Insulation of attic floor AND roof

Is there a reason to install insulation in an unconditioned attic on the floor of the attic, and also the roof (against the sheathing)? The home is in the middle of a major remodel/addition. Baffles are properly installed against the sheathing for air flow, but I don’t see the point or benefit of insulating the sheathing as well as the attic floor.

I just hate to see the guy waste time and money for something that is of no benefit, but I don’t know enough about it to tell him whether it’s unnecessary, or a good thing, or a defect.

You can fully encapsulate the attic , seems to be a newer concept But you have yo make sure its 100% encapsulated. Using batt insulation? Never work with that concept. Usually done with spray foam
Usually see people insulate everything in knee wall attics - wrong. Either treat it as conditioned or cold.
Cold- insulate interior floor joist aka attic floor And interior knee wall
Conditioned - insulate roof rafter bays with air gap above insulation

Waste of money and insulation to do it that way

Thanks Chris. I’ve seen the poly on the sheathing, but not batt, and that’s what he’s using. My understanding was it should be spray foam or poly panels. At least he’s installing the baffles. I just think he’s wasting money on insulation that could go toward his remodel, but it’s not my business what he wants to spend money on. I would think just putting 6 or 8 inch batt on the attic floor would be sufficient, and didn’t see a reason to encapsulate unless he’s gonna finish it for living space (it’s too low to do that BTW)

He’s better off putting all the insulation in one location to increase the overall R-value. If he’s doing it because he’s finishing for living space, he’s screwing up the building’s envelope.

Are they installing HVAC equipment in the attic? That may be the reason.

yes, it is part of the remodel. It wasn’t hooked up yet.

So is the attic really unconditioned space??

The reason for the insulation in the rafters is to improve the efficiency of the HVAC, the reason for it in the floor may be to help keep the conditioned air on the second floor and not allow it in the attic.

Usually in this kind of set up the attic becomes part of the thermal boundary of the home and is considered conditioned space.

I suppose they are in the process of “making” it a conditioned space, then. I didn’t even think about that furnace being installed in the attic as a reason to insulate. Since the ductwork isn’t complete, I don’t know if there will be duct openings in the attic space or not.

There is no second floor, only the attic space. It’s a large addition under construction, and I noticed the lack of vents from the outside (only soffitt and ridge). Perhaps that is the reason they aren’t putting gable vents in, since they are conditioning the attic?

Thanks Peter, I’m continuing to learn, even at my age! :smiley:

In my area running a HVAC unit in an uninsulated attic will cause severe ice dams.
Even if they aren’t planning on heating that space it will help with the overall efficiency of the unit, whether heating or cooling.

Check out this web site, good library of info here.

definitely makes sense, Peter! Thank you.

No reason that I can think of, I would say your Client is wasting his money.

Depending on what the room is below the HVAC unit, the insulation could be as simple as for sound deadening.

Larry, the future utility room is directly under the HVAC unit. The only thing that makes sense to me is what Peter said-that maybe the thing could cause ice dams, or operate more efficient, with the attic encapsulated in insulation.

My first inclination was to tell the dude he’s wasting his money on installing the baffles and batt insulation against the sheathing, just stack it on top of the existing insulation on the attic floor, doubling the insulation thickness.

I’m glad I posted here before finishing up the report. I am gaining some insight as to why he’s doing it that way.

Thanks for responding, guys! Each one of you ROCKS!!!

Intent of the attic space would play into it as well I would think.

If the owners intend to store items left by Grandma, and dads old baseball card collection up there, they may be under the impression adding insulation makes it a better storage space.

What do you mean saying “only soffit and ridge”? That’s all that is needed, and generally the preferred way to vent the attic space.

Studies show adding gables, when ridge vents are installed, can be counter productive; causing more harm than good.

Also with soffit and ridge vents the attic will Not be a conditioned space.


You can’t have both an encapsulated conditioned attic and a vented attic in the same space.

In other words, if the attic is vented, insulation between the rafters is there for looks only and IMO serves no purpose.

Also IMO a well vented attic (soffit & ridge vent) along with a well insulated home is the best defense against ice damming.

It was cross gabled, and the addition to the original bungalow was larger than the original house. It seemed like a lot of roof with only the vented soffit. They didn’t have ridge vent on the new addition.

When I got inside, in the attic, is when I saw that they were encapsulating the new addition. If not, I would have suggested the gable vents, or adding ridge vent to the addition. That’s why I posed the question, why would someone install insulation on the sheathing. It would have been best to just put that insulation on the attic floor, IMO.

But being as the HVAC system is being installed in the attic, it made sense that the equipment might heat up the attic and create ice dams in the winter. The owner wasn’t there to ask, only his wife.

It wasn’t a normal buyer’s inspection. The home owners needed it at their bank’s request for a home equity loan, and I knew it was in the middle of a remodel. I was actually there to verify some foundation issues observed by the appraiser. I was just curious about the insulation.

So, if they encapsulate and heat and cool that attic, doesn’t that make the attic a conditioned space?

I wish I had pics, but I wasn’t there for that. I should have took some anyway.

Were the soffit vents installed to vent the space between the insulation and roof sheathing?

yes, with baffles all the way to the ridge, to create the 2" air space between sheathing and insulation. Problem is, there is no ridge vent, so I don’t understand where the drawn in soffit vent air is exiting? I’m probably giving it too much thought, since I wasnt’ there to inspect what the heck the guy was doing anyway. I was just gonna give him some friendly advice since he hasn’t finished yet.