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Condensation
Question: Our cabin has a metal roof built on trusses and nothing underneath except the insulation on the floor of attic space. It is 28 x 28 and has vents in both peaks and soffit all around. When we were at our cabin last week we notice lots of condensation on the underside of roofing as well as dripping down onto the insulation. What can we do to get rid of this moisture problem.
I am also interested in something to prevent frost on the underside of the metal roof and dripping down on the ceiling. or stopping any other forms of condensation on the underside of the metal roofing.
This is always the worst time of year answering questions as we get too many like yours where the roof assembly has not been built to the building code probably in an effort to cut costs in installing a permenat roof system. The terms cutting costs and permenat just don't go together.

Anyways, there are two sources of condensation. From the normal outside air in the attic that gets hot then cold, condensing on the down side and warm interior (moist) air leaking into the attic, again cooling and forming condensation.

If the insulation is laid on the attic floor, then I would suggest lifting it and installing an air barrier of 10 mil plastic sealing all joints. Then reinstall the insulation making sure that it does not plug the soffit. They make styrofoam tubes to help in this situation.

You say the roof has an vents in both peaks. I assume you mean the top of each gable end. I would measure the size of the vents and calculate the free air space. Then I would calculate the soffit free air. Go to a local building materials supplier to get the free air stats on your soffit.

The soffit and the gable ventilation shoule be equal and total1/300 of the ceiling area or 2.6 SF. You may need to put more ventilation in to comply.

If the situation persists, you can have a skim coat of sprayed in place foam applied to the underside of the metal. This will act as both a moisture barrier and to stop the heat transfer, reducing condensation.

Good luck.
I'll give you the same answer as the last one and I hope I don't sound too calus. I would go after the contractor who built your place as it is not built to the building code for residences.

This is always the worst time of year answering questions as we get too many like yours where the roof assembly has not been built to the building code probably in an effort to cut costs in installing a permenat roof system. The terms cutting costs and permenat just don't go together.

Anyways, there are two sources of condensation. From the normal outside air in the attic that gets hot then cold, condensing on the down side and warm interior (moist) air leaking into the attic, again cooling and forming condensation.

If the insulation is laid on the attic floor, then I would suggest lifting it and installing an air barrier of 10 mil plastic sealing all joints. Then reinstall the insulation making sure that it does not plug the soffit. They make styrofoam tubes to help in this situation.

You say the roof has an vents in both peaks. I assume you mean the top of each gable end. I would measure the size of the vents and calculate the free air space. Then I would calculate the soffit free air. Go to a local building materials supplier to get the free air stats on your soffit.

The soffit and the gable ventilation shoule be equal and total1/300 of the ceiling area or 2.6 SF. You may need to put more ventilation in to comply.

If the situation persists, you can have a skim coat of sprayed in place foam applied to the underside of the metal. This will act as both a moisture barrier and to stop the heat transfer, reducing condensation.

Good luck.

How do I get info on who in my area does the foam spraying? What type of contactor would do this?

I need to have this done or remove my metal roof and lay sheathing and felt paper etc. down. My issue is due to the outside air getting very warm quickly on odd days in the winter rather than warm air escaping into the attic.

Any help will be appreciated.
me and my wife built a small house ,28x40. with a 4,12 pitch and had a metal roof put on the house. they put 2x4 purlins and tyvec house wrap over the purlins and then the metal. well needless to say it is sweting realy bad. i have fully vented sofit and gabel end vents, and have tryed a atic fan to get rid of the moister but it does no good. the celing is insulated with R19 and it is getting wet. what do i do. PLEASE HELP Thank you very much
There is an issue here with several things. For one, the Tyvek housewrap breathes from the inside to the out but not so much from the outside in. I am unsure whether your condensation is collecting on the inside of the Tyvek or on the inside of the metal roofing.

Additionally, for most residential applications, the metal roof panels are often specified by the manufacturer to be installed over solid decking, not purlins. Have you confirmed proper installation with the metal manufacturer.

Additionally, proper ventilation requires intake and exhaust which need to be balanced, or heavier on the exhaust free air flow than the intake. This needs to be set up in a way which achieves airflow throughout the attic. Your situation may be providing only very limited ventilation in the attic.

I would also take a hard look at sources of excessive moisture in the house or attic, such as improperly or unvented bathroom exhausts, etc.

Call me at my office -- 937 773 9840 ext 201 if you'd like to brainstorm a bit more on this issue.
I know in metal roofing there shouldn't be any condensation. If red rossin was run between felt and metal panels - if nothing was put between roof and metal panels they deserve the condensation they have. I would hold roofing contractors responsible for the moisture and not following codes for proper moisture barrier. Good luck.
It's not how the insulation was laid in the attic floor or between the trusses but the moisture barrier being put between the metal panels and existing protective paper - speaking of red rosin. This should take care of any moisture between the panels and avoid any rotting of plywood or other roofing problems because of moisture.
I live in the Albany, NY area and I have just installed a metal roof on my house but was never advised to put a vapor barrier under it. So the metal is laying directly on purlings, which are laid horizontally over the trusses. The roof is 60 feet long, so there is sofit along the 60 feet of the roof on both sides, has sofit on both gable ends, and has vents on the both gable ends. I also have a back porch that is 8 feet by 20 feet and the ceiling is covered with sofit so this will help with the ventilation. I have not sheet rocked yet but the roof has condensation on it and when the sun hits the roof it “rains” inside the house. I’m not sure if the moisture is from the Kerosene salamander I use to heat the place while I work or if this going to happen when I put the insulation up. I will be using R30 insulation for the attic floor. I have asked around and some think the condensation won’t build up once the insulation is up because there is so much airflow. Anything you can tell me will help. Thanks
You do not say whether your drywall is up on the ceilings yet. However, the location for a vapor barrier (typically heavy polyethylene sheeting with the seams taped) would be behind the drywall, underneath the insulation. Try to add this if possible.

Also, you do not say whether there is a ridge vent. However, the only way the soffit vents can effectively act as air intake is if you have an a ridge vent for exhaust.
I am about to invest in a new metal roof for my barn after just having put in new doors. The barn is 55 x 60 feet x 25 feet tall as a peak. Gentle slope - you can walk on it. The barn will house a dozen or so sheep in the winter as well as about 1/4 of it will be for my heated shop. All of these factors could contribute to condensation.

The roof, a painted metal one - not galvanized, will be screwed to purlins laid across rafters ie not plywood.

I have heard from some contractors bidding on the job that all that is needed is 6 mil plastic between the purlins and the metal roofing. One contractor mentioned a product called Tri-Ply by Fortifiber - another said only 1 and 1/2 inch fiberglass insulation would work. I live near Portland OR - its wet with temperature extremes. Please advise.
You live in the condensation capital of the US with slightly temperate weather and moist air. Added to this is the use of your facility. The sheep will give off considerable moisture from breathing and body heat which then raises until it hits the metal where it will cool in the winter months, condensate and drip.

The last thing to put down is plastic directly under the metal. I would recommend using a reinforced high quality underlayment such as Tri-Flex 30 applied directly over the existing roof. Then I would ventilate the air space between the underlayment and the metal at the eaves and ridge both. If you are installing a vertical ribbed panel, choose one with large enough flutes to move air vertically or strap vertically over the rafters first to set the purlins up.

There are other products such as Low-E or Micro-E which is a foil faced thin cellular foam product that acts as an insulation from its heat relective properties which will help keep the barn cooler in the summer and warmer in the winter while controling condensation. (Typically we do not recommend brand names but they are members and can be reached at www.low-e.com)

Hope this helps.

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