Attic Hatch Insulation?

I am thinking of gluing rigid foam polyisocyanurate insulation to the back of our upstairs attic hatch access panels. Any feedback or suggestions?

Bob K.

Polyisocyanurate insulation is eco friendly

First, let’s consider the environmental aspects of the material. Polyisocyanurate (called “polyiso”) is a rigid foam insulation panel that usually has at least one heat-reflective foil face. Although polyiso’s very name sounds as anti-environmental as “clear cutting,” and as toxic as “carcinogen,” it is in fact rather benign.

Virtually all polyiso foam has some recycled content, mostly discarded plastic bottles, and the recycled content of the aluminum foil facing varies between 80 and 100 percent. While the foam was once expanded by blowing ozone-depleting CFC’s through resin, it is now produced with zero-ozone-depleting blowing agents.

With higher R-values (insulating values) than any other readily-available insulation, polyiso’s superior insulating qualities far outweigh its environmental negatives. Both the Environmental Protection Agency and the U.S. Green Building Council, a non-profit industry group that promotes sustainable building practices, have recognized polyiso products as beneficial to the environment.

Polyisocyanurate insulation R value

A 1.5 inch thick polyiso panel is rated R-9 —that’s almost double the rating per inch of typical attic insulations. Ideally, your attic hatch insulation will match roughly the R-value of the rest of the attic insulation, so the “almost double” value provides a handy guide to the thickness of your polyisocyanurate insulation.

For example, if you have standard 6.5 inch-thick fiberglass insulation in your attic (R-19), you would want to install 3 inch-thick polyiso (+ /- R-18) on your attic hatch. Polyiso is available in half-inch-increment thicknesses, so for the example above you could either buy a three-inch thick panel or stack two layers of 1.5-inch thick foam, depending on the panel’s price and availability in your area.

Planning the Installation

Which brings me to polyisocyanurate insulation’s main drawbacks: price and flexibility. Typically available in 4×8 sheets, polyiso is at least twice as expensive as standard insulation, so you don’t want to use it for your (usually small) attic hatch and throw the rest of the sheet away. (That’s an environmental “no-no” anyway.) Try to find a use for the polyiso scraps, or perhaps go in on one sheet with a neighbor who also needs attic hatch insulation.

Polyiso is easy to cut with a hand saw (wear a dust mask), and because of its closed-cell foam structure, it will maintain its structural integrity in a seldom-used opening such as an attic hatch — that is, you shouldn’t have to put a wood frame around it to keep it from disintegrating at the edges. (Wrapping the edges with some reflective metallic tape might be a nice touch, however.)

The foils side should always face toward the living space. You can use contact cement to attach the panel to your hatch. (Be careful to keep the cement away from the polyiso core which might react with it.)

~PSW

Hi Philip,
Our home has a crawl space underneath it with deteriorating fiberglass insulation that needs to be replaced. Can we use a “green” insulation in the crawl space?
— Geoff & Barbara, Oakland, California

If your fiberglass insulation is deteriorating, make sure you have adequate crawlspace ventilation. Mold and bugs do not eat fiberglass, so the deterioration is likely caused by moisture accumulation that has collapsed the air spaces between the fibers — your insulation is probably getting wet. If that’s the case, your new insulation will soon deteriorate as well.

Building codes require that you have a certain number of square feet of ventilation for every square foot of crawlspace. Find out what the code ratio is for your area by calling your local building department.

Then measure your basement vents and compare them to the square footage of your crawl space. You should have at least as much ventilation as is required by code, and ideally more — especially if you live in a moist climate.

Cutting holes into an existing house to add ventilation can be expensive. One easy trick is to replace your crawlspace hatch door with a screened door. (Double screen layers work best —one based on _-inch wire mesh to keep animals out, and one regular window screen to keep bugs out .) Building and hanging a new hatch door is simple and cheap compared to cutting in vents, and a typical hatch door is as big as four to six typical foundation vents.

Also, it’s a good idea to place a heavy layer of black plastic on the floor of your crawlspace to reduce moisture and make it easier to crawl .

One “green” insulation that would work in a crawlspace is made from remnants of the blue jean manufacturing process — parts of the cloth that can’t be used to make clothes. Although the cotton from which the product is made is water-and-pesticide-intensive, the insulation itself is made from a “post-industrial” scrap that would wind up as landfill if it weren’t used as insulation. Also, it’s 100 percent nontoxic — you can put your toddler in a pair of blue jeans.

Blue jean insulation is available in batts, so it is appropriate for installation in crawl spaces. (Cellulose “powder” insulation won’t stay in place, and although foam insulation will stick to the subfloor and joists, it is very expensive.) To find out more, google “green insulation.”

Do you have a question about Your Ecological House? Send it to our editor .