Disadvantages Of Using Fibreglass Insulation In A Cellar


Why do people use fibreglass?

Fibreglass insulation is extremely popular with the DIY market for several reasons. Firstly, it’s readily available at all large home improvement stores; secondly, it’s cheap; and thirdly, it’s a lightweight material that’s easy to work with and simple to remove and replace. Your basement or cellar is very different than any other room in your home. So whilst fibreglass insulation is a great choice for insulating your roof, it’s not such a smart option for basements and cellars. Here’s why:

Disadvantages of Fibreglass

1. Ruined by water and moisture

Much like a sponge, fibreglass absorbs water and humidity. As a result, it can become saturated with moisture via basement flooding, water leaking through walls, or simply from the high humidity levels that occur in this below-grade space.

2. Sagging and falling down

Wet fibreglass loses nearly all of its insulating value. Adding moisture to fibreglass transforms a light, fluffy material into a heavy material that sags, compresses and often falls out of place. Fibreglass batt insulation installed between ceiling joists in a cellar or basement often ends up on the floor if it gets wet.

3. Supports mould growth

It’s not rocket science to figure out that before too long, wet fibreglass is going to encourage mould and mildew growth, which is very bad news for your health. Mold growth that originates in fibreglass insulation can eventually lead to wood rot in nearby structural lumber, which can threaten the building’s structural integrity.

4. Air circulation

Fibreglass insulation can’t stop air circulation. So the insulation does nothing to stop air leaks that occur around cellar windows and around the perimeter of the cellar or basement. Fibreglass insulation does nothing to stop cold, damp air from leaking into the basement and up into the living space above.

5. Compression and settling

Over time, fibreglass insulation can settle and/or compress. This significantly reduces its insulating effectiveness (referred to as ‘R-value,’ for Resistance to heat transfer). In older fibreglass insulation, the R-value will drop as the insulation settles or compacts. Whether installed in wood-framed walls or between joists, fibreglass batts compress easily and are prone to falling out of place. This not only creates a mess; it also renders the insulation all but useless.

6. Loose fibres

Be warned: fibres can loosen and float around, making them really uncomfortable to work with. If you do attempt to work with fibreglass, always wear long sleeves, eye protection, and a hat and gloves to keep the fibres off your skin and nowhere near your lungs.

7. Excellent pest habitat.

Mice, rodents and insects find fibreglass insulation to provide an excellent habitat. Mice find the material’s light, fluffy texture to be ideal for nests. Anyone who has removed old fibreglass insulation from a basement, crawl space or cellar will be able to confirm how much rodents like this material.

8. Environmental impact

Although fibreglass insulation saves energy post-installation, the manufacturing process isn’t terribly green. It takes around three times as much energy to produce fibreglass as it takes to manufacture cellulose insulation.


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