move. The traveling air left behind traces of soot where it tended to migrate the most frequently.

Dismantling the walls is actually rather telling in the case of the house I am working on. As someone who comes from the subtropical southern Florida region, I've never dealt with heating or heat loss to this extreme. It's a bad winter when it dips below freezing for a few hours where I grew up in FL. This has however opened my eyes to why my energy savings was so great when we opened the walls of the second floor of our house in FL and sealed the wire penetrations through the top plate. At the same time we cut 2" foil faced polyiso to fit between the studs, then sealed the gaps and edges with canned foam. Wish I could add 2" polyiso between the drywall and the concrete block wall in the lower story...

 

[cableman]

I still have 2 cantlevers which leak air into 1st floor ceiling/2nd floors floor, that ill pull outside soffits and ridgid board the bays sealing off with more great stuff.
Every little air leak sealed is that much better.
Heres how i did 20 outer wall outlets, used a bic pen body taped to silicone so it was easier getting to the wire holes...

 

[woodgeek]

In my experience, the baseboard covers the sloppy gap between bottom plates, subfloors, drywall etc. And a lot of drywall in old houses has popped off the studs aways, studs are warped, etc.

Bottom line, house framing is only a bunch of separate airtight cavities on the drawings. In reality, there are gaps connecting the cavities throughout most houses.

 

[semipro]

Bottom line, house framing is only a bunch of separate airtight cavities on the drawings. In reality, there are gaps connecting the cavities throughout most houses.

Agreed. Which is why its difficult to have an impact on overall infiltration by addressing leaks at interior points like outlets, baseboard areas, and around windows and doors. Blower door tests done before and after such efforts have shown little improvement in overall air-tightness.
Airtight drywall can be done and is commonly done in Europe. In this case the infiltration barrier is established on the interior shell of the house. However, its very difficult to seal drywall that's not built as "airtight" from the beginning.
Rather than sealing random accessible interior and exterior air passage points a better strategy is to pick either an interior or exterior "plane" as your shell for air sealing and concentrate you efforts on that alone.

 

[semipro]

Every time threads like this come up I like to relate the experience of working with a pro canned foam gun rather than the one-use cans.
https://www.hearth.com/talk/threads/multi-use-foam-applicator-gun-follow-up.107613/#post-1422912

 

[Highbeam]

sorry, i must be missing something.

drywall is either nailed/screwed to the studs. it runs from floor to ceiling save for some gaps at both ends (one is taped and mudded, the other has a floor next to it with base trim (usually). i just don't see how heated air from the inside of the house makes it into the stud cavities unless it's through outlet openings or some other wall penetration. the air is not going through the floors unless there's a utility going through. exterior air might get in depending on sheathing, but that goes straight to the attic and seems like it would help cycle air through there akin to soffit vents.

perhaps i'm just trying to convince myself not to crawl into tight, painful positions....

I've actually hung drywall. I've also had the same question. Sure, you leave the ceiling sheetrock 1/8" to 1/4" shy of the top plate for the sake of installation but when you put the wall sheetrock up you push it up tight to the ceiling rock and then attach it tightly to the top plate every 6". You then mud and tape this inside corner.

The "leaks" being solved by foaming the top plate in the attic are of course the actual wire penetrations but also the failure of your 6" OC top plate attachment screws to hold the wall rock tight to the top plate. I don't see this as being a very likely leak. Flow throuh this leak also depends on a separate leak occurring elsewhere in the wall at an outlet or penetration in the wall to allow air to enter the wall cavity before existing through this theoretical top plate leak.

Get the wire penetrations for sure.

 

[woodgeek]

Let's be empirical....

When I am in my attic, I can look into the gap next to the top plate with a flashlight, and see down 8'. The FG above the gap is stained black in a line due to filtering the air flowing up from the gap, and I have snow melt on the roof in patches over interior walls. I could also see lines of warmth on the top (!) of the FG over the top plates with my IR thermo. Just caulking my top plates dropped my BTU energy consumption by ~15% with no other changes to my house, as determined by logging run hours per degree day before and after.

IOW, its yuuuge.

More....

The 3/16" gap times the 200' linear gap length works out to a three square feet of opening between those cavities and my attic. The 15 wire penetrations are maybe 0.5 square inches each, or one tenth of a square foot. IOW, the plate gap is 30x bigger area than the wire penetrations.

 

[cableman]

I wish i took pics of my top plates, totally agree woodgeek. I wont have a sealed house as if i was building it now, but ill try my best to great stuff the hell out of every gap!