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Community and Q&A

Attic Air-Sealing and Ventilation

Cortland15B | Posted in Energy Efficiency and Durability on

Just got my blower door test done today on my 1946 1 1/2 story home located in northern Minnesota zone 7. It’s 2800 sqft including the basement and my blower door number was 1600 cfm or 4.1 air changes an hour. The house has been extensively remodeled and reinsulated but it’s not quite there. The attic needs to get from R38 made up of two layers of fiberglass batts  to the recommended R60. The 2×4 walls need some exterior insulation as well whenever we decide to reside next. The price per therm for natural gas has almost double this year compared to last. Furnace is a 95% efficiency forced air unit. We have over 10,000 heating degree days a year.

The attic is divided up into 6 smaller attics, I only have access to 2 of them right now as they are sealed up and divided by rooms, stairs, dormers, and old exterior walls.. 

The ridge vent portion of the attic that is above the second floor ceiling has one gable vent on the old side of the house and a continuous ridge vent. There is no access and the area is very small.

Right now only 2 of the attics have ventilation and the rest do not. It consists of gable vents and ridge vents with no soffit vents. This section of the attic they did join the knee wall area to the ridge vents using baffles. 

I want to combine these 2 attic areas by opening up the old exterior wall that separates the addition from the old house in the attic. That would open up and combine 4 attic spaces into 2. 

The two attic spaces I would be combining with the two that have ventilation don’t have gable vents, the soffit has louvered vents on them but they don’t actually go anywhere, they aren’t blocked by insulation there is wood in the way. There are also no baffles in the knee wall area going up to the ridge vent. 

The house gets ice dams focused mostly  on the areas of the attic that don’t have ventilation. It is worse on the south facing roof that gets solar gain but it does happen on the north side close to a chimney that I think is causing some of the problem. 

So my questions are about air sealing and attic ventilation. With the blower door number, do you think I need to take up all of the batt insulation in the attic and air seal or can I forgo that step and just add insulation? With venting, the old parts of the house don’t have enough room in the slant wall above the knee wall to add baffles and keep enough insulation in there. So my plan was to make the gable end vents bigger and hopefully open up the soffit area from the outside when siding/gutters/soffit gets redone. I also plan to add R25 batts along with some shake and rake loose fill fiberglass on the nooks and crannies. That would get the areas of the attic to R60. 

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