# Smashing down blow in insullation



## BackYardBuilt (Jan 12, 2012)

I have blow in insullation in my attic and I want to build a small room up there for storage. I am concerned though if I lay down floor boards over top of the blow in and nail it down that it will severly decrease the insulating capability of the blow in. Does anyone know if this is true? 

Should I just remove the blow in from where I want the room to be and lay down fiberglass batts under the new floor? Or will it make no difference?

Currently I have 21" of blow in up there.

Here are some pictures with illustrations of what i am tryign to do.


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## TarheelTerp (Jan 6, 2009)

Have a yard sale instead.


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## BackYardBuilt (Jan 12, 2012)

Tarheel are you a quitter? :laughing:


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## Windows on Wash (Aug 30, 2011)

I would suggest that you also look for some outdoor storage space (i.e. shed, etc) or try additional shelving. That looks like a bit of a pain in the rear of a project and for minimum yield on storage space.


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## joecaption (Nov 30, 2011)

Unless you have at a bare minimum of 2 x 8's for ceiling rafters with no more then 12' spans that ceiling was not built for any storage.
No the insulation can not be compressed, if you did it no longer would do anything. It needs the air spaces between the fibers.
I agree add a garage, Buy a shed.


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## BackYardBuilt (Jan 12, 2012)

The rafters are 2X8's and nothing that heavy is going up there. It is just christmas light boxes, a fake Christmass tree, some ornaments and baby stuff. We have one kid and more coming so we need a place to store this stuff while its not being used. 

Let me rephrase my "Small Room" comment to long hallway. This room would extent over 35' in length. Yes the room ceiling would be low but it would be very deep to allow storage for a ton of light weight stuff spreadout over a very long span. This is a very small house with no yard, no basement and no room for a garage. I have no choice. I cannot afford to rent a storage locker either. They are $100 a month around here minimum.

So since I cannot compress the blow in like I assumed, can I achieve a descent insullating results by removing the blow in where I am going to put down the floor boards and put in fiberglass batts?


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## titanoman (Nov 27, 2011)

BackYardBuilt said:


> The rafters are 2X8's and nothing that heavy is going up there. It is just christmas light boxes, a fake Christmass tree, some ornaments and baby stuff. We have one kid and more coming so we need a place to store this stuff while its not being used.
> 
> Let me rephrase my "Small Room" comment to long hallway. This room would extent over 35' in length. Yes the room ceiling would be low but it would be very deep to allow storage for a ton of light weight stuff spreadout over a very long span. This is a very small house with no yard, no basement and no room for a garage. I have no choice. I cannot afford to rent a storage locker either. They are $100 a month around here minimum.
> 
> So since I cannot compress the blow in like I assumed, can I achieve a descent insullating results by removing the blow in where I am going to put down the floor boards and put in fiberglass batts?


How far are the joists spanning? Makes a big difference if you're okay or not.
And don't compress the insulation.

Sent from a Samsung Galaxy SII


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## TarheelTerp (Jan 6, 2009)

BackYardBuilt said:


> Tarheel are you a quitter? :laughing:


Space for a few boxes of Christmas ornaments is one thing...
this ain't that.


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## BackYardBuilt (Jan 12, 2012)

The rafters are fine to hold this light weight stuff. I am a mechanical enigneer and trust me, I could put 300 LBS supported over just two of these rafters and it would be fine. The rafters in the attic are exactly the same dimensions that support the second floor. The vertical walls under these rafter run perpendicular under this proposed room which would also provide even more rigid support. I'm not worried about the structural integrity of this house not being able to support some toddler equipment and some x-mas stuff. All I am wondering about is the difference between the fiberglass batts and the undisturbed blow in. 

Thats all I am asking. I think I'll just call the manufacturer and ask them for thier R value of the blow in and compare it to the R value of fiberglass batts under the new floor I will nail down.

Thanks for the help fellas.


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## titanoman (Nov 27, 2011)

BackYardBuilt said:


> The rafters are fine to hold this light weight stuff. I am a mechanical enigneer and trust me, I could put 300 LBS supported over just two of these rafters and it would be fine. The rafters in the attic are exactly the same dimensions that support the second floor. The vertical walls under these rafter run perpendicular under this proposed room which would also provide even more rigid support. I'm not worried about the structural integrity of this house not being able to support some toddler equipment and some x-mas stuff. All I am wondering about is the difference between the fiberglass batts and the undisturbed blow in.
> 
> Thats all I am asking. I think I'll just call the manufacturer and ask them for thier R value of the blow in and compare it to the R value of fiberglass batts under the new floor I will nail down.
> 
> Thanks for the help fellas.


You're an engineer but you keep calling the joists rafters?
What if they span 30 feet?

Edit: Oh. I see they're trusses.


