Insulating One and a Half Story
sbaillie
| Posted in Energy, Heating & Insulation on
I am trying to decide how to vent and insulate the attic in my one and a half story house. The upper 4 feet of wall in the second story is part of the roof, and is already full of loose insulation. This makes it difficult to vent through the soffits. Someone suggested using soffit baffles, but they are almost impossible to install at this time because the roofing nails stick out about an inch through the roof sheathing. I would like to blow in a foot of loose insulation in the attic, but how do I deal with the ventilation? Can I ventilate above the insulation only? Any ideas comments would be appreciated.
Replies
I noticed no one replied to sbaille's question. I am adding a 1/2 story to my exisiting home and was wondering what the best method of insulating the roof/ceiling would be?
I was thinking about adding ventilation baffles in each rafter bay to insure venting through the ridge vent and using R-30 in the 2X10 rafters. I was also planning to use R-13 in the knee walls and the ceiling. SHould the batts in the knee wall and ceiling be unfaced, since the R-30 in the roof will be kraft faced or that new encapsulated style.
Hoping someone can provide some recommendations. Thanks for your help!
What I'm doing for my cathedral ceiling is continuous ridge and soffit venting, with 2x blocking under the sheathing followed by 1/2" foil-faced rigid foam (to form a vent space and a radiant barrier) followed by 5.5" mineral fibre batts, with 2" of rigid foam under the rafters to form a thermal break. The only hole in my roof will be the bathroom stack, and that only because the code tells me so. In my mostly heating climate, VB will probably be OK under the rafters, held in place by the foam, rather than being tacked to the u/s of the foam. I'm probably going with T&G for the ceiling, so I doubt I'll need furring over the foam if I do it carefully enough. I'll put up a few rows and if I don't like it, I'll take it down and furr it with 1x3s.
In the walls I'm going with Icynene spray foam, to give better air infiltration blocking than batts.
As to the retrofit poster who started this thread, I'll throw in my uneducated opinion. If you're not tearing off the roof but you are tearing off the ceiling finish in the sections of sloped ceiling between the knee walls and the ceiling joist/rafter ties, you may be best to strap the U/S of each rafter with 2x4, then block and add foil-faced foam or foam vent baffles as you see fit, then go with batts or dense-pack cells or blown foam as the budget allows. VB on the U/S of the rafters- but it has to be continuous so it won't be great if you don't do the ceiling at the same time. And that would be nasty with all that loose blown insulation in there...The blown foam will give you some advantage by reducing vapour permeation, and if your building inspector and shingles will take it you may be able to get away with an unvented "hot" roof using this method- without strapping the rafters you'll still get a pretty good R value between 2x4 rafter bays. But again, this is just my 2 cents worth, and it ain't even worth that- what I know on this subject is 1/100 as much as some of the guys here who will get around to giving you their opinion shortly!
Edited 9/27/2004 8:03 pm ET by moltenmetal
Use unfaced insulation if the paper is going to be exposed, otherwise
it is concidered a fire hazard.