Spray Foam in Older Homes: What to Check First

Before spray foam in older homes: the walk-through

Western Pennsylvania has plenty of houses built long before modern insulation, and each has its own surprises. These are the things to find before anyone quotes foam:

Knob-and-tube wiring

Knob-and-tube is the oldest wiring you will find in these houses: single conductors strung on ceramic knobs and run through ceramic tubes, in open air. The National Electrical Code (394.12) does not allow it to be concealed in wall, ceiling or attic spaces that are insulated by "loose, rolled, or foamed-in-place insulating material." Spray foam is foamed-in-place insulation, and it surrounds everything it touches.

The DOE's weatherization crews are told to check for live knob-and-tube and either dam the insulation away from it or replace it with modern wiring. Damming works for loose fill on an attic floor. It does not work for spray foam. So before foam goes into any space with knob-and-tube:

1. A licensed electrician tests each run. Wiring that looks abandoned is sometimes still energized.
2. Live circuits are replaced with modern wiring, and the old runs are disconnected.
3. Get it in writing. The inspector may want the record, and your homeowner's insurer may ask about it too.

Balloon framing and fireblocking

Many older houses are balloon-framed. The exterior wall studs run in one piece from the sill to the roof, and the upper floor joists hang on boards let into the studs instead of sitting on top of a wall. The result is a stud cavity that can be open from the basement to the attic, with the floor cavities between stories opening into it.

That is a chimney inside your wall. In winter, basement air rises through those bays and out into the attic, and cold air is pulled in low to replace it. It is also a path for fire, which is why modern codes require fireblocking.

The IRC requires fireblocking in concealed stud walls at each floor and ceiling level and every 10 feet horizontally. Approved materials include 2-inch nominal lumber, ½-inch gypsum board, ¾-inch particleboard, ¼-inch cement-based millboard, and mineral wool or glass fiber batts held securely in place (unfaced fiberglass has to fill the cavity at least 16 inches high). Spray foam is not one of the listed materials. The right order is a real fireblock at each open floor line, then foam to air seal around it. The basement sill and the top of the walls in the attic are where you can usually reach the bays.

Vermiculite and other asbestos suspects

Vermiculite attic insulation is pebble-like and usually gray-brown or silver-gold. According to EPA, the mine in Libby, Montana, supplied over 70% of all vermiculite sold in the U.S. from 1919 to 1990, and that ore was contaminated with asbestos. EPA's advice is direct: assume vermiculite contains asbestos, leave it undisturbed, don't try to remove it yourself, and hire a professional asbestos contractor before renovation that would disturb it. Testing is not needed to take those precautions.

Foaming an attic with vermiculite in it means people kneeling, walking and working in it. That disturbance is exactly what EPA warns against, so abatement comes first. The same caution applies to other old materials in the work area: EPA notes you generally can't tell whether a material contains asbestos by looking at it.

Old insulation comes out where foam goes in

Spray foam bonds to clean, dry wood and masonry. It can't seal through a layer of old batts, loose cellulose or rock wool. Wherever foam is going, such as a rim joist, roof deck or kneewall, the old insulation comes out and the surface gets cleaned. Wet, moldy or animal-soiled insulation should come out regardless. That removal is real work, and it belongs in the quote.

Plaster walls: spray foam needs open cavities

Spray foam goes onto an open surface and rises within seconds (see Spray Foam 101). In a closed plaster wall you can't see it, you can't control its thickness, and expansion in a closed space can crack plaster or push it off the lath.

For finished walls, the options are different products:

• Injection foam: a low-expansion foam pumped into closed cavities through small holes. DOE's insulation guide notes that some foams, such as tripolymer, are made to be injected into wall cavities.
• Dense-pack cellulose: blown into closed cavities through holes at high density.

Both need the knob-and-tube question answered first. In a balloon frame, the bottom of each bay also has to be blocked, or the fill can drop into the floor below.

Spray foam in older homes fits where the cavities are already open: attic roof decks, kneewalls, basement walls, rim joists and any wall being gutted to the studs. A gut renovation is also when the lead and asbestos rules matter most.

Moisture, the roof and the chimney

Old houses often have old roofs. Foaming under a leaking roof hides the leak, so check the attic sheathing first for water stains, dark spots and soft wood, and fix the roof before foam goes under it. Does spray foam trap moisture covers how to manage foamed roof decks.

Three older-house details to watch:

• Spaced board decks. Roofs that once carried wood shingles often sit on spaced boards. Foam needs a continuous surface, so the gaps get a backer first.
• Damp foundations. Old stone and block foundations often wick ground moisture. Sort out drainage before insulating them; see basement wall insulation.
• Chimneys and flues. They need clearance to combustible materials, and foam is combustible. The gap is closed with sheet metal and fire-rated sealant, not foam.

Lead paint

In a house built before 1978, assume painted surfaces may contain lead. Under EPA's Renovation, Repair and Painting (RRP) rule, anyone paid to do work that disturbs painted surfaces in a pre-1978 home must be certified and follow lead-safe work practices. Spraying foam doesn't disturb paint, but the prep often does: pulling trim, cutting access holes and opening plaster. Pennsylvania doesn't run its own RRP program, so EPA administers it here. Homeowners working on their own homes generally aren't covered, though EPA still recommends lead-safe practices.

After the air sealing

Older houses are leaky, and sealing them changes how the house breathes. Two follow-ups make sense once the foam is in: make sure bath and kitchen fans vent outdoors, and have a heating contractor confirm that any natural-draft furnace, boiler or water heater still drafts properly.

Planning work on an older house? Price My Project or call (814) 208-3478, and tell us roughly when it was built.