Floor insulation

Floor systems decided to be the thermal boundary must be insulated and air sealed as per Massachusetts Building Code and Mass Save Application Details.

1 Performance criteria

Create an air barrier across the subfloor by sealing all large openings and gaps including any ducts in unconditioned space. Floor insulation must cover all exposed subfloors to the level specified as continuous a thermal barrier.

2 Preparation

a. Air sealing of a crawlspace or basement ceiling should be done as per section 6.1 above and the MA Basic Air sealing Authorization.

b. Inspection before installation must be as per ASTM C1320-09.

i. Inspect the attic, crawlspace, or another area to be insulated, delay the installation until:

• You rectify the potentially faulty wiring confirmed by the licensed electrician as OK

• Moisture damage and/or entry is rectified and sources controlled

• Ground cover is in place over exposed soil in crawlspaces wherever accessible. The customer is aware of all uncovered conditions.

o If an accessible dirt floor area is vented per code, a vapor barrier is still recommended.

o If a dirt floor area is deemed inaccessible AND insufficiently vented, then sufficient ventilation must be added OR the crawlspace must be made accessible unless the exposed dirt floor comprises less than 10% of the total footprint of the building.

• All openings allowing air between conditioned space and attic are sealed

c. Confirm that caulk, gasket, or another sealant is installed at penetrations of the interior wall or floor including plumbing, electrical, heat registers, and grills

3 Installation

a. Make installation of mineral fiber batt or blanket insulation in open cavities as per ASTM C 1320 and MA code. 

b. Make installation of cellulose or fiberglass blowing wool into closed cavities as per attic floor insulation methods above 6.3.11 or wall insulation in 6.5.

• Gain access to every cavity with the least damage possible and ensure a safe process for painted surfaces in homes made before 1978.

• Material use per unit area shall match the weight required to give target densities of 3.5lbs/cu. ft. for cellulose and 2.2lbs/cu. ft. for fiberglass wool tested for airflow resistance.

  1. Install batt or blanket insulation to:

• Maintain 3” clearance from non-IC rated lights and heat sources, none placed above

• Completely fill every cavity to the required depth or more

• Where double layers are installed over floors, cross the layers with no gaps between layers

d. Where batt fiberglass is installed beneath floors, insulation shall be in full contact with the floor above using wire, screen, and nylon mesh fastened in place

• Fit to length and placed snug to edges without gaps, voids, or compressions

• Cut and fit around all cross-bracing, outlets, wiring, into narrow cavities

• No exposed facings rated higher than flame spread 25 left

• Where vapor retarder is installed, a place to the warm-in-winter side

• Never place insulation between piping and the warm surface, to prevent freezing.

4 Rim Joist Insulation

a. Fiberglass Insulation – When joists are spaced properly, recommend fiberglass insulation for the rim joist area in basements that are in the thermal envelope. A recommendation to air seal the rim joist must be made in conjunction with fiberglass batt insulation to provide an aligned air barrier and thermal boundary.

Spray Foam Insulation – Check with your PA for materials used.

Thermal Barrier Board – This can be recommended in special circumstances. Check with your PA for appropriate situations.

b. Mass Save Contractor will confirm that there is no insulation made between piping and the warm side of the rim joist framing to avoid freezing.

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