Hello, First of all thank you for this forum it has already been helpful and has helped me diagnose my problem. I will try to keep this as short as possible but I don't want to leave anything out. I have a home that was built last spring by a builder who builds "barn" style homes. They migrated from barns only, to barns with living space to barn style homes. Unfortunately they brought barn technology into the barn home and they put metal roofs onto purlins - no deck, no felt and no real vapor barrier. They always put large cupolas on ther homes and they are also vented with full length soffit vents and a ridge cap. Our house does not have a cuploa because the town would not allow it. Needless to say I am writing because we have a major condensation problem. I can actually scrape 1/4" + of frost off the metal roof in the attic. The builder is convinced that it is because we don't have the cupula - they say none of their other homes have condensation problems. They feel the problem will be solved with adding soffit vents on the gable sides (we have a cathedrial ceiling) and possibly adding small wind turbines to force more air flow. After reading your forum I am not convinced.
Some quick facts: we are in a northern climate, our ceilings are unfinished shiplap pine(not tight), directly above the ceilings is blown cellulose (no vapor barrier), in the cathedrial area and above the kneewalls there is foil covered ISO panels above the cellulose to hold it in - in the attic it is just cellulose over the shiplap, those ISO panels are screwed to the underside of the purlins and the ridged roof is screwed to the purlins - so there is a 1 1/2" airspace between the roof and the ISO, in the attic the back of the metal roof is exposed. Under the attic are our bathrooms, including a two person whirlpool tub which we use at least once a week - however we always run the fan when we use the shower or tub for at least an extra 20 min's and it is a decent fan. The humidity in the house is only 35%, it is usually 70 - 90% in the attic.
I already know you are going to say: get the builder back and talk to the roof manufacturer which I have done. The roof manufacturer says that system may be fine and it is really up to the designer to determine what will work. The builder is willing to work with us but points to his other homes to show that he doesn't have problems and wants to keep trying alterations rather than radical surgery. I don't want to just tell the builder what to do because if it does not work he will say "I did what you asked me to do". Telling him he needs to build it to code will not do much because I live in a state that does not adopt codes, enforce codes or even have inspectors. A drawing on a napkin will get a permit as long as you poney up taxes, fees, donate first born child, etc.
Here is my plan, please tell me if I am wasting my time. I am going to shovel the cellulose out of of the attic section by section and set down either poly or 1/2" ISO which I will tape all joints and edges to the joists. I also think I can pull some of the cellulose out of the ceiling above the kneewall so that I can tightly slip cut ISO sheets between the rafters just above the shiplap (obviously the edges wont get taped.) I will then staple a moisture barrier to the back of the purlins in the attic starting above the existing ISO so that if moisture vents out of that insulation pocket in the ceiling above the kneewall it does not go directly onto metal. My feeling is that by doing this I can cut back the amount of moisture in the attic by at least 90% because there is no vapor barrier now. I am hoping the existing ventilation will handle the other 10%. I am thinking that if there is a small amount of dripping the ISO and attic moisture barrier will hold it until it evaporates with the ventilation. Of course it will be holding it agaist the purlins.
If this works it will solve the problem for 2/5th's of our house. I can then bring the builder in, show him what works, and tell him to figure out a way to do the same for the cathedral portion of the building. Again #1 is this worth the time, #2 any ideas for the catherdral portion. I am currently thinking just staple poly to the inside of the shiplap and cover it with new shiplap (not a small job). Any input would be appreciated. Thanks and sorry to be so detailed!
Guest User
2005-02-03 11:46:11.000000
The construction industry in the US has a long way to go to understand the residential home environment and how to build for it. I would agree with you that the main culprit is the lack of a interior air barrier which is more easily rectified in the attic section, however if I read you correct the roof transitions from attic to vaulted half way up the rafter.
I assume that they used a vertical rib steel and you will be relying on the air chamber in the ribs to move the air up the roof in the vaulted areas. The ISO in those vaulted areas may be enough to have serve reasonably as both an air barrier and moisture barrier. You are in a difficul situation.
I think you have a handle on the basics. I would make sure you provide as much intake and exhaust air as possible. Use vented closure strip at the ridge. In the accessible areas where you remove the blown in, I would be use a foamed in place insulation say 1" thick to seal the ceiling areas rather than poly, then shovel the insulation back. Possibly you can get an insulation contractor to do both and make sure you have ample soffitt ventilation. Now is a good chance to run any extra electrical or speaker wires.
If there is no ridge to vent the attic area, I would look to put gable venting in either passive or powered. Now I think you are somewhat stuch with the top. Your idea of pushing ISO board up will do minimal good, and if the situation does not improve then you will need to go at it from the top down or bottom up. Good luck.
