Prewire w/ Spray Foam Insulation

I was wondering if anyone had any tips/suggestions on how to prewire runs thru walls that will have spray foam insulation? In my 2nd level wall cavities I'm getting open cell foam applied which will fill the whole 2x6 cavity so I'm wondering how the wires would hold up in there if they are stapled to the studs, if that is the correct way?

Also with this type of insulation it seems it would be harder to re-located a drop point? IE lets say I have my cables in a box at the bottom of the wall, then I decide to mount a LCD tv 3 ft above and want to pull a pair of Cat5e from the low box up into the area of the TV, would that be difficult?

Thanks,
Ryan

R33BOOT said:

I was wondering if anyone had any tips/suggestions on how to prewire runs thru walls that will have spray foam insulation? In my 2nd level wall cavities I'm getting open cell foam applied which will fill the whole 2x6 cavity so I'm wondering how the wires would hold up in there if they are stapled to the studs, if that is the correct way?

Also with this type of insulation it seems it would be harder to re-located a drop point? IE lets say I have my cables in a box at the bottom of the wall, then I decide to mount a LCD tv 3 ft above and want to pull a pair of Cat5e from the low box up into the area of the TV, would that be difficult?

Thanks,
Ryan

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Hi Ryan,
I have heard several horror stories with people using spray foam and the heat from the chemical reaction melting the lv wire. In addition, I would use a closed cell spray foam and not open cell for several reasons. First closed cell will not hold moisture. Next it is stronger and harder. Nevertheless, I would suggest running all lv wiring in conduit. As far as moving a wire in spray foam insulation I have never had the opportunity to attempt this, but it seams like a real pain-especially if the wire is in conduit.

I have been curious about this for a long time as well, so I have been paying close attention when I see this on a home building show, etc. As I would like to do it in the future and it seems the best insulation option.

One thing I noticed on a recent show was that the foam didn't fill the entire stud depth. So there might still be room to run wire behind the wall. I believe it was closed cell, which doesn't expand as much as open cell and doesn't require a vapor barrier. I have also seen them carve out channels after the fact on some shows and in pictures using a hot knife.

Some other ideas I had was to build out the walls with sleepers, generously use conduit in the walls, and/or use one of those baseboard or crown molding systems that can be removed, to run wire behind.

I have spray foam in all 2x4 window walls to increase R factor and rigidity of the walls. No issue at all with wiring.
Of course, you can never remove those wires without major surgery.
If you think you will be running more wires, then make sure you run some conduit before the foaming.
Most of the time, you don't completely fill the wall with foam due to expansion.
Don't use spray foam around doors or windows or they will be stuck closed once the house settles.

If you knew where all of the line voltage and low voltage wires were located within a given stud bay, then I would think a Flexibit 3+ foot drill bit could slice through the insulation pretty easily, to retrofit a cable where needed.

I consulted someone for the use of spray foam for my MBa floor when we were renovating, to reduce sound penetration (guest BR and playroom/future media room below). Seemed to me that most spray foam installers use either small cell or large cell - they don't really seem to offer a choice, they use one or the other. You might need to find a different installer if you want a different opinion on open cell vs. closed foam.

I have a feeling the closed cell doesn't expand as much, and you may have some room in each stud bay to run new cables when needed.

Overwire now, take lots of pictures before the foam goes in and the drywall goes up.

Edit - and +1, I read somewhere that the foam can melt the cable jackets when it's hardening.

Careful planning, running extra cable, running conduits, and photos of every location I ran cable.

I have Icynene insulation in my home, and couldn't be happier. It's an open-cell foam, and prefer it that way. It doesn't shrink, exhaust VOCs, and doesn't hold water, letting it pass through. This is a big plus, as it doesn't trap water between the insulation and framing/wood that could rot if not permitted to dry out. For example, I developed a leak in my tile roof that I noticed during heavy rains last week. Since water passes right through the Icynene, I noticed the leak right away. The roofer was there the next day and made the repair. Had I used a closed-cell foam, the water would have accumulated between the insulation and the roof panels. It might have taken a ong time to discover the leak, allowing mold and rot to occur. When then water eventually would be discovered, much damage could have occurred. Plus, pinpointing the leak would have been difficult since the water could travel under the closed-cell foam and exit far from the source of the leak. It was easy to find my leak, as the water passed through right under the source of the leak.

There's no problem with Icynene being in direct contact with HV and LV cables. It doesn't do anything to the cable jacket.

You can get more information at Icynene.com.

HTH,

Kevin

Thank's for the info guys. Basically going with open cell foam, it has to fill the entire cavity to get an R20 value. If I went with closed cell it would be only 3" but it's allot more expensive than the closed cell, so I was trying to save on cash. Basically the only rooms that will be open cell where wires would be running is 2 bedrooms on the upstairs. I think i'll be safe if I just run conduit from the boxes to the ceiling at each drop point, what do u think?

R33BOOT said:

Thank's for the info guys. Basically going with open cell foam, it has to fill the entire cavity to get an R20 value. If I went with closed cell it would be only 3" but it's allot more expensive than the closed cell, so I was trying to save on cash. Basically the only rooms that will be open cell where wires would be running is 2 bedrooms on the upstairs. I think i'll be safe if I just run conduit from the boxes to the ceiling at each drop point, what do u think?

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Closed cell has its advantages, but I think for the money open cell is best above grade. Closed cell also isn't truly closed. It will take 20 years but eventually the gas leaks out and is replaced with air and then you have 3 inches of open cell equivalent on the r value.

