Why Not Put Insulation Under The Roof

Senior engineer manager at icynene john broniek makes the case for the unvented attic assembly and why insulating the underside of the roof makes sense.

Why not put insulation under the roof.

This is bad for the environment and for your wallet as you end up spending a lot more on your electric bills. The material is compressible and is thus easy to fit and is less likely to cause cracks. If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value. For the same reason insulation shouldn t touch the roof s underside.

Remember to fit a damp proof membrane if you go with mineral wool. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow. Proper insulation can significantly reduce your energy consumption heat in the winter ac in the summer and reduce your energy costs by hundreds of dollars a year. The problem with the insulation against the sheathing expands.

A roof without good insulation is a great contributor to energy loss. Consider an extreme example in which all of the attic floor insulation is piled up on half the area giving very very high r value there but none elsewhere. The insulation boards are best fitted under the roof structure whilst the mineral wool can be inserted between the beams of the roof. Staple plastic or foam baffles to the roof sheathing near the eaves to keep the material away.

The moisture is held in place by the insulation which allows for damage to the framing and other building components. The percentage of your home s heat that is lost through the roof is on average around 40 percent. If the nasty old insulation was left on the floor of the attic the thermal envelope would be defined by that first layer of insulation so the roof deck insulation would be subject to much different temperature and humidity as allison stated in reason 1 above. This is an extremely large amount of heat that is exiting the building and leaving you and the other residents of the building feeling cold and vulnerable in the chillier months or climates.

Insulation should go up the side and over any tanks or special tank insulation can be used but you mustn t insulate under any tanks as without some heat flowing up from below these are also. This language is in both the residential and commercial codes. The problem arises with moisture.