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FAQ: Insulation

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What should I do about condensation dripping in my living room?
L.B. writes:
Your paper on the insulation of cathedral ceilings in the November 1995 issue of Fine Homebuilding was extremely informative. Our home is a shed type contruction, about 50' x 50', U-shaped, with the tall end 25' high and sloping to the low end (8' high). An atrium stands between two wings, which project back from the massive, open living room which is positioned all the way across the high end of the house. The ceiling is tongue and groove cedar above which are 6" of fiberglass insulation and 3.5" of air space beneith the roof boards to which are nailed the asphalt shingles. Ventilation is provided by 2.5"-diameter circular vents between each pair of rafters across the tall end and across the ends of the two wings at the low end. Ventilation is hindered by an 8' fireplace chimney in the living room, and due to the absence of vents across the 20' atrium header. The house was constructed in 1970 and no vapor barrier was used in the ceiling.

THE PROBLEM: During January of each year, moisture-laden, warm air seeps through the less-than-tight grooves of the ceiling boards and the moisture freezes on the underside of the roof boards. Then the first day that the temperature rises above freezing, the ice melts and we have dripping in numerous locations throughout the living room.

RECOMMENDED SOLUTION: One reliable local contractor has recommended the following as the least invasive and least messy solution: 1. Inside, renail ceiling boards where necessary to eliminate board separation and cracks.

2. From outside, remove old shingles, roof boards, and old insulation.

3. Then fill each rafter cavity with polyurethane, i.e., about 9.5". This would give the needed vapor barrier and greatly inprove the level of insulation. (See paper on insulation by Alex Wilson, March 1996 issue of Fine Homebuilding.)

4. Install roof boards and new asphalt shingles.

QUESTION:
1. How necessary is it to have air space between the top of the polyurethane and the bottom of the roof boards? Could heat buildup or heat dissemination problems develop?

The contractor said that during the past 10 years, they have insulated 6 homes as I have described above---with no air space.. They either used this procedure during new construction or during remodeling to solve a "dripping" problem. The contractor used this method of insulation when he built his own home 6 years ago.

Another reason for not having air-space ventilation in our house is the difficulty of developing a complete ventilation network. The house has no overhangs anyplace, and the vent system is only partial at best at the present time (chimney and lack of vents for straight-through air flow). Also, expecting efficient airflow from the low to high end of each rafter channel, a run of at least 50', through such small openings (2.5") is probably not realistic.

I know that polyurethane is expensive, and we are retired so do have financial limitations. We can handle what is being proposed.

Paul Fisette answers:
I believe that I have a pretty good picture of your home, but it is difficult to express a design using words. However, I do think that our plan sounds very solid. Adding the 9 inches of urethane should provide you with a continuous air barrier and a high-level R-value in the neighborhood of R 55! you also will create an vapor barrier too. If the work is done carefully and you can completely access all areas, you should have very little moist air leaking into the roof area. So ventilation would serve no practical function regarding moisture removal. Also, since you will virtually eliminate heat loss due to air leakage and limit heat loss considerably through conduction, I believe that the role of ventilation regarding the removal of heat from the roof area is insignificant. The only consideration is the life of the roof shingles. Shingle manufacturers will not warranty roof shingles on unvented roofs. HOWEVER, the latest research conducted by Bill Rose at the University of Illinois shows that roof temperature is controlled by shingle color, not ventilation. Additionally, the ventialtion scheme you are using is a best unreliable, and probably doesn't really work at all to move air.

In summary, I would follow the plan you have described. It seems like a well thought-out approach.

The code official may give you trouble. Roof venting is specified in the code. You may be able to convice him/her about your plan by explaining how it will work better than the other options you have. At the worst, leave the non-functional vents in place to pacify the inspector.

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Should I use Cellulose or Fiberglass insulation?
P.T. writes:
I am building (acting as the general) my own house in Elizabeth, Colorado (20 miles SE of Denver). I am at the stage of insulation and keep getting conflicting reports on the cellulose vs fiberglass products. I like the idea of the sprayed in cellulose in the walls and the contractor claims there is never any settling of the product because it is supported by glue when applied. I just wonder if that is correct? All the cellulose product I have ever seen is in the attic area and it has generally settled quite a bit. Do you have a recommendation here? The costs are pretty equal with the cellulose being a few hundred higher ie 2500 vs 2100.

Paul Fisette answers:
Wet-sprayed cellulose is a good product in my opinion. I think that it creates a more airtight, monlythic air barrier/inuslation system. It gives you a quieter house as an extra bonus. The down side CAN manifest itself when you use an inexperienced or unqualified installer that does not install it to the proper density --- or uses too much water in the mix. If the stuff has too much water and then you close up the walls too soon, you create a moist cavity environment that can give you trouble. This is perhaps less of a concern in your dry climate, but it raises hell in humid climates like mine. Overall, I would not worry about wet-spray settling. Another product that you may want to take a look at is Ark-Seal's Blown-in-Batt (BIB) system. This is a loose-fill system (either fiberglass or cellulose) that gets blown into wall cavities behind a thin mesh netting. It does not have the latex adhesive (I think!!). Ark Seal is located in Denver so it should be easy for you to get pricing, information and support. You can also contact Cellulose Insulaton Manufacturers Assocaition (CIMA) to check on appropriate densities (sorry, I don't have this #). You can contact Insulation Contractors Association of America (which is fiber-neutral) and get the CIMA #--- ICAA has good guidelines and information too. ICAA # is not on file here, but they are located in Alexandria VA.

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What about urethane foam insulation?
A.B. writes:
Hi! I'm about to build a house in Western NJ and want to know if there are reported health problems with urethane foam insulation. In particular to a person with asthma.
Also, in a sloped roof (no attic) possibly with metal roof (no shingles), should the foam be sprayed upwards directly into the metal? Or does it require an air barrier? The ceiling will be tongue and groove pine in some parts and sheetrock in the rest. Thanks.

Paul Fisette answers:
I have never heard of health problems associated with urethane.

The building code may require you to leave an air space for ventilation between the underside of the sheathing and the top of the urethane. Check it out. However, from a performance standpoint, a space doesn't achieve anything. The urethane conforms to the cavity size and shape. It effectvely blocks the flow of air and air transported moisture from the living space becasue it completely fills the cavity with air impermeable material. Also is has a low perm rating. And it functions as a vapor barrier when it is applied in deep layer as you are intending to do. The last issue of concern is the roof temperature. Roof shingle manufacturers and building codes say that roof venting lowers roof temperatures to safe levels and is required. Research at the Univeristy of Illinois Champaign/Urbana and at the Florida Solar Energy Center dispel this belief. They have shown that roof color controls roof temperature. Ventilation does not control surface temperatures of a roof.

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