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Adding Attic Insulation

I plan on increasing the amount of insulation in my attic (currently fiberglass bat) and have a question on approach.

The air handlers are in the attic (insulated ducting). The floor is completely cover with plywood (great for storage, not so great for adding insulation).

The easiest approach would be to put insulation in the rafters and create a warm attic. I can do this with propervent to maintain a cold roof. and isolate the soffit venting so it doesn't let air into the attic proper.

Is this resonable, or should I be looking at completely removing the plywood and creating a raised platform with insulation under it?



Re: Adding Attic Insulation

Tony ... welcome to the forum.

In my opinion your idea is good one and is along the current thinking of providing a "conditioned" space ... if you will ... for the air handler and wouldn't hurt for overall insulation value of the home.

The concept of "conditioned " space for the air handler is by insulating not only the underside of the roof but also all areas of the attic including the gable end walls.
What this does is help regulating the temperature in this area from heat buildup in the summer and very cold temperatures in the winter.

During the summer when the temperature is very hot the air handler during the A/C use is working harder trying to generate the cool air because it is inside a very hot environment .... and it will also create a chance of condensation.

In the winter the same situation will be present .... the heating system would normally be inside a very cold environment trying to generate the heat you require ... also creating a chance of condensation.

So by insulating the attic space will aid in reducing the heat gain / loss inside the attic which will also aid in increasing the performance of your HVAC equipment.

If you can lift up the plywood to add insulation to the ceiling below would also help increasing the comfort of the living space ...... since it is the thermo barrier between the attic and the living space.

Hope this makes sense and helps. :)

Re: Adding Attic Insulation

I would insulate under the floor, unless you plan to use the attic as actual living space. We do this in almost all the homes we encounter with this setup. I recommend dense packing cellulose under the floor. This will not only create the thermal boundry with a really good R value if you have 6" joists, but also a much more effective pressure boundry. If you have an older home, open interior wall cavities could be hidden under the floor, creating thermal bypasses to the attic. Dense packed cellulose under the floor will effectively seal any hidden bypasses. When we do blower door diagnostics, which we do on every job, I have gotten my best air infiltration reductions in these situations. My best was an 83% reduction in a home with a floored attic. Normal reductions for homes with open joist attics range more in the 30% to 40% area on average.

Re: Adding Attic Insulation

Thanks for the responses.


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