Attic ventilation in1955 remodel
Our son just moved into his first home in Seattle. This 1918 one story house was remodeled about 1955 by raising the roof and converting the attic to three bedrooms. Their Home Inspector recommended replacing the composition roof, citing improper insulation of attic and kneewall spaces as primary cause of premature failure of roofing. ?? (Age of roofing unknown) No soffit vents were incorporated in original or 1955 remodel of house. Inspector also recommended that all coverings and insulation applied to the attic and finished storage space rafters on the second floor be removed to provide ‘proper’ ventilation of the roof in these unheated spaces.
Limited evidence of moisture staining was found in some areas of the second floor bedrooms. (Attic has a thermo activated gable exhaust fan, and 3 intake vents (approx 8″x8″) in the other 3 gables.
Cost of reroofing, incorporating continuous ridge and gutter pro-flo venting was factored into transaction, and completed prior to move in. (Roofing contractor was never inside the attic to recognize the scope of the work the home owner would next face.) We are now facing the problem of determining what’s the best way to deal with the ‘semi-finished’ attic and storage spaces behind the kneewalls on the second floor. (Attic finish consists of 1×6 shiplap flooring, and 1/8″ hardboard paneling tacked over kraft faced FG batts between 2×4 rafters, with the top 6″ of the FG batts exposed. Exploring the FG batts at the peak of the attic, yields a warm and damp condition, but did not feel wet.
All insulation installed in the 1955 remodel is in the form of rock wool batts, and again was installed in the 2×4 rafter voids in the cathedral ceiling portions of the second floor. What we’ve got now is entry points at the gutters and exhaust point at the ridge vent, but the ease of removing the obstructing rock wool and FG batts is much more daunting that originally surmised.
The HVAC unit for the house is in the crawlspace, exterior finish is resawn shake, and all window glazing has been upgraded to doublepane. Reading the December2003/January2004 article about FG insulation and airflow and recent posting on vapor barriors, moisture barriors, nonvented and vented attics, I’m confused as to what’s the agreed to and best way to tackle this situation.
What’s the word from the experts?
Replies
Well, I am "just" a carpenter, not an expert, but I will take a stab. Others will elaborate better than I can. You will want to find a method that works in your rainy climate, but these are some generalizations:
If you are going to use the attic as living space, you will have to define what will be the thermal boundary of the attic. What you describe is a loosey goosey situation where there isnt any sort of boundary (paneling making for a poor air barrier).
One option would be to install baffles to the underside of the roof deck, from ridge to soffit, providing a ventilated space. Then insulate below the baffles with whatever your budget allows, then redrywall. This would establish a boundary and provide ventilation too.
Check to see if there's knob and tube wiring lurking in the kneewall areas, replace it, then blow the kneewalls tight with cellulose.
Or, you could go with a nonvented, sprayed foam assembly. (since you said the rafters were only 2x4s-which doesnt make sense btw-you are probably looking at collar ties and not the rafters-this could give you the best r value for the space you have). Have the back side of the kneewalls foamed, and foam the floor joists behind the kneewalls, if its accessible.
Some simple answers for you, hope it helps.
Thanks Homer! The semi-finished attic has about 40" of headroom max, so once we get the ventilation issue worked out, this HO has no intentions to use it for anything but longterm storage.
The idea of tearing out the existing wallboard ceilings with their rockwool batts along with the floors in the storage spaces behind the kneewalls and applying cellulose is daunting, as it would impact all 3 bedrooms on the second floor.
I was thinking we might try to create a pathway for ventilation from the soffit to the ridge by forcing the rockwool out from between the seathing and wallboard, but then these no easy way to reinsulate and assure an air space. I think we would also end up inhaling a bunch or Rockwool dust in this process, and that sounds like a poor idea.
BTW, there is some evidence of knob and tube in one unfinished kneewall space, otherwise everything we can see is BX or Romex.
Suggestions?
Sounds like alot of fun.
You are saying that there is 40"above your head, not that there is a 3ft finished crawl space in your attic, right?
Your idea would work to push the batts down somehow. Depending on your strategy, you could leave the knob and tube (if its still connected) if you are not going to dense pack the kneewalls.
H.
We faced a similar problem with a 1960s rancher last year. The elderly lady who owned it needed some additional attic insulation to keep her fuel bills reasonable, but the roof pitch was so low even a midget couldn't get to the edge of the trusses. We ended up installing two turbine vents and relying on the existing gable vents to keep air moving through the attic. Then we blew in 12 inches of cellulose to bring up the R-value to something reasonable. Pur some nylon mesh over the area near the vents so that strong winds can't move the cel.If possible, leave the rock wool where it is and cover it with cell or fiberglass batts.