## What happens if I have gaps in my insulation?

Heat like electricity tends to follow the path of least resistance.

From how insulation works:-

1. The total power of heat through the insulation and the gaps in W is given by:
• P = (Ti - Te)·(ai/Ri + ag/Rg).
1. The thermal resistance of the ceiling in K·m²/W is given by:
• R = (Ti - Te)·a/P.
1. Therefore the effective thermal resistance in K·m²/W is:
• R = a/(ai/Ri + ag/Rg).
where:-
• P is total heat flux in W.
• (Ti - Te) is the temperature difference in K.
• a is the total area in m².
• ag is the gap area in m². (ag = 0.01 a)
• Rg is the gap thermal resistance in K·m²/W. (Rg = 0.30 [AIRAH])
• ai is the insulated area in m². (ai = 0.99 a)
• Ri is the insulated thermal resistance in K·m²/W. (Ri = 2.50 + 0.30 = 2.80)
1. Effective thermal resistance for R 2.5 with 1% gaps is:
• R = 1/(0.99/2.80 + 0.01/0.30) = 2.58 K·m²/W.
1. Effective thermal resistance for R 3.5 with 10% gaps is:
• R = 1/(0.90/3.80 + 0.10/0.30) = 1.75 K·m²/W.

So R 2.5 insulation with 1 % gaps will only add R - Rg = 2.58 - 0.30 = 2.28 to the total R value. (This is a reduction of 8.8 %.)

So R 3.5 insulation with 10 % gaps will only add R - Rg = 1.75 - 0.30 = 1.45 to the total R value. (This is a reduction of 58 %.)

Cellulose fibre is a loose fill insulation which means it leaves NO GAPS.

This 'parallel paths method' is valid for heat flow through the ceiling. Other methods may be required for heat flow along a surface such as a concrete slab. For more information see James M. Fricker [2] and H. A. Trethowen [3].

Cellulose - Naturally Better Insulation
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