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## Gary in WA (Mar 11, 2009)

You will probably find the blow-in is the same R-value per inch as batts, or pretty close. That is only part of the problem. Adding a floor surface will stop any moisture drive (stack effect) to condense water on the bottom of the decking. This is the purpose of attic ventilation. I doubt the moisture will work horizontally to get to the ridge vents, to exhaust outside as planned. The amount of mold would depend on if a vapor barrier was present or not. Here are a few links on that; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

http://www.google.com/url?sa=t&sour...sg=AFQjCNHwd56o0AxLi8-V03E5cMUmwWATQw&cad=rja

http://www.wag-aic.org/1999/WAG_99_baker.pdf

Gary


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## BackYardBuilt (Jan 12, 2012)

titanoman said:


> You're an engineer but you keep calling the joists rafters?





titanoman said:


> What if they span 30 feet?
> Edit: Oh. I see they're trusses.



Titan, I apologize for not using the correct terminology for you to understand my fundamental question which I was seeking advice on. (Which was about insulation and not rafters or joists) I do get some of these defining terms mixed up because I don't use them on a regular basis like I am sure many of you all do. Usually in my field of work we use calculus, physics and statics engineering to determine stress loads, material dimensions, sheer stress minimums, compare graphs, calculate bending moments, moments of inertia and lots of other analysis to make sure that things are safe and run efficiently. Please accept my sincerest apologies for not communicating these terms more clearly.

I find it funny how you seem to question the legitimacy of my being an engineer due to the mis-identification of some simple wooden parts in my attic. I wasn't saying I am an engineer and you should STFU, I was simply saying I am a man who has education in this area to know the limitations of what I am attempting. I really just wanted to end the discussion about, "Is what I am doing safe" and get the real question answered about my insulation dilemma. The pictures I posted clearly illustrate my goal.


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## BackYardBuilt (Jan 12, 2012)

GBR in WA said:


> Adding a floor surface will stop any moisture drive (stack effect) to condense water on the bottom of the decking.


Gary, when you say decking, do you mean the bottom of the roof surface or the bottom of the actual floor boards I will be putting down?



GBR in WA said:


> This is the purpose of attic ventilation. I doubt the moisture will work horizontally to get to the ridge vents, to exhaust outside as planned. The amount of mold would depend on if a vapor barrier was present or not. Here are a few links on that;



Gary, those were some very technical and informative links. Thank you for posting that information.
This room is only going to end up being about maybe 5 ft wide by about 3.5 ft tall. There is at least 20 ft of open insulated attic on each side of the spot I will put this storage area. So what you are saying is that any moisture trying to come up through my second floor ceiling under this storage area could cause mold? Under the new floor I am putting down or on the ceiling itself?


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## Gary in WA (Mar 11, 2009)

Sorry, decking (a framers term) is the sub-flooring. You may get mold on the bottom surface because of the moisture diffusing through the insulation from the warm conditioned room below. This would be the first surface it contacts if colder than the rising air; fig.2; http://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion

Gary


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## BackYardBuilt (Jan 12, 2012)

GBR in WA said:


> Sorry, decking (a framers term) is the sub-flooring. You may get mold on the bottom surface because of the moisture diffusing through the insulation from the warm conditioned room below. This would be the first surface it contacts if colder than the rising air; fig.2; http://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion
> 
> Gary


So is there any way to combat this? 

What if I didn't put any insulation under this new decking in the attic but I fully insulated the outside of this storage room. Walls and ceiling. The soffit air would be able to carry away the moisture then because it would diffuse into the open attic air.


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## titanoman (Nov 27, 2011)

BackYardBuilt said:


> What if they span 30 feet?
> Edit: Oh. I see they're trusses.


Titan, I apologize for not using the correct terminology for you to understand my fundamental question which I was seeking advice on. (Which was about insulation and not rafters or joists) I do get some of these defining terms mixed up because I don't use them on a regular basis like I am sure many of you all do. Usually in my field of work we use calculus, physics and statics engineering to determine stress loads, material dimensions, sheer stress minimums, compare graphs, calculate bending moments, moments of inertia and lots of other analysis to make sure that things are safe and run efficiently. Please accept my sincerest apologies for not communicating these terms more clearly.

I find it funny how you seem to question the legitimacy of my being an engineer due to the mis-identification of some simple wooden parts in my attic. I wasn't saying I am an engineer and you should STFU, I was simply saying I am a man who has education in this area to know the limitations of what I am attempting. I really just wanted to end the discussion about, "Is what I am doing safe" and get the real question answered about my insulation dilemma. The pictures I posted clearly illustrate my goal.

[/QUOTE]

You said you are a mechanical engineer.
And there's no reason for such foul language.


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## Gary in WA (Mar 11, 2009)

If there was a second floor (in place of the attic storage floor), it would be heated and conditioned, air-changes, etc. to remove the moisture one gets in a story above. Your proposal isn't heated, or vented to remove any moisture. Not insulating underneath would cause a cold area that would wick the heat from the room below. 

The insulation would have to be kept back from the side walls (storage) enough to let it breathe, resulting in air movement (heat loss) and insulation loss= heat loss, you would be losing twice as fast or more, than just no insulation. Depending on the stillness of the attic air and currents there, not even mentioning the convective-looping possible. 

Storage in attics is a bad idea, enclosed (no HVAC) storage is also bad, in my opinion. I see why our trusses incorporate storage in design, only because people will store there anyway:http://www.tricountytruss.com/CodeChanges.aspx

Perhaps others can suggest ideas?

