Attic w/Furnace - Insulation

Old 09-23-13, 04:19 PM
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Attic w/Furnace - Insulation

I have a question regarding my house in Michigan.

It is a craftsman style 2 story/ 2-family house, around 100 years old. The 2nd floor/unit has an 80% furnace in the attic for heating.

The attic is not vented or sealed and has about 3 inches of insulation on the floor. I would like to add more insulation in the attic to reduce heating costs and prevent the very large icicles i have in the winter. I'm not sure exactly how about I should go about doing it and it seems people have different opinions.

Should I add insulation on the floor or the ceiling? And should I seal the attic or add ventilation?

Thanks! Help is much appreciated.
Old 09-29-13, 09:06 AM
Join Date: Feb 2008
Location: Lake Wales, FL
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Keeping heat and water vapor in the home, keeping it out of the attic.

You want to keep your home warm, then adding the

right insulation on to the top of the ceiling is

the second best way (and most popular).

The most effective way to insulate, is to fix

sheets of polystyrene across the ceilings just

below the joists and to cover these with


Adding insulation between the joists is second

best because the heat from the room slips past

the insulation, moving through the joists, wood

is not a good insulation and as there is a lot

of it in a typical ceiling lots of heat escapes

this way.

The icicles are the result of water vapor that

is produced in the home by cooking and washing,

finding its way into the attic. The molecules of

water vapor are so small that they can slip

through most things including your ceilings and


There are three ways to stop water vapor

entering the attic, paint the ceilings with

gloss paint, seal the ceilings by fixing a water

vapor proof plastic sheet across the bottom of

the joists, or fix sheets of polystyrene below

the joists, these act to insulate and to stop

the water vapor entering the attic.

Unless you are going to live in the attic, there

is no point is spending lots of money insulating

the roof.

Likewise, once you have stopped the heat from

your home and the water vapor from entering the

attic there is no need to ventilate.

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