Condensation/Insulation/Ventilation


#1

We had a new standing seam roof put on a few weeks ago, replacing asphalt shingles. We think it looks great, but we have a problem with condensation in one of the attics. This attic is directly over a wood stove. We live in New England.

The roofer says that it can’t possibly be his fault. I think he is probably correct, but a) I want to know if it is his fault and 2) I want to know the best way to fix it.

Pictures of the part of the roof I am asking about are here:
picasaweb.google.com/mcorner/Roof#

The condensation is visible on the underside of the ridge cap and the plywood seems very damp (there is a layer of sheathing boards under most of the plywood as well). It is pretty humid up there 70% or so, even though it isn’t humid here right now.

Ventilation:

This is a very old house (parts of it from 1790), so adding ventilation was challenging. There was a ridge vent and he replaced that with a metal ridge cap. There were 1-2" button vents in the soffits, but I know that they are clogged up with insulation. It isn’t as simple as unclogging them (although I haven’t done that yet), because there is a beam that almost entirely blocks the path from the soffits to the ridge. See pictures.

Insulation:

This attic has 5-6" inches of cellulose, which is a totally inadequate R15 (New England). I didn’t really notice this until now.

So the options I see (or combinations):

  1. Try and make these soffit vents work. Clean them out, and possibly replace with a continuous strip. The roof is built so that the plywood/sheathing boards contact the beam, blocking the airflow. Should I shave a bit off the edge of the beam to get air going? Is there a better way to do this?

  2. Add a gable vent of some kind. This is an end of the house without another end for cross-flow ventilation, but we could put square vents lower down (on each side of the chimney) and get airflow from there to the ridge vent.

  3. Add a lot of insulation. My roofer suggested doing this with no ventilation. At R-15 we need more insulation anyway (he said R-60!). Pink bats or more cellulose? If we try and get the soffits working, we will need foam baffles or something to keep the insulation out of the soffits.

Sorry for being long-winded, I want to get you all of the relevant information.

Thanks,
-Mark


#2

You need intake and exhaust of air…get the soffits clear then deal with insulation…


#3

You are probably not going to be able to get that old house to vent properly, it just wasn’t built with ventilation in mind…
You may or may not be able to fix the ventilation by removing the roof.
Each house is different and way back when they didn’t build them all (roughly) the same like they do nowadays.

Adding insulation should help a lot.
I would look into spray in foam insulation for the walls and the attic.
After doing this you may or may not have to look into mechanical’s (air exchangers) to deal with the interior moisture.

There really is no definitive answer to your problem, the solution will be case specific.


#4

If you install a power vent with humidistat it may help your problem, as long as you have intake from somewhere. The plywood by the chimney looks to be rotten. Is this from long term problem with this condensation or a leak at your chimney? If it is long term condensation I would think that the problem existed before your new roof was put in.


#5

The plywood next to the chimney is brand new, that is why it is a different color. There was a nasty leak/chimney moisture problem and I had to reframe that end of the roof. The roofers added new plywood in that section of the deck.

I am cleaning out the soffits right now. I am not sure yet if there is enough of a gap between the roof sheathing and the beam to get enough airflow (a very tough shape to estimate the area of!). I may have to add some space. how much space does a baffle require? Not the width, or the length, but the size of the air pocket?

The spray foam on the interior walls is a good idea, currently it is fiberglass, but without anything to hold it in place, it doesn’t look all that effective.


#6

It looks like the Accuvent baffles are going to be about 1" thick. I am not sure yet how I am going to get past that beam. The pink foam baffles might be a better choice.


#7

Can you get something like this in there?

http://www.roofing.com/images/topics/8626/img_1256405555.jpg


#8

I am not sure what I am looking at :slight_smile:

Are those baffles for ventilation, or something to keep fiberglass against a wall?


#9

[quote=“mcorner”]I am not sure what I am looking at :slight_smile:

Are those baffles for ventilation, or something to keep fiberglass against a wall?[/quote]

The insulation you are looking at is the vaulted ceiling.
The white foam board is the baffle to provide airspace.
There are 1" foam spacers nailed into the rafters to hold the foam boards consistently 1" away from the roof deck.

This may show it better.

http://www.roofing.com/images/topics/8626/img_1256409222.jpg

http://www.roofing.com/images/topics/8626/img_1256409269.jpg


#10

Did they replace the ridge vent with a non venting ridge cap? If so, replace with a venting ridge cap.

I’ve got a post and beam similar to yours.

Install continuous soffit vent from the outside.
Cut the beam between the rafters. A half inch or so gap will likely be enough.
Add a vapor barrier and a lot more insulation.


#11

Ax, thats a pretty righteous chimney. Got any pics of how that finished off?


#12

Thanks for both of the tips, I guess I would rather not rip the roof off and remove all the insulation on the inside of the attic, so adding a gap in the beam seems like the way to go. Thanks Dennis.

The roofer says he installed a venting ridge cap, but I need to double check that. If not I can have him put one in.

I picked up some soffit vents. I also got some plastic baffles (since I am going to add insulation). They might be a little big for a 1/2" cut, but we will see.

I had one question about the vapor barrier. There is 6" of existing insulation, which is half cellulose and half vermiculite. Is it a bad idea to sandwich a vapor barrier between the old insulation and new insulation?

I would rather have my roofer do all this, but as I have discovered, he knows metal, but he doesn’t know enough about ventilation.


#13

You never want the vapor barrier in between layers on insulation. This will prevent the bottom layer from drying. You should remove all the insulation and install poly and then non faced insulation or blown in. This only works if you have sufficient insulation to bury the poly at the tops of the joists.

If you go will closed cell foam you won’t need a vapor barrier.


#14

I know this is an old thread but in the event you are still getting notified, did you fix it? I have a similar problem myself. Thanks.


#15

Wow, yeah, so much has happened. We ended up removing all of the insulation (by an abatement contractor), airsealing the attic, putting in 14" of blown in cellulose, adding some foam spacers to try and get airflow from new soffit strip vents. We rebuilt the top of the chimney (twice) and redid all of the flashing.

Guess what? Still humid and still condenses :frowning: Mostly it gets up the wall and hits the metal flashing (Which is very cool) then drips down. I have basically given up on this solution. Our plan now is to go to a hot roof (spray foam) and finish the attic off instead.

Old houses are tough.