Attic Insulation


Old 09-27-02, 01:47 PM
Visiting Guest
Posts: n/a
Attic Insulation

Hello: I have an attic with no insulation between outside wall studs or roof studs. There is a roof vent and vents at each end with automatic fan. The floor has insulation between floor studs covered over with half inch plywood for storage. It is not heated except for what comes up naturally from house; it gets cold but does not freeze. I have a number of rolls of insulation, probably fibergass pink wool, without vapor barrier, that I would like to use in appropriate way. Would it be advisable to put this between the wall studs or would a vapor barrier be best for that? Also moisture condenses on the protruding roofing nails in the winter at times. Does this mean I should not put insulation there so it would be ventilated? And if I were to put insulation between roof studs would it be vapor barrier or not? Thanks for your help.
Sponsored Links
Old 09-27-02, 08:56 PM
Join Date: Nov 2001
Location: USA
Posts: 1,873
The condensation on the protruding roofing nails is caused by humidity in heat. What you first must determine is what is causing it. Heat condenses on usually the coolest surface in the attic, which are your roofing nails. There are 2 probable causes, one is inadquate free venting and the other is the attic by-pass phenomena.

The rule with free venting is 1 : 150 without a vapor barrier and 1 : 300 with a vapor barrier. Assuming your insulation has a vapor barrier and your attic floor area is 900 sq. ft., the rule 1 : 300 applies and you would require 3 sq. ft. of free venting. 50% (1.5 sq. ft.) would be high vents, such as gable and/or ridge and 50% low vents, such as eave or soffit vents. These vents should not be obstructed, especially the lower vents because insulation is sometimes improperly installed.

Free venting assumes the normal amount of heat with a low percentage of humidity transmitting through the structure into the attic. Attic by-pass means that heat with a much higher percentage of humidity by-passes the thermal boundary of the structure and enters into the attic. Examples of this is an uninsulated attic entrance, bathroom exhaust into attic, recess lighting, openings around chimney chases and plumbing stacks. There are other causes for the condensation on roofing nails, these are the most common.

Adding the insulation that does not have a vapor barrier you have on top of the existing insulation on the floor, is fine because your thermal boundary is the attic floor. A thermal boundary is defined as the area the separates a conditioned (heated and/or cooled) space from an unconditioned space. The temperature in your attic in the winter should be cold to avoid moisture problems and ice damming.
Old 09-29-02, 06:46 PM
Visiting Guest
Posts: n/a
I guess I thought I could use the insulation against the walls of attic to use it and get it out of the way without hurting anything. I am in Philadelphia area and the attic never gets down to freezing, but i do store lots of things there and thought maybe the wall insulation would make it a bit less cold in case I want to work up there in winter. Main object though was just to do something with the 10-12 rolls of insulation. Dont really need to have it warmer.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes