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Adding insulation ontop of finished attic floor


Northern Mike's Avatar
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02-13-12, 06:52 AM   #1  
Adding insulation ontop of finished attic floor

After doing a bit of digging in my attic, I have found that there is ~10" of blow-in insulation under the floor boards in my attic. The attic is ~1350sqft, ~10ft high in the center. ~200sqft of the attic is comsumed by a fnished room, but otherwise, it's wide open. The blow-in was sprayed through small 1.5" holes that had been cut and plugged in the floor.
Because of the crazy amount of oil consumed per month to heat my house, I am looking at adding to the insulation (along with a major overhaul of the boiler).
Would building up another 8-10" of blow-in on top of the floor boards be the best direction? I don't exactly need the space in the attic as the house is pretty large (huge for a family of 4). There is approximately 2-4" of blow-in ontop of most of the attic floor boards. Only a small area has no blow-in ontop of the boards where the door to the attic is located.

Also, what should I do about the attic door? Its an old solid wood door (probably original from the 1930's).

 
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guyold's Avatar
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02-13-12, 08:32 AM   #2  
maybe make the door into a 4 hinge and the bottom swing short enough to step over.

 
Bud9051's Avatar
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02-13-12, 10:31 AM   #3  
Hi Mike,
10" of insulation is already a lot of r-value, so adding more will yield diminishing returns. Air seal from the basement if that is still accessible. Air sealing the ceiling under that attic floor should be done, but that is probably not the direction you are wanting to go. If the heating system is terrible, yes, but if you are still making improvements elsewhere, then hold off so the new one can be sized correctly. Don't let them just install the same size you have, require a heat loss calculation and stay on the small side as those calcs are often already oversized. Lots of reading here on sizing.

As for the door, that needs to be a sealed insulated door, something like an exterior one, or weatherstrip what you have and add a layer or two of Thermax foil faced rigid insulation.

As for getting those heating bills down, the starting place is determining where those dollars are going. There are heat loss calculators on line to pin that loss down to walls, windows, ceiling, basement foundation, or air leakage. Tell us what your heating system is and we can tell you if it belongs on that list.

Bud

 
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02-13-12, 10:57 AM   #4  
Bud,

The house is heated with an oil boiler (hot water). I know for fact that it needs some TLC as the previous owners (who appear to know little about the workings of the house) hired people to fix things for them and only did so if it broke. The boiler does produce a noticeable smoke (from the chimny) when it is running, so I am pretty sure it's not running at it's best. This is on my list to address, but shutting down a boiler (and draining all or most of the pipe work) during the winter and the random weather we have had may not be a great time.

The house itself is a 2 (or three if the room in the attic counts) story house, with a 10-12ft high attic. It was built in the 1930's and from what I can see, has seen a fair bit of renovations over the last 75 years. It is ~2900sqft (plus unfinished basement at ~1345sqft).
The windows, doors, and shingles are all less then 4yrs old.

The reason I am looking at the attic insulation is that I believe that the blow-in insulation under the floor boards in the attic is probably packed pretty tightly. They had used this same technique to insulate the room in the attic/3rd floor and when I pulled one of the plugs in the wall, I could see it was tight. My guess is they drilled the hole, stuck the hose in and ran the blower until it started meeting resistance.

The target areas I am looking at for heat loss / fuel consumption is the attic (blow-in is cheap and probably needed), the boiler (mainenance and adjustments definately overdue) and the unfinished basement (that is a lot of concrete walls not insulated).
I'll be cutting a couple of holes into the inside of the outter walls to run power and communication jacks soon, so I should know as soon as I do this what insulation is in the walls. They currently feel warm to the touch.

Here is a couple outside pics of the house from the summer.


In the pic below, you will see a window in the attic. The same window on the other side of the house is for the 12'x14' room.

 
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02-13-12, 01:50 PM   #5  
Tightly packed cellulose is what you want to reduce air leakage and insulate.

If you double what you currently have up there for insulation, figure about 5% of your total heating costs as savings. Insulate and air seal the basement rim joist foundation down to one foot below grade and add another 5% to 10%. If the boiler hasn't been serviced in a while, definitely have that done and they should give you an efficiency number when done. Look for 85%. The new high efficiency 90+% boilers are high maintenance and only yield those high efficiency numbers under certain conditions.

Bud

 
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02-28-12, 10:56 AM   #6  
Mike - I recently did this along the same lines. I first added AtticCat underneath my floor boards. I had some existing rock wool insulation already, but that was only about an inch or 2 thick. I then rolled down batts of R-30 unfaced insulation on the attic floor boards. I'm using part of my attic for storage, so I did not insulate the whole attic. But if you can get to R-60 in your attic, that should help big time.

 
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