Insulation, Radiant and Vapor Barriers - Attic Humidity and Additional Insulation

Hello,

I am looking into having additional insulation blown into my attic. I have had a couple of contractors come over to give me price quotes and several concerns have come up. Before that a little detail about the structure of the home. The roof is a Mansard style roof, so there is very little attic space, maybe 3 feet of space and the roof line is relatively flat. Additionally the "roof line" extends down to the first floor and this is where the ventilation soffets are installed. The home was built in 1970.

1) One of the estimators said he noticed some evidence of condensation on the inside of the roof. He said there are some nails that have come through the roof from the shingles and are rusting and form "dark spots" on the wood where it penetrates the wood. He also said that there is no ventilation in the attic which means the moisture coming up from the house gets trapped. He said that there is no opening to the soffets on the first floor and that it looked like the soffets were installed after the fact and are basically doing nothing except putting cold air in the open space between the 2nd floor walls and the roof line. I am concerned if I add more insulation (I currently have probably about an R-15 rating....6 inches of insulation) and get the rating up to R-40+ that the temperature in the attic air space will become colder and will create more condensation because of the lower temperature. Is this a reasonable concern? Any opinions on what to do to improve the ventilation or minimize the risk of condensation? I really don't want to install an attic exhaust fan. This contractor said if you manage the humidity in the home (keep it below 25% in the winter and lower on really cold days) it should not be a big issue. I am really concerned about moisture/mold/mildew. I am over reacting? I have not been up to the attic to do a detailed inspection

2) He recommends putting BAT into the eaves where the soffets are installed to improve the thermal efficiency and the cover them with insulation. Does this seem reasonable?

3) He also said that there are open penetrations between the baseboard and the hardwood floor. He could stick a thin probe between that space all the way through the wall and to basically the air space between the roof line and the second floor wall. He recommended calking between the floor and the baseboard molding. That makes sense, but I would also like to spray some type of foam insulation onto the "outside" portion of the wall (this would be the part of the wall that is exposed to the air gap between the roof line that extends from the second floor down to the first floor and bedroom wall). There is enough access to get up there and do "some" spraying. Any products that anyone can recommend.

4) Any recommendations on what to use to insulate the attic? If I use the Icynene product will that minimize the air leakage from the home and better control the humidity?

I know lots of questions, but it seems whenever I embark on these things you really need to understand what is going on or you can get yourself in trouble.

Thanks!

Hi tl, the information you are getting is partially correct. The rest isn't necessarily wrong, just not complete. Let me just outline where you want to go.

A Mansard roof style is difficult to insulate and vent in the same space, but that is what must happen. Exception would be a "hot roof" but I won't go into that. You need to establish air flow from your soffits, along the underside of the roof sheathing, all the wat to the attic where it can exit. This natural convection will carry away any warm moist air that leaks from the house. Keeping the humidity in the house low will obviously help, but at the expense of a rather dry house, cough, cough. The correct approach to reducing the moisture migrating into the attic would be air sealing and vapor barriers (VB). Where VB's should and may have been installed during construction, if they are missing, a layer or two or three of the proper paint or some wall paper can do the job.

Air sealing issues can be extensive. but very necessary as the contractor noted the air gap under the baseboard. A blower door test and infrared camera would shock you as to how much heat you are loosing. On the lower floors the drafts may be noticable, but on the upper floors, the warm air is leaking out and often goes unnoticed, except for the heating bills. Enough of my babble for now, let go find some links for you to read and we will continue later.
Welcome To Home Energy Magazine Online (http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/95/950309.html)
http://www.ccfoam.com/resources/Residential/Reading%20Room/EPA%20ThermBypassGuide_web.pdf

Bud

Bud,

Thanks for your help. I look forward to additional information from you. I will be going up in the attic this weekend to do some further inspection. I don't think any vapor barrier is installed on the home as it was built in 1970, so that is probably not a viable option.

If the access to the soffets is blocked as my contractor mentioned, what do you think is the best way to open them up? Should I see if I can drill some holes or remove some non-load bearing wood to install some baffles?

Thanks

Pictures would help. Unsure if it was built without venting or the venting has been blocked or covered. Photobucket.com and post the link over here with the link tab above.

bud

Bud has it right, humidity/condensation comes from within the home.

You can resolve this by opening windows or having a dehumidifier or fitting and using extractor fans in the kitchen and bathroom, avoid drying clothes indoors.

All humidity comes from the way we live, when the home was built, there wasn't the pressure to have tight warm homes, heating was cheap and homes were full of holes.

Blocking the holes means the humidity/water vapour we produce by breathing and sweating, cooking and washing is not sucked away by the passing wind. And finds its way into the roof space through holes round light fittings, pipes, doors etc; where it condenses on the nearest cold object.

A modern home should be built almost air tight with a plastic membrane covering the upstairs ceilings and probably a forced ventilation system to change the air and get rid of the water vapour.

An ultra modern home will be as air tight as it is possible to make it. And warmer and cheaper to run.

Probably, the best way to proceed is to remove the ceilings and fit almost water vapour proof membranes and then replace the ceilings.

A cheaper way is to paint the ceilings and walls with gloss paint, to keep the water vapour in the rooms and open the windows from time to time.