Fiberglass Insulation in Leesburg, VA: Blown Attics and Open Walls

Fiberglass is the material behind most Leesburg attics. Potomac Station, on the east side off Battlefield Parkway, has over 1,400 single-family homes and townhomes with similar floorplans, and Potomac Crossing (1988 to 2006), Exeter and Greenway Farm add hundreds more. That sameness helps estimating, because one layout repeats along a street. Our crews reach them by Leesburg Pike, which is Route 7, renamed from Harry Byrd Highway in December 2021, and by Sycolin Road and the Leesburg Bypass. Out toward Lucketts, on US 15 north of town, the houses are older and one-off, and open framing there is a different conversation.

We use fiberglass in three forms: blown loose-fill for attic floors, BIBS (Blow-In-Blanket System) for open wall cavities, and dense-pack for some closed walls. None of them seals air. This page covers which form suits which Leesburg house, the depths and densities involved, and what two typical scopes cost.

Blown Fiberglass, BIBS and Dense-Pack: Matching Form to House

Where fiberglass fits

• Blown attic floors. Loose-fill fiberglass runs about R-2.2 to R-2.9 per inch, so R-38 to R-49 takes roughly 13 to 17 inches. One manufacturer chart lists 16.75 inches for R-49 and 20 inches for R-60, and reports negligible settling. It is often the lowest-cost route to R-49 over tired batts.
• BIBS in open cavities. Fabric is stapled across exposed studs and the fiber is blown in through a slit, which gives about R-15 in a 2x4 wall and up to about R-23 or R-24 in a 2x6. That means additions and gut renovations, never finished walls.
• Dense-pack fiberglass. The same fiber can be packed into a closed wall through drilled holes, at a density that depends on the product data sheet (2.2 to 2.3 pounds per cubic foot or more for two common brands). For most older walls we still lean on cellulose, but fiberglass is an option.

Where it falls short

• Ducts in an unconditioned attic. More depth on the floor will not stop losses from a duct run in a hot attic. Foam at the roofline can.
• Very leaky attics. Cellulose resists air movement through the fill better. Our spray foam versus cellulose article walks through the same question for attics.
• Tight, irregular bays. A cut batt can be the better detail.
• Metal-clad farm buildings. Condensation forms behind panels, so read the agricultural insulation guide first.

Prep, Depth and Ventilation in a Fiberglass Attic

A blown attic is only as good as its prep. ENERGY STAR tells contractors to seal the attic floor before adding insulation, so top plates, wire holes and bath fan housings are sealed first. Baffles go in at the eaves so the required 1-inch space under the roof sheathing stays open, and wind does not wash the fill away from the soffits. Attic ventilation in Northern Virginia follows a 1 to 150 ratio unless a balanced split between upper and lower vents allows 1 to 300.

Depth is checked with rulers stapled to the framing, with the count printed on the bag label. Recessed lights that are not IC-rated get a 3-inch clearance or a replacement, knob-and-tube wiring is never covered, and vermiculite is left alone as suspected asbestos. Gray streaking on old batts is dust filtered from leaking air, so it points to gaps rather than a defect, and we seal at that spot. New construction and additions follow the 2021 Virginia code: R-60 in the ceiling, or R-49 at full uncompressed height.

Permits and Offices for Fiberglass Work

Blowing fiberglass over an existing attic floor is usually not a permit item. The Virginia code does not name insulation and leaves minor work to the building official, so we confirm with Loudoun County at 703-777-0220 first. Walls of an addition or an accessory-building conversion sit inside a larger permit, and the insulation inspection comes before drywall.

The County, not the Town, issues building permits for Leesburg addresses. Property outside the Town, including Lansdowne and Lucketts, also gets its zoning permit from the County. Historic review in the Old and Historic District covers exterior changes.

Further Reading on Fiberglass Around Leesburg

Compare materials on our Leesburg insulation overview, or check whether we cover your address on the service areas page. For the honest tradeoffs, see fiberglass versus spray foam in Virginia and spray foam in Ashburn and Loudoun County. Nearby, we also provide fiberglass in Ashburn, fiberglass in Sterling and fiberglass in Herndon.