Old house, very shallow stud bays


I have a weird ice dam problem. My old house has 2 bedrooms upstairs under roof. Small flat ceiling and small attic crawls space. Sloping walls. 4 foot knee walls.

I have HUGE ice dams every winter, especially over bathroom and kitchen (1st floor). I started out wanting to insulate the roof / attic for energy savings, but have decided stopping those ice dams is even more important. I’ve been working on this for several years.

Original plan was to vent and insulate attic.

Roof had no ventilation, and I added ridge roof vent (“I added” = “hired someone” … I’m absolutely unhandy), and soffit vents for each stud bay. In attic crawl space added a new layer of rolled bat over OLD GRAY insulation.

Still huge ice dams.

Finally opened access doors to knee walls. (I don’t like spiders …) and found there is old bat insulation stapled to the roof side of knee wall space, and a couple of layers of old newspaper stapled to lath/plaster (warm side of) kneewall.

I figure warm air from kitchen / bathroom is rising into knee wall, rising furthere inside roof insulation, until it hits the sloping roof / wall where there is no insulation. Air warms roof, snow melts, trickles down and freezes into ice dams.

The sloping roof/wall only has about 4 inches of space between the roof and lath/plaster. How the heck do I insulate that?

I figure I can tear insulation out of knee wall along roof, then reinsulate the knee wall’s warm sides – floor and interior wall.

Still, air from soffits will rise into knee wall space, then hit the uninsulated slope and warm up, then enter insulated attic crawl space … and I’m back to the warm air warming roof, melting snow, trickle down, freeze into ice dam.

I’ve been asking for ideas at a lot of web sites. Suggestions so far:

1.) Cut foam insulation boards so they will fit between studs, and slide into the slope. Don’t worry about keeping roof cold, 'cause it won’t fit tight anyhow and air will still move.

2.) Inject foam insulation. I read a lot about this, and it looks like the best idea. Would close off air movement entirely in slope. I’d have to add a mushroom air vent to knee wall space, gable end vents to attic crawl space, to keep an air pathway, but that’s do-able. However, while some contractors around here do spray gun foam insulation of open construction, no one within 150 miles does injection foam.

3.) Pour tiny styrofoam beads into the space. I’d have to do something so beads don’t pour into knee wall space, and still have to consider cold air circulation against roof.

And anyhow, would 2-3 inches of any insulation in sloping roof/ wall do any good?

However, if I don’t insulate the slope …

I’m very confused.

Don’t criticize builder, in the 1920’s my GRANDFATHER was a master carpenter and he built this house. In those days, the upstairs had no heat at all, except what came up stairwell, and the door at the stair bottom was usually kept closed …


Sounds like heat tapes are your best bet.


With homes with knee walls im very leary of using ridge vent. Solely because there is a break in the knee walls for intake. Sadly there is only one fix that i know of that would work and it is ugly.

First off the soffit vents do they have baffles to supply the ridge vent above the knee wall, if not where is its source of intake? Homes like yours ridge vent was not designed for. As far as adding insulation thats a great idea what kind really depends on how far you want to go. FOam inbetween the rafters i dont agree with. That will limit the airflow to the ridge vent. TO remove ice damns you must completely insulate and completely ventilate. The only way i know of ventilating the knee wall is 2 ways. Putting gable style vents in the side wall to remove some of the hot m,oist air. Or not my favorite adding vents over the knee wall and im not a fan of that. On the gable style vents i have had success from ice damning on a home we did the roof and siding a few years ago. No it still shows up but not as much as before. Heat tape to me is a product used when there is no more solutions left. I dont use the stuff on roofs, gutters yes not roofs. If a roof is properly ventilated then heat tape is not needed. Send us a few photos of your home and your attic and knee walls so i can have a better understanding of what we are talking about.