Prewire w/ Spray Foam Insulation

[Ranger Digital]

Lou correct. Adding radiant barrier is a COMPLETE waste of money and has zero affect on adding value.

wlj, correct as well. securing the wires in the wall cavity being foamed is a MUST. When the foam expands it will lift the wires right out of the cavity and sure enough, they will be cut when the foam is trimmed.

I know this sound trunkslammish, but we use duct tape to secure them to the studs (not the OSB back wall as it doesnt stick worth a crap. Explained to the builder and home owner that its a temporary "mount" and they have no problem with it. The insulators LOVE following our low voltage installs as they NEVER cut wires anymore because we take that extra step. Not that I have ever had wires melt, but it stands to reason the duct tape may help that? No idea.

We tried nailing but if you dont nail/secure them every freakin feet they sure do get expanded with the foam. Cheesy as it sounds, duct tape is a simple solution that just plain works. We often will not tape them until the day before foaming which sometimes requires a return trip but not big deal. In texas, if we leave they duct tape there for a week it sometimes can come unsecure thus rendering the effort worthless.

Ahhh, duct tape. The redneck answer to everything. lol

Lou, 8 tons in a spray foam house?? Never heard of such. Does sound like overkill. One of the great benefits of foam is it drastcially reduces the tonnaged needed on a house. No offense but it sure sounds like it was not calculated right by the AC company. Maybe they are not familiar with foam? Happens all the time. Some dont get it. Once I had to show an AC man actual white papers to prove him wrong.

 

[drvnbysound]

Has anyone had experience running wiring through the foam (after drywall)? There is a couple I know, who just bought a town house which has sprayed-in foam insulation. They have asked me about wiring for surround sound, but I have no idea how to go about doing it through the foam, or how to suggest going about doing it.

 

[apostolakisl]

Lou correct. Adding radiant barrier is a COMPLETE waste of money and has zero affect on adding value.

wlj, correct as well. securing the wires in the wall cavity being foamed is a MUST. When the foam expands it will lift the wires right out of the cavity and sure enough, they will be cut when the foam is trimmed.

I know this sound trunkslammish, but we use duct tape to secure them to the studs (not the OSB back wall as it doesnt stick worth a crap. Explained to the builder and home owner that its a temporary "mount" and they have no problem with it. The insulators LOVE following our low voltage installs as they NEVER cut wires anymore because we take that extra step. Not that I have ever had wires melt, but it stands to reason the duct tape may help that? No idea.

We tried nailing but if you dont nail/secure them every freakin feet they sure do get expanded with the foam. Cheesy as it sounds, duct tape is a simple solution that just plain works. We often will not tape them until the day before foaming which sometimes requires a return trip but not big deal. In texas, if we leave they duct tape there for a week it sometimes can come unsecure thus rendering the effort worthless.

Ahhh, duct tape. The redneck answer to everything. lol

Lou, 8 tons in a spray foam house?? Never heard of such. Does sound like overkill. One of the great benefits of foam is it drastcially reduces the tonnaged needed on a house. No offense but it sure sounds like it was not calculated right by the AC company. Maybe they are not familiar with foam? Happens all the time. Some dont get it. Once I had to show an AC man actual white papers to prove him wrong.

RandgerD, I think 8 tons is more than necessary also and I questioned them on that. I figured 6. I went ahead with it anyway because they are two stage units. They spend most of the time at low stage which has a higher seer, is completely silent, and absolutely draftless. They do hit high stage about 10% of the time cooling on the downstairs units and 50% of the time on heating according to the log that infinity thermostats have (though heating is only about 20% of total time). At least no worries about having a large party on a hot day and failing to keep temp. I also have massive attic space that I may build out and won't have to add extra HVAC capacity for.

Also, now 103 outside roof 137 and inside roof 87.

I did my own low voltage and stapled it and it all stayed put (as did the electricians with the high voltage). I did do a nice job with the staples (no slack).

And as far as running wire after the fact. As mentioned, open cell easily can be poked through but you will screw it up, especially if you don't keep it to a single clean pass. Romex can just be pushed through it for several feet. Flimsy wires like cat 5 and speaker wire will need to have a fish tape pushed through.

 

[86turbodsl]

Being a builder, I have lots of experience with spray foam and ONLY use spray foam. Dont spend the extra money on closed cell. Only use closed see when the foam will be expost to the eliments (like under floor on a raise room).

You ALWAYS foam the roof, not the attic floor or ceilings. The whole goal is to encapsulate the home, kinda like an igloo cooler. Most AC venting is run thru attics. If you foam the attic floor, you COMPLETELY lose the value spray foam adds to the AC system as 7-13% of AC cost is attributed to lose thru vents (they leak).

We simply will NOT build without foam. Company policy. Its a mute point though as I am winding down both the commerical and residential contruction businesses. Two much work and not near as much fun as low voltage! Nothing to do with economy but personal goals and wants. Commercial is particulary profitable but if dont want to do something then why do it? Life is too short.