I have open cell in my whole house and it was sprayed right onto the wires, both low voltage and high voltage. I watched the guys spray the stuff and touched it immediately after it hardened and it wasn't hot.

I agree with the other comments. Use conduit when in doubt. Take lots of pictures. You can poke wires through the open cell but you will mess it up. You can also easily dig the stuff out with a bare hand if you need to make a little space for a box. And it does insulate great! 6000sf, 12 foot ceilings, 103 outside, all electric house, highest bill ever $380.

Also, highly recommend spraying the roof deck (not attic floor) so that the attic is inside the insulated envelope of the house. It will make working in the attic much more pleasant and avoid the problem of light cans and other ceiling penetrations being big leaking holes.

Lou,
My house is all electric too, I bought it half-built. It's a solar passive home. I'm basically doing R20 in the walls, but the whole 1st level is ICF Foundation. Then in the roof I'm doing an closed to open cell combo R60 value. That's great on your electric... what are u running for Hot Water, Solar HW? or something else. My home has a radiant floor being driven by an electric on-demand tankless, I'm hoping it performs well... but I'm not sure if I want to spend the cash on Solar HW ($9,000 w/ 4500 of it back at end of year) or just do something like a Heat Pump Hybrid (but only 50gal) any suggestions?

I'll probably be safe and run conduit, but am going to inquire to the insulation guy about burning wires lol... thanks

Lou Apo said:

Also, highly recommend spraying the roof deck (not attic floor) so that the attic is inside the insulated envelope of the house. It will make working in the attic much more pleasant and avoid the problem of light cans and other ceiling penetrations being big leaking holes.

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If the OP does go this route, depending on location, I would strongly recommend looking into a radiant barrier first.

Found a relevant thread at AVS

http://www.avsforum.com/avs-vb/showthread.php?t=832496

worth a look, but a lot of conjecture in that thread

Edit - relevant CT forum thread

http://www.cocoontech.com/forums/index.php?showtopic=10463

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).

Have DOZENS of installs directly on HV and LV wire. Have NEVER EVER had a wire melt.

Have had to go back in an add wires down a wall with spray foam. A simple, heavy fish tape will usually work and just fine. Once I had to use a long stick or piece of metal, but its not a huge challenge. Of course, conduit is better. Foam easily moves and you can tear up quite a bit fishing wires thus reducing the foams insulation value.

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.

As far as what Digital Ranger says, ditto from me. My experience of one is totally consistent with his multiple homes.

I am not 100% sure on this, but I don't think radiant barrier works if you apply another material directly to it (spray foam). I think you need an air space which would definitely complicate things and I am not convinced it would help. I live in Texas, the summer sun beats on that roof like you wouldn't believe. I have cement tiles and in the afternoon you absolutely can't touch them for more than a second without getting burned. In the attic, you can touch the foam and it is room temp to the hand. I'll take my infrared thermometer up there this afternoon and measure the roof temp on the outside and roof temp on the inside and tell you what the numbers are. It should be interesting.

I did say my house was all electric, but I may have exagerated a little. I do have propane for hot water and cook top. Hot water is via 2 on demand tankless units. Hot water isn't a big consumer of energy here as the cold water is in the 80's for much of the year. $9,000 for solar water sounds like a payback loser to me. If you do that, you are strictly doing it to be green. I think your green dollar would benefit both your wallet and the environment more if you put the cash towards a better HVAC unit or better windows, or better doors, or better insulation. . . you get the point.

Since heating the house is a minor consideration, radiant floor is not necessary. Heat and cooling is via Carrier infinity heat pump. Three units (2 3 ton, 1 2 ton). They work great as well. The 8 tons of total may be slightly more than necessary, especially on cooling. The system seems to work harder during our very short cold season than during the 100 degree summer heat. The system is nearly silent and contributes greatly to the low electric bills. I also have a wine room with a 1/4 horse compressor, and a bunch of refridgerators/freezers.

There are a lot of things I would do differently if I could rebuild my house, but the insulation and HVAC would be a for sure repeat as is.

It is 2 pm. The current air temp outside is 100 and it is sunny. Using my IR point and shoot thermometer, the outside roof temp is 140 +/- 1 and the inside roof temp is 79.5 +/- 1. The air handling units and duct work run through the attic and I am sure some cooling affect is had from that but there are no air registers up there. The house is 76 and there is no insulation between the house and the attic (just drywall).

Hi,

I've had Icynene spray foam insulation for about 6.5 years now, and it's wonderful stuff! Very highly recommended.

One tip that I haven't seen mentioned is the need to make sure your wires are well secured to studs prior to having the foam applied. The foam when sprayed is almost like a cake batter, then it expands very rapidly a few seconds after application. Wires that aren't securely affixed move with the foam as the foam expands. This can be a problem if the wire is caught in the foam that expands past the stud cavity and is subsequently trimmed off. I lost an alarm wire this way, but fortunately saw it in time to make a repair.

I had no problems with melted insulation either either low or high voltage wires, though the spray foam does adhere to the wire (and everything else). For all intents and purposes, anything in the wall when the foam is applied becomes a permanent resident. Also, Icynene becomes rigid once it hardens, and doesn't "bounce back" once it's compressed. This means that attempting to remove or fish wires in the wall after-the-fact may cause significant damage to the foam insulation. You'll want to run conduit in walls where you think you might want additional wires in the future.

Hope this helps,
-Bill