1) Top-down snowmelt: We’ve got an old (1790ish) 1 1/2 story cape with an attic that covers maybe 2/3 of the second-floor footprint. The attic has two gable-end windows that I was ecstatic to see when we bought the place, thinking those would be enough to keep cold air circulating and preventing this problem. Reinsulated that attic before the first winter, packing the older cellulose as far down into the joist bays as I could, then 6″ fg btw the joists, another 12″ fg perpendicular to the first layer.
Now, even on hard frost mornings you can see the line across the roof where the attic floor starts – frost below the line, none above. When there’s snow accumulation (we’re in NH), it always starts melting from the top down. Doesn’t melt fast, but does melt, then refreezes on the lower part of the roof. We have a 30″ ice belt so it doesn’t usually make a critical back up.
There’s an attic fan that every year gets covered up with the same amount of insulation as the rest, the door leading up to the attic is insulated with foamboard, and, and, the woodstove chimney goes through the house at one end of the attic. It’s warm (not hot) to the touch up there.
Possible that’s putting out enough heat to overcome the two open gable windows? I’m skeptical, but curious about other’s thoughts.
2) Much, much shorter – Have a couple barn doors that are going to need replacing. Has anyone here ever seen something like a breadboard bottom on these to avoid the wicking problem from the endgrain? A solid attachment might be a challenge, but I like challenges like this (and if you have ideas, let’s compare notes *after* I’ve done them!).
Thanks,
Rick
Replies
The insulation you describe does nothing to prevent the movement of air through the attic floor.
Every wire coming up through a top plate is also a hole allowing air to move into the attic. Likewise all ceiling fixtures (lights, fans).
Those holes need to be foamed shut.
There is probably a gap around the woodstove chimney where it comes through the attic floor. This is trickier, be sure the material you use is not flammable.
The tops of walls may have gaps between the framing and the plaster (this is common when the finish is drywall, I'm not sure about other finishes).
It could be that the heat from the chimney is also a problem, but I'm not sure what you would do about that....
There is a nice article about door building in the current issue of Fine Homebuilding. It may or may not apply to your doors.
Rich Beckman
Another day, another tool.
Edited 12/27/2004 5:59 pm ET by Rich Beckman
To add to Rich's comment around the chimney, I did an energy upgrade for a client this summer, and the energy evaluator said to flash around the chimney. I "L" bent flat flash and tacked it to the wood surround. Followed up with masonry cement in a caulking gun between brick and flash... not sure if it will hold that much but overall it was pretty tight.
Thanks for the varied suggestions. We don't have near the ice problem other newer houses have around here, but it still gives me a day or so every winter I need to go around the house and clear the ice off the snow belt. Gonna take a closer look for other openings/gaps/whatever.
My guess is that since you say the chimney in the attic is warm, that is the primary source of the heat. Perhaps you could frame the chimney in and insulate the framing. In otherwords, box it in floor to rafters. Naturally you would leave space between teh chimney and insulation. Do your homework as to the necessary standoff for the chimney material involved. Justs a thought.
It might not work 100% , since the heat from the chimney MUST go somewhere. Some would be chaneled to the roof. And some would escape by raising the flue temperature. And some would heat the insulation and raditate into the attic. But I would bet you would cut hte temperature considerably.
I'll leave the first part to the others that have more expertize in that stuff..
for the door, I'd recommend the the breadboard has the tongue and the planks the groove, to avoid a water trap. fasten sparingly with a fastner that will give..nails comes to mind, or elongate the holes that screws will pass through to allow the door to swel and shrink.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
How much insulation do you have in the sloping section of the second story ceiling? My home is a 2 story Victorian about 1865. I used to get warm air from my basement going up the walls [ 2x2 studs nailed to the sleepers on the inner coarse of brick ] all the way to the attic. Maybe this might be something you could check.
Have about 6" packed cellulose in there. I'm pretty confident it's well-packed b/c on heavy frost mornings that part of the roof doesn't thaw till the sun hits it. There's a definite frost line across the roof at the attic floor level, frost below the line and less/no frost above.
What sort of insulation do you cover the fan with? If it's just batts, they do nothing to prevent air flow. An airtight foam box is advisable for both the fan and the stairs. There are some kits out there that Velcro to the floor to provide a better air seal. Ingenuity and some weatherstrip could likely accomplish the same thing.
AndyAndy Engel
Senior editor, Fine Woodworking magazine
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
Thanks. I do just cover the fan door with batts. Not sure what's normal in attic fans, but this doesn't run till you pull a rope/pulley system that opens a door in the upstairs ceiling. I'll try jiggering something more substantial around that. The door to the attic stairs has styrofoam on the backside. Not sure what more I can do there.Thanks again.