Your way may be right for your location, but it's not true everywhere. I'd direct the astute reader to www.buildingscience.org and read up on the different building envelope types and particularly anything written by Dr. Lstiburek. Open cell foam is not correct everywhere.

 

[apostolakisl]

Being a builder, I have lots of experience with spray foam and ONLY use spray foam. Dont spend the extra money on closed cell. Only use closed see when the foam will be expost to the eliments (like under floor on a raise room).

You ALWAYS foam the roof, not the attic floor or ceilings. The whole goal is to encapsulate the home, kinda like an igloo cooler. Most AC venting is run thru attics. If you foam the attic floor, you COMPLETELY lose the value spray foam adds to the AC system as 7-13% of AC cost is attributed to lose thru vents (they leak).

We simply will NOT build without foam. Company policy. Its a mute point though as I am winding down both the commerical and residential contruction businesses. Two much work and not near as much fun as low voltage! Nothing to do with economy but personal goals and wants. Commercial is particulary profitable but if dont want to do something then why do it? Life is too short.

Your way may be right for your location, but it's not true everywhere. I'd direct the astute reader to www.buildingscience.org and read up on the different building envelope types and particularly anything written by Dr. Lstiburek. Open cell foam is not correct everywhere.

If I lived on the Gulf Coast I think I would consider closed cell becuase of hurricane issues. Closed cell really strengthens the building and wind driven rain won't damage the stuff. Considering how expensive it is, however, I doubt it would ever be a cost effective insulation solution compared to open cell from a strictly insulation perspective. Perhaps if fuel costs were extrememly high like in a remote cabin where propane needed to be trucked in for miles.

 

[Kevin L]

Hi, Lou.

I'm on the Gulf Coast, too (Southwest Florida.) I have Icynene (open-cell) in my home. Water just passes through and is not retained in the foam. It's not likely it would ever get wind driven rain (other than a leak on the roof) since the entire roof is enclosed without any venting. Even my soffits are hardiboard with stucco over it, sealing the attic. And if I didn't have the open-cell foam, I wouldn't have found the roof leak until it caused extensive damage.

86turbodsl gives a good recommendation with www.buildingscience.org. It has great information about sealing the "envelope." That's where I did a lot of my research before deciding on Icynene. So far, I've been extremely pleased with my decision, especially when I have to work up in the attic.

Kevin

P.S. Glad those storms are staying in the Atlantic!

 

[Smarty]

86turbodsl gives a good recommendation with www.buildingscience.org. It has great information about sealing the "envelope." That's where I did a lot of my research before deciding on Icynene. So far, I've been extremely pleased with my decision, especially when I have to work up in the attic.

P.S. Glad those storms are staying in the Atlantic!

Yes, "buildingscience.org" is a great resource and is "engineeringly" accurate.

....as commented by a spelling impared heat transfer and thermodynamics P.E. (me).

 

[apostolakisl]

Hi, Lou.

I'm on the Gulf Coast, too (Southwest Florida.) I have Icynene (open-cell) in my home. Water just passes through and is not retained in the foam. It's not likely it would ever get wind driven rain (other than a leak on the roof) since the entire roof is enclosed without any venting. Even my soffits are hardiboard with stucco over it, sealing the attic. And if I didn't have the open-cell foam, I wouldn't have found the roof leak until it caused extensive damage.

86turbodsl gives a good recommendation with www.buildingscience.org. It has great information about sealing the "envelope." That's where I did a lot of my research before deciding on Icynene. So far, I've been extremely pleased with my decision, especially when I have to work up in the attic.

Kevin

P.S. Glad those storms are staying in the Atlantic!

Kevin,

I'm with you on the open foam. That is what I put in my house. The consideration for structural rigidity with closed cell is valid though. It's like filling your walls with epoxy. I did a lot of research before building my house and if I recall the above website Open cell also adds some rigidity but is quite minimal. Huricanes and tornadoes will find a closed cell house to be a worthy opponent. Open cell will let water through so you kind find a leak, but it will also act like a sponge and hold water for much longer after the fact. If you have a true leak and need to find it, I agree that open cell is better.

I'm more or less beign devil's advocate here since I am pretty sure I would go with open cell again even if I were building in Naples. I love the stuff I have. As I mentioned above, it maintains a 60 degree temp gradient through my roof wihtout any active conditioning of the attic space.

The situation that I would for sure go with closed cell would be a very challenging vapor barrier situation or a limited space situation.

 

[KevB]

Hi guys

I built my own house with 2x4 staggered studs on a 2x8 plate. This eliminates thermal bridging through studs....which is a lot. Used open cell foam in the entire cavity. I stapled my cat 5 ...and a spot I missed....the wire came out with the foam.

Foam did not melt or damage any wires. (cat 5 and alarm etc).

Huge heat loss is your rim joist cavity. Closed cell foam is a must in that area because it also provides the vapor barrier.

For what it's worth...

kev

 

[86turbodsl]

Huge heat loss is your rim joist cavity. Closed cell foam is a must in that area because it also provides the vapor barrier.

