Installing insulation in a new dwelling or adding insulation to an existing building can make a significant difference to the comfort and energy performance of a home, but it is vital that the insulation is installed correctly.
To install insulation without compromising its effectiveness, you need to consider a range of issues such as:

thermal bridging; […]

Roofs and ceilings:
Roofs and ceilings work in conjunction to one another when it comes to insulation:

Install insulation under the roofing material to reduce radiant heat gain.
Install insulation in the ceiling to reduce heat gain and loss. In most cases ceiling insulation is installed between the joists.

To reduce the risk of electrical short circuiting, […]

Insulation products come in two main categories — bulk and reflective — which are sometimes combined into a composite material.
To compare the insulating ability of a product, its Material R-value, which measures resistance to heat flow, must be considered. The higher the Material R-value, the higher the level of insulation. Products with the same Material R-value have the same insulating performance if installed as specified.
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Insulation is a general term used to describe products that reduce heat loss or gain by providing a barrier between areas that are significantly different in temperature. Insulation therefore reduces heat leakage in winter and protects your home from getting too warm in summer.
Insulation also acts as a sound barrier by reducing the level of sound transmitted from one room to another via partition walls or ceiling voids. […]