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I am gutting an old home that was built in 1863 where the second floor is really a half floor. The timber used to build the home was all rough sawn thus not spaced evenly nor deep enough to meet normal insulating requirements. I have only 3-1/2″ of space between the roof boards and the edge of the rafters. I think I should install plastic spacers to allow proper venting, but then that leaves even less depth. Do I need to add sleepers to increase the depth of the rafters? And what would be the best insulation to use?
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Hi Hadden,
Assuming that you are not doing any work on the exterior part of the roof I would use Styrofoam SM 2" thick.
Start by installing blocking strips set back 2" from the inside edge of your rafters. This will allow the 2" styrofoam to rest solidly against the blocking and be flush with the inside face of your rafters.
Then you install 2 x 2s cross ways to your rafters and add an additional 1 1/2" of SM. This will end up dropping your roof line by only 1 1/2 inches, and give you 3 1/2"of SM insulation. It will minimize thermal bridging, and still allow ventilation between your insulated ceiling and your roofing materials.
No need to use a vb when you use ridget insulation as described.
Gabe
*Hadden, I am not quite sure what you mean by half floor, but I will assume you refer to the rafters and 2cd floor joists rest on a common wall plate. My next question would be do you have a flat ceiling or is it peaked, following the rafters to the ridge? Is your roof sheathing skipped sheathed and what do you have for roofing material? I ask these questions to maybe be able to offer some alternatives. The house I live in now, we totally renovated a few years ago. It was balloon-framed with a 3feet wall off the second floor. Rafters were 2x4 a nominal 16inch centers. Collar ties across the rafters were at 7ft8in off the floor. I built kneewalls at 5ft heigth which with the flat ceiling of the collar ties reduced my rafter length on the inside of the room to six feet. The flat ceiling was easy to use blown-in, 20inchs of insulII fiberglass. The walls were blown-in to 5" of the same. The remaining pitched ceiling, I furred down with 2x2 (1-1/2x1-1/2") which gave me approx 5-1/2inchs. I ran rosin paper against the roof sheathing as a wind paper and also to keep the insulation from blowing through the skip-sheathing. This was again blown-in using the same bibb system. I was able to get away with being tight to the sheathing because of the skip-sheathing and because I have a delta-ribbed metal roof. Ventilation is not a problem here. I also have gable vents in the attic area. The entire wall and roof area was covered with a foil paper, taped seams and furred out using 1x2s. 5/8 drywall was hung over all. The foil paper provided a radiant barrier with a 3/4inch deads air space beyound the insulation. A few winters ago we hit 40-50 below zero for a few weeks at a time and stayed comfortably warm. The only source of heat is a NG parlour stove downstairs. Excuse the long windedness of the reply, I am trying to illustrate an approach to your situation. Your temperature ranges will determine how much insulation you need. And attic insulation is much more valuable than walls. By using the collar ties for a ceiling, I reduced the effect of the smaller space of the pitched rafters with regards to heat loss. For reference my house is 28feet from plate to plate with a 10/12 pitch. Gabes suggestion is another possibility. I am assuming he is refering to extruded polystyrene rather than expanded polystyrene when he refers to styrofoam. The extruded has twice the R-value about 6/inch. Any rigid you should caulk the edges well to minimize air infiltration from both directions. Hope this is helpful or at least entertaining. Walk good David
*Thanks for your help....The upstairs has a 19" Kneewall and then the rafters acting as a cathederial cieling. The pitch is steep - 15/12.The roof is made of old 1-1/4 boards with small spaces in between them and is covered with felt and asphault shingles. Collar ties do exist very simular to what you have, so deep insulation in that area is easy...It really is just about the same 6' area between the kneewalls and the the collar ties as your's. Your advice is great and in Cleveland we don't get near as cold thank goodness....I guess I'm a wimp!
*Hadden, Glad I could help. But unless you plan on reroofing and providing some sort of air flow above your roof sheathing, you will need to provide it on the inside of your rafters. Gabes suggestion is a good one for that area. It sounds like you can afford abit more depth in furring out your rafters on the slope. I would take advantage of that to provide good insulation and 2inchs of airflow from soffet to attic/ridge venting. You can use a waxed cardboard stapled into the rafters to achieve the necessary spacing and keep insulation out. If you do insulate your attic as a flat ceiling, remember to bring your air shields up higher than your insulation will be. Otherwise your insulation will block your air flow. Walk go
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I am gutting an old home that was built in 1863 where the second floor is really a half floor. The timber used to build the home was all rough sawn thus not spaced evenly nor deep enough to meet normal insulating requirements. I have only 3-1/2" of space between the roof boards and the edge of the rafters. I think I should install plastic spacers to allow proper venting, but then that leaves even less depth. Do I need to add sleepers to increase the depth of the rafters? And what would be the best insulation to use?