Gary


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## BackYardBuilt (Jan 12, 2012)

GBR in WA said:


> If there was a second floor (in place of the attic storage floor), it would be heated and conditioned, air-changes, etc. to remove the moisture one gets in a story above. Your proposal isn't heated, or vented to remove any moisture. Not insulating underneath would cause a cold area that would wick the heat from the room below.
> 
> The insulation would have to be kept back from the side walls (storage) enough to let it breathe, resulting in air movement (heat loss) and insulation loss= heat loss, you would be losing twice as fast or more, than just no insulation. Depending on the stillness of the attic air and currents there, not even mentioning the convective-looping possible.
> 
> ...


Gary, I was thinking about the physics of this last night and I had a feeling that the air temperature inside the room would be an issue like you said above. Basically, wherever the warm air meets cold air, ( Or vice versa in the summer time ) needs to be inside of an open air attic so that this newly formed moist air can travel up and out the top of the ridge vent. As long as the air passes through different floors that are pretty much the same temperature, you wont be getting moist air formation on the underside of the decking.

So I started to think of it like this. What if I made this room with no insulation under the floor but insulated the entire outside of the room and ducted HVAC air into the room to keep it at the same temp that the rest of the house is. 

There is a duct that I can see in cutout where all of the drain stacks, electrical, water supplies and the HVAC runs down to the furnace. I could tap into that duct and use it to heat the room.

There sure is a lot of work going into doing something like this right but I still am all for it if you guys think it will work.

Gary thanks for your patience and explanations. They are really making the understanding of all this easy.


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## Gary in WA (Mar 11, 2009)

Exactly, it needs to be conditioned, essentially a "new room". Only problem (major) is that these are trusses, not joists. So, no-can-do..... Even with a "room" not touching the trusses, with its own floor system, it has to meet minimum building Code for attic storage (headroom, egress, etc.): http://docs.google.com/viewer?a=v&q=cache:EJENK_uA9RQJ:www.cr-ar.com/pdfs/Building%2520Code%2520Changes.pdf+R602.3(1)+2006&hl=en&gl=us&pid=bl&srcid=ADGEESh311Kosslp7jsjp9WhUXxZsgSiyNaWb-eW0YminVwmPUavLlW75BKLoV9em4LFCAydmTGQlkUFOPm8AqHkRP5wLQGQQGkwyzAGtlN4D2DqCiCLwprOpEbvvjeGk6CEhyHiVdtK&sig=AHIEtbRa4Ah_IICPQ3BR1txlzU01V4JQIg

I'd try another idea. Backyard sheds, etc.
Sorry we couldn't help more...

Gary


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## BackYardBuilt (Jan 12, 2012)

GBR in WA said:


> Exactly, it needs to be conditioned, essentially a "new room". Only problem (major) is that these are trusses, not joists. So, no-can-do..... Even with a "room" not touching the trusses, with its own floor system, it has to meet minimum building Code for attic storage (headroom, egress, etc.): http://docs.google.com/viewer?a=v&q=cache:EJENK_uA9RQJ:www.cr-ar.com/pdfs/Building%2520Code%2520Changes.pdf+R602.3(1)+2006&hl=en&gl=us&pid=bl&srcid=ADGEESh311Kosslp7jsjp9WhUXxZsgSiyNaWb-eW0YminVwmPUavLlW75BKLoV9em4LFCAydmTGQlkUFOPm8AqHkRP5wLQGQQGkwyzAGtlN4D2DqCiCLwprOpEbvvjeGk6CEhyHiVdtK&sig=AHIEtbRa4Ah_IICPQ3BR1txlzU01V4JQIg
> 
> I'd try another idea. Backyard sheds, etc.
> Sorry we couldn't help more...
> ...


Well it looks like this stuff will maybe have to go to a friends house! LOL It won't be long before my wife and I can move out of here anyway. We have absolutley no room in this house or a yard! We moved in here while I was finishing up college because it was CHEAP!!! After I got a job we just stayed because it was so close and convinient to my employer plus the payments were great too. 

Plan is to pay down my student loan debt so we can have 20% to put down on a house in the suburbs. 

Thanks for trying to help me out. :thumbup:


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## danpik (Sep 11, 2011)

I think you are overthinking this whole project. why do you want to build a room up there? Millions of homes in this country alone have attic storage on simple floors. 

Now to give my opinion on your original question. The insulation as it is, is needed to keep the heat in your home. Removing it or compacting it will lessen the effectiveness of it. a simple solution would be this. Add some 2 x 10 floor joists over the current 2 x 8's you say are up there. But, instead of going right over the tops of the existing I would run them perpendicular 16" on center. This will then allow you to put down a plywood floor over the insulation. Depending on the size of the attic opening you may need to cut these down in size which will allow them to fit. Also leave a small (~1/4") gap between the sheets to allow for air movement. To prevent the vapor issue that was mentioned in an earlier post, ensure that the plywood has a ~1" air gap between it and the insulation. This will allow the plywood to breath and prevent the formation of condensation. Once the plywood is doen then load it up to your hearts content. Of cours this is providing that you did all of the load calculations needed to ensure the existing structure can handle the additional load


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