caulking around boxes

[RustyShackleford]

Homeowner asks about caulking unused knockouts and around wires entering boxes (for air sealing on new construction). Seems like I've heard something about 100% silicon caulk attacking plastic, possibly a problem with PVC (Carlon blue) boxes and sheathing on NM - anyone heard of this ?

 

[John120/240]

I do not know of any issues about silicone caulk affecting plastic boxes. They get spray foam insulation all over everything. If caulk and plastic boxes were a problem I think it would have been discussed before now.

 

[GoldDigger]

I do not know of any issues about silicone caulk affecting plastic boxes. They get spray foam insulation all over everything. If caulk and plastic boxes were a problem I think it would have been discussed before now.

Silicone is more of a problem for wires, relays and other components than for boxes or raceways, and even then not much.
One problem is that while curing silicone releases acetic acid (recognize the vinegar smell?) which is corrosive to fine wires and semiconductor devices and is slightly electrically conductive until the curing process is complete.

 

[RustyShackleford]

Ok, maybe stick to latex caulk to be sure. Or other types of silicon caulk, like GE Silicon II, that use a different solvent than acetic acid.

 

[jumper]

Ok, maybe stick to latex caulk to be sure. Or other types of silicon caulk, like GE Silicon II, that use a different solvent than acetic acid.

Check 334.80 for derating issues in this application.

 

[renosteinke]

I suppose we ought to get used to this.

Canada already requires boxes on outside walls to be sealed. I think putty pads are the usual method.

The 'green' press, including Fine Homebuilding magazine, have been harping the 'airtight walls' theme for about a year now. Folks who ought to know better - having been around the last time we tried this, during Carter's 'energy crisis,' which spawned a 'mold and argon' crisis during the Regan years - are again jumping on this bandwagon.

I've already had one service call where the cause of the water heater not firing properly was inadequate make-up air. Expect a lot of 'trouble' calls for 'malfunctioning' CO detectors, as air-tight homes lead to appliance back-drafting.

 

[steve66]

They make the foam gaskets that go between the device and the wallplate.

That sounds much easier to me.

 

[Gregg Harris]

I suppose we ought to get used to this.

Canada already requires boxes on outside walls to be sealed. I think putty pads are the usual method.

The 'green' press, including Fine Homebuilding magazine, have been harping the 'airtight walls' theme for about a year now. Folks who ought to know better - having been around the last time we tried this, during Carter's 'energy crisis,' which spawned a 'mold and argon' crisis during the Regan years - are again jumping on this bandwagon.

I've already had one service call where the cause of the water heater not firing properly was inadequate make-up air. Expect a lot of 'trouble' calls for 'malfunctioning' CO detectors, as air-tight homes lead to appliance back-drafting.

The proper amount of combustion air to fossil fuel equipment should not rely on air leakage from the building onvelope.

 

[kwired]

I suppose we ought to get used to this.

Canada already requires boxes on outside walls to be sealed. I think putty pads are the usual method.

The 'green' press, including Fine Homebuilding magazine, have been harping the 'airtight walls' theme for about a year now. Folks who ought to know better - having been around the last time we tried this, during Carter's 'energy crisis,' which spawned a 'mold and argon' crisis during the Regan years - are again jumping on this bandwagon.

I've already had one service call where the cause of the water heater not firing properly was inadequate make-up air. Expect a lot of 'trouble' calls for 'malfunctioning' CO detectors, as air-tight homes lead to appliance back-drafting.

An installer of combustion products needs to realize that in a building that is well sealed there needs to be an intake or makeup air of some kind otherwise they will have problems with that appliance.


Few years ago I had a small restaurant owner call me complaining the gas company shut off the gas because the gas water heater kept blowing out pilot from backdrafting because of cooking exhaust hood, and refused to reconnect gas until problem was solved.

This owner was just the property owner - not the restaurant operator. His solution was to install an electric water heater. One look at the elecrical system and I knew right away that to add a water heater was not a quick and simple solution and that he would not like the cost, and suggested it would be much less cost for him to install some make up air provision. All he could think about was how much unconditioned air would be sucked into the building. I could not convince him that if the fan is pulling air out then an equal amount of air has to come in, and if you don't give it an easy place to come in it will find every crack possible to try to pull it through, including the exhaust of the water heater.

 

[RustyShackleford]

Check 334.80 for derating issues in this application.

Sure, this was discussed in another thread talking about firecaulked framing penetrations. Basically, as I understand it, you have to apply Table 310.15(B)(3)(a) current derating if the cables are caulked, even though they may not be "installed without maintaining spacing for a continuous length longer than 24". However, for typical NM branch circuits (20amps on 12ga, 15amps on 14ga) you're good for up to 9 CCCs regardless (since 70% of the 90-degree column in Table 310.15(B)(16) is more than 20amps/15amps).

 

[RustyShackleford]

I think putty pads are the usual method.

What are these putty pads ? Caulking around where the wires pass thru knockouts could be a waste of time, as torquing on the wires when I put in the outlets etc will likely dislodge the caulk.

The 'green' press, including Fine Homebuilding magazine, have been harping the 'airtight walls' theme for about a year now. Folks who ought to know better - having been around the last time we tried this, during Carter's 'energy crisis,' which spawned a 'mold and argon' crisis during the Regan years - are again jumping on this bandwagon.

Most believe energy efficiency is a good thing, but any new technology will have growing pains.

Keeping moisture-laden air out of the walls is actually a good way to PREVENT moisture problems. Of course, if the wall is vapor-tight, moisture can get trapped inside; but a well-designed airtight wall will prevent moisture getting trapped. This is especially problematic in the hot humid south, where the usual practice of putting a vapor barrier between the interior and the insulation actually causes problems in the summer. This is an artefact of what I like to call a "northern centric" view of building, where the inside of the house is assumed to be warmer and more humid than the outside. Our building code actually warns about putting a poly vapor barrier on the inside (or outside, of course) of the insulation.

As others have pointed out, it's a shoddy plan to rely on a leaky building envelope to supply combustion air for fossil fuel (or wood, for that matter) burning appliances inside the house.

I think you're thinking of radon, not argon. Again, relying on a leaky house is a bad plan; mitigation before it gets inside the house is recommended. Of course, extremely airtight houses DO have inside air quality issues, but these can be addressed using air-to-air heat exchangers.

 

[infinity]

Sure, this was discussed in another thread talking about firecaulked framing penetrations. Basically, as I understand it, you have to apply Table 310.15(B)(3)(a) current derating if the cables are caulked, even though they may not be "installed without maintaining spacing for a continuous length longer than 24". However, for typical NM branch circuits (20amps on 12ga, 15amps on 14ga) you're good for up to 9 CCCs regardless (since 70% of the 90-degree column in Table 310.15(B)(16) is more than 20amps/15amps).

That is correct if the NM cables are caulked in a hole through wood. {334.80}