Question on Roof Ventilation
My roofing engineer urged me to rip out the ceiling where we had our
suspect roof leak (and where the roofer had repaired the ceiling after
putting his foot through it!) and guess what I found?
NO vapour barier!!!! Insulation jammed right to the roof sheathing clogging up the ventilation for the roof.
This caused a huge condensation problem on the first warm day of spring
when coincidentally, it rained. My roof leak turned out to be a ventilation problem!
Question: Do the California Eichers have ventilation running through the
roof from end to ridge vent? Does this ventilation run through the chimney? How do you install a skylight and maintain the ventilation through that area?
Curious and want to know more about this type of roofing/attic/ceiling.
Didn't know that any Eichler had this kind of constructon (ceiling, **attic**, roof), or I'm just not visualizing correctly.
I've taken apart many Eichler roofs and found no vapor barrier persay, just tar paper, "some" insulation (some times) then the built up T&G.
Once insualtion gets wet, it needs to be replaced. Have advised many who have had contractors say "it'll dry out over time". BS if it's inside a wall or attic with poor ventilation. Rot is what will result.
Hi Ben! Picture this: Beams (douglas fir in my case) supporting roof
rafters which in turn support the roof sheathing and then the roof (used to
be tar and gravel but is now torch down membrane)
Betweent the ceiling drywall and the roof sheathing (plywood) is the following: First, a vapour barrier (plastic sheeting) Here in Canada this
goes on the warm side of the insulation.
Second: insulation batting
Third: Approx. 2-4 inches of air space
Fourth: Roof sheathing (plywood)
The beams support the roof rafters. In between the roof rafters (18 inches wide) is where the insulation goes. The air space above should be
continuous to the ridge vent, and also to the outside fascia or soffit vents
so that air travels between the rafters. This will keep the rafters and beams from rotting should there be a moisture problem from roof leaks or
condensation.
Cramming insulation into that air space is a real no-no and the cause of
much rotting wood and roofs, but it's amazing how few people are aware
that ventilation is a necessity.
Looking for any and all comments.
Agree, too many don't know the HOW2's of the vapor barrier.
It's always on the "warm" side (winter conditions) and the insulation on the "cold" side of that barrier.
Think your "colder" weather has this "thicker" construction, as I've never seen it on any Eichler here in the SF Bayarea (that I've eyeballed).
Am more and more leanig towards the sealed glass insulation. Haven't seen any at the local hardware/builders, but have come across it on the internet. Basicly rolled spun glass insulation in sealed plastic bags. Make much more sense and wonder how much more?
So the Eichlers in my area has the beam supporting the tongue/groved 2x8 redwood planks that make up the ceiling & roof rafter. Then the tar paper moisture barrier (really to keep the liquid tar from leaking in), then insulation (only some have it), then the T&G. We don't get snow & ice down here... :)
Mine has +2 inches of insulation on top of the OEM T&G, then T&G and now a foam roof on top of all that (the max number of roofs that local building codes will allow). So my roof has about 5 inches of insulation plus whatever R value the T&G's add.
Thanks for the very good description and good luck!
Here is a good graphic showing an Eichler roof cross-section.
http://www.dura-foam.com/roof_system.htm
Many roofs also have a layer of foam board right on top of the wood. Original Eichlers had 7/8" of fibreglass flattened under the tar roof.
You are describing a more common sloped roof section. In cold regions, moisture drive is a guaranteed problem. Moisture goes 'toward the cold' and can saturate insulation.
Eichler ceiling boards breathe well because they have gaps between each piece of the tongue and groove ceiling boards. The redwood helps a lot. Without these two features, there would not be very many Eichlers today.
