Monday, August 6, 2012

Ventilating A Residence Attic

A home well-built in 1990, was with thoughtless attic ventilation. Repairs of soffit inlets are presented in a Picasa Web Album. Here are some of the photos.

Most plywood baffles were fully pinched against roof sheathing. Provide access, and repair within the attic. Let minimum path area be at the inlet screens.

Enlarge slots from outside. Knock off points with a chisel. Clean out another bird's nest, not observed from the attic.

The inlet area of this 650 sq ft attic is increased from 0.6 sq ft, to 2.2 sq ft. Exhaust area remains 2.2 sq ft. 

A minimum ventilation area goal for this attic size, as expressed by Joe Lstiburek of Fine Homebuilding, is 2.2 sq ft total, 1.3 sq ft in eaves inlets, and 0.9 sf in peak exhaust. The rule is 1 sq ft total for every 300 sq ft of attic area, minimum, split 60%, 40%.  A well-ventilated attic should have double these areas, in still the 60/ 40 split. I should increase the inlet area further, before any increase of exit area. Without a large increase of inlet area, there must be no powered attic ventilation, even though I carefully sealed the attic floor, reaching through all that loose-fill.


Ling Mancil said...

Won’t it be a problem if those get into the general ventilation? It really is a problem when birds and other animals can get into the attic, especially when they start inhabiting that particular part, compromising insulation and ventilation. Not to mention whatever they drag into the space can get dragged into other parts of the ventilation later on.

Ling Mancil

Phil Norman said...

Hello Ling,

I didn't think to show appearance when completed at any of the soffit vent positions. I reset the screens immediately as I went along. The change of appearance is not detectable from the ground.

Phil Norman

Scarlet Weingarten said...

Looks solid despite having to work with the old setup. It’s good that you were able to remedy most of the problems and seal them up properly. Improper attic ventilation can be quite troublesome. and could compromise the whole attic. And it could even damage the roofing in the long run, with moisture that can build up over the changing seasons.