Basements, Attics and Crawl Spaces - Attic insulation

Ok. Here's the problem.

Second floor. There are attic spaces on the front and back of the house. The walls of the second floor rooms are accessible in the attic spaces. These walls now have 3-1/2 inches of insulation. I want to add unfaced R30 bats to the wall. How do I attach the bats to the wall. Is there a normal method or do I create some sort of strapping to hold the bats in place. I would prefer to run the bats horizontal. The current 3-1/2 bats are vertical. I could run cardboard on every other stud and staple through that but it would compress the bats and reduce the insulation at that point.

I did think of hiring a couple of dozen bathing babes to hold the insulation in place but what a waste.

Thanks for the help.

Sounds like you are describing a side attic and want to insulate the kneewalls. First of all the batts must go vertical and not horizontal. For any insulation to work it must fully touch the surface that its insulating which means no gaps. If you put them on horizontally cause stapling them will be easier then you will have gaps where the batts arent touching the stud bay Total waste of time and money.
put them up the correct way and cover the entire back of the wall with either 1 or 2 inch pink foamboard nailed or housewrap. Tape and seal all seams. Make sure the joist spaces where the wall meets the floor arent open. If they are then cut and fit 2 inch foamboard into each space and seal with sprayfoam. If the floor of the attic is over living space it should be insulated as well just like a normal attic.
Of course this is the way to do it if you are not using the attic spaces for storage. If you are then you have to insulate the slope
Go to this link to read more on how its done so you dont waste money or your time.
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I might add: putting up r30 batts here is a waste and ineffective especially if the batts arent covered like i mentioned and protected from cold air. Cold air circulating thru fiberglass batts will lower the effective R value (wind wash) This is why its better to fit the proper size batt into the space and just cover it with the foamboard. A 3 1/2 inch batt covered with 2 inch R10 foamboard taped and sealed will give you a good solid R23 wall here as opposed to an R30 one that will be effectively much lower if exposed to cold air. worse yet R30 batts stapled horizontally with gaps behind them on the stud bays is about as good as having no insulation at all there.

Hi sunblock and welcome to the forum. Adding very thick layers as you have suggested is not a common practice, although I think we will have to figure it out soon. I'm assuming you are dealing with the typical attic spaces created in a cape style home. If that is the case, then you have two options. Insulate the wall and floor space and leave the remaining void cold as part of a typical vented attic space. Or use rigid insulation over the rafters (vented above) and allow the attic space to be heated and become part of the conditioned living space. The rules for insulation, vapor barriers, and air sealing have to be followed in both cases. Here is a link to describe some of the thinking.

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If you stay with what you have described, simply create a second wall about 10" behind the existing one, vertical straps from each rafter to a cleat on the floor. Then stack the new insulation from the floor up to fill the space. This avoids attaching it to the existing wall as it simply is filled in tight behind it. Adjust the depth of the wall to match the insulation you are using, either on edge or cut in half and laying flat. If you wish to protect the exposed fiberglass, use a ½" or 1" layer of EPS (no foil) as a wall surface.

See what you think,
Bud

Gentlemen. Thank you for the responses. I do appreciate the effort.

Mr. Bud9051 I think you certainly grasp my situation. An amplification. The attic is insulated with 3-1/2 inch bats in the floors and covered with 3/4 inch plywood so it can be used for storage purposes. The room walls are insulated with 3-1/2 inch bats and then there is a slope inwards (the rooms have vertical walls up to about 6 feet and then slope up about 4 or 5 feet and then a flat ceiling) with 3-1/2 inch bats up the slope and above the ceiling. The entire attic spaces are open via large vents at the front and ends.

Most articles concerning ADDING attic insulation state to use unfaced insulation running at right angles to existing insulation (unless it's blown in). The additional insulation added to the existing insulation will give the total insulation (probably a bit less because of settling of the original insulation).

We don't use the attic spaces so I decided to add insulation. The plywood flooring runs right to the bottom of the downward slope so there is no problem with blocking airflow (also, since the attic is fairly open to ventilation). It's easy to do the floor with R30 unfaced bats, just roll them out and cut to fit and make them tight to each other. Done deal. I just thought I would see if I can do the walls with the R30 bats while I was at it. It's an interesting engineering problem. How to attach R30 unfaced bats to the surface of a standard stud wall with 3-1/2 faced bats already installed in such a way that they will not significantly sag and comfortably hold in place to the wall. Adding insulation to an already insulated space that has faced bats requires unfaced bats, otherwise a moisture problem will be created. I am totally unconcerned about air flow. There are millions of homes with blown in insulation in vented attic spaces. It is a common accepted practice and unfaced bats and blown insulation have essentially the same properties for insulation.

Actually I thought of using chicken wire and running wire from the studs (with wall board screws) out to the chicken wire to hold it in place. That way the bats would stay tight all around and the weight would be controlled at each level. I see no reason the recommended method of running additional insulation at right angles to the existing insulation can't be done on the walls. That would hold everything in place nicely. I just thought that there might be a common normal way that this is done by contractors. Is it possible that millions of homes can never have their vertical attic walls insulation increased because the contractors have never done it before.

A second wall using chicken wire doesn't look all that bad (although I still like the bathing babes). I don't want to use anything that will create a moisture problem.

I think I better buy some of those knee protectors for crawling around.

Thank you very much for the information.