Recommendations on increasing insulation value?

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  #1  
Old 12-15-09, 12:32 PM
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Question Recommendations on increasing insulation value?

I'm new here. My wife and I purchased an early 1900's Four-Square in the suburbs of Boston. The house has a hipped roof with a 4ft ridge and no soffit vents. The attic is not finshed and roof deck interior is not insulated. The attic floor is insulated with (I think) rock wool all the way out the soffits. The floor depth is 6 inches. The attic floor is covered in 1x6 boards (nailed) and we need the space for storage.
From the insulation calculators I've got between an R-20 to R-25 from the existing insulation. I'm trying to figure out a way to increase the amount of insulation while still allowing the storage space and access to the ceiling below. I had two thoughts:
1) Put a layer of foam board over the existing 1x6 boards and some plywood or osb on top of that. If a 2" board is an R-10 then my total insulation for the floor will be between R-30 and R-35. 4 inches of foam board would be R-40 to R-45.
2) Pay someone to come in a sprayfoam the underside of the roof deck including the soffit area.
Option #1 is cheaper but, I'm worried about moisture buildup underneath the foam sheeting.
Option #2 is more expensive but, I won't lose any height in the attic.
Can anyone provide any other options or recommendations?

Thanks,
Brian
 
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  #2  
Old 12-16-09, 10:18 AM
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Insulation

A labor intensive solution would be to remove the 1x6 attic floor. Then add a 2x4 on edge to the top edge of the joists to increase the depth.
Add more insulation.
Re-install the attic floor boards.
 
  #3  
Old 12-16-09, 10:41 AM
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Those attic floor boards present two problems. One, they limit the depth of the insulation below. Two, they hide potential problem air leaks which transport moisture into the attic. If there were no air leaks and a good vapor barrier on the ceiling below, you could place some rigid foam board over the top with another layer of osb and not have a problem. But there are most likely leaks and the existence of a vb may be unknown, so Wirepuller's suggestion of removing the boards begins to sound better and better.

Once removed, you could locate and seal the tops of all walls below, electrical, plumbing, and other leaks, and then add or replace the insulation as you choose. You could even stand 2x6's on edge. The point is, it will be done right, you will enjoy the comfort, and others who purchase your home in the future will gladly pay a bit more for a job well done.

As for spraying foam on the bottom of the roof deck, I try to recommend that only when other options do not exist.

Bud
 
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Old 12-20-09, 10:27 AM
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Bud, Wire,

Thanks for the suggestion. I was hoping pulling up the existing floorbaords wouldn't be an option. However, I would rather do it right once than do it wrong twice

The ceilings below are plaster & lathe so I doubt there is any kind of vapor barrier. And I think it would be cost prohibitive to drop all of the ceilings to put a vapor barrier in. I also would be concerned about removing all of the rock wool and placing a vapor barrier on top of all of the existing utilities (electrical, etc.) since it might disturb something.

How would I stand a 2x4/6 on edge and fasten it down? I could glue and toenail it in but, would it be strong enough? Are there joist hangers or braces (found at a home center) for this kind of application?

Also, what kind of insulation can I put on top of rock wool? Batt, blown fiberglass, blown cellulose?

Thanks.
 
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Old 12-20-09, 10:56 AM
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I think toe screwing would be a good way to go. This way you don't risk knocking any plaster loose when you hammer all those nails in. Screw them into the rafters at the ends as well.
 
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Old 12-20-09, 07:34 PM
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Check to see where your interior walls are below. Seal all holes through their top plates with canned foam. Toe-nail or screw upright 4x4 chunks 12' (or as required for attic R-value) high on end on the walls to put your platform on. Insulate as required for your area.
The rock wool may be R-13-17 only. Insulation Comparison Chart
Span the 4x4's with 2x6 or strong enough wood and build between with smaller wood. Find your wall/platform span and we will help you. Add plywood or 1x4 spaced wood on deck for ventilation around rubbermaid containers. (May need diagonal bracing on 4x4's)
Add intake soffit vents and ridge turtleback exhaust vents for proper attic ventilation: http://www.fureyco.com/content/image...ng_The_Air.pdf When removing the attic flooring, use a circular saw to cut both sides along ceiling joists. Leave the nails in the 1-1/2" wide boards alone. Done!
And no plaster pops with the free firewood, already cut to 14-1/2 or 22-1/2" long without nails!
Be safe, Gary
 
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Old 12-23-09, 07:48 PM
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GBR,

I re-read your post several times and there is some parts I don't understand. I must be thick :

1) why use the 4x4's? Are adding say a 2x6 along the existing joists not going to be strong enough?

