Fine Home Building Insulating Knee Walls Roof Vented Roof

If you choose an air permeable insulation like fiberglass or cellulose most building codes require the roof assembly to include a ventilated air gap directly above or directly below the roof sheathing.

Fine home building insulating knee walls roof vented roof. A vented attic where insulation is placed on an air sealed attic floor is one of the most underappreciated building assemblies that we have in the history of building science. The ridge is about 40 feet long and there is currently a ridge vent but no other roof vents no soffit vents and no gable vents. Of 4 companies i called i finally got a quote andwhat they propose is to install vent baffles on underside of roof osb and then fg batt insulation. Floor area is 1200 sq ft.

The standard roof ventilation requirement used in building codes and asphalt roofing manufacturers calls for 1 square foot of net free ventilation area for every 300 square feet of ceiling area attic floor area when vents are evenly divided half of them high on the roof at the ridge gable or a high roof and half low on the roof at. I live in peachtree city ga and have a house with 9 of these knee wall areas i need to properly insulate. So much information has been devoted to the subject of roof venting that it s easy to become confused and to lose focus. My 1914 house needs to be re roofed this summer but i am at a loss re ventilation.

Blown insulation in the knee wall and top attics. So i ll start by saying something that might sound controversial but really isn t. Unfortunately the space on the unconditioned side of the knee wall often is not well sealed or insulated and the wall structure by itself does not provide enough of a thermal barrier to adequately maintain the temperature of the conditioned side of the knee wall in a vented non conditioned attic. I installed baffles between the roof and insulation shown to allow for the air to flow from the soffit to the roof attic as shown in the second picture.

The house was built in 2001 and now only has batt insulation on backside of drywall of knee. The attic space contains no mechanicals and is not used for storage. Sloped roof assemblies can be insulated with a wide variety of insulation materials including spray foam fiberglass batts or blown in cellulose. Added bonus the floor of this knee wall leaked too so there is a line of foam just above the floor joist.

If you ve got a roof over your latest building project chances are you ve also given some thought to roof venting. We prefer cellulose but we use fiberglass sometimes too. The first picture is looking up at the angled roof of the knee wall. The third shows the baffle extending up into the roof attic.

15 articles and videos from the fhb archive that will take you through every step of the roof venting process. The shortest distance from the top of the knee wall to the top of the outside wall beneath is still along the roof line and you avoid having to insulate the floor behind the knee wall.