I just finished ripping the old roof off of my place, it was a layer of 2″ cedar tongue and groove planks, topped by Homasote, plywood and shingles.
We took it down to the cedar planks and I am in th process of putting new trusses over the existing roofline to raise the pitch to a 8:12. In a normal trussed building I would put a layer of plastic between the ceiling (drywall) and the insulation in the attic, however I’m wondering if all the spaces in the cedar is going to let so much moisture through that I will have a problem with condensation on the plastic, and then rotting of the cedar.
I ask this because this is a week long project and I have covered the cedar with plastic at the moment to keep some of the heat in the house while the new roof goes up, there is a lot of condensation under the plastic already, but I don’t know if that is because there is no insulation covering it at the moment, and with the cold weather we have it is just looking bad, or if that is how it is going to be when everything is closed up.
Robert
Replies
The contrast between hot and cold is certainly making it worse. What are your chances of getting some one in quick to spray urethyne insulation directly to the tops of those cedar planks before getting the new roof sheathing in the way?
Or -
How were you going to insulate it?
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius
I am putting in R-40 fiberglass insulation batts (10.5").
The old roof was a 3:12 and 5:12 pitch with an offset center, the new one is 8:12 and symetrical, I also have added 24" to the apparent wall height with stub walls on the rafter ends so I have lots of room for insulation with a cold air space above. The new rafters do not sit on the old roof as they are a scissors design and only touch at the ends, so I can put down insulation with no gapping. I don't think spray in would work as the cedar moves during the seasons and I think it would end up cracking the insulation if it was bonded directly to it, not to mention that there are big enough gaps in some places that it would probably end up coming thru when it was sprayed.
You don't think the current condensation is a problem?
Robert
The pictures are great for showing job conditions and what it is you are doing (tho' you did good with words) but they don't show the condensation/frost problem.
I don't think it is likely to be a problem if you leave the plastic down and have a good snug layer of insulatioj to R-40 without drafts. The thing that causes trouble is allowing dew points. Either you stop the vapour from getting to a cold spot, or you eliminate cold spots or both. Take that principle and study all the old threads under venting or vents or condensation and you can assess it better on site. I'd hate to opine from here..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius
I will be running a continous vent along the bottom of the eaves, with a ridge vent along the entire roof so I will have plenty of venting. I think I will insulate and close it in, and then check in in a couple of weeks and see if there is still condensation in the areas I have it now.
Thansk for your help.
Robert
piffin's right--sure you're gonna get condensation right now on the warm (humid) side of the plastic--just get that insulation between the vapour barrier and your dew point - and let that space breathe, and you should be o k . Snow already, eh? Have fun.