Blown cellulose or fibreglass: compare the actual products and application charts
A community-hall estimator is asked to change the specified attic cellulose to fibreglass while retaining dense-packed wall work. The revised quote lists a material price difference but has not checked either product’s application and coverage basis.
Start with the location and permitted application, then compare the actual products. Natural Resources Canada describes cellulose as treated shredded newsprint and loose-fill glass fibre as material prepared for blowing or pouring. It distinguishes wall and horizontal application behaviour. Those descriptions do not make every product interchangeable: use the required depth, coverage, density, preparation and equipment information for the actual attic or wall method.
Compare the complete installation rather than the bag price
- Identify the specified and proposed applications. Separate open attic fill, dense-packed cavities and any stabilized or wet-applied method. Record the actual products and current manufacturer charts for each location. Confirm that the proposed material is permitted in the intended assembly and method. A bag suitable for one application cannot be assumed suitable for another merely because both charts display thermal values.
- Compare depth and quantity on a matching basis. Use the required thermal value and each applicable chart’s installed and settled-depth information, coverage basis and bag weight. Check available space and protected ventilation provisions. Make a changed quantity visible in the quote instead of retaining the old product’s count. Do not compare a loose-fill depth with a dense-pack cavity figure as though they describe the same installation.
- Check preparation, handling and equipment consequences. Review the actual receiving condition, permitted machine and application requirements, dust and handling controls, and any drying or covering condition. Obtain the necessary technical and safety answers for the proposed work. A material-family description does not establish a universal moisture tolerance, fire-resistance assembly, equipment setting or personal-protection selection for every supplied product.
- Retain the received location-specific decision. Route a proposed change through the actual substitution and design process with its revised installation and commercial information. Keep an unchanged wall method distinct from the proposed attic change. Give the crew the received product, applicable chart and required checks. A revised price alone does not authorize swapping materials or remove the need to verify the actual installation.
Common mistakes
- Choosing from bag price alone.
- Using one product’s coverage chart for another.
- Mixing attic and dense-pack application figures.
- Treating a revised quote as the received substitution decision.
Checklist
Retain a comparison for each location
- Actual products and permitted application methods.
- Required thermal value and matching chart basis.
- Depth, quantity and available-space consequences.
- Preparation, handling and equipment requirements.
- Received material decision and crew references.
Check your understanding
The replacement bag has a similar thermal value per inch. Can the original quantity and method remain unchanged?