2)
Add plywood or 1x4 spaced wood on deck for ventilation around rubbermaid containers.
Does this mean leave 1 inch between any ply/osb sheets? rubbermaid containers?

3) Since the ridge is only 4 ft long, I don't think there would be enough venting done by a ridge vent. The space is about 25ft x 25ft.

I like the idea of cutting along the joists!

Thanks for clarifying,
Brian
 
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Old 12-24-09, 05:46 PM
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The 4x4's, 12" not feet, lol, are tall enough to istall your required attic insulation R-value under the raised platform. The 4x4's hold it up, like a dock over a pond. You span from 4x to 4x which are on the walls top plates, not worrying of extra loading on the ceiling joists OR the thermal break you now have by not stacking directly on top. 2x6 R-value:ColoradoENERGY.org - R-Value Table
I meant use 1x4's for the floor, to let any moisture from below to rise with the air, exiting out the top vents, not collecting on the underside of the plywood (a vapor retarder). 25 x 25 = 625sq.ft. / 150 = 4.17 / 2 = 2.09 x 144 = 301 sq.inches of soffit. Same of ridge vents. It depends on what type of soffit vent you decide to use to get the spacing required for the inches per foot. At the ridge, you would need to divide the NFVA of that particular vent against the 301, to find how many you need.

Be safe, Gary
 
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Old 12-28-09, 07:07 AM
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Thanks GBR it makes more sense now.

I was thinking, is there any reason I can't do the following:

Use 2x6's and place them perpendicular to the existing joists? I could space them futher apart (24" OC opposed to the existing 16" OC) which would mean less load on the existing. Also, I could use batt insulation (over the rock wool) which would be quicker to install.

-Brian
 
  #10  
Old 12-28-09, 02:42 PM
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Yes, you could. You would not create a thermal break at the 1-1/2" of wood to wood, perpendicular. But that wouldn't account for much. You would still be putting the new joist and materials load on the old ceiling joists, which are rated for the span without the additional weight.
The rock wool should be flush or just above the tops of the joists or the R-value will decrease with any air gaps. If you go cellulose, watch the joist on center layout for the added weight: Residential ENERGYSmart Library

Welcome To Home Energy Magazine Online

I found this interesting: Cellulose vs. Fiberglass attic insulation: Which is better?

Find your R-value requirements: Insulation Fact Sheet

General venting and your attic access: http://www.nrel.gov/docs/fy00osti/26450.pdf
Be safe, Gary
 
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Old 04-12-10, 07:20 AM
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Unhappy

Originally Posted by GBR in WA View Post
Yes, you could. You would not create a thermal break at the 1-1/2" of wood to wood, perpendicular. But that wouldn't account for much. You would still be putting the new joist and materials load on the old ceiling joists, which are rated for the span without the additional weight.
The rock wool should be flush or just above the tops of the joists or the R-value will decrease with any air gaps. If you go cellulose, watch the joist on center layout for the added weight: Residential ENERGYSmart Library

Welcome To Home Energy Magazine Online

I found this interesting: Cellulose vs. Fiberglass attic insulation: Which is better?

Find your R-value requirements: Insulation Fact Sheet

General venting and your attic access: http://www.nrel.gov/docs/fy00osti/26450.pdf
Be safe, Gary
So I need to reconsider the "perpendicular framing" idea? I don't want to add the extra load on the existing joists (thnx Gary) However, I don't know how I'm going to support the platform (attic floor) at the edges. My house is layout is similar to this: Aladdin Pre-Cut Homes from Aladdin - The Hudson
and the roof is hipped. The top plate of the exterior walls are at the far ends of the roofline. With the roof pitch angle I can't see putting 4x4s taller than the existing roof sheeting. And the bedrooms below the attic don't have any other structures to base the 4x4s on.

So confused.
 
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