General insulation questions


Old 08-04-02, 10:41 AM
Thread Starter
Join Date: Mar 2002
Location: USA
Posts: 148
Received 0 Votes on 0 Posts
Question General insulation questions

I live in a ~1800 sq ft house in the Dallas, Texas area. As you image, it gets quite hot here in the summer, but does also get below freezing in the winter.

The house was built in 1981. There's about 3 inches of blown insulation in the attic. I believe that this is cellulose insulation. It does not appear that there is a vapor barrier in the attic. There are no soffit vents on the house.

I realize that 3 inches of insulation is not all that great, and I can really feel the difference between different areas of the house that have different depths of insulation.

I am planning on adding more blown insulation to the attic and cutting soffit vents. The house has 2 gable vents and 2 of those spinning thingie vents on the roof.


1) Should there be a vapor barrier in there? Above or below the insulation? If I need one, what do I do about the insulation already up there?

2) What's the "recommended" R-value? I believe R-30 was suggested by some java applet I used. Is there a resource that can compare additional savings for each additional unit of insulation?

3) Soffit vents: a good idea?

Here in Dallas in August, it gets quite hot in the attic and I do see signs of deterioration in the rafters. I'm under the impression that adding more insulation and cutting soffit vents will help the health of the attic, lower my energy bills, and help keep the house at a comfortable temp. And feedback, ideas, generalities, resources, etc. that can help me make wise decisions is appreciated.

Sponsored Links
Old 08-04-02, 12:06 PM
Banned. Rule And/Or Policy Violation
Join Date: Nov 2001
Location: USA
Posts: 1,875
Received 0 Votes on 0 Posts
You can go to and read topic " Insulation Guidelines." It also discusses radiant barriers and at the bottom, radiant heat control with roofing materials. All this is written by Oak Ridge National Laboratory and was done primarily because of what is known as the "Sick Building Syndrome" (SBS).

Today we are introducing methods and products to structures that were never done before. Manufacturers test their products and applications under highly controlled conditions. The problem here is when that product or method of installation interacts with other products and/or methods of application, within the same structure. In some cases, it has resulted in structual damage and/or Indoor Air Quality (IAQ) concerns. When we consider the number of components in a structure, the number of methods of application, the climate for your area and the occupants themselves, all this must work together to assure the integrity of the structure.

What Oak Ridge has attempted to do here is set standards that reduces the risks to SBS. Though there are many who may argue that their application is different than Oak Ridge testing, Oak Ridge used the prevailing method of application. The fact sheets and handbooks on this site should answer most of your questions.

If you would like more information, at the bottom of this message is a www icon and click on that it will bring you to my site. You should read topics, "Insulation, Ventilation, Air Boundary and Thermal Boundary."
Old 08-04-02, 12:33 PM
Visiting Guest
Posts: n/a

Radiant barriers would be ideal here because you do not have to fight alot of insulation to install.

There are two differnt methods to install depending on whether you have a rafter/joist or trusses.

In any case you want to install directly over the existing material NOT TO THE BOTTOM OF THE rafters or upper cord. The tests you will read about on the web wrere all rafter installations and that is not the best way even though they got VERY GOOD results.

It is not recommended to install soffit vents only. This will cause air to flow over the insulation. I have seen ceilings blown clear of insulation for up to 3' from soffit air flow. While you're doing all this go with a ridge vent system this allows the soffit vent to help vent the entire attic with air flow under the sheathing wrere it should be. Check;

I have about 30 years of doing these types of installations. If you want more detailed info, let me know. It's easy and the results are immediate.

Thank you for considering my opinion.
Old 08-05-02, 06:24 AM
54regcab's Avatar
Join Date: Jul 2002
Location: Oklahoma City
Posts: 661
Received 0 Votes on 0 Posts
Lightbulb 2 turbines

It seems EVERYBODY uses TWO turbines regardless of how big the house is.

You should have 3 up there to do the job right, one per 500 sq ft.

Also you need AT LEAST 120 sq in of soffit vents per turbine (200 would be better) for them to work properly.

Without proper intake these (or any other vent) is useless !!
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
Ask a Question
Question Title:
Your question will be posted in: