Subscribe or Renew Membership Subscribe Renew

Foam insulation and wiring

gdavis62's picture

In my little town, sprayfoam urethane has been a popular option for insulating new homes.  Expensive, but four foamers compete for the business, and the going rate is about $0.60/bf.

Used to be we would complete all mechanical rough ins before a foam up, but no more.  The building department now has decided no electrical wiring can be buried in foam, so now we can do some of the rough ahead of foam, but not all.  Wiring in walls or roofs that are to be foam-insulated must be done afterward, and the sparkies hate chopping that stuff.

How is it where you are?

Gene Davis, Davis Housewrights, Inc., Lake Placid, NY



(post #94921, reply #1 of 8)

Oh man.  That defeats to whole purpose of the using foam.

Did they give any reason?

(post #94921, reply #2 of 8)

Two.  Fire hazard because heat from wiring might set foam ablaze.  Expansion and movement when the foam is placed (encasing wiring) might pull wiring connections apart.

I could say that cellulose might catch fire.  I could also say that careless bums installing fiberglass batts might dislodge wiring and connections.

But you can't argue with the man.

Anybody seeing this in other jurisdictions?

Gene Davis, Davis Housewrights, Inc., Lake Placid, NY



(post #94921, reply #3 of 8)

Cellulose does not support a flame.

Hmmm.  I have wiring in service that runs through foam.  Now I worry.

I wonder if this is the wave of the future.  Would be devastating to the foam market. Seems as an alternative, they could potentially 'derate' the wiring (require fatter guage), or require conduit.

The pulling apart connections thing seems way off the mark.  If anything, the foam freezes everything in place.

(post #94921, reply #4 of 8)

Hasn't been too much of a hassle, now that I have seen one done under the new mandate.  We have to build with 2x6 walls here, and typical wall fill when doing a sprayfoam job is 3 inches.  Not quite as easy doing all the hole boring for wiring as for plain stud cavities, but the sparkies are still able to get their stuff in the 2 to 2-1/2 inches of cavity remaining.

They've a little digging to do for some of the boxes, but hey, these guys have every kind of chopping, sawing, and boring tools known to man.  Holes-R-us, their trucks ought to say.

Gene Davis, Davis Housewrights, Inc., Lake Placid, NY



(post #94921, reply #6 of 8)

<Hmmm.  I have wiring in service that runs through foam.  Now I worry.>

Well ya, that ones been rockin' my cradle for a while now.

What's an alternative besides not using foam, putting it inside conduit?

Is it an exaggerated concern? I don't know.

Seems on a balance scale where'd you have to judge I'd say it leans to the nay.

"just nail that board up there!!!"


"look, lady..."


(post #94921, reply #8 of 8)

"Fire hazard because heat from wiring might set foam ablaze. Expansion and movement when the foam is placed (encasing wiring) might pull wiring connections apart."

The FG insulation MIGHT ripe all of the insulation off the wire and and cause a short.

An astrode MIGHT crash into the building code office, kill all of the inspectors and raise the average IQ of city hall by 50 points.

IMHO the later is more likely to happen then the first 3 combined.

If any one wants to fight this it should be easy.

First contact the supplier of the foam. They should have evaluation reports from that test for these kinds of things.

Then looking at this in detail, ask then (building inspectors) at what tempature the foam will catch fire and then ask them what the temp rating of the wire is?

Then ask how the connections can be "pulled apart" when they are usually not made up until AFTER the drywall is up.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #94921, reply #5 of 8)


  I used SIP's and they have channels where you run wires in them already.. Sounds like your guy is assuming facts not in evidence but you know the story somebody sold him a bill of goods and you'll have to sell him another bill in order to get it done.. I suggest that you build a mock up and have him try to prove his case..

(post #94921, reply #7 of 8)

Not sure how sound the logic is that a Romex job could be destroyed by spray foam. Maybe. As for setting it on fire I don't know but suspect that the foams are self-extinguishing if not retardant. Not sure why a overloaded cable would pose more of an issue in foam than say a piece of lightered pine I see in old Florida homes.

I would think the pine would be more of a hazard because it typically has a good air supply while a fire in the foam would likely be smothered. I would think more testing would be in order to draw definitive conclusions so rules can be developed.

One issue I am familiar with is that Romex or any other cabling system, as opposed to a raceway system like conduit, can be problematic when foamed in. In these situations replacement, repair and upgrading of those portions foamed in. In fiberglass or, with more trouble, cellulose insulation cables can be snaked in. I have snaked through foam but it is a vastly more difficult situation as you need to literally drill through the foam and do it blind.

My suggestion is that if you intend to use spray in place foam install conduit in the areas to be foamed. Either PVC, EMT or flex. Possibly mixed to accommodate different situation in a single area. Once the conduit is run you can foam to your hearts content. This allows the wiring to be pulled in, changed and repaired much more easily.