For what it's worth...

kev

Rim joists are a commonly under insulated area. The real major cause of heat loss isn't conduction it's infiltration, and ANY foam, open or closed, will make a major dent in that factor. I have 2.5 inches closed cell in my walls and it's equivalent to 5 inches of cellulose blown in. I used CC because I needed the vapor barrier in my wall profile. It's not that much more expensive around here than open cell.

Also, while I would advocate spraying underside of roof deck with foam, MANY shingle manufacturers WILL NOT warranty their products in that non-cooled application. Something to consider before doing that.

 

[wlj]

Also, while I would advocate spraying underside of roof deck with foam, MANY shingle manufacturers WILL NOT warranty their products in that non-cooled application. Something to consider before doing that.

You've raised a great point! Elk (now GAF-Elk) is (was?) willing to stand behind Icynene applied directly to the underside of the roof deck. They had provided me with a signed letter about 7 years back saying they'd uphold their full warranty. Getting the letter was quick and simple, just a phone call to customer service as I recall.

Cheers,
-Bill

 

[apostolakisl]

closed cell was about twice the price in my bidding experience here in Austin TX.

Interesting point about the roof warranty. I have cement shingles and they have a small (mabye 1/2 in) air space under them as part of the normal install. Plus, I am not sure that they would have trouble like asphalt shingles would with the extra heat (that may or may not actually happen). Good plan to get it in writing about the roof warranty.

Also, I know that the wood is supposed to be a thermal bridge (poorer insulator), but when I measured the temp with my IR "laser" thrmometer of the spray foam surface and the wood surface, the wood was 1 degree cooler (of course there was a thin layer of spray foam on the wood). These were, I think, 2 x 12's.

 

[KevB]

I don't know if the Americans down south are familiar with ICF construction, but a lot of people up here in Canada are going this route. Insulated concrete forms(ICF) reduce our energy consumption by half....two reasons...stops air infiltration and prevents thermal bridging.

Closed cell up where I live is 2 to 3 times the cost of open cell. Up in Canada it doesn't make sense to spray foam to your roof deck...heating your attic isn't cost effective .

I went a different route...I have a wood basement that is made and insulated of 2x10s.....and a wood floor. It's better than any concrete basement I've ever had.

Kev

 

[apostolakisl]

I don't know if the Americans down south are familiar with ICF construction, but a lot of people up here in Canada are going this route. Insulated concrete forms(ICF) reduce our energy consumption by half....two reasons...stops air infiltration and prevents thermal bridging.

Closed cell up where I live is 2 to 3 times the cost of open cell. Up in Canada it doesn't make sense to spray foam to your roof deck...heating your attic isn't cost effective .

I went a different route...I have a wood basement that is made and insulated of 2x10s.....and a wood floor. It's better than any concrete basement I've ever had.

Kev

Yes, I actually looked at that option. It was way way more expensive. There are a handful of homes in Austin built that way. It really doesn't make sense when you look at the fact that the inside/outside temp difference in Austin is almost never more than 30 degrees. We will get a couple weeks in the winter where there will be a 50 degree difference. I would bet the average in/out gradient here is around 20 degrees.

If I lived in Canada (burrrrrr), where your temp difference is like 200 degrees (OK maybe 80) and is that way for several months, it would probably make more sense.

I wouldn't be so sure that insulating the underside of the roof deck still isn't a bad idea even in cold climates. You don't really heat the attic, it does passively pick up the heat from the house below it. The idea is the superior air infiltration block that you get doing it that way. You don't have to worry about all of the ceiling penetrations leaking (light fixtures) and it opens up the world of using your attic for storage at a reasonable temp. Also makes life a lot easier for rerouting/adding fixtures/wires.

 

[KevB]

Hmmm..ya...I would have to disagree.

When it comes to spraying the roof deck....regardless of how air tight your house is....cold/hot will always enter your home. So up here where the temperature can go to -35C on a really cold day and I can have closed cell insulation with an Rvalue of 7+ per inch(which I do)things still get cold. If I have my roof deck sprayed with that closed cell, I may not have vents up in my attic distributing my hot air, but I will be passively heating my attic. Now in my case with a 12/12 pitch, the effect volume of air that I will be passively heating would be the same as the volume of one of my floors...plus some of a second floor. Thats a lot extra heating I have to do. The best way to utilize spray foam is to spray the top side of the ceiling once all wiring is complete. However, we seal everything so rippen tight with tuct tape and accoustant sealant that air inflitration becomes a non issue. We now need to increase resistance of cold/hot.

I know that it some areas in the south, basements are not built....and storage in the attic is quite useful. But where ever your insulation ends is how much house you're heating/cooling.

A good example of what I mean is radiant floor heating systems. They are sealed with no air infiltration whatsoever... so why the need for insulation under the concrete? It significantly slows the heat from moving to the cooler earth. It makes a massive difference when a closed cell rigid foam board is put under the rebar before the concrete is poured. This helps to slow the natural conduction of hot to cold.

Of course...I'm not sure if this is helping the topic of this forum ..


kev